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Guidance Document on Surfacing Options for Highways

2010 Edition

Technical Advice Group Hampshire County Council

Capital House Andover Road

Winchester Hampshire SO23 7BH

HAMPSHIRE COUNTY COUNCIL ENVIRONMENT DEPARTMENT TECHNICAL ADVICE GROUP GUIDANCE DOCUMENT ON SURFACING OPTIONS FOR HIGHWAYS CONTENTS Page Number

1 INTRODUCTION.................................................................................................... 1

2 SCOPE .................................................................................................................. 2

3 SURFACING – GENERAL .................................................................................... 3 3.1 Preliminary Works............................................................................................................. 3 3.2 Effect of Existing Substrate on Material Choice......................................................... 3 3.3 Ironwork............................................................................................................................... 4 3.4 Overlay or Inlay? ............................................................................................................... 4 3.5 Inter-layer Bonding ........................................................................................................... 4 3.6 Joints.................................................................................................................................... 4 3.7 Quality Assurance............................................................................................................. 5 3.8 Materials Testing Strategy (MTS) ................................................................................. 6 3.9 Layer Thicknesses and Weather Considerations for Hot Applied Materials ....... 6 3.10 Deferred Set Materials..................................................................................................... 8 3.11 Traffic Noise ....................................................................................................................... 8

4 SELECTION OF AGGREGATES AND BINDERS ................................................ 9 4.1 Aggregate Properties ....................................................................................................... 9 4.2 Aggregate Selection for Surface Courses................................................................... 9 4.3 Binders ..............................................................................................................................14

5 SELECTION OF APPROPRIATE SURFACING TYPE ...................................... 14 5.1 Relative Properties of Surfacing Materials................................................................18 5.2 Guidance on Choice of Surfacing ...............................................................................21 5.3 Sites with a Speed Limit of 40 mph or Greater ........................................................25 5.4 Sites with a Speed Limit of Less than 40 mph .........................................................35 5.5 Detailed Consideration Of Alternative Surfacing Materials ...................................43

6 SURFACE DRESSING ........................................................................................ 47 6.1 Surface Dressing on Carriageways ............................................................................47 6.2 Surface Dressing on Footways....................................................................................48

7 REHABILITATION OF THE EXISTING SURFACE............................................. 49 7.1 Pothole Repairs and Patching .....................................................................................49 7.2 Reinstatements Within Special Surfacings ...............................................................51

7.3 Retexturing .......................................................................................................................51 7.4 Repave/Remix .................................................................................................................53 7.5 Crack Sealing Techniques............................................................................................53 7.6 Asphalt Rejuvenation .....................................................................................................54

8 ROAD RECYCLING ............................................................................................ 55 8.1 In-situ Recycling ..............................................................................................................55 8.2 Ex-Situ Recycling – ( Cold Recycled Bituminous Bound Material) .....................56

9 CONCRETE SLAB CARRIAGEWAYS ............................................................... 56 9.1 Joints..................................................................................................................................56 9.2 Exposed Slabs.................................................................................................................57 9.3 Overlaying.........................................................................................................................57

10 HIGH FRICTION AND DECORATIVE SURFACINGS .................................... 58 10.1 High Friction Surfacings (decorative surfacings derived from HFS systems)...58 10.2 Coloured 'Gateway' Surfacings - General .................................................................61 10.3 Resin Bonded Surfacing................................................................................................61 10.4 Resin Bound Surfacings................................................................................................61 10.5 Decorative Asphalts. ......................................................................................................61

11 BLOCK PAVING AND NATURAL STONE PAVING....................................... 62 11.1 General Guidance...........................................................................................................62 11.2 Block Paving for Vehicular Areas................................................................................62 11.3 Block Paving for Pedestrian Areas .............................................................................64 11.4 Block Paving for Shared Areas....................................................................................65 11.5 Improving Skid/Slip Resistance ...................................................................................65 11.6 Natural Stone Paving .....................................................................................................66

12 ASPHALT REINFORCEMENT GRIDS............................................................ 66 12.1 Choice of Grid Reinforcement......................................................................................66 12.2 Thermal cracking.............................................................................................................66 12.3 Cracking with some anticipated Vertical Displacement expected .......................67 12.4 Clay Shrinkage cracking................................................................................................67 12.5 Concrete Joint problems/severe Clay Shrinkage cracking....................................67 12.6 GridSeal ............................................................................................................................67 12.7 Guide to Successful Installation ..................................................................................68

13 FOOTWAYS .................................................................................................... 68 13.1 General Guidance...........................................................................................................68 13.2 A note on Slurry Treatment of Footways ...................................................................69

APPENDIX A: PERMITTED PAVEMENT OPTIONS................................................. 74 Appendix 7/1/A .............................................................................................................................75 Appendix 7/1/B .............................................................................................................................76 Appendix 7/1/C .............................................................................................................................77 Appendix 7/1/D .............................................................................................................................79

Appendix 7/1/E .............................................................................................................................80 Appendix 7/1/F..............................................................................................................................81 Appendix 7/1/G.............................................................................................................................82 Appendix 7/1/H .............................................................................................................................83 Appendix 7/1/J ..............................................................................................................................85 Appendix 7/1/K .............................................................................................................................87 Appendix 7/1/L..............................................................................................................................88 Appendix 7/1/M.............................................................................................................................90

APPENDIX B : KEY CHANGES SINCE 2002 EDITION......................................... 93 B.1 Revised Bituminous Material Standards....................................................................93 B.2 New Materials and Processes .....................................................................................98

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Published April 2010

1 INTRODUCTION

The last 50 years have seen significant changes to road legislation and automotive technology. Higher traffic loadings now impose greater stresses on road materials and have highlighted some weaknesses in traditional surfacing materials. There is a need now also to consider the sustainable use of materials and the potential influence of climate change on the future performance of materials. The highways industry has responded by both improving the specification and properties of traditional materials and by developing new surfacings However, there is no one surfacing material that is "perfect" for all applications and some, whilst ideal in certain circumstances, would be totally unsuitable in others. Additionally, the costs between materials can vary significantly.

Purpose of this Document

The purpose of this document (first published in February 1989) is to provide Highway Engineers with guidance on the various highway surfacing materials/products on the market so that the most suitable and cost-effective material is selected on a site specific basis. As far as is possible, all the guidance is based upon practical experience both within Hampshire and nationally.

The Highway & Transport Branch strongly support the use of environmentally sustainable or 'green' alternatives to conventional maintenance operations. Many 'green' solutions are now incorporated into standard maintenance treatments.

This document aims to provide Engineers with a combination of information, advice, guidance and Departmental policies/standards. All guidance/ information is given in normal type and Engineers are encouraged to use their judgement on a scheme specific basis. All text in bold type, however, are requirements with which Engineers must comply unless a departure has been agreed at SMG level in advance. The requirements noted are generally due to National/County Standards or because specialist advice is crucial to obtain a satisfactory product and for ' best value' in the particular activity concerned. Failure to comply with these requirements could produce sub-standard works and possibly even leave the County liable to legal action.

Since the previous edition of this document there have been numerous changes to Standards, Specifications, Materials and Practice and it is these changes which have prompted this revised edition. Many staff will already be familiar with the changes and it is not necessary to know the full detail in order to use this document. Accordingly these are not dwelled upon but have been summarised as Appendix B for those new staff who may appreciate the background.

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. Both the Highways and Transport Branch Management Team and the Highways Technical Group (formerly Departmental Standards Committee) have endorsed this document prior to publication.

This heavily revised edition has only been published after a comprehensive internal consultation process. However, it is recognised that the document may contain errors, omissions, contradictions, etc. It is also likely that particular scenarios may not be covered. For these reasons, feedback from Engineers (both positive and constructively negative!) would be welcome. Any such feedback should be sent to the Technical Advice Group - Tel. 01962 845735, Fax. 01962 854045 or email –[email protected]

2 SCOPE

Whilst this document has been formulated primarily as a guide to the selection of surface treatments for highway maintenance works in areas not subject to special requirements, the concepts are equally valid for new works in similar areas. The document complements but is not intended to replace “The Highways Environment - Design guidelines for Special Areas” or “Traditional Materials – a guide to the use of natural materials in the Highway”, both of which remain current and should be referred to when considering surfacing works in “special areas”. The purpose of this document is to provide sufficient guidance for Engineers to enable them to specify safe and durable surface treatments which will give an adequate level of performance over their service life.

Reconstruction and similar treatments are generally outside the scope of this document and hence materials primarily involved in such operations (e.g. Base and sub-base) are not covered.

Eight basic groups of surface treatment are covered:

Bituminous surfacings - HRA, AC, Thin Surface Courses, SMA, etc. Surface dressing Rehabilitation of existing surfacing Road recycling Treatment of concrete roads Special surfacings (High Friction Surfacing, Coloured Surfacing, etc) Block paving and Natural Stone Paving. Footway surfacings Flow charts are used to guide users to the most appropriate group for any given maintenance scenario. Within each group, the merits of a range of possible treatments are discussed and the preferred option is suggested for any particular set of circumstances. In all cases the preferred option has been selected for its engineering properties.

mailto:[email protected]

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However, there may well be over-riding environmental conditions which will affect the choice of treatment/material e.g. Conservation Areas.

The intention is that this document should have a long life and therefore no attempt has been made to quantify prices. Prices can be influenced by many factors and specifiers are encouraged to evaluate prices at scheme level. Prices for most of the processes covered will be available through the Term Highway Contract.

3 SURFACING – GENERAL

3.1 Preliminary Works

Whilst all the materials quoted should perform adequately under the circumstances discussed, it should be borne in mind that any surfacing/surface treatment is only as good as the base upon which it is laid. THERE CAN BE NO SUBSTITUTE FOR ADEQUATE PREPARATORY WORKS. This is particularly the case where the surfacing selected is potentially permeable. As may be the case with negative textured surfacing, see section 3.2 and 5.5.3

3.2 Effect of Existing Substrate on Material Choice

When resurfacing, the nature and performance of the existing surfacing should be considered carefully and the new material specified to overcome any deficiencies (e.g. if the existing surfacing has rutted badly then it would be wise to consider removing all the rutted material - Binder Course and Base as well if affected - and replacing it with more deformation resistant materials). If the works are sufficient to justify it, an investigation or testing should be carried out to establish the extent and cause of any deficiencies. In maintaining County roads it must be remembered that many have evolved over time and are not constructed to modern standards. A consequence of this is that they are relatively thin and can exhibit more flexibility than a modern designed carriageway. Any surfacing to be applied needs to be able to accommodate this movement if it is to provide a durable running surface. It is essential also that evolved highways are sealed effectively to prevent deterioration. Where a potentially porous surfacing e.g. a Thin Surface Course is being considered, an investigation should be undertaken to determine the potential for water penetration and the consequent need for additional waterproofing measures e.g. a dense binder course or a thick seal/bond coat. Additionally, where a thin surfacing has been used previously consideration should be given to the potential for increased noise arising from maintenance in accordance with section 3.11 below

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3.3 Ironwork

It is highly desirable that ironwork is raised BEFORE any surfacing work is undertaken. This provides a surface with a better riding quality and is usually more pleasant aesthetically. Further, by raising ironwork before surfacing no patching is needed and this prevents the normal problems associated with fretting and potholing of reinstated material near ironwork. If, for whatever reason, ironwork cannot be raised until after surfacing has been completed, consideration should be given to the use of the Paco-Patch process or an infra–red repair in order to ensure a good weatherproof joint.

3.4 Overlay or Inlay?

Overlaying should be the first process considered when renovating a carriageway as this takes advantage of the materials already in place, strengthens the road and is the least disruptive. Where the situation requires an inlay the excavated surface must be cleaned free of any loosely bonded material and should be as uniform in depth and surface profile as possible.

3.5 Inter-layer Bonding

A good bond is essential between pavement layers in order to realise the maximum structural potential. A tack coat or bond coat shall be applied in association with all bituminous layers to promote adhesion (ref SHW Cl 903.4). The Specification for Highway Works (Clause 920) requires all tack coats and bond coats to be applied by metered spray tanker. However, it must be recognised that this is not always practical for works on the County network including footways and indeed the BBA/HAPAS certificates for some proprietary products still permit manual spraying. As a consequence, although application by tanker is to be preferred the Engineer will be allowed discretion to consider all reasonable means of application provided care is exercised to ensure the recommended rate is applied uniformly.

3.6 Joints Careful consideration must be paid to joints in the surfacing. Any joint

can be considered to be a weakness in the system. The fewer the number of joints the better. Where joints cannot be avoided they shall be positioned to avoid areas of stress away from vehicle wheel paths and as much as possible away from turning movements or acceleration and braking zones.

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When surfacing bends, care should be taken to ensure that consistent road surface properties are provided throughout. There should be no significant change in surfacing type within such bends. This would present drivers and particularly motorcyclists with different road surface properties which could lead to accidents. If necessary, surfacing should be extended to move surface changes into a generally straight section of carriageway.

Finally any joints must be properly formed, prepared and

constructed in accordance with the requirements of the Specification for Highway Works and BS 594987. The width of joint cut back or offset from layer joints beneath is the one exception to this. Generally on County works the minimum width of cut-back for B and C roads shall be 150mm and for A and Trunk roads 300mm. The requirement should be stated in Appendix 7/2.

3.7 Quality Assurance It should be noted that all suppliers of coated materials into

Hampshire are required to operate quality systems complying with ‘QA Sector Scheme No. 14 – Production of Asphalt Mixtures’ to assure the quality of their products.

‘Sector Scheme No. 14 – Production of Asphalt Mixtures’ came into

operation with effect from 1 April 1999. This scheme is now routinely called up in the 'Specification for Highway Works' (SHW) and is implicitly required under the IWF 1 and THC Contracts which refer to SHW. Other forms of contracts will need to make specific reference to this scheme (or to SHW).

Plants not-registered under Sector Scheme 14 shall not be

approved for supply to any works within Hampshire. If in doubt contact TAG.

Under Sector Scheme 14, the ability of a production plant to mix material

of consistent quality can be judged in terms of an Operating Compliance Level (OCL) value based on compliance rates for the last 32 samples tested. The lower the OCL value the greater the compliance rate. No 'minimum' OCL value has been set so a production plant can still claim accreditation under Sector Scheme 14 even though the material produced may not be of consistently good quality. Accordingly, Engineers are strongly advised not just to rely on a Suppliers QA status but to also require sight of OCL values pertinent to the anticipated period of supply and to consider the need for specific scheme testing (see Section 3.8 re HCC's Materials Testing Strategy).

Any failures by the contractor to comply with their own quality procedures should be reported formally to them and if no satisfactory reply is received, a complaint should be made to their accreditation body.

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In addition to quality assured supplies, the SHW requires that companies laying asphalts be accredited under Sector Scheme 16. This move is supported by HCC with a view to making the requirement mandatory from 2010. In the meantime, where a company not accredited to Sector Scheme 16 is proposed, Engineers should satisfy themselves through taking up references that the company is competent to undertake the work.

3.8 Materials Testing Strategy (MTS) Contractor – making best use of routine quality control data. For larger

one-off schemes the testing strategy to be employed in each instance will be determined on a scheme by scheme basis considering the nature of the works, although in general terms it is likely the majority of responsibility will rest with the Contractor.

Engineers supervising works should be demanding sight of the appropriate evidence on a routine basis.

Experience shows however, that it can take some time for this data to be

made available and many Engineers require the sanction to call up a limited amount of audit testing to provide early confidence.

To facilitate audit testing, or to challenge quality control data in the event of a dispute on THC works, a centrally held budget has been established to enable the County Highways Laboratory to undertake spot sampling work on an ad-hoc basis. Call off against this budget is apportioned annually in line with the RS/SM budget for each Highway Unit.

For larger works and/or where full monitoring of laying operations is

needed then provision for testing should be made within the scheme budget.

To call up sampling and testing under the Materials Testing Strategy, contact the County Highways Laboratory 01962 774502.

3.9 Layer Thicknesses and Weather Considerations for Hot Applied Materials

Unless constrained by special circumstances all material thicknesses

and temperatures shall be specified to comply with the requirements of BS 594987 or the appropriate BBA HAPAS Certificate.

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The requirements for wind speed and air temperatures in

Clause 945 of the SHW (Specification for Highway Works) shall be adhered to whenever bituminous materials are laid. Failure to do so can severely affect material compaction and chipping embedment especially in cold weather.

During periods of cold weather bituminous materials cool down rapidly

and if adverse conditions are anticipated and cannot be avoided an increase in layer thicknesses may prove advantageous where this can be accommodated. However, where considering thicker layers it may be necessary to alter the grading or nominal size of aggregate to prevent other problems arising.

The laying of high stability HRA mixtures in thin lifts in cold weather can

give rise to particular problems with workability and chipping retention/embedment. Accordingly the preferred thickness for HRA surfacing is now 45mm. Where this cannot be accommodated and adverse conditions cannot be avoided it may be necessary to reduce the nominal size of chippings ( subject to meeting texture criteria ) or even preheat the substrate in order to achieve a satisfactory result.

Some binder modifiers can be used to improve the workability/'cold weather working' properties of a mixture e.g. EVA, SBS, SBR, Wax, etc. Any such proposal shall be discussed first with TAG (01962 845735) because such modifiers can have significant implications on many aspects of a materials performance - see also Section 3.2.

The suppliers/applicators of some proprietary products will not guarantee

their product/work if laid during winter months. This should be taken into account by Engineers when planning works.

Conversely, if subject to trafficking at elevated temperatures many

materials can be subject to fatting and deformation. This is particularly the case if trafficked before the freshly laid mat has cooled sufficiently. Spraying the rolled surface with a fine spray of cold water can reduce delays but should only be used where really necessary.

Even after initial cooling, freshly laid materials with dark binder rich surfaces are likely to absorb more solar radiation than matured surfaces and can thus be subject to elevated temperatures in service until the aggregate becomes exposed. With climatologists predicting hotter summers, it would seem sensible to programme resurfacing of heavily trafficked sites during the autumn as this will reduce the number of hot days the material will be subjected to during its early life.

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3.10 Deferred Set Materials Deferred set material shall not generally be used for permanent works in footways or carriageways to avoid subsequent instability, deformation or tacky binder being tracked, particularly to un-wanted locations. Deferred set material may be used for temporary works or very small scale potentially permanent works such as pothole repairs as directed in TAG Report TAG/P262 (August 2002) - 'Investigation into Improving the Performance of Pothole Repairs in Hampshire (Phase 2)’. The distinctive smell of deferred set materials (creosote or kerosene) makes them easy to identify. In addition the delivery note should include the letters DS in the description of the material e.g. AC 6 med surf 100/150 DS.

Whilst deferred set material should not have been used for anything

other than temporary works since 2002 it may occur in older works or as part of specialist applications (e.g. car parks). Where deferred set material has been used and overlaid before the flux oils have evaporated the material often remains mobile and is liable to excessive deformation. Where such issues are identified any underlying deferred set material should be removed and replaced with conventional hot material prior to surface repairs to avoid repetition.

If it is suspected that deferred set material may have been used in

contravention of policy then any investigation to determine the extent of deferment should be carried out sooner rather than later as it becomes more difficult to quantify the initial degree of deferment as time goes by.

3.11 Traffic Noise When planning resurfacing or surface dressing operations, engineers

should consider the implication of road traffic noise arising from the new surface in accordance with the relevant procedure in HMMP.

Noise is unlikely, generally, to be an issue where; Traffic speeds are likely to be less than 30MPH, Vehicle flows are likely to be less than 32,000 vehicles per 18

hour day, There are no properties within the immediate vicinity of the

surfacing works, The texture depth of the new surface is likely to be the same as or

less than existing and/or roadside noise levels are predicted to be less than 78dB(A) after the works.

However, since the introduction of the Environmental Noise (England )

Regulations in 2006, plans are being developed nationally to manage and reduce environmental noise generally. Arising from this exercise a

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number of major road sites in Hampshire have been flagged as “first priority locations” for detailed study with a view to introducing noise mitigation measures where possible. These first priority locations are shown on maps available at http://www.defra.gov.uk/corporate/consult/noise-action-plan/map-list.htm and particular attention should be paid to the specification of surfacing at these locations with a presumption in favour of low-noise materials where this is feasible and appropriate. See Appendix A 7/1/H to 7/1/L.

4 SELECTION OF AGGREGATES AND BINDERS

4.1 Aggregate Properties

The physical requirements for aggregates are stated in BS EN 13043 and the associated guidance document PD 6682-2. These requirements are much as previously although the terminology and the test method may have changed.

The following are the essential criteria and test methods:

Resistance to fragmentation, measured by the Los Angeles test method.

Freeze-thaw resistance determined by measuring the water absorption

value as a screening test or more specifically using the magnesium sulfate soundness test.

Resistance to polishing of coarse aggregate for surface courses, measured by the polished stone value (PSV).

Resistance to surface abrasion, measured by the aggregate abrasion value (AAV).

Further detailed guidance for the polished stone value (PSV) and aggregate abrasion value (AAV) required are given in section 4.2.

4.2 Aggregate Selection for Surface Courses In order to provide adequate levels of skid resistance and durability Engineers must specify an aggregate which is appropriate to site conditions and traffic flow. Hampshire County Council’s policy on the management of skid resistance is described in the documents ‘Skid Resistance Policy (Strategy)’ and ‘HCC Procedure for Management of Skid Resistance’. As well as monitoring the network by means of skid testing, a key factor in the provision and maintenance of adequate levels of skid resistance is

http://www.defra.gov.uk/corporate/consult/noise-action-plan/map-

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the selection and specification of aggregates with regard to Polished Stone Value (PSV). Although surface texture is an important property of a road surface, particularly at higher speeds, it is the ability of the aggregate to resist the polishing effects of traffic which has the greatest effect on skid resistance and safety in the wet, particularly in the medium to long term life of a surfacing or dressing.

Table 4/1 PSV and Table 4/2 AAV should be used to select the appropriate aggregate properties with respect to Site Category and commercial traffic flow. As in previous editions of this guide the tables are based on advice given in Highways Agency standards, currently HD 36/06 ‘Surfacing Materials for New and Maintenance Construction’, amended for use on the local road network.

In the table the Site Categories and target skid resistance values reflect the level of risk or ‘difficulty’ of the site while the traffic flow is proportional to the intensity of polishing the aggregate is likely to be subjected to. Unless specific growth rates are known the commercial traffic flow at the end of life of the proposed surfacing should be estimated assuming a nominal growth rate of 2% per annum. For Asphalt mixes (including TSCs where appropriate preservative treatments are applied) a service life of 20 years may be assumed whereas for surface dressings a life of 10 years would be a more realistic assumption. However it is advisable to err on the side of safety when estimating design life as future maintenance frequency cannot be predicted with certainty.

The main differences from earlier versions of this table concern site category definitions and target skid resistance values, mostly those for approaches to junctions, roundabouts, signals and the bend categories. These changes reflect amendments to site category definitions and changes in risk levels introduced in HD36/06 as a result of continuing research by TRL. Additionally for ‘non-event’ sites the very lowest PSV aggregates permitted in HD 36/06 have been excluded, reflecting the increased risks associated with the un-designed nature of many of our roads.

It is important that the Notes for Guidance accompanying the PSV table are read before finalising specifications as the selection of the appropriate site category is more complex than in previous versions. An additional traffic category of 0-50 cv/day has now been introduced to the table as an HCC amendment to cover the lesser used C class and unclassified roads which make up a large proportion of our local network.

Occasionally a blend of coarse aggregates are proposed for incorporation into a mixture and in such cases the assessment of the overall material's skid resistance cannot be determined with certainty unless both aggregates comply with the minimum value specified. TAG shall be consulted in all cases where a supplier proposes combining different coarse aggregates, chippings or pre-coated chippings.

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Aggregates shall be specified in terms of Polished Stone Value (PSV) and Aggregate Abrasion Value (AAV). The term "Hardstone" shall NOT be used in isolation as this is ambiguous. Occasionally a supplier will suggest that an aggregate performs better than the PSV results indicate. This may be the case but this should not be accepted without suitable evidence being provided and TAG approving.

Conversely some aggregates, particularly those with an AAV of less than

6, tend not to perform as well as their PSV result would suggest when subjected to high stress traffic situations. TAG can advise on which sources have been found to react in this manner.

It should be noted that whilst aggregates come in a variety of colours and

PSV grades it is not always possible to obtain the exact colour/PSV combination that may be desired on some schemes (e.g. in conservation areas). It is important that all Environment Department staff note that safety issues are of paramount importance and PSV requirements shall not be reduced just to allow a particular coloured aggregate to be used. Not withstanding this, if there is a choice of aggregates with a suitable PSV for the particular scheme then colour should be taken into consideration, especially in conservation areas

TAG is available to advise on required aggregate properties and also holds further records relating to this matter.

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Table 4/1 MINIMUM PSV OF CHIPPINGS OR COARSE AGGREGATE IN UNCHIPPED SURFACINGS

FOR NEW SURFACE COURSES

Estimated commercial traffic flow at end of life of surface ( cv/lane/day )

Site Description

Site Category

Target Skid

Resistance (SFC)

0-50# 51-250

251-500

501-750

751-1000

1001-2000

> 2000

Dual Carriageways – non-event sections. As above – elevated risks. See note 1

B 0.35 0.40

55 55

60* 60

60 60

60 60

60 65

60 65

Single carriageways – non-event sections. As above – elevated risks. See note 1

C 0.40 0.45

55 60

60* 60

60 65

60 65

65 65

65 68+

Gradients 5% - 10% Gradients > 10%

As above – elevated risks

G1/G2 0.45 0.50 0.55

55 60* 68+

60* 60

68+

60 68+ HFS

60 68+ HFS

65 HFS HFS

65 HFS HFS

Approaches to pedestrian crossings and other high risk situations. See note 2

K 0.50 0.55

65 68+

65 68+

65 68+

65 HFS

68+ HFS

68+ HFS

Approaches to major and minor junctions on dual and single carriageways. Approaches to roundabouts.

See note 3.

Q1 Q2 Q3

0.45 0.50 0.55

60* 60* 68+

60 65

68+

65 65

68+

65 65

HFS

68+ 68+ HFS

68+ 68+ HFS

Roundabout circulation areas and exits (incl. mini). As above – elevated risks. See note 4.

R 0.45 0.50

60 68+

60 68+

60 68+

60 68+

60 HFS

65 HFS

Dual C/way bends, radius < 500m ( >=50mph) See note 5.

S1 0.45 0.50

55 68+

60 68+

60 68+

60 68+

60 HFS

65 HFS

Single C/way bends, radius 100-250m ( >=50mph) Single C/way bends, radius < 100m ( >=50mph)

As above – elevated risks. See note 6.

S2 0.45 0.50 0.55

55 60* HFS

60 65

HFS

60 65

HFS

65 68+ HFS

65 HFS HFS

68+ HFS HFS

Consult TAG

# This category is intended to cover the lightly used rural and urban C class and unclassified network. * May be lowered to 55 based on local experience and if there is no evidence of above average wet-skid accidents (consult Safety Engineering)

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Table 4/1 Notes for Guidance : -

1. For dual and single carriageway non-event sections (B and C) the default target skid resistance appropriate for average conditions, where traffic is free flowing and braking does not regularly occur, is as shown in bold. Where there are felt to be additional hazards (eg restricted sight lines, regular overtaking, poor geometry etc) or the site has an above average wet skid accident history, select the higher level.

2. For approaches to pedestrian crossings, etc. (site category K) use the lowest target skid resistance (bold) in situations where approach speeds are slow and visibility is good. For crossings in 40mph or greater zones or where, for other reasons, heavy braking may be anticipated use the higher level.

3. Site category Q covers a wide range of junction approaches:- Q1 applies to:- Approaches to roundabouts (incl. mini roundabouts) and signals in 40mph or less zones; Approaches to

junctions on major roads in 40mph zones and Approaches to junctions on minor roads – any speed limit. Q2 applies to roundabout and signal approaches and to and across junctions on major roads in 50mph or greater zones. Q3 applies to Q1 and Q2 categories where there are significantly higher risks. Definition: Major Rd = traffic has permanent priority; Minor Road = traffic is required to give way.

4. For roundabout circuits (R) generally use the default level in bold. However, where circulation speeds are high, where there is frequent use by cyclists and motorcyclists or where there is an absence of signalised control on grade-separated junctions select the higher level.

5. For S1 bends raise the target skid resistance to 0.50 where traffic needs to slow down to safely negotiate the bend, where there is adverse camber or where the road geometry presents an increased hazard. Otherwise select the default target skid resistance shown in bold.

6. For S2 bends the default target skid resistance of 0.50 can be lowered to 0.45 if a detailed site investigation shows the bend to have a reduced accident risk. The higher target of 0.55 band should be used only where a risk assessment identifies enhanced risks such as adverse camber or where the road geometry presents an increased hazard.

7. For all site categories the higher target skid resistance should be selected where a site has a known history of wet skid accidents showing a significantly higher level than the county average for a given site or length of road.

8. For sites which encompass multiple hazards, a target skid resistance appropriate to the feature with the highest level of risk should be selected.

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Table 4/2

MAXIMUM AAV OF CHIPPINGS, OR COARSE AGGREGATES IN UNCHIPPED SURFACES, FOR NEW SURFACE COURSES (HD 36/06)

Traffic (cv/lane/day) at

design life <250 251-

1000 1001-1750

1751-2500

2501-3250

>3250

Max AAV for chippings for hot rolled asphalt and surface dressing, and for aggregate in slurry and microsurfacing systems

14 12 12 10 10 10

Max AAV for aggregate in thin Surface Course systems, SMA, exposed aggregate concrete surfacing and Asphalt Concrete Surface Course

16 16 14 14 12 12

Note 1: For roads carrying less than 1750 cv/lane/day, aggregate of

higher AAV may be used where experience has shown that satisfactory performance is achieved by an aggregate from a particular source.

4.3 Binders

For surfacing materials generally 40/60 pen binder will be adequate for Hot Rolled Asphalt (HRA) and Thin Surface Course (TSC) mixtures, 100/150 pen for Asphalt Concrete (AC) mixtures including footways and 70/100 where stiffer AC mixes are required.

The use of 160/220 pen binder is now generally limited to materials for footway works only at particularly cold periods. However, consideration must be given to the effect of subsequent high temperatures.

There are also many binder additives, e.g. polymers and waxes, available which

improve specific aspects of a bituminous materials performance. Before approving the use of any additive, the advice of TAG shall be sought.

5 SELECTION OF APPROPRIATE SURFACING TYPE Selection of the most appropriate surface treatment in any given situation involves

consideration of numerous factors. There will often be more than one potential option and opinions will inevitably vary. The Technical Advice Group can assist with complex problems, however, the key issues have been mapped into a series of flow charts below, the combination of which should steer engineers in the right general direction. Outcomes from the flow charts direct engineers to the relevant more detailed sections of this document which will provide the guidance necessary to identify the criteria required to specify/order the appropriate process/material effectively.

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MAINTENANCE TREATMENT CHART

Does Deflectograph indicate low residual life or

Is road showing signs of structural distress (SCANNER/CVI)

Yes No

Undertake Investigation to determine most

appropriate course of action

Is surface Profile/Drainage generally good

Yes No

Select Treatment from Surface Treatment Chart

Consider need for regulating/profile – planning and

select surfacing from Resurfacing chart

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RESURFACING CHART

Does road carry high speed traffic - >40mph

Yes No

Refer to Table 5/2 Refer to Table 5/3

Does layout comply with modern geometric design criteria

See 5.5.2

Yes

Is noise an issue See Section 4.11

No

Yes

Does site include Steep Gradient

Use Positive Textured Surfacing eg HRA

Yes No

Regulate/resurface using positive texture surfacing eg HRA

Regulate/resurface using a negative textured surfacing + initiate programme

of Preventive Maintenance

Referring to Tables 4/1 and 4/2 to provide a surfacing incorporating the appropriate aggregate

(depends upon traffic flow, actual gradient etc)

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SURFACE TREATMENT CHART

Is surface deterioration limited to minor defects only, ie no significant cracking present

Yes No

Is skid resistance adequate?

Refer to SCRIM data or commission survey

Consider patch and surface dress or

Microasphalt Surface Clause 960AR

Yes No

Consider rejuvenation to extend life

See Section 7.6 and Clause 990AR

Has existing surface polished rapidly?

Yes No

Consider Surface Dressing See

section 6.1 (may require warning

signs or retexturing as a temporary

measure)

Consider Retexturing

See section 7.3

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5.1 Relative Properties of Surfacing Materials As mentioned in the introduction to this document not all surfacings are created

equal. Table 5/1 gives a general overview of the relative properties of the 'common' surfacing materials when applied to carriageways. It is subjective and may not be unanimously accepted but nonetheless represents a considered judgement based on the typical type of site each material will be used on and the typical aggregate and texture properties specified.

Since the publication of the previous edition of this guide in 2002 experience of

negative textured surfacings such as Porous Asphalt, Stone mastic Asphalt (SMA), Thin Surface Courses and Ultra Thin Surface Courses on County roads has matured somewhat.

Experience shows that the life expectancy of generic SMAs can be relatively

short. It is evident that the technology is still evolving and the industry is moving away from generic mixes in favour of proprietary Thin Surface Courses, the performance of which is regulated through the BBA/HAPAS approvals process. The relative values given for these materials have been tweaked since 2002 to reflect this broader experience. More detailed guidance on the issues to be considered when using such materials are contained in sections 5.5.1, 5.5.2, 5.5.3, 7.1 and 7.2, B1.10 of this document. It is now recommended that proprietary thin surface course materials be used rather than generic SMAs (those specified in BS EN 13108-5). The full requirements of SHW clause 942 should be called up in order to specify these products.

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TABLE 5/1 - RREELLAATTIIVVEE PPRROOPPEERRTTIIEESS OOFF TTYYPPIICCAALL SSUURRFFAACCIINNGG MMAATTEERRIIAALLSS FFOORR CCAARRRRIIAAGGEEWWAAYYSS

RELATIVE PROPERTIES MATERIAL

(In descending order of typical layer thicknesses from 50mm-3mm)

Skid Resistance

Durability Deformation Resistance

Cracking Resistance

Riding Quality/ Profiling Ability

Structural Contribution

Noise Characteristic

Spray Control

Performance Mixture Clause 943 5 5 6 4 4 6 2 3

Hot Rolled Asphalt

Marshall Design 5 5 5 4 4 6 2 3

Recipe Mixture 5 6 4 5 4 5 2 3

High Stone Content* 4 5 * 5 5 4 5 6 3 1

Porous Asphalt 5 1 5 3 5 3 6 6

Asphalt Concrete 3 3 4 3 5 5 3 3

Thin Surface Course Clause 942 5 4 5 3 4 4 5 5

Micro- asphalt Surface Course (12-18mm)

3 2 2 1 2 1 4 3

5+ 2 1 3+ Surface Dressing, Single

Surface Dressing, Racked in

5+ 3 n/a n/a n/a n/a

2 2

High Skid Resistance Surface Treatment 6 2 n/a 1 n/a n/a 3 2

Block Paving 2 4 4 n/a 3 6 1 n/a

Poor Good Excellent

1 2 3 4 5 6

*The higher value for skid resistance of High Stone Content Asphalt only applies where speed limit < 40mph Reducing over time increased risk of icing

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5.2 Guidance on Choice of Surfacing Detailed guidance on material selection is presented in tabular form with one

table for sites with speed limits and/or 85th percentile speeds of '40mph (64kph) or greater' and one table for sites with 'speed limits and/or 85th percentile speeds of less than 40mph (64kph)'. This distinction is made due to the greater need for macrotexture at higher speeds where the risk of aquaplaning is elevated.

The previous concerns regarding use of Generic Stone Mastic Asphalt (SMA)

on any road with a speed limit of 40mph or greater have to a degree been overcome by the evolution of proprietary Thin Surface Courses (TSC) which can retain an adequate macrotexture in service. However, caution still needs to be exercised in the use of TSC in recognition of potential low early life skid resistance, slip resistance issues for horses and the potential increase in vehicle speeds arising from the low noise /smooth ride provided.

TSCs shall not generally be used on evolved highways with geometry

outside the parameters set down in Volume 6 of the DMRB. Under exceptional circumstances e.g. where there is no viable alternative, TSCs may be used at such sites in combination with other measures to reduce risk with the approval of the appropriate Area Director.

In recognition of the developments in TSCs, the former HCC specification for

Thin Surface Course Systems (Clause 960AR and previously Clause 942SR) has been withdrawn in favour of the new Clause 942 included in the latest 900 Series of SHW. Clause 942 and the new BS 594987, which is called up therein, have addressed the issues which previously concerned HCC including requiring a 5 year guarantee. Similarly Clause 970AR for Generic SMA is withdrawn.

Further guidance on use of TSCs is set out in Section 5.5.2 of this document 6mm TSC is a relatively new material although feedback from a Highways

Agency trial on the A34 trunk road near Winchester suggests it could be a more highly textured yet more durable alternative to 6mm Dense Surface Course (AC 6 dense surf), being better able to resist the scuffing actions of tyres on vehicles with power steering. This potentially makes it suitable for residential locations. It is not referred to in Tables 5/2 and 5/3 but is included within the mixtures in the THC. In addition to 6mm TSC, many manufacturers offer “industrial” versions of their 10 and 14mm TSCs with a denser grading aimed at reducing scuffing on low speed sites where requirements for macrotexture are less critical.

Guidance on the preferred surfacing materials and any surface texture

requirements are given based on the combination of site category and projected commercial vehicle traffic flow at the design life (i.e. in 20 years time allowing for the projected growth rate) - see Section 3 also.

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Tables 5/2 and 5/3 set out the information referred to above. Subsequent to the tables are notes giving additional information and guidance on the various materials and their specifications. It is important that the supplementary information is considered fully to ensure that the selected material is specified appropriately.

The 'Site Categories' in Tables 5/2 and 5/3 are derived from HD36 in the Design

Manual for Roads and Bridges (DMRB) with minor amendments applicable to County roads

. Tables 5/2 and 5/3 also include reference to the 'Road Hierarchy' introduced in the 1989 edition of the LAA Code of Good Practice (COGP) and reinforced in the latest revision – “Well Maintained Highways”. The Hierarchy correlates reasonably well with Reinstatement Categories as defined in the New Roads and Street Works Act (NRSWA). However, there is an element of overlap and the traffic flows noted in the COGP are current, whereas those in Tables 5/2 and 5/3 are the anticipated flows at the end of 'Design Life' (i.e. 20 years). Engineers should therefore exercise caution in selecting the most appropriate surfacing material, assessing traffic flows at design life (see section 3.1) rather than just use the road hierarchy bands in a simplistic manner.

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Table 5/2 Classification of Sites by Traffic and Stress Condition - Speed Limit 40mph or Greater Road Hierarchy - COGP Category 4a + 4b 3a + 3b 2

Traffic Design Life (20 yrs) (Commercial vehicles per lane per day)

Section

Site

Category (HD36)

Site Definition

Up to 50 51- 500

501- 1000

1001- 1500

1500-2000

2001-2500 > 2500

5.3.1 C Estate Roads

5.3.2 B Dual carriageway (non-event sections and minor junctions) Recipe HRA or Thin S/C Level 3

7kN HRA or Thin S/C Level 1

943 (45°C) or Thin S/C Level 1

5.3.3 C Single carriageway (non-event sections and minor junctions)

Recipe HRA or Thin S/C Level 3 or AC 14 CGSC



5.3.4 As 5.3.2 and 5.3.3 above, but with channelised/slow moving traffic anticipated during summer months 7kN HRA or Thin S/C Level 1 943 (45°C) or Thin S/C Level 1

5.3.5 Q1,Q2,Q3 G1

Approaches to and across major junctions (all limbs) Dual and single carriageways Gradient 5% to 10%, longer than 50m:



5.3.6 As 5.3.5 above, but with channelised/slow moving traffic anticipated during summer months or in a south-facing cutting




5.3.7 G2 Gradient steeper than 10%, longer than 50m: Dual and single carriageway 7kN HRA 943 (45°C) 943 (60°C)

5.3.8 R Roundabouts (including exits) † 7kN HRA or Thin S/C Level 1



5.3.9 As 5.3.7, above, but with channelised/slow moving traffic anticipated during summer months or in a south-facing cutting 7kN HRA

7kN HRA (up to 250 cv/l/d)

otherwise 943 (45°C)

943 (60°C)

5.3.10 As 5.3.8, but with channelized/slow moving traffic anticipated during summer months or in a south-facing cutting


7kN HRA (up to 250 cv/l/d)

Otherwise 943 (45°C)

or Thin S/C Level 1


5.3.11 K Approach to roundabout, traffic signals pedestrian crossings, railway level crossings and similar features



943 (60°c) or Thin S/C Level 2

Con

sult

TAG

(i) A TEXTURE DEPTH OF 1.5 mm (SANDPATCH) OR 1.03 (MINI TEXTURE METER) SHALL BE SPECIFIED FOR ALL MATERIALS UNLESS MARKED *, or †. SEE THE RELEVANT SECTION FOR FURTHER ADVICE (ii) NO TEXTURE DEPTH NEED BE SPECIFIED FOR MATERIALS MARKED (iii) † – SEE SECTION 5.3.8. (iv) GUIDANCE ON THE SURFACING OF BENDS IS GIVEN IN SECTIONS 5.3.12 AND 5.3.13.

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GENERAL NOTES TO TABLE 5/2

1 Where TSC (Thin Surface Course) is considered on evolved highways with questionable geometry (see 5.5.2) in areas with speed limits of 40 mph or greater, guidance from the Technical Advice Group should be sought and the approval of the appropriate Area Director, or his nominated representative, shall be obtained as necessary.

2 Where Clause 943 HRA - 943 (45ºC), 943 (60ºC) or TSC – 942 Level 1, 942 Level 2 - is proposed, guidance from the Technical

Advice Group (TAG) shall be sought and design information passed to TAG for comment. 4 Where the existing surface has rutted it may be necessary for the affected construction to be planed out prior to laying Clause 943

HRA, or Thin Surface Course mixtures. Failure to do this is likely to lead to continuing deformation under the new, deformation, resistant, material.

Key AC 14 CGSC = Asphalt Concrete 14mm Close Graded Surface Course 7kN HRA = 30/14 HRA - 6-8kN stability Thin S/C = Thin Surface Course 943 (45°C) = HRA meeting 45°C wheel tracking specification 943 (60°C) = HRA meeting 60°C wheel tracking specification

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5.3 Sites with a Speed Limit of 40 mph or Greater

5.3.1 Shared Surface and Residential Roads serving up to 50 Dwellings (C) - these roads should never have a speed limit of 40mph or greater and hence are

not covered by Table 5/2. In the unlikely event that such a road is the subject of surfacing works it should be considered to be within the most appropriate of the other site categories covered by Table 5/2.

5.3.2 Dual Carriageway (non-event sections and minor junctions)

(B) - these site categories have been considered jointly as it is likely that any scheme

involving a dual carriageway will also include at least minor junctions. Generally, this type of site will require a material resistant to deformation (rutting)

and with the ability to maintain a relatively high level of surface texture. The traditional and preferred option is an HRA 30/14F surf 40/60 des with a Marshall Stability specified appropriate to the traffic flow of the site. On very heavily trafficked sites traditional HRA is liable to rut and hence a Clause 943 asphalt should be specified. On very lightly trafficked sites rutting is unlikely to be a problem and durability is the main requirement. In such circumstances a lower stability (4kN-8kN) mix HRA (with a higher binder content) is to be preferred. A proprietary Thin Surface Course may be an alternative, see also Section 5.5.2 for more detailed guidance.

The PSV required is also related to traffic flow and the class of site. Refer to Table 4/1 to select the appropriate level.

Summary

Traffic Flow at Design Life (comm. veh/lane/day)

Preferred Material /Specification THC/IWF Appendix

Up to 50 HRA 30/14F surf 40/60 rec + PCCs – BS EN 13108-4 Table 4 7/1/M 51 to 1500 HRA 30/14F surf 40/60 des + PCCs – BS EN 13108-4, Table 4

Marshall Stability = 7± 1kN 7/1/B

1501 to 2500 HRA 35/14F surf 40/60 des + PCCs to Clause 943

45°C wheel tracking Level 1 7/1/C

>2500 HRA 35/14F surf 40/60 des + PCCs to Clause 943


Up to 2500 Thin Surface Course System 45°C wheel tracking Level 1 7/1/H or 7/1/L

N.B. For HRA and 14mm TSC a 1.5mm (sand patch) surface texture shall be

specified. A 1.2mm texture depth may be appropriate for 10mm TSC material

subject to an appropriate risk assessment.

The PSV and AAV of Precoated Chippings (PCCs) and the coarse aggregate in a Thin Surface Course shall be specified in accordance with section 4 of this document.

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5.3.3 Single Carriageway (non-event sections and minor junctions) –

(C) these site categories have also been considered jointly as it is likely that any single carriageway site will also include minor junctions. The selection of materials for these site categories is almost identical to those for dual carriageways. The only exception being in the 'up to 50 cv/l/day' band where a AC14 close surf 100/150 is considered as an acceptable alternative surfacing. It does not have the same degree of macrotexture as HRA and chippings and this should be considered when selecting a material for a particular site - if in doubt specify the 4kN to 8kN HRA 30/14F mixture.

Summary

Traffic Flow at Design Life (com veh/lane/day)

Preferred Material/ Specification

THC/IWF Appendix

Up to 50 HRA 30/14F surf 40/60 rec + PCCs - BS EN 13108-4,

Table 4 or, AC 14 close surf 100/150 - BS EN 13108-1

7/1/M 7/1/D

51 to 1500 HRA 30/14F surf 40/60 des + PCCs – BS EN 13108-4

Table 4 Marshall Stability = 7±1 kN

7/1/B





Up to 2500 Thin Surface Course System 45°C wheel tracking

Level 1

7/1/H or 7/1/L

N.B. For HRA and 14mmTSC a 1.5mm (sand patch) surface texture shall be

specified. For 10mmTSC A 1.2mm texture depth may be appropriate subject to an appropriate risk assessment. AC14 shall only be used on sites where a surface texture of 1.0mm or less is deemed acceptable.

The PSV and AAV of Precoated Chippings (PCCs) and the coarse

aggregate in an Asphalt Concrete or Thin Surface Course shall be specified in accordance with section 4 of this document.

5.3.4 Dual/Single Carriageways (include. minor junctions) with channelised/slow moving traffic anticipated during summer months

- in summer when road temperatures are higher surfacing materials can approach the softening point of the bitumen in the mixture. Slow moving traffic results in longer loading times and hence the road surface is more liable to deform and rut. Channelised traffic results in more concentrated wheel track loading. Due to these factors, sites of these types need stiffer, more deformation resistant, mixtures than would otherwise be required.

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Summary



THC/IWF Appendixc

Up to 1000 HRA 30/14F surf 40/60 des + PCCs - BS EN 13108-

4, Table 4 Marshall Stability = 7±1 kN

7/1/B


45°C wheel tracking requirements Level 1 7/1/C




Level 1 7/1/H or 7/1/L


specified. A 1.2mm texture depth may be appropriate for 10mmTSC material subject

to an appropriate risk assessment.


5.3.5 Major Junctions (within 50m) and Gradients of 5% to 10% for more than 50m

(Q3 + G1) These sites are similar in nature to those in 5.3.4 and hence material specifications are similar. Gradients (uphill) and major junctions tend to suffer from deformation/rutting due to increased traffic loading times.

Summary



THC/IWF Appendix

Up to 1000 HRA 30/14F surf 40/60 des + PCCs - BS EN 13108-

4, Table 4 Marshall Stability = 7±1 kN

7/1/B






Level 1 7/1/H

N.B. For all materials a 1.5mm (sand patch) surface texture shall be specified.

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5.3.6 Major Junctions and Gradients of 5% to 10% with channelised/slow (Q3 +G1) moving traffic anticipated during summer months or a south-facing

carriageway- section 5.3.4 explains why channelised/slow moving traffic during summer months requires extra deformation resistance in a surfacing. South facing sloping carriageways will be exposed to more sun/heat than similar carriageways facing in a different direction. This also means that even greater deformation resistance is needed.

Summary Traffic Flow at Design Life (com veh/lane/day)


THC/IWF Appendix

Up to 500 HRA 30/14F surf 40/60 des + PCCs - BS EN 13108-4,


7/1/B





>2500 Consult TAG See TAG

Up to 2500 Thin Surface Course System

60°C wheel tracking Level 2

7/1/L


The PSV and AAV of Precoated Chippings (PCCs) and the coarse

aggregate in a Thin Surface Course shall be specified in accordance with section 4 of this document.

5.3.7 Gradient Steeper than 10% (for longer than 50m)

(G2) Steep gradients require good resistance to deformation (uphill) and high levels

of texture to prevent aquaplaning (downhill). The performance of Thin Surface Course systems on such sites in Hampshire has not been as good as on other sites and hence they have not been included as an option. On steep gradients hard braking or turning by heavy commercial vehicles may result in a shearing action developing between the Thin Surface Course and the old surface causing potholes to form.

On steep gradients the control of the rate of spread of Precoated chippings can be problematic and the need for skilled and experienced laying operatives is essential.

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Summary



THC/IWF Appendix



7/1/B







The PSV and AAV of Precoated Chippings (PCCs) shall be specified in accordance with section 4 of this document.

Thin Surface Course systems shall NOT be used on sites of this category.

5.3.8 Roundabouts (including exits) (R) Roundabouts require high levels of deformation resistance from surfacing

materials. On small diameter roundabouts the turning action of traffic can cause excessive chipping loss if too high a rate of spread of chippings is used. To prevent this, as recommended in BS 594987, a slightly lower surface texture (1.2mm) will be acceptable as vehicles must slow down to negotiate the roundabout. However, on large diameter roundabouts where the majority of chippings can be applied by machine, a 1.5mm surface texture is required as vehicles have to turn less and traffic speeds are higher.

Engineering judgement must play an important part in determining which level of

surface texture to specify but roundabouts with "centre islands" of less than 10m diameters should normally require only a 1.2mm surface texture. Depending on size and layout roundabouts with larger central islands, where traffic speeds are expected to be greater, should normally have a 1.5mm surface texture specified.

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Summary



THC/IWF Appendix

Up to 500 HRA 30/14F surf 40/60 des + PCC's - BS EN 13108-4,


7/1/B



1501 to 2500 HRA 35/14F surf 40/60 des + PCCs to Clause 943 60°C wheel tracking Level 2

7/1/C


Up to 2500 Thin Surface Course System

60°C wheel tracking Level 2 (see also 5.5.2 and 5.12) 7/1/L

The PSV and AAV of Precoated Chippings (PCCs) and the coarse aggregate in Thin Surface Course systems shall be specified in accordance with section 4 of this document.

5.3.9 Gradients steeper than 10% for >50m with channelised/slow moving (G2) traffic anticipated during summer months or an uphill, south-facing

carriageway –

as previously noted gradients resulted in longer loading times for the road surface which can result in deformation. Additionally, the importance of surface texture is greater for sites with gradients to help prevent skidding. Consequently, minimal textured surfaces (e.g. High Stone Content asphalt) are not advisable in such cases. see comments in section 5.3.6.

Summary



THC/IWF Appendix

Up to 50 HRA 30/14F surf 40/60 des + PCCs - BS

EN 13108-4, Table 4 Marshall Stability = 7±1 kN

7/1/B

51 to 1000 HRA 35/14F surf 40/60 des + PCCs to

Clause 943 45°C wheel tracking requirements Level 1

7/1/C

1001 to 2500 HRA 35/14F surf 40/60 des + PCCs to

Clause 943 60°C wheel tracking Level 2

7/1/C


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N.B. For all materials a 1.5mm (sand patch) surface texture shall be specified. The PSV and AAV of Precoated Chippings (PCCs) shall be specified in

accordance with section 4 of this document. Thin Surface Course systems shall NOT be used on sites of this

category.

5.3.10 Roundabouts with channelised/slow moving traffic anticipated during summer months or an uphill, south facing carriageway

See comments in section 5.3.6 and 5.3.8. Summary



Diameter of Central Island (m)/texture

THC/IWF Appendix

Up to 50 HRA 30/14F surf 40/60 des + PCCs - BS EN

13108-4, Table 4 Marshall Stability = 7±1 kN

<10m=1.2mm texture 10m=1.5mm texture

7/1/B


45°C wheel tracking requirements Level 1 <10m=1.2mm texture 10m=1.5mm texture

7/1/C


60°C wheel tracking Level 2 <10m=1.2mm texture 10m=1.5mm texture

7/1/C

>2500 Consult TAG Any See TAG


Level 2

<10m=1.2mm texture 10m=1.5mm texture

7/1/H

N.B. The PSV and AAV of Precoated Chippings (PCCs) and the coarse

aggregate in Thin Surface Course Systems shall be specified in accordance with Section 5 of this document.

5.3.11 Approaches to Roundabouts, Traffic Signals, Pedestrian Crossings, (K) Railway Level Crossings and similar features –

These types of sites are subjected to the greatest traffic forces. The continual braking and acceleration combined with long traffic loading times due to low speeds and frequency of stopping means that these types of sites exhibit the most potential for rutting and surface deformation. Hence they require the strongest materials in terms of deformation resistance. It is especially important to note on such sites that any rutted material (even Binder Course and/or Base(roadbase)) must be removed prior to treatment if a 'long term' solution is required. Otherwise the surface will continue to deform and result in even high deformation resistant materials copying the underlying rutted profile. Where necessary Heavy Duty Asphalt Concrete (HDM) Binder Course and Base materials (containing 40/60 pen binder) or Clause 929 materials,

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specifying either 45°C or 60°C wheel tracking requirements should be used to give greater resistance to deformation.

Thin Surface Courses may be acceptable on a site specific basis subject to guarantees being secured that surface texture will be maintained. The advice of TAG (01962 845735) should be sought in such circumstances - see also section 5.5.2

Summary Traffic Flow at Design Life (com veh/lane/day)


THC/IWF Appendix


Table 4 Marshall Stability = 7±1 kN 7/1/B





>2500 Consult TAG See TAG Up to 2500 Thin Surface Course 60°C wheel tracking Level 2 7/1H


specified. A 1.2mm texture depth may be appropriate for 10mm TSC material

subject to an appropriate risk assessment. The PSV and AAV of Precoated Chippings (PCCs) and the coarse

aggregate in Thin Surface Course Systems shall be specified in accordance with section 4 of this document.

5.3.12 Bends of Radius - 250m to 500m (S1)

Bends do not suffer 'structurally' from specific vehicle loading forces beyond that normal to the nature of the road (e.g. single/dual carriageway, approach to a roundabout, etc.). Consequently, specific surfacing advice is not considered necessary. Where such sites are to be treated Engineers should use the most appropriate site category within Table 5/2 and specify the surfacing material accordingly, taking account of commercial vehicle flows. Surface texture is an important property on bends and thus where Hot Rolled Asphalt or Thin Surface Course is used a 1.5mm surface texture shall be specified.

5.3.13 Bends of Radius -100 to 250m and less than 100m (S2) The guidance given in 5.3.12 is also valid for these tighter bends. However,

the need for high levels (1.5mm) of surface texture and a uniform road surface is even greater, given the high braking stresses surfacings are subjected to. Consequently, Asphalt Concrete Surface Course or Thin Surface Course should not be specified for such sites and chipped HRA is preferred.

Where forward visibility is poor or where there is a history of wet skid accidents the surfacing should be specified in consultation with SET. Under such circumstances it is likely that HFS will be required.

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Table 5/3 Classification of Sites by Traffic and Stress Condition - Speed Limit Less Than 40mph Road Hierarchy - COGP Category 4a + 4b 3a + 3b 2

Traffic Design Life (20 yrs) (Commercial vehicles per lane per day)

Section

Site

Category (HD36)

Site Definition

Up to 50 51 - 500

501 - 1000

1001 - 1500

1500 - 2000

2001 - 2500 > 2500

5.4.1 C Estate Roads (level/straight) AC 6 DSC

5.4.2 C Estate Distributor Roads and Estate Roads with steep gradients or tight bends

AC 10 CGSC

5.4.3 B Dual carriageway (non-event sections and minor junctions) HSC or

5.4.4 C Single carriageway (non-event sections and minor junctions) 7kN HRA or TSC Level 1 †

7kN HRA or TSC Level 1

943 (45C) or TSC Level 1

943 (45°C) or TSC Level 1 †

5.4.5

Q1,Q2,Q3

R

Approaches to and across major junctions (all limbs) Roundabouts (including exits)

HSC or 7kN HRA or

TSC Level 1 †

7kN HRA or TSC

Level 1 † 943 (60°C) or TSC Level 2 †

5.4.6 G1 Gradient 5% to 10%, longer than 50m: Dual and single carriageways

7kN HRA or TSC Level 1 †


5.4.7 As 5.4.6, above, but in a south-facing cutting

5.4.8 G2 Gradient steeper than 10%, longer than 50m: Dual and single carriageways

7kN HRA 943 (45°C) 943 (60°C)

5.4.9 As 5.4.8 above, but in a south-facing cutting 7kN HRA 943 (45°C) 943 (60°C)

5.4.10 K Approach to roundabout, traffic signals, pedestrian crossings, railway level crossings and similar features

7kN HRA or TSC Level 1

†



Consult TAG

KEY

High Stone Content asphalt should only be used on sites where there is no history of wet skid accidents. No texture depth specification is applicable for this material. † Where materials will soon be covered with high skid resistant surfacing a smoother textured material such as High Stone Content asphalt or gritted TSC may

provide a better base. See section 10.1 and/or consult Technical Advice Group to discuss the issues. NB (i) For HRA mixtures a surface texture of 1.2 mm shall be specified in all circumstances. (ii) For TSC mixtures a surface texture of 1.3 mm shall be specified in all circumstances (iii) For Bends of Radius less than 500m see Section 5.4.11.

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GENERAL NOTES TO TABLE 5/3 1 Where Clause 943 HRA - 943 (45ºC), 943 (60ºC) or TSC – 942 Level 1, 942 Level 2 - is proposed, guidance from the Technical Advice Group

(TAG) shall be sought and design information passed to TAG for comment. 2 Where the existing surface has rutted it may be necessary for it to be planed out prior to laying Clause 943 HRA, or Thin Surface Course

mixtures. Failure to do this is likely to lead to the old surface continuing to deform under the new, deformation, resistant, material. Key AC6 DSC = Asphalt Concrete 6 mm Dense Surface Course AC10 CGSC = Asphalt Concrete 10 mm Close Graded Surface Course AC14 CGSC = Asphalt Concrete 14 mm Close Graded Surface Course 7kN HRA = HRA 30/14 – 6-8kN stability TSC = Thin Surface Course HSC = High Stone Content Asphalt 943 (45°C) = HRA meeting 45°C wheel tracking spec 943 (60°C) = HRA meeting 60°C wheel tracking spec

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5.4 Sites with a Speed Limit of Less than 40 mph 5.4.1 Shared Surface and Residential Roads serving up to 50 properties (level/straight) (C) Most estate roads carry very few commercial vehicles with only the weekly refuse

collection vehicle and occasional delivery vehicles trafficking them, apart from cars. Consequently, an Asphalt Concrete Surface Course is normally adequate for the loads imposed. The preferred surfacings for shared surface and residential roads serving up to 50 dwellings are detailed in the MASS document. The low vehicle speeds mean that only a nominal amount of surface texture is necessary. In the unlikely event that such a road is expected to carry more than 50 commercial vehicles per lane per day by the end of the surfacing 'design life' (i.e. 20 years) then it should be considered to be within the most appropriate of the other site categories covered by this table. Additionally, on steep sites or those with very tight bends more surface texture would be beneficial - see section 5.4.2.

Summary



THC/IWF Appendix

Up to 50 AC 6 dense surf 100/150 - BS EN 13108-1

7/1/F

>50 See most appropriate of the other site categories N/A

N.B. The PSV and AAV of the coarse aggregate (retained on 2.36mm sieve) in the

AC 6 Dense Surf shall be specified in accordance with section 4 of this document.

The fine aggregate (passing 2.36mm sieve) plays a significant part in the

skid resistance of AC 6 Dense Surf hence limestone aggregate or natural sand fines shall not be permitted.

Limestone Coarse Aggregate shall not be permitted in any surfacing

mixtures for carriageways. 5.4.2 Estate Distributor Roads and Estate Roads with Steep Gradients and/or (C) Tight Bends

- these sites are similar to those in 5.4.1 except that the gradients/bends make more texture than that given by a 6mm nominal size material desirable - i.e. a 10mm Close Graded Surface Course is appropriate.

Summary



THC/IWF Appendix

Up to 50 AC 10 close surf 100/150 7/1/E

>50 See most appropriate of the other site categories N/A

N.B. The PSV and AAV of the coarse aggregate in the AC 10 Close Surf shall be

specified in accordance with section 4 of this document.

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The use of crushed rock fines has created problems with the durability of AC 10 Close Surf in the past. Consequently, a mixture of 'crushed rock with sand fines' other than limestone shall be specified.

Limestone Coarse Aggregate shall not be permitted in any surfacing

mixtures for carriageways. 5.4.3 Dual Carriageway (non-event and minor junctions) – (B) these site categories have been considered jointly as it is likely that any scheme

involving a dual carriageway will also include at least minor junctions. As mentioned in 5.3.2, sites of this type require a material resistant to rutting but

due to lower traffic speeds associated with Table 5/3 surface texture is less important - providing a site does not have a history of skidding accidents. However, as traffic flows increase and congestion rises texture becomes more important, even at speeds below 40mph.

Consequently High Stone Content (HSC) asphalt is given as an option for sites

carrying up to 500 cv/lane/day where no history of skidding accidents exists. 55/14F (14mm nominal size) material gives more texture than 55/10F (10mm) material but the latter is less liable to segregation and slightly more tolerant of hand laying/raking operations. Engineers should bear these factors in mind when choosing which of these materials to specify.

Summary


History of Skidding Accidents


THC/IWF Appendix

Up to 500 No HRA 55/14F (or 55/10) surf -

BS EN 13108-4, Table 4 .Marshall Stability = 7 kN minimum

7/1/G

Up to 500 Yes HRA 30/14F surf 40/60 des + PCCs –

BS EN 13108-4, Table 4 Marshall Stability = 7 1 kN Surface texture = 1.2mm minimum

7/1/B

501 to 1500 Yes/No HRA 30/14F surf 40/60 des + PCCs –


7/1/B

1501 to 2500 Yes/No HRA 35/14F surf 40/60 des + PCCs to

Clause 943 45°C wheel tracking requirements Level 1 Surface texture = 1.2mm minimum

7/1/C

> 2500 Yes/No HRA 35/14F surf 40/60 des + PCCs to

Clause 943 60°C wheel tracking Level 2 Surface texture = 1.2mm minimum

7/1/C

Up to 2500 Yes/No Thin Surface Course (TSC) Level 1

Surface Texture = 1.2mm minimum 7/1/L

N.B. The PSV and AAV of the PCCs and coarse aggregate in the High Stone

Content asphalt and TSC shall be specified in accordance with section 4 of this document.

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At traffic levels where TSC is given as an alternative to Clause 943 asphalt it

shall be specified to have the equivalent wheel tracking properties. [See Section 5.5.2 for additional guidance/requirements.]

5.4.4 Single Carriageways (non-event sections and minor junctions) (C + C)- these sites are very similar in terms of traffic stresses to those in 5.4.3 and hence

the same vehicle flow/material parameters have been used

Summary




THC/IWF Appendix


BS EN 13108-4, Table 4 Marshall Stability = 7 kN minimum

7/1/G

Up to 500 Yes HRA 30/14F surf 40/60 des + PCCs -


7/1/B



7/1/B

1501 to 2500 Yes/No HRA 35/14F surf 40/60 des + PCCs

to Clause 943 45°C wheel tracking requirements Level 1

7/1/C

Surface texture = 1.2mm minimum

> 2500 Yes/No HRA 35/14F surf 40/60 des + PCCs to Clause 943 60°C wheel tracking Level 2 Surface texture = 1.2mm minimum

7/1/C

Up to 2500 Yes/No Thin Surface Course (TSC) Level 1

Surface Texture = 1.2mm minimum 7/1/H or

7/1/L



At traffic levels where TSC is given as an alternative to Clause 943 asphalt

it shall be specified to have the equivalent wheel tracking properties. See Section 5.5.2 for additional guidance/requirements.

5.4.5 Approaches to and across major junctions and roundabouts – (Q1 + R) at speeds below 40 mph these site categories are similar in terms of the vehicle

stresses applied. Additionally, roundabouts in areas with speed limits less than 40mph tend to be of a more similar size and hence only a single surface texture level need be specified.

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Summary




THC/IWF Appendix


BS EN 13108-4, Table 4 Marshall Stability = 7 kN minimum

7/1/G

Up to 500 Yes HRA 30/14F surf 40/60 des + PCCs –


7/1/B



7/1/B



7/1/C



7/1/C

Up to 2500 Yes/No Gritted Thin Surface Course (TSC)

Surface Texture = 1.2mm minimum Consult TAG for Specification

7/1/H




it shall be specified to have the equivalent wheel tracking properties. [See Section 5.5.2 for additional guidance/requirements]

5.4.6 Gradient of 5% to 10% for more than 50m – (G1)

as previously noted gradients resulted in longer loading times for the road surface which can result in deformation. Additionally, the importance of surface texture is greater for sites with gradients to help prevent skidding. Consequently, minimal textured surfaces (e.g. High Stone Content asphalt) are not advisable in such cases.

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Summary



THC/IWF Appendix


Table 4 Marshall stability = 7± 1kN Surface texture = 1.2mm minimum

7/1/B




> 2500 HRA 35/14F surf 40/60 des + PCCs to Clause 943 60°C wheel tracking Level 2 Surface texture = 1.2mm minimum

7/1/C

Up to 2500 Gritted Thin Surface Course (TSC) Level 1

(min. 40 mm thick) Surface texture = 1.2 mm minimum Consult TAG for specification

See TAG

N.B The PSV and AAV of the PCCs and coarse aggregate in the TSC shall be

specified in accordance with section 4 of this document. At traffic levels where TSC is given as an alternative to Clause 943 asphalt


5.4.7 Gradient of 5% to 10% for more than 50m on a south facing carriageway (G1) - the comments in 5.4.6 are equally valid for these sites where the extra surface

heat resulting from a south facing carriageway makes deformation resistance even more important. Minimal textured surfaces (e.g. High Stone Content asphalt) are not advisable.

Summary



THC/IWF Appendix

Up to 500 HRA 30/14F surf 40/60 des + PCCs –

BS EN 13108-4, Table 4 Marshall stability = 7± 1kN Surface texture = 1.2mm minimum

7/1/B

501 to 1500 HRA 35/14F surf 40/60 des + PCCs


7/1/C


1501 to 2500 HRA 35/14F surf 40/60 des + PCCs to Clause 943 60°C wheel tracking Level 2

7/1/C


> 2500 HRA 35/14F surf 40/60 des + PCCs to Clause 943 60°C wheel tracking Level 2 Surface texture = 1.2mm minimum

7/1/C

Up to 2500 Gritted Thin Surface Course (TSC) Level 2

(min. 40 mm thick) Surface texture = 1.2mm minimum Consult TAG for specification

7/1/H

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N.B The PSV and AAV of the PCCs and coarse aggregate in the TSC shall be specified in accordance with section 4 of this document.



5.4.8 Gradients steeper than 10% for longer than 50m (G2) - sites of this type require similar resistance to deformation to those in 5.4.7. The

steeper nature of these sites makes texture and skid resistance very important despite traffic speeds of below 40mph.

Summary




THC/IWF Appendix

Up to 500 Yes/No HRA 30/14F surf 40/60 des + PCCs –


7/1/B



7/1/C


1501 to 2500 Yes/No HRA 35/14F surf 40/60 des + PCCs to Clause 943 60°C wheel tracking Level 2

7/1/C



7/1/C

N.B The PSV and AAV of the PCCs shall be specified in accordance with

section 4 of this document. 5.4.9 Gradients steeper than 10% for longer than 50m in a south facing carriageway

– (G2) the comments in 5.4.8 are equally valid for these sites with a slightly greater

resistance to deformation necessary due to the higher road temperatures commonly occurring in south facing carriageways.

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Summary




THC/IWF Appendix

Up to 500 Yes/No HRA 30/14F surf 40/60 des + PCCs -


7/1/B

501 to 1000 Yes/No HRA 35/14F surf 40/60 des + PCCs to

Clause 943 45°C wheel tracking requirements Level 1

7/1/C


1000 to 2500 Yes/No HRA 35/14F surf 40/60 des + PCCs to Clause 943 60°C wheel tracking Level 2

7/1/C


> 2500 Yes/No Consult TAG See TAG

N.B The PSV and AAV of the PCCs shall be specified in accordance with

section 4 of this document. 5.4.10 Approaches to Roundabouts, Traffic Signals, Pedestrian Crossings, (K) Railway Level Crossings and similar features

- as mentioned in 5.3.11, these sites are subjected to great braking/acceleration forces and relatively long vehicle loading times. Therefore, deformation resistance is a prime requirement. Old rutted material should be removed prior to any surfacing works otherwise the new material will tend to copy the profile of the old surface over time. Where necessary Heavy Duty Asphalt Concrete (HDM) Binder Course and Base materials (containing 40/60 pen binder) or a design AC (Clause 929) material requiring a wheel tracking level similar to the surface course, should be used to give greater resistance to deformation.

Summary



THC/IWF Appendix

Up to 50 HRA 30/14F surf 40/60 des + PCCs –


7/1/B

51 to 1000 HRA 35/14F surf 40/60 des + PCCs


7/1/C


1001 to 2500 HRA 35/14 surf 40/60 des + PCCs to Clause 943 60°C wheel tracking Level 2

7/1/C


Up to 2500 Gritted Thin Surface Course (TSC) Level 1 Surface texture = 1.2mm minimum Consult TAG for specification

7/1/H

> 2500 Consult TAG See TAG

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N.B The PSV and AAV of the PCCs and coarse aggregate in the TSC shall be specified in accordance with section 4 of this document.



5.4.11 Bends of Radius - less than 500m

At speeds below 50 mph bends of radius 100m - 500m and, or less than 100m, are not considered as specific site categories. At such speeds there is little risk of aquaplaning and hence such sites should be assigned the most appropriate site category from Table 5/3. However, where sites include bends of radius less than 100m, Engineers are advised to consider the issues raised in Section 5.3.13 and exercise 'engineering judgement' when specifying surfacings. Traffic flows will need to be taken into account as part of this exercise.

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5.5 Detailed Consideration Of Alternative Surfacing Materials 5.5.1 Porous Asphalt

The use of Porous Asphalt is no longer advocated due to the very short service life which can be anticipated and problems with severe icing. Where the need to control noise and spray on the highway are paramount, refer to the section on Thin Surface Courses (TSC). Where a porous surface is required for drainage purposes then, for very lightly trafficked situations only, permeable block paving may be considered, but it must be borne in mind that this requires a completely different form of construction.

5.5.2 Thin Surface Courses (TSC ) - laid 30mm to 50mm thick Thin Surface Courses (TSCs) have evolved out of Stone Mastic Asphalt (SMA)

technology. Stone Mastic Asphalt (SMA) was originally developed in Germany to resist the

abrasive effects of studded tyres. German SMA is a very dense, binder rich material which yields both high resistance to deformation and great durability. Unfortunately the SMA mixes developed for use in this country were modified to accommodate the need for surface texture which resulted in a more open structure and consequent poor durability. The majority of suppliers have now moved away from “generic” SMA to develop their own proprietary Thin Surface Course materials, incorporating fibres, polymers or other additives to extend durability. These TSCs are now generally covered by BBA/HAPAS approvals and Clause 942, requiring a guaranteed life of at least 5 years. TSCs in general offer some vehicle noise and spray reduction properties but even though Clause 942 requires a guaranteed life of five years, the expectation of durability is still significantly reduced when compared to HRA. Where there is an overwhelming need to exploit the benefits of TSCs this should be done with the knowledge that an ongoing programme of preventive maintenance will be required – see Section 6.4 on Rejuvenation treatments.

It should be borne in mind also that the structural contribution of TSCs is

somewhat less than that of HRA/Asphalt Concrete in terms of load bearing capacity - of the order of 50% in many cases - and they can suffer from fatigue cracking when laid on a very flexible substrate. Accordingly these materials should only be used where structural improvement is not an issue and the underlying construction is sufficiently stiff/impermeable. TSCs are generally laid 30mm thick for a 10mm nominal sized material and 35mm thick for a 14mm sized material (although this can be increased to 40mm and even 50mm, if necessary).

TSC requires no pre-coated chippings to be applied and hence the roller can

stay tight behind the paver making these materials less susceptible than HRA to the effects of cold weather during laying. Additionally, the lack of a chipping machine on site means that no side loading is required and hence less of the carriageway needs to be closed off. This may mean that sites can be resurfaced

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with TSC under traffic control whereas HRA surface would necessitate a road closure but this is not always the case.

It is for the above reasons that TSC is a popular material with Contractors and

the public. Accordingly, TSC is often proposed as an alternative to other surfacing materials - especially HRA and chippings. Where such proposals are forthcoming they should be subject to very careful scrutiny, especially where such proposals are received at the last minute. Under the relatively rare circumstances where it is decided retrospectively to approve the use of TSC in lieu of HRA, etc. engineers must review associated requirements for testing to make it clear such approval is conditional on such additional testing as may be required for TSC works. The benefits of TSC are only achieved if it has been properly compacted. This is ascertained through determining the 'air voids' content and wheel tracking characteristics of cores taken from the TSC as laid.

In addition to the guidance contained herein Reference should be made to CSS document ENG/1-03 “Advice Note for the Specification of Thin Surfacings”.

When first laid TSCs generally have a very binder rich appearance with a binder

film thickness significantly greater than that of 'conventional' materials such as HRA or Precoated chippings. Consequently it can take significantly longer for traffic to wear the binder away and expose the coarse aggregate - up to 3 years on lightly trafficked sites. It is now generally accepted that early life skid resistance under dry conditions can be nearer to the wet skid resistance levels typical for surfacings like HRA.. It appears that once a skid is initiated the heat generated in the vehicle tyres can liquefy the thick binder film on the TSC and this might catch some drivers unawares. Additionally, it is now accepted that new TSC surfaces can pose an enhanced risk of slipping to horses – ref CSS/British Horse Society Report ENG/3-05 “Horses and Highway Surfacing”

Accordingly when utilising TSCs, engineers must take steps to minimise the risk

of skidding and to warn road users as appropriate. To minimise risks it is now recommended in Hampshire that grit to HCC clause 973AR be applied during the laying of new TSC surfacings as follows:

1. On all sites to be overlaid by a non-thermoplastic based high friction

surfacing as a matter of course (see also Section 10).

2. On a site specific basis based on engineering judgement:-

i. bends with a radius <250m (where speed limit is 40 mph or greater);

ii. gradients of greater than 5% where more than 50m long (single carriageways - both directions and dual carriageways - downhill only);

iii. roundabouts (not mini-roundabouts); iv. within 75m on the approaches to any roundabout, junction,

pedestrian crossing, traffic signals, railway level crossings or similar features.

v. Sites used regularly by horses

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During periods where TSC is uncovered awaiting a high friction surfacing 'Slippery Road' signs shall be erected and maintained until such time as the HFS has been applied. A period of up to 12 weeks after gritting may be stipulated by some Contractors before they will guarantee the performance of High Friction Surfacing. Such periods must be identified through early discussions with Contractors so that they can be built into works programmes if necessary.

For all other sites where TSCs are applied, a risk assessment shall be undertaken. Where there is a perceived risk of skidding in early life, ‘Slippery Road’ signs shall be erected and maintained until such time as the aggregate becomes exposed.

In addition to early life issues, consideration must be given to the potential impact on driver behaviour in a wider context. TSCs shall not generally be used on evolved highways with questionable geometry ( ie outside the parameters set down in Volume 6 of the DMRB ) where the speed limit is 40 MPH or greater. Under exceptional circumstances eg where there is no viable alternative, TSCs may be used at such sites in combination with other measures to reduce risk with the approval of the appropriate Area Director.

5.5.3 Micro- Asphalts (Thin Surface Courses) laid less than 25mm thick Micro asphalts were originally developed in France and the technology has

been imported into the UK. These materials are generally laid cold, although some may be laid hot and are an ideal solution for heavy fretting or ravelling.

Micro asphalts are thick enough to regulate minor surface imperfections and are

more beneficial to riding quality than a surface dressing. However, they do not add significantly to the structural strength of a pavement and Micro asphalts should not be applied to any road which exhibits a significant amount of cracking or deformation.

The decision whether to use a Micro asphalt instead of a conventional HRA/Asphalt Concrete surfacing or surface dressing will generally require engineering judgement, however, the following are some factors to assist in making this decision:

i) Based on analysis of the 'Code of Good Practice' a Micro asphalt should

typically be considered for any site which generates a HAMP rating of less than 105 for resurfacing but which would require more than 10% by area to be patched prior to surface dressing.

ii) Micro asphalt is likely to be more practical than a conventional surfacing

where kerb heights are limited. iii) Micro asphalt can be an alternative to surface dressing on sites where

the existence of surplus chippings would be unacceptable;

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iv) Micro asphalt can be an alternative to surface dressing where aggressive power steering is likely to cause stripping

v) Micro asphalt can be used to tidy up roads (see 5.4.1 and 5.4.2) or

bituminous footways which have suffered poor or numerous utility reinstatements and where a more even surface and uniform appearance is desired;

vi) In specifying Micro asphalt care needs to be taken in respect of surface

texture. The relative lack of surface texture obtained from many micro asphalts make them unsuitable for use on anything other than estate roads/estate distributor roads. However some products such as Ralumac 2000 do now guarantee a good rugous texture which makes them applicable to a much wider range of roads.

On concrete carriageways where there is a joint problem the joints must be

adequately repaired either prior to the Micro-asphalt being laid or afterwards using a suitable joint treatment (e.g. Fibrescreed). There is a need also to consider the potential for increasing the temperature range of the road by applying a darker surface in such a thin layer. This may increase further cracking or joint deterioration as a result of the larger temperature range the concrete is subjected to.

In any situation, consideration must be given to the effect on existing covers and

frames. Whilst the use of a Micro-asphalt may eliminate the need to raise ironwork, this is not always the case, since the final thickness can vary.

5.5.4 Permanent Cold-Lay Surfacing Materials (PCSM)

As a result of developments under the New Roads and Street Works Act (NRSWA) a number of PCSMs have been approved by BBA/HAPAS for use as Surface Courses and Binder Courses in footways, cycleways and carriageways. As time progresses more and more PCSMs are likely to be approved and will be increasingly used by Utility companies. It is also possible that Contractors on maintenance schemes may propose the use of PCSMs in the future.

It is important to note that under the BBA/HAPAS approval system PCSMs are

individually categorised in terms of their equivalence to conventional hot-lay materials. PCSMs may be approved for use within footways only or also carriageways. Additionally, they may be approved for use in only the Binder Course or also as a Surface Course and finally their equivalence to 40/60 pen, 100/150 pen or 160/220 pen binder grades is also categorised. It is crucial that PCSMs are only used in the locations for which they are approved and that they are equivalent in performance to the grade of hot material normally specified. If a 160/220 pen equivalent PCSM were used in place of a 100/150 pen or 40/60 pen hot-lay material excessive deformation is likely to occur under traffic.

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Subject to ensuring BBA/HAPAS approved PCSMs of the correct grade are used in the correct place, they can generally be used in Hampshire.

5.5.5 Grouted Macadam Surfacings

Grouted macadam surfacings (e.g. Miles Macadam’s Hardicrete) have been developed for use in ports to withstand the exceptional forces associated with the tracking of container cranes. They consist of an open-graded bituminous 'receiving course' into which is vibrated a grout to provide an extremely strong material that is highly resistant to deformation, fuel spillages and fretting. These materials have the potential to offer solutions to very high stress highway sites but must be applied to a very sound substrate and cured fully before trafficking or they may fail prematurely.

The material can also be coloured and the combination of factors have led to it

being specified on a number of schemes where durable colour was as, if not more, important than stability. Variations exist in terms of the degree to which the grout penetrates the 'receiving course' and the type of grout (cementitious or asphaltic) used. The most long established products now have BBA/HAPAS approval. It is recommended that only BBA/HAPAS approved materials and appropriately certificated Contractors are used for laying this type of material.

Use of these materials is not without its pitfalls and problems have been

experienced with delamination of road markings. Where cementitious grouts are used the laitance must be removed and a suitable primer applied prior to marking.

TAG shall be consulted over any sites where Engineers feel such materials are necessary due to their specialist nature – Tel 01962 845735.

6 SURFACE DRESSING

6.1 Surface Dressing on Carriageways

Surface dressing is to be undertaken in accordance with the Highways Maintenance Management Plan as part of the annual programme of works.

Surface dressing should only be used where the road is sound structurally, riding

quality is acceptable and there is a reasonable degree of certainty that the dressing will perform acceptably in service. The widespread introduction of power steering across a range of vehicles and the damage which can ensue can render dressings unsuitable in locations where aggressive manoeuvring can be anticipated e.g. tight culs-de-sac.

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Where used appropriately surface dressing will seal the surface, restore texture depth and improve skidding resistance. If carried out at an appropriate time, dressing can prolong the life of the pavement but will not strengthen or reshape the road.

Current policy is that all surface dressing works are let under 'end-performance'

contracts. The 'Client' specifies the required PSV of the aggregate (see section 4.1) and recommends the chipping size (considering noise, etc) but the Contractor is otherwise responsible for the design of the dressing. However, it is advisable that Engineers are familiar with the requirements of Road Note 39 and RSDA (Road Surface Dressing Association) publications and aware of the wider design criteria such as traffic flow, road surface hardness, etc.

Generally, straight K1-70 emulsion is used on minor rural roads with polymer

modified emulsion binders being used on principal roads, 'high stress' minor roads and urban minor roads. Chippings will generally be 14mm, 10mm or 6mm nominal size aggregate with smaller chippings racked in. 14mm chippings shall not be used in the fast lane of dual carriageways or on urban residential roads where noise from the surface would be excessive. However, the largest possible size chipping shall be used everywhere that noise is not an issue. This should ensure the dressing does not suffer from premature embedment, resulting in a loss of texture and possibly skid resistance after few years.

Where isolated more serious deterioration has taken place within sites to be

dressed, limited local patching will be required and particular attention should be paid to the riding quality of such repairs (see also Section 7.1).

Deferred set materials shall not be used in pre-patching for surface dressing (see also Section 3.10). Hot dense materials using an aggregate of an appropriate PSV (in case the surface dressing is delayed or cancelled) must be used at all times with the material chosen to provide a surface hardness comparable with the existing surface . Patching should ideally be carried out in the year prior to surface dressing so that the material has had a chance to mature prior to the application of a surface dressing and thus avoid the potential for differential embedment.

6.2 Surface Dressing on Footways In recent years surface dressing of footways has advanced with the development

of purpose built machinery. The spray applied bitumen is never left exposed prior to the application of the chippings and this is more acceptable in Urban areas. A County wide programme is organised annually as for carriageway works. The contractor should be informed where there are numerous vehicle crossovers, existing evidence of damage by power steering or where vehicles may park on the footway so that the dressing can be tweaked accordingly. There is a possibility that dressing may not be feasible in some circumstances.

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7 REHABILITATION OF THE EXISTING SURFACE

7.1 Pothole Repairs and Patching

Under the new Term Highway Contract the Contractor is responsible for the

permanent repair of spot defects if they are called in as ‘emergencies’. It is the Contractor’s choice whether to undertake a one-hit permanent repair immediately or undertake an interim temporary repair/s prior to a permanent repair later. Where the option to undertake an interim repair is taken up the decision as to which of the various possible methods to use also rests with the Contractor however it is anticipated the programme for such works may be established in consultation with local client engineers.

To inform any such debate, guidance on the most practical solution under any

given circumstances, arising from an internal study conducted during 2001/2, is reproduced below as Table 7/1.

In undertaking permanent repairs, the objective must be to realise a surface

finish which matches as closely as possible that of the original and adjacent surface. This is particularly the case for reinstatements in high stress areas such as bends – see section 3.6

It must be recognised that many modern surfacing materials e.g. TSCs are

designed specifically to be laid by machine and special skills/care is required in order to lay them effectively by hand even where hot-boxes are used. Some manufacturers offer variants which are modified slightly (generally smaller nominal size or denser to resist segregation) for hand lay work. Even with Hot Rolled Asphalt, it is usual to reduce the stone content from 30/35% to 15% for hand-lay work

When pre-patching for surface dressing works, patching materials should match

the hardness of the existing surfacing as closely as possible to avoid differential embedment. Where in doubt HRA with chippings or High Stone Content (55%) asphalt are likely to give good service. More detailed guidance is contained in the document "Preferred Method for Patching" produced by the Standing Committee for Highway Maintenance (ISBN-0902319-96-5). Patching should ideally be carried out in the year prior to surface dressing so that the material has had a chance to stabilise prior to the application of a surface dressing. It has been suggested that if more than 10% of the area needs to be patched it may be more economic to resurface instead of patching and subsequent surface dressing.

The edges of patches should be saw cut and the cut faces and the prepared

base painted with bitumen to enable a good bond with reinstatement materials to be achieved.

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Table 7/1 - Guidance on the Suitability and Economics of Patching Methods

TREATMENT

Pothole Repair

2-Man Hot Patching

4-Man Hot Patching Jetpatcher Infrared

Isolated Pothole <1m2 in area and <250mm deep £

Isolated Pothole >1m2 in area and/or >250mm deep

T £ ?

Isolated Pothole - with adjacent multiple cracking

T £ ?

Multiple Potholes - within a 10-15m lane length - with/without adjacent cracking

T ?

Multiple Potholes - over a 50m lane length - with/without adjacent cracking or severe fretting

T £ ?

Reinstatement Joints Open joints associated with utility reinstatements or old patching

? ?

Submerged Pothole - any size or adjacent surface condition

T SP/A2

grout only

Minor £ ? Fretting - isolated small/medium Severe £ ?

Minor £ Fretting - larger areas or multiple smaller ones in close proximity

Severe £

Slight loss ?

HIGHWAY DEFECTS

Loss of riding quality

Severe loss ?

KEY: Based upon combination of treatment properties and cost: = Treatment likely to be suitable and economic in most cases ? = Treatment likely to be suitable and/or economic in some circumstances but not others = Treatment unlikely to be suitable and/or economic in most cases T = Suitable as a temporary repair but should be scheduled for a permanent treatment £ = Suitable treatment but unlikely to be economic in most cases SP/A2 = CMS Pozament’s SP/A2 Set Accelerated Grout NOTES: At ambient temperatures of 30C or less, deferred set may not have sufficient mobility to perform well in pothole

repairs. Where feasible, a permanent hot repair should be scheduled instead under such conditions. Larger repairs will probably require a permanent repair to be scheduled due to the greater risk of deformation on

larger repairs. Infrared patching will be less economic during cold weather periods due to the length of time needed to raise the

surrounding road surface to the required temperature to enable it to be scarified. Only suitable in instances where depth of pothole is of approximately 100mm maximum depth with bituminous

material visible at the base of the pothole.

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7.2 Reinstatements Within Special Surfacings Reinstatements/patching within areas of special surfacings (e.g. Thin Surface

Courses, Stone Mastic Asphalt, Porous Asphalt, Coloured Surfacings, Calcined Bauxite etc) on a 'like for like' basis are often expensive and/or impractical due to the small quantities involved. The 2002 revision to the ‘Specification for the Reinstatement of Openings in Highways (SROH) – S6.4 - includes requirements in relation to this which are also applicable to HCC maintenance works. Table 7/2 is based upon these requirements but does include some differences. Where surface texture values are noted these are nominal values as most reinstatements are of insufficient size to allow for anything other than hand chipping.

TABLE 7/2

Acceptable Alternative Material For Reinstatements/Patching

Primary Material SPEED LIMIT < 40mph

SPEED LIMIT 40mph OR GREATER

Comments/ Limitations

Thin Surface Courses (TSC) Stone Mastic Asphalt (SMA)

14mm/10mm TSC as appropriate to reinstatement and nature of site 1.2mm surface texture

14mm TSC unless very small areas involved 1.5mm surface texture

Specify TSC mixtures to match existing as closely as possible but may be necessary to go one size smaller for handlay.

Calcined Bauxite Surfacings

Only calcined bauxite materials under clause 924SR to be used

As for sites <40 mph.

BBA/HAPAS grade 1 to be used.

7.3 Retexturing

Under certain circumstances, where the only defect is polishing or localised loss of surface texture to the existing surfacing, it may not be necessary to resurface. Provided the existing surfacing material is basically sound it may be possible to restore surface texture and hence skidding resistance by retexturing. Various methods are available but they need to be applied selectively to ensure the results meet expectations.

Experience has shown that where retexturing is used to remove excess surface

bitumen and uncover otherwise sound aggregate (e.g. fatted surface dressings) a long term improvement in skid resistance can be obtained. However, if the aggregate present is of a sub-standard Polished Stone Value (PSV) for the site category and/or traffic flows then retexturing may only provide a short term solution. Polishing will start to reoccur once trafficking recommences. Trials have shown that where PSV is seriously inadequate then skid resistance values can return to their previous levels within as little as 2-3 months.

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Based on experience in Hampshire, Table 7/3 below has been prepared giving

guidance on the technique/s likely to give the best results under any given circumstances.

Table 7/3 Guidance on likely effectiveness of Retexturing Techniques

Suitability of Process Surfacing

Type Original Condition

Effect required from Treatment

Bush Hammering (eg Klaruw)

Shot Blasting

High Pressure Water Jetting

Chipped HRA

Polished Aggregate

Restore Microtexture

Likely to be effective

Likely to be most effective

Not Suitable

Chipped HRA

Embedded Chippings

Restore Macrotexture

Not Suitable



Chipped HRA

Embedded Chippings and Polished Aggregate

Restore Microtexture and Macrotexture

Not Suitable


Not Suitable

Close Graded Macadams/ HSCA/NTSC

Polished Aggregate




Not Suitable

Close Graded Macadams/ HSCA /NTSC

Inadequate surface texture due to abrasion


Not Suitable



Close Graded Macadams/ HSCA/NTSC

Excess binder on or in surface

Restore Microtexture and Macrotexture

Not Suitable

Not Suitable


Surface Dressing

Excessive Embedment / Fatting


Not Suitable

Not Suitable


Concrete Polished aggregate




Not Suitable

Concrete Loss of Surface Texture

Restore Macrotecture

Grooving necessary for high speed sites

Only suitable on low speed sites

Not Suitable

HSCA = High Stone Content Asphalt NTSC = Negative Textured Surface Courses

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A specification for retexturing - Clause 773AR has been included in the new Term Highway Contract.

7.4 Repave/Remix

Where only the very uppermost layer of a surfacing has deteriorated or where the height available for an overlay is restricted it may be possible to achieve savings over conventional resurfacing or inlay by using Repave or Remix. With these processes only part of the original surfacing is planed away and the remainder heated to accommodate a reduced surface course inlay.

Where Repave/Remix are being considered, an investigation will be required to assess the existing surfacing material/s for suitability (HD31/94).

Repave and Remix were developed originally using HRA for the inlay but more recently they have been undertaken successfully using TSC bonded to HRA.

Repave/Remix processes are only likely to be viable for large schemes and shall only be used with the approval of the relevant Area Director following discussion with the Technical Advice Group.

7.5 Crack Sealing Techniques

Where the surface is cracked locally but otherwise sound then consideration should be given to sealing the cracks to prevent the ingress of surface water and further deterioration.

Engineers should however be aware that excess sealant can be slippery and is particularly hazardous to two wheeled vehicles. The aim therefore should be to achieve maximum penetration of the cracks yet limit surplus sealant on the surface to a minimum.

The previous HCC requirement for a maximum band width of 25mm has proven

impractical and this has had to be relaxed to a maximum band width of 40mm on the basis that the materials which are now to be used shall have better skid resistance properties than those used in the past. The requirement for a maximum thickness of 3mm remains unchanged.

In recognition of the greater width, the Highways Technical Group (formerly the Departmental Standards Committee) has declared the use of surface applied aggregate, previously optional, mandatory for all bituminous sealants. Therefore, a 3mm coated grit of sufficient PSV to provide a skidding resistance value of 55 (minimum) shall be applied to all bituminous over-band sealing.

The requirement for coated grit may be waived for non-bituminous (e.g. resin based) sealants where it can be demonstrated that a skid resistance value of 55 (minimum) can be achieved as laid and maintained for 12 months.

Bituminous Sealant shall be applied strictly in accordance with the

Specifications laid down in the Term Highway Contract (THC) for the Treatment of Joints and Cracks in Concrete and Bituminous Pavements. Approved Non-Bituminous Sealant shall be applied strictly in accordance with the manufacturers method statement.

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In high stress situations e.g. areas of High Friction Surfacing, where a skid

resistance value in excess of 55 is required, cracks should be repaired using a narrow Rout & Seal technique where the sealant remains slightly below the level of the surface and does not affect skid resistance adversely.

7.6 Asphalt Rejuvenation

Aside from the obvious deterioration caused by the action of traffic, bituminous surfacings are degraded over time by the combined effects of temperature fluctuations, oxidation, moisture and ultra-violet light. These factors together strip out the more volatile fractions of the bituminous binder, rendering it more brittle over time. The degradation manifests itself through loss of aggregate from the surface. This process effects all surfacings but has become more marked with the more widespread use of negative textured materials in recent years. If left untreated, progressive ravelling can erode these surfacings away to the full depth of the course in as little as eight years and sometimes less. The conventional solution to this problem would be to surface dress, however a dressing is not always appropriate. The aggregates available for dressing are generally now limited to a maximum of 65 PSV so dressing an existing surface which had say 68+PSV aggregate could potentially give rise to a skidding problem. Also, where a negative textured surfacing (SMA or Thin Surfacing) has been used to provide a quiet surface then a dressing may be unacceptable on the grounds of increased noise.

However, all is not lost as the degradation of surfacings can be slowed down and their life extended significantly through the timely application of rejuvenation sprays. These sprays replace the volatile bituminous fractions lost from the upper layer of the surfacing without completely masking the texture or covering high PSV aggregate. Various grades of sprays are under development from preservatives to rejuvenators to restoratives.

Trials are ongoing to determine the optimal timing of these respective treatments. It has been confirmed that treatment of deteriorated surfaces can be effective for several years but experience elsewhere suggests treatment prior to significant deterioration, topped up at five yearly intervals is likely to provide the greatest benefit in the long term.

This concept of preventative maintenance marks a significant departure from conventional practice but is considered essential in order to sustain negative textured surfaces where these are used in accordance with HCC noise policy.

A specification for the intermediate rejuvenation type treatment, Clause 990AR has been included in the THC contract.

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8 ROAD RECYCLING

The Environment Department has a policy of encouraging environmental initiatives and is keen to promote the use of road recycling where appropriate. Under certain circumstances it may be that the road structure has failed totally, possibly through the action of frost, and resurfacing or other conventional surface treatments are no longer appropriate. In these situations, either reconstruction or road recycling has to be carried out. The policy is to use recycled materials even when reconstructing but under certain circumstances in situ recycling may offer both financial and environmental benefits.

8.1 In-situ Recycling

A design guide and specification for structural maintenance of highway pavements by cold insitu recycling was originally set down in TRL Research Report TRL386 and has been developed further to encapsulate plant mixed materials in TRL611. A design philosophy is now available to accommodate a wide range of constituent materials and achieved stiffnesses.

Either cement, bitumen or a combination of both may be used as a binder for

recycling works. The choice will depend on site specific requirements and the type and quantity of road metal available for recycling. It may be necessary to modify otherwise unsuitable material by pre-treatment with lime and/or aggregate of a particular grading. Machines are now available which can recycle existing roads in-situ from approximately 1 metre wide up to the full width of the carriageway.

On lightly trafficked minor roads it may suffice to apply a surface dressing to the

recycled material. However on more heavily trafficked roads the recycled material is best relegated to the 'base' and Asphalt surfacing courses used above it. For type and thickness of bituminous surfacing to be applied reference should be made to the earlier sections of this policy document.

Sites with extensive ironwork in the road, shallow services, variable construction

and/or clay sub grades are less likely to be suitable and/or economic to recycle. Sites with few services, little ironwork, consistent construction and/or sand/gravel sub grades are far more satisfactory.

The pavement and mix design processes involved in road recycling are not

straight forward and hence the Technical Advice Group shall be contacted for advice on the testing required and suitability of the Contractor's design proposals.

In-situ recycling should only be carried out with the approval of the

relevant Area Director following discussions with the Technical Advice Group.

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8.2 Ex-Situ Recycling – ( Cold Recycled Bituminous Bound Material)

In recent years some considerable ex-situ recycling work has been undertaken in Hampshire. In this process lime/pfa is added to screened road planning’s together with some additional foamed bitumen in a mobile or static plant. The recycled material can then be laid and compacted using conventional paving plant. Experience has shown that quality control and mix design testing are critical to the success of the process together with a high standard of workmanship. This process has been used extensively for base or sub-base substitution in all classes of road. It has also been used to replace sub-base and binder course material in footways. On some occasions only surface dressing has been required to provide the surface course. Hampshire standard detail drawings now include Cold Recycled Bituminous Bound Material (CRBBM) in footway construction and for haunch repairs on B, C and U class roads . The material is generally mechanically stable once fully compacted and can be trafficked for a short while. Due to the nature of the recycled material traffic should only be allowed to run on it for as short a time as possible. The recycled material has a ‘drier’ appearance and hence has a tendency to fret under turning/braking traffic. It will deform if vehicles are allowed near an unsupported edge or to stand for a time on a freshly laid surface. The material will usually gain sufficient strength to act in its primary capacity within the first day or so but where used as a binder course, does not provide the support required for ironwork for some months. Ironwork should be bolted down under these circumstances.

A Heavy Duty Grade, incorporating cement, is also available and should be used on A class roads or anywhere a faster cure/load bearing capacity is required. It must be recognised though that unlike the standard material the Heavy Duty Grade has a very limited installation window of only a few hours. The THC, IWF and Hampshire’s Model Contract Document all include a specification (Clause 948SR) for CRBBM.

9 CONCRETE SLAB CARRIAGEWAYS The maintenance of concrete slab roads can prove particularly troublesome.

9.1 Joints

Where the joint edges are basically sound, joint sealing treatment shall be

carried out in accordance with Hampshire's Term Highway Contract.

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However, where the joint edges have deteriorated serious consideration should be given to the use of a rout and seal treatment such as the Fibrescreed recessed joint treatment systems. The depth and width needing to be routed out will vary both within a site and between sites. However unless all deteriorated material is removed any treatment will last only a minimal time. It is important to ensure adequate supervision is given to such works as instances where Fibrescreed type material has not bonded to the surrounding surfacing (due to excessive moisture and poor preparation) have been noted.

9.2 Exposed Slabs

Where the concrete is to be left exposed, treatment may be limited to stabilisation of voids by grouting and superficial repairs using rapid hardening cement and/or epoxy mortar. Detailed guidance on repairs to concrete carriageways is contained in the Highways Agency/Britpave manual titled ‘Concrete Pavement Maintenance Manual’ (ISBN 0-946691-89-4) (Environment Library Ref R7895) and HD 32/94 of Volume 7 of the Design Manual for Roads and Bridges.

9.3 Overlaying

Where an overlay is to be applied, consideration must be given to possible movements at joints. It is very important to ascertain whether any movement occurring is thermal in nature or whether the concrete slabs are 'rocking'. With 'rocking slabs' it may be possible to visually see the slabs moving as a result of commercial vehicle movements. However, if when standing near the suspect joint, ground vibrations are felt then it is reasonable to think that slabs are 'rocking'. TAG can advise on suitable survey work to identify the degree of movement and whether treatment is necessary.

The consequences of thermal movement (reflective cracking) may be overcome in one of the following ways:

By applying a very thick overlay, usually 150mm minimum such that

thermal stresses are negated. This is very expensive and often not a practical solution. A nominal reduction in the thickness of overlay required can be achieved in one of two ways as follows:

By reinforcing the overlay. Various grids have been used successfully at a

number of sites in Hampshire, in particular on the A338 at Blashford and the B3004 near East Worldham.

Additionally, more recent work using metal meshes has indicated that these may offer improved performance. In all cases, the appropriate manufacturers instructions for installation shall be adhered to rigidly. General guidance on the use of asphalt reinforcement grids is given in section 12.

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By employing a Stress Absorbing Membrane (SAM) at the interface. SAMs ensure that localised stresses are dissipated within the overlay such that reflected cracking does not occur. A number of proprietary SAMs are available, some preformed, others applied hot. Again the manufacturers instructions must be adhered to rigidly. SAMs may be applied locally or as an overall mat, although experience now suggests that local treatments are not particularly effective and SAMs tend to be less effective than reinforcement. The cost and benefits of SAMs and reinforcement should be considered on a site to site basis.

Where slabs are very badly deteriorated and where an overlay can be

accommodated, it may be possible to convert the existing pavement into a flexible sub-base/base layer using a “crack and seat” technique. However, cracking and seating should only be undertaken following an investigation to confirm there is a substantial granular base beneath the concrete. Failure to observe this caveat is likely to result in a structural failure.

As an expedient, on structurally sound sites where the opportunity for overlay is severely restricted, consideration may be given to polymer modified ultra-thin surface courses such as Tarmac’s Masterlayer, although the longevity of these products is not yet known.

10 HIGH FRICTION AND DECORATIVE SURFACINGS

10.1 High Friction Surfacings (and decorative surfacings derived from HFS systems)

Surface dressings can provide very high levels of skid resistance initially, but they

cannot generally cope with the extremely high stresses generated on the approaches to certain junctions, roundabouts, pedestrian crossings and traffic signals, etc. Although conventional bituminous surface courses are better able to cope with the stresses in such situations the skid resistance they can provide is limited by the properties of naturally occurring aggregates.

In circumstances where design criteria make it necessary to employ an aggregate with a PSV greater than 70 it will be necessary to use a proprietary High Friction Surfacing System. These processes (e.g. Spraygrip, Keygrip Epoxy 924, Safetrack HW etc) incorporate Calcined Bauxite which is a 'man-made' aggregate with an extremely high PSV.

Because of the stresses generated by vehicles braking on HFS it is imperative

that such treatments are laid on a 'sound' surface. Where the existing surface is cracked, rutted, polished, fatted and/or contaminated in some other way then it is likely some form of pre-treatment will be necessary. Under extreme circumstances it may be necessary to overlay or plane out and inlay a new receiving course prior to application.

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High friction surfacings may be hand or machine applied with either a thermosetting binder (e.g. epoxy, methyl Methacrylate (MMA), poly urea etc.) or a thermoplastic binder commonly used. Thermoplastic binders are hot applied usually by screed box leaving a ridged finish. Whereas, the others are applied cold (or warm) and produce a uniform finish. Thermosetting binders, particularly epoxies, generally offer superior performance (durability) but have tended to be slightly more expensive, some are slower to cure and otherwise less convenient than thermoplastics. This has led to thermoplastics often being used out of expediency but leading to maintenance problems in the longer term.

On traffic sensitive sites where frequent re-treatment cannot be tolerated then epoxy systems offer the greatest durability. However, the introduction of MMA binder recently has delivered a thermosetting system which can be laid and be subjected to traffic after one hour curing at any time of the year. As with all HFS materials the substrate must be sound, clean and dry prior to application. When laying HFS on open graded surfaces installers will often recommend the use of a scratch coat to reduce the demand for resin. However, experience indicates a high risk of de-bonding problems where scratch coats have been used and such recommendations should be resisted where possible.

A 3 year 'end-performance' specification for high friction surfacing treatments has

been incorporated within all of Hampshire’s standard contracts. The use of such a specification should ensure the performance of these products whilst allowing the maximum market competition in terms of both type and cost.

Where 'High Friction' surfacings are required to be applied to “fresh” surfacing

then there are some important factors to take into account. Firstly, the surfacing should be comprised of a material resistant to embedment of the resin system and low in texture to prevent the new resin pooling in the interstices between aggregate particles. Excess texture requires extra resin to be applied which will increase costs. The recommended receiving course for High Friction Surfacing is High Stone Content HRA or lightly chipped 30/14 or 35/14 HRA. The occasional practice of applying high friction surfacings to un-chipped 30/14 HRA shall cease. In such circumstances if the high friction surfacing wears away over time there would be no chippings within the surfacing to offer 'back up' skid resistance.

Thermoplastic and MMA materials can be applied to new bituminous surfacings

after 24 hours, although a longer period of trafficking is recommended, but Epoxy and polyurethane systems should only be applied to new surfacings after they have been trafficked for a minimum of 3 weeks. Trafficking wears away surface bitumen and exposes the aggregate to help produce a good bond with the resin system. Where binder rich surfacings such as TSCs are used then the wear period can be extended significantly, although this can be reduced by the application of sharp grit during the laying process

The specification covering the application of grit is covered by clause 973AR which is available from TAG and has been incorporated into the MCD, THC and IWF.

Whichever generic HFS solution is chosen, only those products holding the appropriate BBA/HAPAS certification are to be used. In view of the

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minimal cost differentials involved the Highways Technical Group (formerly Departmental Standards Committee) has advised that only Type 1 HFS materials and suitably certificated laying contractors be used for all carriageway HFS works to achieve the best possible life.

It should be noted however that not all Type 1 HFS materials are equal and

HAPAS certificates should be studied in detail to evaluate any limitations on the use of particular products.

Where maintenance or replacement of calcined bauxite materials is required

some factors need to be considered. A re-treatment (on top of the old one) may be possible providing the old treatment is not debonding from the underlying surfacing. In general terms cold applied treatments can be used to overlay cold applied treatments, hot applied treatments can be used to overlay both hot applied and cold applied treatments but cold applied treatments cannot be used to overlay hot applied treatments. However, engineers must be aware of the overall cumulative thickness of treatments that build up. Overlaying is best left until the original treatment is substantially worn away, as an excess build-up can lead to thermal cracking. In some instances it may be necessary to remove residual HFS prior to re-application. However, where a calcined bauxite treatment has to be removed care must be taken as burning off can release toxic fumes. Consequently, removal or repair of these products including superimposed road markings should be carried out using grinding/planing techniques (specialist fine planers now exist) or very high pressure water jetting. Accordingly, a risk assessment must be undertaken in all cases. Where burning cannot be avoided, operatives must be equipped with appropriate breathing apparatus. In such cases a more detailed risk assessment must be undertaken to assess any measures necessary to eliminate any danger to pedestrians in the immediate vicinity.

Following discussions by the Highways Technical Group ( formerly Departmental

Standards Committee ) all road markings on high friction surfacings shall be at least level with the surrounding high friction surface after treatment. It is accepted that markings may need to be applied in advance where a delay is envisioned and it is sometimes expedient to 'mask' road markings prior to re-treatment. However this practice can leave the markings below the level of the surrounding HFS which allows surface water to sit on top of the road marking thereby reducing night time visibility and causing a potential safety problem in the event of freezing temperatures also occurring. Under such circumstances, it will often be necessary to reapply markings on completion of HFS works.

High friction surfacings were intended to be used as an accident remedial

measure but now such treatments proliferate for other purposes. Their effectiveness in terms of impact on road users has been diluted. Consequently for this reason, and because of maintenance costs associated with such treatments, Engineers are advised to consider carefully whether such treatments are necessary. Guidance can be obtained through 'Safety Audits' or advice sought from the Safety Engineering Team.

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10.2 Coloured 'Gateway' Surfacings - General

Coloured surfacings are becoming increasingly common as a 'gateway' effect on the boundaries of residential areas. These treatments are very similar to the High Friction surfacings, but the aggregate used is of a lower PSV. Traffic stresses are reduced due to the lesser braking effects they are subject to, hence natural aggregates can be used instead of calcined bauxite.

It should be noted that unless the aggregate colour matches the pigment colour

used, the colour of the surfacing will change under trafficking as the binder is worn away and the aggregate exposed. The use of excessively bright colours should be avoided as they may be unpopular with the public and members on environmental grounds. Additionally, the use of very pale colours may result in insufficient contrast with road markings.

10.3 Resin Bonded Surfacing

These systems are in essence the same as HFS, or Gateway Surfacings using a thermosetting binder. A resin is applied to the prepared substrate on to which a selected aggregate is broadcast and the system allowed to cure. The aggregates used are usually fine grades (0/4 mm) of clean natural stone chosen for their appearance as well as the necessary engineering properties. On occasions the aggregate may be artificially coloured but this can fade or wear over time. Often the resin is pigmented to provide the desired colour. These systems are usually applied to pedestrian areas and have also been used on carriageways but with mixed success.

10.4 Resin Bound Surfacings

Products of this nature are produced in a similar manner to Asphalt Concrete. The binder, often clear but may be pigmented thermosetting resin, is mixed with a selected aggregate. The mix is then applied uniformly over the sub-strate and compacted. The aggregate is usually maximum 6 mm nominal size and can be graded or single size. Single sized aggregate may be used to convey a degree of porosity to the material thus allowing water to percolate through to the underlying material. In this form it is often used to surface tree pits. Layer thickness will be a minimum of 12 mm up to about 18 mm.

Life expectancy will vary with the choice of aggregate and the use of the areas to which it is applied but the range is approx. 5-15 years.

10.5 Decorative Asphalts

These consist of a range of asphalt concretes or hot rolled asphalts. The mixes are ‘normal’ asphalts but the binder used is a specially formulated clear binder. This allows the natural colour of the aggregates to be displayed. The aggregates are selected for their appearance in addition to the necessary engineering

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properties. This is often a difficult process as the essential properties are rarely matched by the desired appearance.

The binder tends to be ‘softer’ than those used for many surfacing materials, so their use is limited to pedestrian areas or lightly trafficked carriageways.

The production and laying techniques are essentially as any asphalt with the exception that all equipment needs to be kept scrupulously clean to avoid contamination.

11 BLOCK PAVING AND NATURAL STONE PAVING

11.1 General Guidance

Block paving is now an accepted surface treatment on the Highway and is the preferred solution for shared surface applications. Blocks can be made of concrete, fired clay or sawn from stone. This section addresses concrete and clay pavers. The use of natural stone blocks is dealt with in Section 11.6

Specifiers should be aware that clay pavers tend to polish more than concrete pavers, encourage the growth of moss/lichen and can become very slippery when wet. For this reason concrete pavers are the preferred option. Clay pavers are not to be used in the carriageway and may only be used in the footway subject to confirmation of PPTV criteria or satisfactory evidence of long term performance elsewhere

11.2 Block Paving for Vehicular Areas

The design and installation of block paving schemes shall be carried out in accordance with BS 7533 with special attention paid to the section giving guidance on sites requiring a modified design due to factors such as channelised traffic, etc.

All block paved roads shall be designed for traffic flows of greater than

0.5msa or any such higher value as may be appropriate. Designs for traffic levels of 'up to 0.5msa' shall not be permitted.

The riding quality of block paving is likely to be poor in relation to most other

surfacing types and should therefore only be used on very low speed roads where this characteristic is not so important. Although water dispersal offered by blocks is generally good due to the chamfered edges and good paths for water to escape, the texture of the blocks themselves is usually smooth and the overall skidding resistance will be governed by the aggregate used within the blocks.

The resistance to polishing of concrete blocks, clay pavers and natural stone

products is measured using the Polished Paver Test Value (PPTV) test – BS 7932: 2003. This is analogous to the Polished Stone Value (PSV) test used for aggregates and allows the skid resistance of block paving units to be specified using Table 4/1 in Section 4.1 substituting PPTV for PSV. Independent

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test results of less than nine months old for the particular product to be used should be obtained. Due to a number of factors, evaluation of PPTV test results is not as straight forward as it should be. Consequently, Engineers are strongly advised to consult the Technical Advice Group (01962 845735) on this subject. Additionally, suppliers may provide test data on a similar product saying that as the same raw material is used this result is representative of the proposed product. This is only partly true as the PPTV of a product depends upon both the raw materials used and the manufacturing process. All must be identical if a substitute PPTV result is to be considered representative.

The majority of blocks on the market have relatively low skid resistance and are not generally suitable for use within 50m of roundabouts, pedestrian crossings, traffic signals, railway level crossings or similar features. However, care should be taken to ensure that blocks of an adequate skid resistance are always specified by using Table 4/1 (substituting PPTV for PSV).

It is important to note that the PPTV required by Table 4/1 is not generally

dependent upon traffic speeds and hence skid resistance standards in traffic calmed areas should be identical to those used normally. Although traffic calming reduces vehicle speeds it also increases the degree of potential conflict between pedestrians and vehicles. The reduced speed and the typical site features introduced as part of a traffic calming scheme tend to bring pedestrians and vehicles together in the same road space. Consequently, until more research into accident rates and severities in traffic calmed areas has been undertaken, the standards required by Table 4/1 shall be used.

Research has shown that the quality of bedding sand is critical to the

performance of block paved roads. Sands shall be specified to comply with the relevant category in BS 7533: Part 3. In residential highway situations a bedding sand of at least a Category 1B shall be specified with Category 1A sand specified on all classified roads.

Experience has shown that the majority of sands do not comply with the

carriageway grades of sand in that they have excessive fines. Sampling and testing of such sands by the County Highways Laboratory is strongly advised. TAG can provide information on possible sources of carriageway grade sands (01962 845735). In addition, potential sources for the different sand grades can be found on the Internet – http://paving.org.uk/laying_and_jointing_material.php

Some companies now offer crushed recycled glass sand for laying course material. Providing this also complies with the requirements for laying course material it should perform well and it has been suggested that it may actually reduce weed growth.

Blocks may be used decoratively, to delineate pinch points in estate roads, or

even to construct rumble strips. If blocks are to be installed as part of a resurfacing scheme, consideration should be given to the difference in thickness involved. Blocks for use in any trafficked area shall be a minimum of 80mm thick. A course of blocks would be a minimum of 110mm thick (including sand bedding) and this must be considered at an early stage.

http://paving.org.uk/laying_and_jointing_material.php

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In traffic situations block paving shall only be laid in a 45º herring bone pattern. Experience has shown that if laid in running/stretcher bond the blocks are not confined enough to resist movement caused by traffic and increased noise is generated. Any other pattern will require specialist restraint measures and TAG should be consulted.

Inappropriate street furniture can cause problems with block paving sites and

should be avoided. The use of ironwork that can have blocks inset seems an elegant solution but needs very careful consideration. Such covers are generally much heavier than conventional cast covers and invariably require mechanical aids for lifting which is not always possible due to physical restrictions or TM requirements. Also many Utility Companies refuse to accept such covers.. Careful detailing of blocks around street furniture and ironwork needs to be provided as the appearance of schemes can be ruined by poor attention to these items. Surrounding blocks should be mortared in place. Sanding of blocks around covers must be undertaken with care, especially where inset covers are to be used. Instances where sand has become lodged between cover and frame have occurred which has led to difficulties in lifting the covers. In some cases the whole frame has lifted out, disturbing the block paving, when this has been attempted.

Where block paving will be suction swept an appropriate sealant (e.g.

'Keybond' from Marshalls) shall be specified to prevent loss of sand in the early life of block paving. If possible reduction of the vacuum on the sweeper is also desirable. The sealant may initially reduce the skid resistance of the blocks but needs to wear off relatively quickly. Where skidding is likely to be a problem signs should be erected. Advice should be sought from the sealant manufacturer some materials do not affect the skid resistance.

Attention is drawn to the possible need to top-up jointing sand on a number of

occasions until full penetration/stability is achieved - this may also require the delay in application of the sealant or an additional application after stability has been achieved.

There is also a wealth of informative literature available from the manufacturers of these products. A list of suppliers can be obtained from Interpave, the Concrete Block Paving Association.

11.3 Block Paving for Pedestrian Areas

Increasing numbers of claims are being received from members of the public who slip over on footways or other pedestrian areas. Research has shown that the incidence of pedestrians slipping increases markedly when the coefficient of friction drops below 0.4. Whilst there are no national standards for footway slip resistance the Highways Technical Group (formerly Departmental Standards Committee), based on the research currently available, have decided that until further research is carried out, an absolute minimum PPTV of 45 shall be specified for new works. For heavily pedestrianised areas (e.g. city centres) or where there are expected to be concentrations of vulnerable

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people or where gradients of steeper than 5% exist, a minimum PPTV of 55 shall be specified for blocks/pavers/slabs whether manufactured from clay, concrete or natural stone.

Further investigations have highlighted the need for a degree of surface texture

in footway materials. High PPTVs on their own do not necessarily provide sufficient protection from slipping. Paving materials should have some texture to provide sufficient contact area with footwear so that there is enhanced slip resistance in wet conditions. Polished and semi-polished products should be avoided. The Technical Advice Group can provide further guidance on this issue.

(K) Failure to specify sufficient PPTV levels for products runs the risk of resulting

in claims against the Highway Authority and expensive remedial treatments. Section 11.5 gives some guidance on improving the skid/slip resistance but such measures do not offer long term solutions. If a paving product is used which has inadequate resistance to polishing the only long term solution is likely to be to replace it with a more suitable product. Again the design and installation of block paving schemes shall be carried out in accordance with BS 7533

11.4 Block Paving for Shared Areas

Where blocks/pavers/slabs are to be used by both pedestrians and vehicles then such areas shall be designed, specified and constructed as in '11.2 Vehicular Areas'. Although, using slabs carries additional problems as by the nature of their size they are more vulnerable to breaking when trafficked. It is recommended that slabs to be over-run incorporate fibre reinforcement and a maximum size of 450 x 450 mm be used to reduce the possibility of failure.

11.5 Improving Skid/Slip Resistance

Problems with poor skid/slip resistance (particularly on clay and stone products) have resulted in a number of trials into ways of improving these properties. Methods used have included shot blasting, bush-hammering and chemical etching.

Shot blasting has generally produced only short term improvement (see also

section 6.1) – typically 2 to 3 months. Bush-hammering has been shown to give a longer improvement (approx 12-24 months) but does affect the appearance of the paving more than shot-blasting. It also carries the associated risks of breaking paving slabs and removing jointing material. The appearance of the paving ‘mellows’ with further pedestrian/vehicular trafficking but rejointing can add significantly to treatment costs overall. Chemical etching (e.g. ‘Slipstop’ process) has only been trialled but results indicate it performs similarly to shot blasting – depending upon the strength of the acid used. This type of treatment also affects the appearance of the paving.

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Engineers are advised to contact TAG (01962 845735) for further advice when considering such treatments.

11.6 Natural Stone Paving

Guidance on the use of natural materials in highway situations is available in a document called ‘Traditional materials – a guide to the use of natural materials in the Highway’. When specifying natural stone paving , in addition to defining criteria in respect of resistance to polishing, abrasion and weathering, consideration need also to be given to the edge profile and surface texture to be provided. Paving materials must have some texture to provide sufficient contact area with footwear so that there is enhanced slip resistance in wet conditions. Polished and semi-polished products should be avoided and the preference shall be for a “coarse textured” finish in accordance with BS EN 1341 with an average peak to trough dimension of 2mm. This equates to a surface texture, as determined by the sand patch method, of approximately 0.7mm.

12 ASPHALT REINFORCEMENT GRIDS

12.1 Choice of Grid Reinforcement

Asphalt reinforcement grids have been extensively used in Hampshire over the last 10-15 years with generally good results. However, experience has shown that different types of grid perform better in certain situations:

12.2 Thermal cracking

'Fine' cracks with no vertical displacement (e.g. reflective cracking over lean concrete, small works joint treatment) –Glass Fibre Grid with/without geotextile backing depending on site specific circumstances e.g. GlasGrid, Polyfelt, Rotatex, Rotaflex or equivalent.

The grid shall comply with the following requirements:

i) it shall be a glass-fibre mesh or a composite glass-fibre mesh on geotextile backing;

ii) it shall have a minimum tensile strength of 100kN/m in both longitudinal and transverse directions;

iii) The thicker the overlay the better. The minimum overlay thickness for the grid shall be 40 mm (some manufacturers require 50mm).

The grid shall be fixed to the carriageway using a bond coat approved by the grid supplier/ manufacturer or may be self adhesive.

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12.3 Cracking with some anticipated Vertical Displacement expected

Glass Fibre Composite Grid The grid shall comply with the following requirements: i) it shall be a composite glass-fibre mesh on geotextile backing; ii) it shall have a minimum tensile strength of 100kN/m in both

longitudinal and transverse directions; iii) The thicker the overlay the better. The minimum overlay thickness for

the grid shall be 40 mm (some manufacturers require 50mm). e.g. ABG Rotaflex 838SL, Polyfelt PGM-G 100/100, GlasGrid CG100, or

equivalent The grid shall be fixed to the carriageway using a bond coat approved by the

grid supplier/ manufacturer. An additional advantage of this type is that it provides a waterproof membrane

within the pavement reducing the ingress of water to the lower layers.

12.4 Clay Shrinkage cracking

Wider cracks with some vertical stepping - Polypropylene grid with/without geotextile backing depending on site specific circumstances e.g. Netlon AR1, Netlon AR-G or equivalent.

AR1 is difficult to install as it needs to be tensioned when being laid. The minimum overlay thickness for the grid shall be 70 mm. The composite grid shall be fixed to the carriageway using an emulsion bond

coat approved by the grid supplier/ manufacturer.

12.5 Concrete Joint problems/severe Clay Shrinkage cracking

Metal mesh either nailed or with slurry fixing system e.g. Bekaert's Mesh Track 1 or 2. Alternatively Maccaferri’s RoadMesh S, L or SL. Dependant on site requirements.

12.6 GridSeal

This is a proprietary system comprising of a composite reinforcing grid and a heavy application of a polymer modified bitumen followed by chippings to allow subsequent laying operations. This may be used in more demanding situations to protect against cracking propagation. Advice should be sought from Technical Advice Group and the supplier during the design stage if this system is to be considered.

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12.7 Guide to Successful Installation

In all cases the grids must be laid by contractors experienced with the laying of that type of product and strictly in accordance with the manufacturer's instructions. The following are a few points in need of particular note.

i) Special care shall be taken to ensure ‘rucks’ in the grid are kept to a

minimum and shall be cut and lapped where necessary or where instructed by the Overseeing organization.

ii) All grids must be laid flat, there must be no change in level. (some grids are capable of being laid on a planed surface)

iii) Unless otherwise approved by the Overseeing organisation, only a bond coat approved by the grid supplier/manufacturer shall be used;

iv) Should an emulsion bond coat be used it must be allowed to ‘break’ before applying the overlay or the composite grid.

v) Once the grid is laid it must remain dry until covered with the overlay. vi) Working methods shall ensure construction traffic does not run over

the uncovered grid more than is absolutely necessary; vii) All areas of reinforcement grid shall be covered by surface course

material by the end of the working day.

viii) Reinforcement grids shall be laid in widths of at least 1.5m such that they extend (as far is practical) a minimum of 0.75m, in all directions, beyond any crack or construction joint formed as a result of the works.

The decision as to which type of grid to use is complex and the mechanism of the deterioration resulting in the need for the grid must be understood. Consequently, it is strongly recommended that TAG should be consulted (01962 845735) on sites where grids are considered necessary.

13 FOOTWAYS

13.1 General Guidance Footway surfacings can take the form of Asphalt, Concrete or Natural Stone

flags, Block paving or Path gravel. 'TRL Application Guide 26 - Footways: Design and Maintenance (version 2)' provides comprehensive guidance on the design, construction and maintenance of footways. AG26 does not consider Path gravel but Hampshire’s Standard details and the associated Notes for Guidance include all of these materials.

The constructions included in the Standard details assume a sub grade

equilibrium CBR of 3% or greater. If it is believed the sub grade is poorer than

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this the sub base thickness should be increased to account for this, 'TRL Application Guide 26’ provides guidance on this or TAG can assist.

It is recommended that any flags used in areas of possible over running by

vehicles should incorporate fibre reinforcement and should have a plan area no greater than 450 mm x 450 mm. Any larger will be liable to break when loaded. It has been noted that tactile paving at corners has often suffered in this way despite the fact the units are 400 mm square. Substituting 100 mm x 200 mm concrete block paviours, with surface blisters, in this situation has largely overcome this problem.

The following tables extracted from 'Application Guide 26' and amended with

current terminology may be of use. See also section 3.10 on use of deferred set materials.

13.2 A note on Slurry Treatment of Footways

The use of basic slurry seals on footways has caused problems in the past (which has led to complaints by the public) and the process is no longer recommended for highway applications. However, micro-asphalts for footways have been developed as a true alternative to surface dressing and provision has been made to call these up under the Term Highway Contract.

For the time being however, the use of footway micro-asphalts should remain subject to approval by the appropriate Area Director.

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Table 13/1 – RELATIVE PROPERTIES OF TYPICAL SURFACING MATERIALS FOR FOOTWAYS

RELATIVE PROPERTIES

Slip

Resistance

Durability Surface Evenness Structural

Contribution

Appearance Unit cost

MATERIAL

Initial Long Term

Concrete 3 6 5 4 6 5 2 Block Paving Clay 2 6 5 4 6 5 2

Concrete 3 5 5 3 4 3 3 Slabs Natural

Stone 1- 4 5 5 3 4 6 1

Asphalt Concrete 4 4 6 6 6 4 4

Surface Dressing 5 3 n/a n/a n/a 4 6

Micro Asphalt 4 3 4 5 n/a 4 6

Poor Good Excellent

1 2 3 4 5 6

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TABLE 13/2 – MAINTENANCE TREATMENTS COMMON TO ALL TYPES OF FOOTWAY/ CYCLEWAY SURFACING

Treatments Defect Problem Temporary Long-term Depressions & bumps

Hazard for users Fill or ramp. Contact Undertaker if cause is failed reinstatement

Reshape surfacing

Rutting Hazard for users Fill Reshape surfacing.

Prevent overrun or reconstruct if necessary.

Slippery surface Hazard for users Warn users or restore macro

and/or micro texture Clean, restore texture or renew surfacing

Surface contamination

Hazardous Unsightly

Clean or neutralise Replace surfacing if necessary. Clean

Vegetation Tree roots cause

trips Warn users or ramp trees Reshape surfacing.

Consider replacing with a more suitable variety

Vegetation obstructs

footway Trim growth Consider increasing

frequency of maintenance Surface slippery Warn users. Clean Water Surface water Salt if freezing Reshape surfacing to

correct gradients and crossfalls

Blocked drainage Clear blockage Rectify any damage caused Burst mains Inform Undertaker, make safe

Reshape = relay modular paving, replace Asphalt Surface Course (and Binder Course) or overlay with new Surface Course,

overlay with thick slurry or use retread. Renew = relay modular paving using new units, remove and replace old asphalt material or concrete, or use retread.

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TABLE 13/3 - MAINTENANCE TREATMENTS: ASPHALT SURFACING Treatments Defect Problem Temporary Long-term Mosaic cracking Embrittled surfacing

Structural failure - -

Seal or replace surfacing. Replace surfacing, reconstruct if problem recurs.

Linear cracking Water ingress, trips - Seal, replace surfacing or

reconstruct if necessary Loss of surface aggregate

Loose or uneven surface

- Seal or replace surfacing

Potholes Trips, water ingress Fill holes Patch or replace surfacing

TABLE 13/4 - MAINTENANCE TREATMENTS: MODULAR SURFACING Treatments Defect Problem Temporary Long-term Broken or damaged modules

Unsightly appearance, water ingress

- Replace damaged modules, resurface or reconstruct if problem is due to overrun

Loss of jointing material

Water ingress, modules can move/rotate

- Replace jointing material, seal joints

Missing modules Holes, trips Fill holes Replace modules Rocking modules Hazard to users Relay modules Reconstruct if problem is

due to overrun Spalling of arrises or surfaces

Unsightly appearance

- Replace damaged modules

Trips Hazard to users Relay modules Reconstruct if problem is

due to overrun Widening of joints Water ingress,

modules can move/rotate

Fill wide gaps if a hazard Relay surfacing and edge restraint if necessary

Note: When relaying modular surfacing it is preferable to relay the whole area between edge

restraints.

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TABLE 13/5 - MAINTENANCE TREATMENTS: CONCRETE SURFACING Treatments Defect Problem Temporary Long-term Damaged joints Spalling, cracking,

water ingress - Seal cracks. Overlay or

replace joints and/or concrete

Cracking Unsightly, water

ingress - Seal cracks. Overlay or

reconstruct Weathering Scaling,

delamination, aggregate exposure

- Overlay or reconstruct

Corrosion of steel Cracking, rust - Seal cracks Trips Hazard for users Ramp or feather Overlay or reconstruct

TABLE 13/6 - MAINTENANCE TREATMENTS: KERBS AND EDGING Treatments Defect Problem Temporary Long-term Damaged or missing item

Loss of edge support - Replace kerb or edging

Horizontal or vertical steps

Hazard for road users and/or pedestrians

Relay item Seal cracks. Overlay or reconstruct

Poor channel alignment, delamination, aggregate exposure

Drainage dysfunctional

- Relay or replace kerb or edging

Vegetation Water run-off

prevented Remove vegetation, apply weed killer

Increase vegetation control maintenance frequency

Trips Hazard for users Relay item Replace kerb or edging

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APPENDIX A: PERMITTED PAVEMENT OPTIONS Requirements for Regulating Course The following table gives the regulating materials permitted under this contract and the range of thicknesses they can be laid over. Regulating thicknesses of less than 10mm/15mm (dependent upon the materials permitted within each surfacing appendix) shall be achieved within the thickness of the overlying bituminous material, unless otherwise agreed by the Overseeing Organisation. All Regulating Course material shall be laid in accordance with BS 594987 Table A 1 Regulating Materials

Ref No Layer

Thickness (mm)

Regulating Material Grade of Binder Special Requirements

1 0 – 20 HRA 0/2 F surf 40/60 des to –BS EN 13108-4 40/60 pen only Wheel Tracking Level 1

to BS 598 part 110

2a 15 to 25 SMA 6 reg 40/60

2b 25 to 35 SMA 10 reg 40/60

2c 35 to 45 SMA 14 reg 40/60

2d 50 to 65 SMA 20 reg 40/60

Stone Mastic Asphalt to Clause 937

40/60 pen Wheel-tracking criteria to match that specified for Surfacing Course.

3 35 - 65 HRA 50/14 bin des 40/60 to –BS EN 13108-4 40/60 pen

Wheel-tracking criteria to match that specified for Surfacing Course.

4a AC 20 dense bin 40/60 des to –BS EN 13108-1 & Clause 929 40/60 Pen

4b AC 20 dense bin 100/150 des to –BS EN 13108-1 & Clause 929 100/150 Pen

4c

50-100

AC 20 HDM bin 40/60 des to –BS EN 13108-11 & Clause 929 40/60 Pen

Coarse Aggregate to be crushed rock or slag. Fine aggregate to exclude natural sand fines Wheel-tracking criteria to match that specified for Surfacing Course. Where no requirement is stated these may be recipe mixes

5a AC 32 dense bin 40/60 des to –BS EN 13108-1 & Clause 929 40/60 Pen

5b AC 32 dense bin 100/150 des

to –BS EN 13108-1 & Clause 929 100/150 Pen

5c

70-120

AC 32 HDM bin 40/60 des to –BS EN 13108-1 & Clause 929 40/60 Pen

Coarse Aggregate to be crushed rock or slag. Fine aggregate to exclude natural sand fines Wheel-tracking criteria to match that specified for Surfacing Course Where no requirement is stated these may be recipe mixes.

For possible use in cold winter weather conditions

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PERMITTED PAVEMENT OPTIONS - FLEXIBLE AND FLEXIBLE COMPOSITE CONSTRUCTION The following example Appendices are reproduced from the Term Highway Contract which provides a limited pallet of materials. As a consequence some materials referred to in the body of this document may not be included here.

Appendix 7/1/A HRA 30/14 F surf 40/60 PSV (see note 2) Hot Rolled Asphalt (4kN to 8kn design Mix ) 1 Location as instructed

2 Grid for checking surface levels of pavement courses (702.4)

Longitudinal dimension: 10m

Transverse dimension: 2m

3 Surface regularity (702.7): Category of road, A

4 Coated chippings (915): Nominal size

Minimum PSV: 60 or 65 (see Note 2)

Maximum AAV: 12 (See Note 2)

5 Surface texture required (921): 1.03 (SMTD) / 1.5mm (sandpatch), or 0.90 (SMTD)/1.2 mm (sandpatch) (see Note 3)

6 Regulating course (907) Table 1 mixture options 1, 3, 4a, 5a, or 5b

Surfacing Surface Course

Clause: 911

Material: Rolled Asphalt

Binder: 40/60 Pen

Thickness: 40mm or 45mm – as instructed (see Note 4)

Special requirements: BS EN 13108-4

Table 4 Column No 30/14 F or 35/14F

Coarse Agg. – minimum PSV = 50

Marshall Stability Range; 4kN to 8kN (across the whole of the ± 0.6% binder content tolerance) Minimum Target Binder Content: Bact 7.0%

Maximum Flow: 5.0 mm

Notes: 1. CE Type Test Data shall be forwarded to the overseeing organisation for approval, at least 10 days

before laying is due to commence, clearly stating the proposed source of supply.

2. PSV and AAV values shall be specified in accordance with Tables 5/1 and 5/2 of Hampshire County Council’s ‘Guidance Document on Surfacing Options for Highways’

3. On roads with speed limits of 40mph or greater a minimum surface texture of 1.5mm sandpatch (1.03 SMTD equivalent) shall be specified, for roundabouts see section 5.7 on roads with speed limits less than 40 mph a texture of 1.2mm sandpatch (0.90 SMTD equivalent) will be sufficient.

4. On new works or where resurfacing a thickness of 45mm should be specified wherever possible for better heat retention and chipping embedment. For inlay works 40mm thickness may be specified as this will tie-in better with the thickness of older asphalt surfaces.

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Appendix 7/1/B 7kN Design Mix Hot Rolled Asphalt 1 Location as instructed





4 Coated chippings (915): Nominal size 14/20mm



5 Surface texture required (921): 1.03 (SMTD) / 1.5mm (sandpatch), or 0.90 (SMTD)/1.2 mm (sandpatch) (see Note 3)

6 Regulating course (907) Table 1 mixture options 1, 2a to 2d, 3, 4a, 4c, 5a, or 5c


Clause: 911

Material: Hot Rolled Asphalt

Binder: 40/60 Pen

Thickness: 45mm or 50mm – as instructed (see Note 5)


Table 4 Column No 30/14 F or 35/14F

Coarse Agg. – minimum PSV = 50

Marshall Stability Range; 4kN to 8kN (across the whole of the ± 0.6% binder content tolerance)

Minimum Target Binder Content: Bact 7.0%

Maximum Flow: 5.0 mm

Notes: 1. CE Type Test Data shall be forwarded to the Overseeing Organisation for approval, at least 10 days

before laying is due to commence, clearly stating the proposed source of supply.

2. PSV and AAV values shall be specified in accordance with Tables 5/1 and 5/2 of Hampshire County Council’s ‘Guidance Document on Surfacing Options for Highways’.

3. On roads with speed limits of 40mph or greater a minimum surface texture of 1.5mm sandpatch (1.03 SMTD equivalent) shall be specified, for roundabouts see section 5.7 on roads with speed limits less than 40 mph a texture of 1.2mm sandpatch (0.90 SMTD equivalent) will be sufficient.

4. Regulating mixtures to be machine laid using 100/150 Pen binder (Table 1: 4b and 5b) should be considered only during periods of cold winter weather as they are less resistant to deformation.

5. On new works or where resurfacing a thickness of 45mm should be specified wherever possible for better heat retention and chipping embedment. For inlay works 40mm thickness may be specified as this will tie-in better with the thickness of older asphalt surfaces.

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Appendix 7/1/C HRA 35/14 F surf 40/60 des PSV (see note 2) Hot Rolled Asphalt (Performance Related) 1 Location as instructed





4 Pre-coated Chippings: Nominal size 14/20mm



5 Surface texture required (921): Sand patch texture requirements (See note 3)

Level Minimum sand patch texture depth new (mm)

Minimum sand patch texture depth at 2 years

(mm)

Loss of texture between 12 months and 2 years (%)

2 1.5 1.5 40 max

1 1.2 1.2 40 max

No individual 50m section shall be less than 80% of that specified for the relevant ‘level’, nor more than 2.2 mm.

6 Regulating course (907) Table 1 mixture options: 2a to 2d, 4c, or 5c

7 Coring and testing for the determination of wheel tracking shall be carried out in accordance with Clause 943 & BS 594987

8 Wheel-tracking test temperature, rate and rut depth (to BS 598-110)

Wheel-tracking levels (See Notes 4 and 5)

Wheel tracking requirements

Level

Test temperature Rate (mm/hr)

Mean / [max} Rut depth (mm)

Mean / [max] 2 60 5.0/[7.5] 7.0/[10.5]

1 45 2.0/[3.0] 4.0/[6.0]

‘Mean’ is the mean result of 6 consecutive results and ‘max’ is the maximum value measured on a single core.

Surfacing: Hot Rolled Asphalt (performance Design Mixture)

Clause: 943 and BS EN13108-4: Table No 4

Column No 35/14F

Special Requirements: If modified Binders are to be used, only Pre-blended modified binders are acceptable

Material: HRA 35/14 F surf 40/60 des PSV (see note 2)

Binder: 40/60

Thickness: 45mm or 50mm – as instructed (see note 4)

Coarse Aggregate: Minimum PSV = 50

Binder volume: Not less than 15.5%

Air voids: Not greater than 7.5% for any pair of cores and not greater than 5.5% for the mean of any six consecutive cores.


before laying is due to commence, clearly stating the proposed source of supply. A job Mixture Approval trial may be required before the starting date where the relevant wheel-tracking/air voids data is not available. This should be taken into account when programming works – see also Note 5.

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2. PSV and AAV values shall be specified in accordance with Tables 5/1 and 5/2 of Hampshire County

Council’s ‘Guidance Document on Surfacing Options for Highways’.

3. The surface texture needed should be assessed by the Overseeing Organisation on a site specific basis. Sites where speed limits are 40mph or greater shall be specified with Level 2 criteria, for roundabouts see section 5.7. Surface texture for sites with lower speed limits shall be in accordance with Level 1 criteria.

4. The wheel tracking level needed should be assessed by the Overseeing organisation on a site specific basis taking account of the nature of the site and commercial vehicle flows. Reference should be made to the ‘Guidance Document on Surfacing Options for Highways’.

5. Results from wheel-tracking and air voids tests shall be provided a the approval stage to the Overseeing Organisation. Wheel-tracking testing shall be carried out at 45°C or 60°C, as appropriate to the specification. All results shall be no more than 12 months old. Where such data is not available, a Job Mixture Approval Trial shall be required for each unique mixture.

6. This material is not suitable for laying 40mm thick. It will be usual to specify 45mm thick, unless the Overseeing Organisation as reason for 50mm. The Contractor has the option of laying the material 50mm thick although, 45mm has been specified, to overcome practical difficulties e.g. poor weather conditions. However, only the specified thickness will be paid for.

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Appendix 7/1/D AC 14 close surf 100/150 PSV (see note 2) Asphalt Concrete 1 Location as instructed





4 Surface texture required (921) N/A

5 Regulating course (907) Table 1 mixture options 1, 3, 4a, 4b, 5a, or 5b


Clause: 912

Material: AC 14 close surf 100/150 PSV (see note 2)

Binder: 100/150 Pen – See Note 1

Thickness: 40mm


Coarse Aggregate: Crushed rock or slag only

Adhesion agent required if quartzite, basalt or other igneous rock.


Maximum AAV: 16 (see Note 2)

Fine Aggregate: Crushed rock and natural sand mixture

Notes: 1. 160/220 pen binder may be considered for use during the winter months but care must be exercised

as such materials may deform during later periods of warm weather.


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Appendix 7/1/E AC 10 close surf 100/150 PSV (see note 2) Asphalt Concrete 1 Location as instructed






5 Regulating course (907) Table 1 mixture options 1, 3, 4b, 4b, or 5b


Clause: 912

Material: AC 10 close surf 100/150 PSV (see note 2)

Binder: 100/150 Pen – See Note 1

Thickness: 30mm





Maximum AAV: 16 (see Note 2)

Fine Aggregate: Crushed rock and natural sand mixture




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Appendix 7/1/F AC 6 dense surf 100/150 PSV (see note 2) Asphalt Concrete

1 Location as instructed




3 Surface regularity (702.7): Category of road, B


5 Regulating course (907) Table 1 mixture options 1, 3, 4b, or 5b


Clause: 909

Material: AC 6 dense surf 100/150 PSV (see note 2)

Binder: 100/150 Pen (see Note 1)

Thickness: 25mm




Minimum PSV: 55 (see Note 2) Maximum AAV: 16 (see Note 2)

Fine Aggregate: Crushed rock other than limestone




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Appendix 7/1/G HRA 55/14 F surf 40/60 des PSV (see note 2) Hot Rolled Asphalt 1 Location as instructed






5 Regulating course (907) Table 1 mixture options 1, 2c to 2d, 3,, 4a to 4c or 5a to 5c


Clause: 911

Material: High Stone Content Asphalt

Binder: 40/60

Thickness: 45mm

Special requirements: BS EN 13108-4 Table No 4 Column No 55/14F

Marshall Stability Range: 7kN minimum (across the whole of the ±0.6% binder content tolerance)


Maximum Flow 5.0mm

Wheel Tracking Requirement Level 1

Crushed rock or slag excluding Limestone

Nominal size: 0/14mm


Maximum AAV: 12 (see Note 2) Notes: 1. CE Type Test Data shall be forwarded to the Overseeing Organisation for approval, at least 10 days

before laying is due to commence, clearly stating the proposed source of supply. PSV and AAV values shall be specified in accordance with Tables 5/1 and 5/2 of Hampshire County Council’s ‘ Guidance Document on Surfacing Options for Highways’

2. PSV and AAV values shall be specified in accordance with Tables 5/1 and 5/2 of Hampshire County Council’s 'Guidance Document on Surfacing Options for Highways'

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Appendix 7/1/H 14 mm Proprietary Thin Surface Course 1 Location as instructed





4 Course Aggregate: Nominal size: 0/14mm

Minimum PSV 68, 65 or 60 – See Note 2

Maximum AAV: 12

5 Surface texture required (921): 1.2 mm sandpatch or mini texture meter 0.9 (SMTD)

6 Regulating course (907) Table 1 mixture options 2a to 2d, 4a, 4c, 5a or 5c

7 Wheel-tracking test temperature: 60°C


Wheel-tracking levels (see Note 5)


Level Test Temperature C Rate (mm/hr)

Mean/[max] Rut depth (mm)

Mean / [max]

3 60 5.0/[7.5] 7.0 / [10.5]


Surfacing: Surface Course

Clause: 942

Material: 14 mm Proprietary Thin Surface Course

Binder: Thickness: 35mm or 40mm – as instructed

Special Requirements:

Minimum target binder content: Bact 6.0%

Binder volume: Not less than 12%

Binder drainage composition: Not more than 0.3% by mass at target binder

Laboratory air voids content: 2.0% to 4.0% within the range ± 0.6% of target binder

Noise Level: 0, 1, 2, or 3 as instructed (see Note 6)

Surface texture Where a minimum level of 1.2mm is specified the maximum texture for a 50m section shall be 1.5mm Where a minimum level of 1.5mm is specified the maximum texture for any 50m length shall be 2.0mm.

Polymer modified binders If used they shall be pre-blended only

Notes: 1. CE Type Test Data shall e forwarded to the Overseeing Organisation for approval, at least 10 days

before laying is due to commence, clearly stating the proposed source of supply. This should be taken into account when programming works.

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2. PSV and AAV values shall be specified in accordance with Tables 5/1 and 5/2 of Hampshire County

Council’s ‘Guidance Document on Surfacing Options for Highways’

3. For sites where speed limits are under 40mph a 1.2mm texture depth will normally suffice. On all other sites, or in situations of heavy braking and/or cornering, a 1.5mm texture shall be specified.

4. Where required, by the Overseeing Organisation, proprietary thin surface courses shall be gritted in accordance with clause 973AR.

5. Results from wheel-tracking tests to BS 598 Part 110 shall be provided at the approval stage to the Overseeing Organisation. Testing shall be carried out at 60°C with results being no more than 12 months old. The HAPAS recommendation is that until experience using the EN standard has been gained, comparative tests should be carried out in accordance with BS EN 12697-22 using the small device method B.

6. Please select one of the following levels: Level 0 No requirement Level 1 Equivalent to HRA surfacing materials - 0.5 dB(A) Level 2 Quieter than HRA surfacing materials - 2.5 dB(A) Level 3 Very quiet surfacing material - 3.5 dB(A) Only for the most sensitive of locations.

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Appendix 7/1/J 10mm Proprietary Thin Surface Course 1 Location as instructed







Maximum AAV: 12

5 Surface texture required (921): 1.2 mm sandpatch or mini texture meter 0.9

No individual 50m section shall be less than 1.0mm nor greater than 1.5mm (sandpatch)

6 Regulating course (907) Table 1 mixture options 2a to 2d, 4a, 4c, 5a or 5c

7 Wheel-tracking test temperature: 60°C


Wheel-tracking levels (see Note 4)


Level Test Temperature C Rate (mm/hr)

Mean/[max] Rut depth (mm)

Mean / [max]

3 60 5.0/[7.5] 7.0 / [10.5]



Clause: 942

Material: 10 mm Proprietary Thin Surface Course

Binder: Thickness: 30mm


Minimum target binder content: Bact 6.2%

Binder volume: Not less than 12%

Binder drainage composition: Not more than 0.3% by mass at target binder composition

Noise Level: 0, 1, 2, or 3 as instructed. (See Note 5)

Laboratory Air voids 2.0% to 4.0% within the range ± 0.6% of target binder content. Polymer modified binders If used they shall be pre-blended only.




3. Where required, by the Overseeing Organisation, proprietary thin surface courses shall be gritted in

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accordance with clause 973AR.

4. Results from wheel-tracking test to BS 598 Part 110 shall be provided at the approval stage to the Overseeing Organisation. Testing shall be carried out at 60°C with results being no more than 12 months old. The HAPAS recommendation is that until experience using the EN standard has been gained, comparative tests should be carried out in accordance with BS EN 12697-22 using the small device method B.


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Appendix 7/1/K 6mm Proprietary Thin Surface Course 1 Location as instructed






Minimum PSV 55, or 60 – See Note 2

Maximum AAV: 16

5 Regulating course (907) Table 1 mixture options: 2a to 2d, 4a, 4c, 5a or 5c


Clause: 942

Material: 6mm Proprietary Thin Surface Course

Binder:

Thickness: 25mm


Minimum Target Binder Content Bact 6.8%

Binder volume Not less than 12%

Binder drainage composition Not more than 0.3% by mass at target binder

Laboratory air voids content 2.0% to 4.0% within the range ± 0.6% of target binder

Polymer modified binders If used they shall be pre-blended only

Noise level: 0,1,2, or 3 – as instructed (see Note 4)

Notes: 1. CE Type Test Data shall be forwarded to the Overseeing organisation for approval, at least 10 days



3. Where required, by the Overseeing Organisation, proprietary thin surface courses shall be gritted in accordance with clause 973AR.


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Appendix 7/1/L Thin Surface Course Systems (Micro Asphalt) 6,8 or 10 mm 1 Location as instructed





4 Course Aggregate: Nominal size: 0/6mm, 0/8 mm or 0/10 mm


5 Surface texture required (921): Sand patch texture requirements – see note 4

Level Minimum sand patch texture

depth new (mm)

Minimum sand patch texture depth

at 2 years (mm)

Loss of texture between 12 months

and 2 years (%)

2 1.5 1.5 40 max

1 1.2 1.2 40 max

No individual 50 m section shall be less than 80% of that specified for the relevant ‘level’.

6 Regulating course (907) Table 1 mixtures; 1,2a to 2d, 4a, 4c, 5a or 5c


Wheel-tracking level – (see Note 5)

Maximum wheel tracking Requirements

Level

Test

temperature (C) Rate (mm/hr)

Mean/[max]

Rut depth (mm)

Mean/[max]

3 60 5.0 / [7.5] 7.0 / [10.5]


Surfacing: Micro Asphalt Surface course

Clause: 942

Material: Micro Asphalt Surface Course

Binder:

Thickness: 15mm or 20mm

Special Requirements: Polymer modified ‘bond-coat’ shall be used in all situations – See Note 3

Binder volume Not less than 12%

Binder drainage composition Not more than 0.3% by mass at target binder

Noise level: 0,1,2, or 3 – as instructed (see Note 6)

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Appendix 7/1/L (Continued) Thin Surface Course Systems (Micro Asphalt) 6,8 or 10mm Notes: 1. CE Type Test Data shall be forwarded to the Overseeing Organisation for approval, at least 10 days

before laying is due to commence, clearly stating the proposed source of supply. This should be taken into account when programming works

2. PSV and AAV values shall be specified in accordance with Tables 5/1 and 5/2 of Hampshire County Council’s ‘Guidance Document on Surfacing Options for highways’ (currently under review, but available to view upon request).

3. The distributor used to apply the polymer modified ‘bond-coat’ shall have been calibrated no more than 6 weeks prior to surfacing works commencing. This should be taken into account when programming works.

4. The surface texture needed should be assessed by the Overseeing Organisation on a site specific basis. Sites where speed limits are 40mph or greater should be specified with Level 2 criteria. Surface texture for sites with lower speed limits should be specified with Level 1 criteria.

5. Results from wheel-tracking tests to BS 598 Part 110 shall be provided at the approval stage to the Overseeing Organisation. Testing shall be carried out at 60°C with results being no more than 12 months old. The HAPAS recommendation is that until experience using the EN standard has been gained, comparative tests should be carried out in accordance with BS EN 12697-22 using the small device method B.


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Appendix 7/1/M HRA 15/10 F surf 40/60 rec PSV (see note 2) Hot Rolled Asphalt (for hand laying) 1 Location: This material shall only be used in patching and for reinstatement in front of kerbs or

transverse trenches, unless otherwise instructed.

2 Coated chippings (915): Nominal size: 14/20mm

Minimum PSV: 60

Maximum AAV: 12

3 Surface texture required (921): 0.90 (SMTD) / 1.2 mm (sandpatch)

4 Regulating course (907): Table 1 mixture options: 1,3, 4a to 4b, or 5a to 5b


Clause: 910

Material: Hot Rolled Asphalt

Binder: 40/60 Pen

Thickness: 40mm

Special Requirements: BS EN 13108-4

Table 4, Column No 15/10F

Coarse Agg. Crushed rock or Slag – minimum PSV = 50


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Binder Course

Table A 2 – Schedule of Binder Course Mixtures

Element Clause Material Binder Grade

Layer Thickness

(Mm) Special

Requirements

Binder Course 905 HRA 50/14

bin 40/60 40/60 pen

As instructed

BS EN 13108-4 Coarse Aggregate to be crushed rock or slag.

906 AC 20

dense bin 40/60 rec

40/60 pen

906

AC 20 dense bin 100/150

rec

100/150 pen

Binder Course

929 AC 20 HDM

bin 40/60 des

40/60 pen

As instructed (between

50mm and 100mm)

BS EN 13108-1 Coarse Aggregate to be crushed rock or slag. Fine aggregate to exclude natural sand fines. Compaction to Clause 929

Binder Course 937 SMA 20 bin

40/60

40/60 pen


50mm and 65mm)

60˚C Wheel-tracking criteria applies: Max. wheel-tracking rate = 5.0mm/hr Max. Rut Depth = 7.0mm


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Base Mixtures Table A 3 – Schedule of Base Mixtures

Element Clause Material Binder Grade

Layer Thickness

(Mm) Special Requirements

906 AC 32 dense base 40/60

rec

40/60 pen

906

AC 32dense base

100/150 rec

100/150 pen

929 AC 32 HDM base 40/60

des

40/60 pen


70mm and 120mm)

BS EN 13108-1 Coarse Aggregate to be crushed rock or slag. Fine aggregate to exclude natural sand fines. Compaction to Clause 929

Base

948SR

Cold Recycled Bitumen Bound

Material

Supplier’s choice (

up to 190 pen base bitumen max.) to achieve

end-performa

nce criteria

150mm

Ex-situ recycling ONLY. Min. Indirect Tensile Stiffness Modulus (Dry): Individual Value = 2000MPa Mean Value = 2500Mpa Min. Indirect Tensile Stiffness Modulus (water saturated): Individual Value = 1500MPa Mean Value = 2000Mpa Minimum added bitumen content = 3.5%. Compaction = 93% Min. PRD

Base 1030 C8/10 Wet

Lean Concrete

N/A As instructed

(minimum 150mm)

To be fully compacted by internal vibration only. Crack inducers to be max 3m centres. Must achieve equivalent of 7 days strength before overlaying permitted. ST mixes not permitted.


For use on Footways, ‘U’-Class and ‘C’-Class roads ONLY unless otherwise specified.

For use in narrow widening (<1m)

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APPENDIX B : KEY CHANGES SINCE 2002 EDITION

B.1 Revised Bituminous Material Standards B.1.1 Aggregate Sizes.

In the 2003 revision of BS 594 and BS 4987 the material sizes 40mm and 28mm were dropped and replaced with 32mm materials and the range of aggregate size was used in material descriptions e.g. 0/14, 14/20, etc. These changes were to align with BS EN 13043 which was to be implemented shortly afterwards.

B.1.2 Binder Grades

Although the designation of binder grades changed at the beginning of 2002, the terms in general use did not completely follow the standard for some while. Below is a Table which compares the terms which were in common use and those in BS EN 12591 which should have been used and which now have been reinforced by being included within the new standards.

Table B1 Comparison of Binder Grade Descriptions

Recent use New standards 35 pen 30/45 pen 50 pen 40/60 pen

70/100 pen 125 pen 100/150 pen

Binder Grades

200 pen 160/220 pen B.1.3 BS EN 13108 and PD 6691

January 1st 2008 saw the implementation of BS EN 13108 Bituminous mixtures – Material specifications. BS 594-1 and BS 4987-1 were superseded by this document. This has brought yet more changes in terminology and material designations. Being a European standard BS EN 13108 allows various choices to be made in many aspects of specifying the materials. This is to accommodate the requirements of the many users of the standard in different countries and in part to allow the development of materials and test methods. This could promote chaos within the industry with manufacturers and clients each using differing criteria to define mixtures. In order to standardise on these many aspects and enable BS EN 13108 to be workable PD 6691 became effective on 1.1 2008. This provides a guide to which choices are recommended for the products currently used in the UK. By all parties following this guide, those materials which are required and what is provided should be understood by all.

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Following the issue of BS EN 13108 the European terminology will be used throughout the industry. All bituminous materials will be generally referred to as Asphalt. Macadam materials will be know as Asphalt Concrete (AC).

Hot Rolled Asphalt will remain the same (HRA). Stone Mastic Asphalt will also continue as before (SMA). B.1.4 New Bituminous Product Descriptions

The new product descriptions which have been included in BS EN 13108 have six elements:

i) Mixture type; AC = Asphalt Concrete

HRA = Hot Rolled Asphalt SMA = Stone Mastic Asphalt PA = Porous Asphalt

ii) Nominal maximum size of Material in mm e.g. 32, 20, 14, 10, 6 iii) Material Grading description; dense (formerly Dense graded)

close (previously Close graded) open (was Open graded) med (from Medium graded) F (only for HRA fine grading) C (only for HRA coarser grading)

iv) Material Course; base = Base

bin = Binder Course surf = Surface Course

v) Binder Designation; e.g. 40/60, 100/150 vi) Additional Information; e.g. des = Designed mixture

rec = Recipe mixture PSV 60 = required minimum PSV of coarse aggregate or PCC

In ii) above the sizes are again described by the upper sieve size rather than the range as mentioned in B.1.1 above. However when referring to aggregates it is still the range (e.g. 8/14) that is used. It can be seen that those designations included in items iii) & vi) above are only relevant to certain types of mixture and for this reason those items are not always included in a material description.

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B.1.5 Comparison of Old and New Material Designations

Below are some typical examples showing the comparison of previous designations with the new nomenclature:

Table B2

B.1.6 Transport, Laying and Compaction Standards

Another significant change is that BS EN 13108 does not address the aspects of Transport, Laying and Compaction of bituminous mixes which were formerly specified in BS 594-2 and BS 4987-2. These two standards were also withdrawn on 1.1.2008 being replaced by BS 594987.

B.1.7 The Specification for Highway Works

In addition to these new standards the Highways Agency issued Interim Advice Note IAN 101/07 in November 2007 to be effective from 1.1.2008. This was to ensure that the 900 Series of the Specification for Highways Works (SHW) did not conflict with these new standards.

An amendment to IAN 101/07 was issued in February 2008 and this revised 900 series was included in the SHW amendment of August 2008.

In addition to conforming to or promoting the use of these new standards this new 900 Series has strengthened the requirements for compaction, bonding layers together or sealing them from the ingress of water. Combining and adopting the requirements of BS 594987 as required by the SHW will greatly improve the durability and serviceability of maintenance and new works.

More detail of these publications will be provided throughout this guidance

document as appropriate.

B.1.8 Deformation Resistance Test Methods

Many of us have become familiar with specifying materials to Clauses 942 or 943 which require materials to display resistance to deformation under trafficking. This has been established by testing the Wheel Tracking Rate to BS 598 -110. Although

PREVIOUS MATERIAL DESCRIPTION NEW MATERIAL DESCRIPTION 0/32 HDM 50 Base to Clause 929 AC 32 HDM base 40/60 des. 0/20 DBM 100 pen Binder Course AC 20 bin 100/150 rec.

0/6 Dense Graded Surface Course 190 pen AC 6 surf 160/220 10 mm SMA Surface Course 100 pen SMA 10 surf 100/150

30% 0/14 HRA Surface Course Table 6 Col. 6/4 HRA 30/14F surf 40/60 rec. 0% 0/2 HRA Surface Course Table 3 Col. 3/1 HRA 0/2F surf 40/60 des. 60% 0/20 HRA Binder Course Table 2 Col. 2/4 HRA 60/20 bin 40/60

55% 0/10 HRA Surface Course Table 4 Col. 4/4 HRA 55/10C surf 40/60 des.

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the levels specified in each of these clauses differed from each other the test methods remained the same. A Wheel Tracking Test is also included as a requirement in several of the parts of BS EN 13108, those being Parts 1,4 and 5 for Asphalt Concrete, Hot Rolled Asphalt and Stone Mastic Asphalt respectively. Unfortunately, the Wheel Tracking Tests chosen in this standard are European methods relatively new to the UK. The standard called up is BS EN 12697-22 which although issued in 2003 has not been adopted into general use until now. Although similar to the BS 598-110 method there are sufficient differences both in the test procedure and the method of calculating the result that we in the UK have no experience of what may be appropriate values to specify. Advice contained in PD 6691 states that in the interim, until sufficient experience has been developed, the previously existing values be required using BS 598-110 as the test method. The levels required are stated in Tables B4, C3 and D7 for Asphalt Concrete, Hot Rolled Asphalt and Stone Mastic Asphalt respectively. Additional advice is to have comparative tests to the new standard in order to develop experience with those results. A limited comparative study was carried out by TRL, the results are reproduced in PD 6692: 2006 Table 4. Having mentioned HRA in this connection BS EN 13108-4 only classifies deformation resistance in terms of Wheel Tracking Rate there is no provision for using Marshall Stability as has been possible in the past under Clause 911 and BS 594-1. Similar to the above situation advice has been issued jointly by CSS (County Surveyors Society) and the QPA (Quarry Products Association) ‘It is therefore recommended that, on a contract-by-contract basis and by specific arrangement with their supplier, specifiers may continue to call up HRA (Marshall) Stability at Design Binder Content as determined by BS 594987: 2007 Annex H. This can be declared in the “Other Information” reported on CE Mark certificates.’

B.1.9 CE Mark

A mixture may have a CE Mark assigned to it if certain conditions are met. There follows a quote from the guidance provided jointly by the CSS & QPA.

‘A mixture is demonstrated to be in conformity with the European Standard if there is a valid Type Test (and Report) in accordance with BS EN 13108 Part 20 for the particular mix and if it is produced at a plant operating in compliance with the requirements of Factory Production Control in accordance with BS EN 13108 Part 21. When these elements are assessed and approved by competent Notified Bodies, then the producer will be free to affix the CE mark to the documentation associated with the materials’.

The CE mark declaration covers constituents, grading, binder content and any performance properties claimed or specified. Suppliers will provide this information on request.

The Public Procurement Directive brings these products under Trading Standards law. Therefore, by specifying a CE marked product clients will be provided with a greater degree of assurance that the materials have been fully assessed in terms of the declared performance as well as being quality controlled during production.

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This will minimize the amount and duration of assessment procedures necessary before and during contract works.

Details of the processes undertaken by the supplier in the evaluation of conformity can be found on the MPA website at: http://www.mineralproducts.org/prod_asp01.htm (The MPA was formed at the beginning of March 2009 through the merger of the Quarry Products Association (QPA), British Cement Association (BCA) and The Concrete Centre).

This should help us when assessing a product as much of the basic testing will have been completed and the results available. Once a product is CE Marked no alterations can be made to constituents or their proportions, as that would not then be the same product. The downside to this is that re-evaluation is not required for another 5 years Unfortunately, some manufacturers take a rather liberal view on changing constituents, so if there is any doubt request recent verification test results to confirm the performance. It has been stated by several suppliers that the Industry intends to CE mark all of its Asphalts. This will obviously take some time but some are already available.

B.1.10 CE marking and HAPAS (Highway Authority Product Approval Scheme)

Since introduction of the new European Standards for Asphalt in 2008, many run-of-the-mill surfacing materials are now covered by the CE marking protocol. However, proprietary mixes continue to be certificated through the Highway Authority Product Approval Scheme (HAPAS). Under HAPAS, British Board of Agrément (BBA) certificates are granted for products which deliver a range of defined performance criteria over a two year period.

The materials most likely to be offered with BBA/HAPAS approvals are 'Thin Surface Courses'. Unfortunately the term 'Thin Surface Course' within HAPAS covers a wide range of materials including Stone Mastic Asphalt ( the use of which is no longer advocated ), Hot mix Thin Surface Courses (e.g. Premier Pave, MasterPave, ULM, etc.) and Ultra Thin Surface Courses (e.g. Micro asphalts.) Under HAPAS these materials are classified as follows:

(i) Thin Surface Course Type C - products laid 26mm to 40mm thick (ii) Thin Surface Course Type B - products laid 18mm to 25mm thick (iii) Thin Surface Course Type A - products laid 12mm to 18mm thick

BBA certificates will indicate which class any particular material falls into and sets

out any limitations as to use e.g. traffic loadings, temperature/general weather constraints, etc. Some materials may be totally inappropriate under certain circumstances. When considering the use of Thin Surface Courses, engineers should therefore refer to the detail of the relevant BBA certificate to check approval is still current and to ensure any restrictions on use/application are obeyed. Certificates are downloadable from www.bbacerts.co.uk

Unlike CE marking one rather dubious aspect of the HAPAS approval is that it allows manufacturers to substitute some constituents with others, mostly coarse aggregate. Again if the material proposed differs in any way from those detailed in

http://www.mineralproducts.org/prod_asp01.htm

http://www.bbacerts.co.uk

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the certificate, engineers should demand evidence to demonstrate performance will not be compromised

B.2 New Materials and Processes

The Highway & Transport Branch strongly support the use of environmentally 'green' alternatives to conventional maintenance operations. Many 'green' solutions are now incorporated into standard maintenance treatments.

B.2.1 Cold Recycled Bituminous Bound Material

These products which consist of more than 90% recycled material also only utilise about 20% of the energy for production that would be required for a hot mix material. As a consequence they fit very well with one of the County Councils corporate aims of sustainability. Following trials using this material approximately 7 years ago, the material has quickly gained a place as a well used addition to our standard range of materials. (see Section 8.2)

B.2.2 EME 2 Base and Binder Course Asphalt Concrete

Enrobé à Module Élevé (EME) is a material developed in France nearly 20 years ago and has been in common use there since. It is a very stiff material having low permeability, good deformation resistance and durability. This is achieved by using a carefully graded aggregate mix with a relatively high binder content, the binder being a very low penetration grade. Use of this material as a base and binder course can enable the total thickness of a road construction to be reduced due to its high structural contribution. However, the mix does require heavy compaction to achieve its full potential and this in turn requires a very firm foundation, Class 3 or 4 according to DMRB HD 26/06 Pavement Design. There is also a requirement to monitor the compaction with density testing including taking routine cores. Of the two classes of material used in France EME 2 has been adopted by the HA including it as specification clause 930 in the SHW. This class has been selected as the high binder content variety with the intention this will provide the most durable alternative. Very limited opportunities for use within Hampshire are anticipated, due to the associated requirements which accompany it.

B.2.3 Natural Stone Paving

The increased use of natural stone paving over recent years has resulted in it being included now within the section on block paving. Problems experienced with pedestrian slip resistance on some materials has led to guidance on this aspect being included (see Section 11.5).

B.2.4 Asphalt Rejuvenation

Do you have a tired worn out road surface? Would you prefer not to use surface dressing s a remedial treatment? Then you should look at the anti ageing process for road surfaces, see Section 7.6 for more information on Rejuvenation solutions.

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