london asphalt specification revision

Version 2nd Edition

LONDONWIDE ASPHALT SPECIFICATION

Guidance on the selection and recommendations for the use of road surfacing materials

September 2009 � Please consider the environment and do not print this document unless you really need to

London Centre of Excellence

London Technical Advisors Group

Transport for London

LCE, Lotag HMSG and TfL Streets LONDONWIDE ASPHALT SPECIFICATION


Version 2nd Edition

Document control sheet

Client: LoTAG / Transport for London Job No: 11412

Project: London-wide Asphalt Specification Project Revision Status 2nd

Edition

Title: LONDON ASPHALT SPECIFICATION Guidance on the selection and recommendations for the use of road surfacing materials and European Standards for Asphalt

Prepared by Reviewed by Approved by NAME

NAME

NAME

ORIGINAL Ian Walsh Andy Simms Rob Penman

DATE SIGNATURE

SIGNATURE

SIGNATURE

10 Sept. 2009

NAME NAME NAME

DATE SIGNATURE SIGNATURE SIGNATURE

NAME NAME NAME

REVISION

DATE SIGNATURE SIGNATURE SIGNATURE

Copyright Jacobs U.K. Limited. All rights reserved. No part of this report may be copied or reproduced by any means without prior written permission from Jacobs U.K. Limited. If you have received this report in error, please destroy all copies in your possession or control and notify Jacobs U.K. Limited. This report has been prepared for the exclusive use of the commissioning party and unless otherwise agreed in writing by Jacobs U.K. Limited, no other party may use, make use of or rely on the contents of this report. No liability is accepted by Jacobs U.K. Limited for any use of this report, other than for the purposes for which it was originally prepared and provided. Opinions and information provided in the report are on the basis of Jacobs U.K. Limited using due skill, care and diligence in the preparation of the same and no warranty is provided as to their accuracy. It should be noted and it is expressly stated that no independent verification of any of the documents or information supplied to Jacobs U.K. Limited has been made.

LCE, Lotag HMSG and TfL Streets LONDONWIDE ASPHALT SPECIFICATION


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Contents

1 Introduction 1

1.1 General Introduction 1

1.2 Preface to the document 1

2 The new European and British Standards for Asphalt supply and installation 3

2.1 The New European Product Standards for asphalt 3

2.2 The European Standards for Microasphalt and Surface Dressing 7

2.3 The Short List of Asphalt materials for use in Construction and Maintenance 9

2.4 BS 594987, the new British Standard for Transportation and Laying Asphalt 10

2.5 Performance parameters in European Standards 10

2.6 National Highway Sector Schemes 11

2.7 BBA Highway Authorities Product Approval Scheme (HAPAS) 16

2.8 Specifying non-HAPAS Approved proprietary products 17

3 Pavement Design 18

3.1 Introduction 18

3.2 Evaluating existing pavement structure and condition 18

3.3 Defects 19

3.4 Assessing the structural strength of the existing road 25

3.5 Traffic Volume 26

3.6 Structural design and material selection 27

3.7 Selection of surfacing types and thickness 30

3.8 Safety 32

3.9 Sustainability 36

3.10 Surface water and drainage requirements 42

3.11 Aesthetics - surface type and characteristics 43

3.12 Noise reduction characteristics 44

3.13 Innovation 45

4 Surfacing Materials selection 46

4.1 Introduction 46

4.2 Slurry surfacing 46

4.3 High Friction Surfacing [HFS] 47

4.4 Microasphalt 48

4.5 Surface Dressing 48

4.6 Resin bound surfacing 49

4.7 Hot mix asphalt surfacing 50

5 Binder Course Materials selection 56

5.1 Introduction 56

5.2 Stone Mastic Asphalt [SMA] binder course 56

5.3 Hot Rolled Asphalt [HRA] binder course 57

5.4 Dense Rolled Asphalt Concrete binder course 57

6 Base Materials selection 59

6.1 Introduction 59

6.2 Dense Asphalt Concrete base 59

6.3 Hot Rolled Asphalt base 60

7 Summary of selected asphalt layers by Road Type 61

7.1 Road Type 1 61

7.2 Road Type 2 61

7.3 Road Type 3 and 4 61

8 Preferred options for materials selection 62

9 Draft Appendix 7/1 for preferred materials 63

9.1 Surface course materials 63

9.2 Binder course materials [also suitable for regulating] 66

10 Draft Bill of Quantities for preferred materials 68

Appendix 1: Translations of all mixes notified from BS to EN Standards 71

Appendix 2 Summary of relative performance of surface courses 74

LCE, LoTAG HMSG and TfL Streets LONDONWIDE ASPHALT SPECIFICATION


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1 Introduction

1.1 General Introduction

Based on Gershon Efficiency saving practices, London Centre of Excellence

funded a project to carry out a review of asphalt materials used for highway

construction and maintenance and to make recommendations for a simplified

list. The project sponsors, LoTAG HMSG and TfL Streets approached

Jacobs to undertake this project, which was commissioned through the

Ringway Jacobs Highway Works Maintenance Contract for TfL Central Area.

LB Lambeth project managed this work.

The purpose of the original project brief to Jacobs was:

• To review the content of specifications and bills of quantities

submitted by London Boroughs and TfL and to propose a

standardised, agreed list of materials

• To encourage optimisation and standardisation of materials which are

durable and economic to procure

• To convert all references to British Standards within contract

documentation to the new European Standards for Asphalt

implemented on 1 January 2008.

In addition it was expected that the project would bring the following

additional benefits:

• To gain cost savings from the economies of scale and to encourage

competition.

• Facilitate business processes, tendering and reduce the cost of

preparing contracts

The sponsors also requested that for the selected materials Appendix 7/1

and Bills of Quantities templates should be provided and Notes for Guidance

on materials selection and use prepared, taking account of sustainability and

safety issues.

During Sept and Oct 2007 consultations took place with LOTAG members

and TfL to finalise the document with a series of presentations,

At the request of LOTAG the document was reviewed, assisted by a

questionnaire of their members. This was completed, with this document, in

September 2009

This Guidance Note uses the agreed list of a standardised and reduced

number of asphalt materials developed from the Review, and provides

guidance on their use in the context of other materials available to specifiers.

The use of a reduced list of asphalt materials for highways maintenance is often cost neutral and in many cases can deliver good financial returns

The use of a reduced list of asphalt materials for highways maintenance should provide opportunities for improved quality in manufacture and less waste



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This document also gives more general guidance on pavement design considerations

and on materials selection. The principal changes to the document in this revision are

related to these aspects.

The referencing system used for surfacing type selection and in the Bill of Quantities

remains unchanged.

1.2 Preface to the document

This Guidance note has been issued for the use of the initial commissioning party comprising the project board (London Centre of Excellence, LoTAG HMSG, TfL Streets and LB Lambeth) and its members. It is laid out in a number of sections to give users ready access to the information they need to implement the necessary changes to all of their documentation that refer to Macadam or Asphalt. This could include drawings, existing and proposed scheme and term maintenance contracts, developer agreements, schedules and the ordering systems to their contractors. The specification that underpins most asphalt procurement and installation in the UK is the Specification for Highway Works [SHW] published by the Highways Agency and available free of charge by downloading from http://www.standardsforhighways.co.uk/ The SHW is updated from time to time. This Guidance document references the 08/08 update to the SHW Most contracts use the version current at the time the contact is let, however with long term contracts, a failure to allow for updates to the specification can lead to significant obsolescence. Section 2 contains details of the European Standards for asphalt, the EN 13108 series which replaced the British Standards BS 594 -1 and 4987 -1 in January 2008. All Local Authority contracts must use these European Standards for their procurement. Information is supplied on the preferred short list of materials agreed as a result of the consultation, using the European Standard terminology. Transportation and laying is covered by a new British Standard BS 594987: 2007, though the Specification for Highway Works Clause 903 is slightly different in detail, in particular with respect to the air voids requirements for compacted material and the treatment of joints The Guidance makes recommendations concerning the quality of asphalt produced by asphalt plants and recommendations for audit testing. Paragraphs have been added describing in more detail National Highway Sector Schemes and BBA HAPAS and what to do if products do not have independent assessment Section 3 considers best practice in Pavement Design, considering the fact that most is targeted at repairing defects. The relevant documents for pavement design are iscussed and extracts provided for convenience. The causes of common defects are identified, i.e. fretting, deformation, cracking; including reflective cracking. Suitable treatments for these as well as low skid resistance are suggested. The road hierarchy used in the Guidance Document is outlined. The safety of the surface, especially early life skid resistance, is discussed and recommendations are made.


Guidance on the selection and recommendations for the use of road surfacing

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Methods of improving the sustainability of maintenance operations are outlined, including the need to determine and minimise the carbon footprint. Attention is drawn to the Exchange Carbon Trading Scheme commencing April 1 2010. Aesthetics and noise reduction have not been ignored. Section 4 has short updated sections on the options for surfacing materials for maintenance - Slurry Surfacing, High Friction Surfacing, Microasphalt, Surface Dressing, Resin bound surfacing and Hot mix asphalt; Thin Surface Course Systems (TSCS), Hot Rolled Asphalt and Asphalt Concrete. Materials are recommended, using EN13108 nomenclature, for the three traffic categories, based upon the NRSWA definitions, Type 1, Type 2 and Types 3 and 4 roads. Thickness examples for overlay have been provided Section 5 describes the materials choices for binder course Section 6 describes the materials choices for base materials and includes cold mix asphalt Section 7 provides a summary chart that identifies for each road type the asphalt materials options and gives them a materials reference Section 8 provides a summary chart that gives designers various options for surface, binder and base course selection, using the materials reference. Section 9 provides Appendix 7/1 information on the materials recommended for use. Section 10 gives a typical Bill of Quantities for the materials.



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2 The new European and British Standards for Asphalt supply and installation

2.1 The New European Product Standards for asphalt

European Standards superseded the British Standards for Asphalt on January 1st 2008

This made obsolete: British Standards BS 594-1:2005 Hot Rolled Asphalt, BS4987-

1:2005 Coated Macadam and BS 1447 Mastic Asphalt

The use of British Standards for asphalt procurement by public bodies became illegal

in Summer 2008.

The replacement European Standards are as follows:

• BS EN 13108-1 Asphalt Concrete (replaces BS 4987-1)

• BS EN 13108-2 Asphalt Concrete for Very Thin Layers

• BS EN 13108-3 Soft Asphalt (Nordic countries)

• BS EN 13108-4 Hot Rolled Asphalt (replaces BS 594-1)

• BS EN 13108-5 Stone Mastic Asphalt (not BBA HAPAS Thin Surface Course)

• BS EN 13108-6 Mastic Asphalt (replaces BS 1447)

• BS EN 13108-7 Porous Asphalt

They are supported by two standards that relate to Quality Assurance matters

• BS EN 13108-20 Initial Type Testing

• BS EN 13108-21 Factory Production control [FPC]

These are discussed in Sections 2.1.1 and 2.1.2 below.

The suite of test methods in the BS598 series which supported the British Standards for materials; have all been superseded by 44 new test methods in the EN 12697 series. Information on which are used is given in PD 6691:2007 Asphalt - Guidance on the use of BS EN 13108 Bituminous mixtures – Material specifications

Whilst many tests methods are similar to those in the British Standards, some are

completely new. The most significant of these is the new Small Wheel Tracking test,

which uses the equipment familiar to UK Laboratories but uses a different test protocol.

This new method gives values that users of the British Standard will find unfamiliar so a

transition period has been permitted which is almost at an end. There is also a Heavy

Wheel Tracking test for base materials using a test originated in France.

The Wheel Tracking Test is used to ensure adequate rut (deformation) resistance of

surface courses and binder courses. Work is still ongoing to define values for the Wheel Tracking Rate [WTR] using the European test protocol in BS EN 12697-22:2003. Until data is validated the test in BS598:110 is being used. This is referenced in PD 6691:2007. Guidance will be available on the new specified values shortly



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There are two Classes for wheel tracking in PD6691 Annex C

WTR 1 refers to testing at 45ºC and is for normal use

WTR 2 refers to testing at 60ºC and is for heavy traffic as it is more onerous.

The major noticeable change in the European Standards is that the term ‘macadam’ has

been changed to a name commonplace worldwide, ‘Asphalt Concrete’.

The nomenclature for products has been rationalised so that all the essential information

is contained within the product description. For example: AC20 dense bin 40/60.

For completeness Appendix A contains a list of translations for all those materials that

London Boroughs said they used in the data provided by participants to the

questionnaire exercise carried out as part of the project.

The rationalised, short list of asphalt materials recommended for highway construction

and maintenance are given in Section 2.2.

Guidance on where these materials should be used on the network is given in Section 3.

2.1.1 Initial Type Testing

BS EN 13108 standards require the asphalt producer to demonstrate that a mixture conforms to the detailed specification requirements using procedures known as Initial Type Testing. This is similar to but replaces, the requirements in Specification for Highway Works [11/04] Clause 929 for a mix approval for every scheme The supplier installs the trial site and carries out the required tests; in all cases air voids after compaction and in addition for design mixtures, deformation resistance, using the small wheel tracking device. This confirms the target mix design formula, to which standard tolerances are applied as described in EN 13108-21. The Type Test Report is part of the evidence needed to prepare a valid CE mark certificate

2.1.2 Factory Production Control

The Factory Production Control (FPC) requirements set out BS EN 13108-21 are similar to the long established procedures in National Highway Sector Scheme 14 for the production of asphalt mixtures with which suppliers are familiar. The aim of factory production control procedures is to ensure that the mixture is produced in a consistent way, using the agreed constituents, so that its binder content and grading reflects the mixture formulation derived from the Type Test Report. There are different levels of compliance within the Factory Production Control Process as shown in the table below. Sector Scheme 14 has been amended to conform to EN 13108-21 Operating Compliance Levels [OCL] based upon the results of 32 tests, together with some additional requirements on permitted deviation for target binder contents. Temperatures of mixtures is not included in OCL

Operating Compliance Level [OCL]

Number of tests in previous 32 not conforming

i.e. % non-compliance

A 0-2 < 6%

B 3-6 9% - 18 %

C 7+ >18%



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A consequence of the change is that material quality becomes part of the product specification. However there is a recognition that materials can be supplied not complying with the specification. Clients need to take a view on what level of compliance they are prepared to accept

London plants generally comply with OCL level A. LOTAG and TfL have agreed to add a clause to make this a requirement.

Appendix 0/2 Additional Clause 901.19 Quality Assurance Asphalt shall be supplied by CE marked plants operating at OCL level A.

If Clients suspect, or have evidence of, a systematic failure of a plant to comply, this should be brought to the attention of the Nominated Body (the correct title for the Certification Body of a CE marked product). If proved to be correct, it could lead to draconian penalties through Trading Standards legislation. However in order to this a statistically significant number of test results are necessary which is likely to be impracticable in the context of Local Authority maintenance schemes, though possible for large HA motorway contracts

Clients are encouraged to show interest in the quality of material supplied by regularly seeking data on the OCL of the plants their contractors use to and be prepared to eliminate plants that persistently do not meet the required OCL. .

Audit testing Any audit testing of supplied material will need to have a sufficiently large number of samples to demonstrate that the OCL level is not being achieved. Only then can serious discussions be carried out with the supplier on a firm basis. It is suggested that up to 30 samples may need to be tested, for binder content and grading, to clearly show the Factory Production Control is not working effectively, depending upon the quality of the plant; the poorer the plant the greater the number required. BS EN 13108 does not deal with the subject of “acceptance testing” as this is a contractual issue. Sampling and testing should be carried out by a UKAS accredited laboratory.

Testing of installed material is still a very important activity to ensure the performance of the road pavement. A UKAS accredited technician should visit or be present on all sites where asphalt is being laid.

Measuring the laid voids using indirect density gauges, and deformation resistance measured on cores if specified, are particularly important for fitness for purpose and durability. Within the Specification for Highway Works [08/08] it is a mandatory requirement for design binder courses. Specialist calibrated indirect density gauges are required on thin layers; otherwise this can only be done by using cores taken



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subsequently. This may require traffic management and will leave visual evidence of coring if carried out after the surface course has been laid. Monitoring the rate of spread of bond/tack coat, and keeping laying records of truck deliveries, weather and temperatures of material are all necessary for contractors compliance with Sector Scheme 16 Asphalt Laying . BBA HAPAS Approved Thin Surfacing is unaffected by European standards therefore any current QA regime can continue. With the 5 years guarantee, fitness for purpose becomes much more significant than any audit test results.

2.1.3 CE marking

The procedures for the evaluation and attestation of conformity in the BS EN Standards for bituminous mixtures are a formal process leading to a declaration of conformity in the form of a CE mark certificate. As part of the complex procedures for CE marking, each production plant will be subject to Initial Inspection and Continuous Surveillance (audit) by a third party Certification Body with Notified Body status. All plants and all mixes are now delivered with CE marking Sector Scheme 14 contains additional details to the requirements in EN 13108-22 to assist auditors to carry out expert and consistent auditing to maintain a similar level of quality across the industry European Standards relate to the performance of a product as manufactured. They do not cover installation. The quality of installation in the UK is covered by Sector Scheme 16.

2.1.4 UK Published documents

PD 6691 Asphalt – Guidance on the use of BS EN 13108 Bituminous mixtures – Material specifications The European Standards contain details of all mixtures required for roads anywhere in Europe. The standardisation rules then permit a member nation to select from this large range to produce a document containing details of the mixtures preferred by that nation The National Guidance Document on the use of BS EN 13108 is published by BSI as Published Document PD 6691 and has been drafted to contain all the relevant information required for specifying and producing asphalt materials. The UK British Standards Committee (B510/1) contains representatives of all sides of industry who have carried out this task PD 6691 includes guidance on constituent materials, performance classes for specified mixture characteristics e.g. temperature, void content, stiffness etc., as well as a series of Appendices containing example specifications for ‘traditionally’ specified UK asphalt materials. The materials which are explicitly considered in PD 6691, in view of their importance in the UK, are: Asphalt Concrete, Hot Rolled Asphalt, and Stone Mastic Asphalt.



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PD 6691 is as much, if not more, relevance to specifiers and producers of asphalt as the material EN’s themselves. PD 6691 retains some of the traditional BS nomenclature as additional mixture descriptors for Asphalt Concrete to better describe the grading or texture of many of those (macadam-type) materials i.e. dense, open, medium (graded), heavy duty etc. In the case of HRA, the mixture designations have reverted to those used in BS594 before the 2003 revision, removing the % descriptor. For all materials, the small sieve introduced in 2003 has been removed from material descriptions. The relevant tables of BS 6691 can be referenced by Clients in documentation and have been included in the relevant clauses in the updated Specification for Highway Works (08/08). The references can also be used in Appendix 7/1. PD 6692 Asphalt – Guidance on the use of BS EN 12697 “Bituminous mixtures – Test methods for hot mix asphalt A second Guidance Document, PD 6692, provides advice on the use of the EN Test Methods for asphalt which are called up by BS EN 13108. PD6692 lists and gives particular details of the sample preparation and test methods relevant to UK, as referenced in BS EN 13108 and PD 6691. It is of particular interest to UK test laboratories. 2.2 The European Standards for Microasphalt and Surface Dressing

BS EN 12271: 2009 specifies a range of categories for properties of Surface Dressing to enable users to select appropriate limiting values for a wide range of uses, from footpaths to motorways. The specifier needs to define categories for properties relevant to the particular end-use of the surface dressing as tabulated below

BS EN 12273:2009 specifies a range of categories for properties of slurry surfacing and microsurfacing to enable users to select appropriate limiting values for a wide range of uses from cycle paths to heavily trafficked roads. The specifier needs to define categories for properties relevant to the particular end-use of the slurry surfacing and microsurfacing as tabulated below.

European Standards are not easy to use and the new ENs are complemented by a new Published Document (PD) 6689 from BSI which gives guidance on the use of both standards to deliver levels /classes of in-service performance in the United Kingdom. Customers who use this method of procurement via for example, SHW Clauses 918 and 922, for these products, should find the EN with PD 6689 straightforward

The latest date for the implementation of these new European Surface Treatment Standards is January 2011. From that date CE marking should be in place and Public Procurers must start using the new standards.

In advance of implementation, a Type Approval Installation Trial [TAIT] has to be carried out over a period of a year so that visual assessment and macrotexture can be



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measured on the installed product. This enables the acceptable performance categories, as summarized below, to be placed on the CE Certificate.

This assessment is carried out by the Contractor, provided he has a Factory Production Control certificate from a Notified Body, to demonstrate he has a Quality Assurance protocol in place; including design procedures; the TAIT itself need not be inspected. Different TAITs may be carried out for different end uses, demonstrating the ability of the contractor to provide performing products for different traffic situations and stresses. The number of TAITs needed relates to the type of road maintenance contracts the contractor wishes to carry out. If he only wants to work on footways, just one TAIT may be sufficient. PD6689 provides guidance on the number of TAITs to cover the whole network. Because they can be identified in normal contract work, fitted in easily and self-assessed, the TAIT is not foreseen as an onerous task.

Surface Dressing installers already have Certificated Quality Assurance schemes to NHSS 13 but some still have yet to organise their TAIT data. The number of certificated Microasphalt companies is small but growing.

Properties for which information will be provide on a CE Certificate are as follows

EN 12271 Surface Dressing EN 12273 slurry surfacing and microsurfacing

Suppliers can declare ‘No Value Determined’ if necessay



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2.3 The Short List of Asphalt materials for use in Construction and Maintenance

The list of 17 materials in the table below should fulfil most of the requirements for construction and maintenance.

The Reference key may be used for pavement construction options, Appendix 7/1 and Bills of Quantities at the users discretion.

2.3.1 Surface Courses

ST14 HAPAS TSCS PSV XX Macrotexture level 3, 2 or 1

ST10 HAPAS TSCS PSV XX Macrotexture level 3, 2 or 1

S1H HRA 35/14 F surf PMB PSV50 des WTR 2**+ PCC PSV XX

S2H HRA 35/14 F surf 40/60 PSV50des WTR 1** + PCC PSV XX

S3H HRA 30/14 F surf 40/60 PSV50 +PCC PSV XX

S3A AC10 close surf 100/150 PSV XX

For footways and cycleways

FSA AC 6 close surf 100/150 PSV 50

2.3.2 Binder Courses

Bi1S SMA 14 bin 40/60* des WTR 2**

Bi2S SMA 14 bin 40/60* des WTR 1**

Bi3S SMA 10 bin 40/60

Bi1H HRA 60/20 bin 40/60* des WTR 2**

Bi2H HRA 60/20 bin 40/60* des WTR 1**

Bi3H HRA 60/20 bin 40/60

Bi2A AC 20 HDM bin 40/60

Bi3A AC 20 dense bin 100/150

BiRH HRA 50/10 reg 40/60


BiFC 14 proprietary cold mix to Clause 948

BiFA AC14 dense bin 100/150

2.3.3 Base Courses

Ba1H HRA 60/32 base 40/60***

Ba2H HRA 60/20 base 40/60

Ba2A AC 32 HDM base 40/60

Ba3C 20 proprietary cold mix Clause 948

Ba3A AC 20 dense base 40/60


BaFC 14 proprietary cold mix Clause 948

BaFA AC14 dense base 100/150

* a proprietary polymer modified binder mix may be more appropriate to meet the Wheel Tracking

Rate class [WTR ]

** WTR 1 and WTR 2 refer to the classes of performance given in PD 6691 using the small [UK]

wheel-tracking machine

*** 30/45 pen grade bitumen may be required for major schemes

PSV XX refers to the relevant PSV required for the site. c.f. Section 3.6

S = Surface course Bi =Binder Course Ba = Base Course 1, 2, 3 = road type from the NRSWA hierarchy where the material, should be F = Footway T = Thin Surface Course Systems followed by aggregate size S = SMA H = HRA A = Asphalt Concrete C = Cold Mix



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2.4 BS 594987, the new British Standard for Transportation and Laying Asphalt

The specifications in the BS EN 13108 set of European Standards only apply to the mixture at the time that it is loaded into the delivery vehicle. The methods of transport, laying and compaction bituminous mixtures are covered by ‘national regulation’. For the UK, BSI has published BS 594987 Asphalt for roads and other paved areas – Specification for transport, laying, compaction and type testing protocols BS 594987:2007 replaces BS 594-2:2003 and BS 4987-2:2003.

The requirements of BS 594987 draw on current best practice and are included in Series 900 of the Specification for Highway Works [08/08].

The requirements for transportation and laying to be in accordance with BS594987:2007 should be inserted into the contract.

The requirements for tack coats and/or bond coats are as described in BS 594987. Bond coats are now mandatory between all layers. Clause 903 of the Specification for Highway Works [08/08] contains some requirements that are additional to those in BS 594987. These are intended to reduce the amount of surface water penetrating the pavement at joints. They include additional binder to be applied at the joint and additional cores be taken to measure compaction. However these will be accompanied by some increased cost. They may also be less practicable in a heavily trafficked urban situation.

It is recommended that Specification for Highway Works Clause 903 is implemented on current and new contracts except for sub clauses 21 to 26.

Useful information is provided in BS 594987 Table 6A to Table 6D.for the requirements for the nominal thickness of a layer and the minimum thickness of a layer at any point. These have been used in this document. The laid thickness of Thin Surface Course Systems (TSCS) to Clause 942 is critical to material performance and may mean that a binder course regulating course and/or milling out of the existing surface may be required. The thickness and requirements for the size of aggregate and use of a binder course are discussed in Section 3.7.

BS 594987 recommends minimum materials’ delivery temperatures and temperatures prior to rolling in Table A.1. BS 594987 specifies minimum rolling temperatures in Table 8 for HRA mixtures and Table 9 for designed asphalt concrete mixtures.

2.5 Performance parameters in European Standards

European Standards are based upon the premise that it is the performance of the product that is important and the product supplier is responsible for carrying out a mix design to meet the performance class selected by the purchaser from one of the classes in the relevant standard. This Guidance Document links the material performance requirements in the European

Standards to the traffic levels pertaining at the site. This option has been chosen for the

heavy and normal traffic categories c.f. Sections 5 and 6.



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HRA mixtures are still to be designed using Marshall Stability and Flow but the Wheel

Tracking test is used to define performance.

HRA Marshall Stability (4 – 8)kN roughly equates to WTR class 1

HRA Marshall Stability (6 – 10)kN roughly equates to WTR class 2

For lightly trafficked roads defined as NRSWA Road Types 3 and 4, (which comprise the majority of the network), recipe mixtures are available for Hot Rolled Asphalt. However for Asphalt Concrete, whilst these mixtures are available the use of a designed mix has been generally recommended to ensure consistent performance during installation. As the performance parameters are based upon laboratory work, to achieve these in-service it is essential that materials are installed correctly. SHW Clause 903 together with BS 594987, and any additional requirements, set the installation standard to be achieved. Sector Scheme 16 is the underpinning supplement to ISO9001 to ensure that quality standards are maintained.

Only contractors certificated to Sector Scheme should be used and they are responsible for not only their own quality but also the quality of the work of their subcontractors.

2.6 National Highway Sector Schemes

National Highway Sectors Schemes were developed by CSS and HA with the co-operation of UK Accreditation Service [UKAS], Certification Bodies and Industry just 10 years ago. The principal drivers were that Clients recognised that operating Second Party QA schemes, such as that for asphalt manufacture, and trying to ensure installed quality by random inspection and testing were no longer appropriate, when highway construction and maintenance was being outsourced to long-term contractors who must be responsible for the installed quality. However the Ultimate Clients still have the responsibility for highway safety and ensuring value for money which can only be demonstrated by ensuring durability for a period possibly longer than the term contract.

BS EN ISO 9001 and its predecessor BS 5750 provided the opportunity for Clients to use independent professional Certification Bodies to provide an audit function of their Contractors’ Quality Management System.

The underlying principal is that a good quality system would deliver a good quality product all of the time.

Inspection and Testing, by their very nature, can only prove snapshots or samples of product delivery. Testing cannot always be carried out because of site constraints such as access, because the installation process makes testing impossible or because of the destructive nature of some tests. It can lead to arguments about the validity of results especially with CE Marked products. Inspection requires teams of trained and competent staff for which it can be difficult to provide continuity as workloads fluctuate; it also blurs the responsibility for quality.

Asphalt is covered by the Factory Production Control [FPC] processes within European Standards. Additional requirements for the use of external audit by Certification Bodies of the system and to cover the items not included within FPC e.g. Contract Review and



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detailed training requirements for supervisors and operatives, can be included within a Sector Scheme, as has happened with Asphalt Production NHSS 14.

System Certification is not a guarantee of quality. It is a mechanism to improve the chances that good quality work will be delivered. Where a Client is not prepared to accept any lowering of standards, even inadvertently, he will have to supplement the schemes with his own Inspection and Testing.

Sector Scheme 13 covers Surface Dressing and Microasphalt. The Secretary of the NHSS committee responsible is Howard Robinson, RSTA.

Sector Schemes 14 covers Asphalt Manufacture and Sector Scheme 16 Asphalt Laying. The Secretary of the NHSS committees responsible is Malcolm Simms, MPA.

Suppliers must confirm their registration to an NHSS with “schedule of suppliers” and can log their Certification and scope on www.scheduleofsuppliers.co.uk which is searchable. It should be noted that this list may not be complete and the absence of a company from that list does not necessarily mean that they are not certificated. If in doubt ask the company for their certificate of registration and ensure that the relevant Sector Scheme is clearly referenced in their scope.

Each Sector Scheme Committee meets at least annually to manage the operation of their scheme and make any necessary changes to the documentation. This could take account of any feedback, including that from other NHSS, changes in available training and reference documents and improvements to the scheme as a result of its operation.

Quality Management System Documentation

The Quality Management System needs to contain all the key elements to ensure the consistent manufacture and installation of a product. These should be familiar to most people, as BS EN ISO 9001 principles are now widely used by Clients and Consultants. They may be summarised as follows:

• A Quality Plan to set out how the contractor will address all the problems that will need to be solved during the process of manufacture and/or installation, and may be generic to the Scheme. It will normally contain a Method Statement for a particular job.

• Documents giving a detailed record of what, when, how, by whom and what with, tasks were carried out and the results of inspections and testing.

• The Client’s order documentation and details of the review of these prior to accepting the order [contract review] to ensure they are practicable, appropriate resources are available for the tasks and they are possible in the timescale.

• The role of management in delivery of the Quality Management System.

• The training and competency requirements for staff and operatives.

• Policies for procurement and subcontracting.

• How non-conforming product is identified and the actions to be taken to correct the problem and prevent its recurrence.

• Details of the internal audit process – normally every aspect of the process is covered over a 12mth period, including site works, by the contractors own auditors.

• What the organisation is doing to continually improve the quality of its service to customers.



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Whilst these are spelt out in general in ISO 9001, it was recognised that additional guidance was required both for companies seeking certification to National Highways Sector Schemes and for their Certification Bodies to ensure a consistent approach to the certification process. This is provided in the Sector Scheme Documentation.

Sector Schemes build on the systems-based approach by giving appropriate emphasis and clarity to key areas within the systems. Specific requirements such as the type and frequency of quality control testing, compliance levels and corrective and preventive actions are set out to try to ensure that the systems deliver a suitable level of quality and consistency. Details training requirements for staff and operatives and also the knowledge competency of Auditors are spelt out.

The documents can also be use by Contractor’s QA staff and customers to help identify particular important features of a scheme.

The Sector Scheme documents can be viewed by using the link below under “Sector Schemes for Quality Management in Highway Works”: http://www.ukas.com/information_centre/Publications/PubsForCBAccred.asp

All the documents for all the schemes follow the same format. They contain definitions of staff and operatives, jargon definitions and details, clause by clause, of any special interpretation of ISO9001. They do not repeat any ISO9001 clauses. There follows a series of Appendices as follows the titles of which are largely self explanatory.

Appendix A - Detailed requirements for the contents of Quality Plans.

This can contain draft checklists

Appendix B – Reference documents

This lists the key reference documents e.g. Specifications, BS and EN Standards, trade and other bodies best practice guidance documents.

Appendix C - Training Requirements and Health and Safety.

It will normally contain details of what knowledge is required, and how and from whom the training can be obtained. An appropriate level of CSCS Card is mandatory for all schemes. In most Sector Schemes, including Sector Schemes 13 and 16 a schedule of competencies has been provided.

Appendix D - Sample record of training and competencies attained

Appendix E - Calibration.

Requirements for all equipment that takes a measurement

Appendix F - Certification Bodies.

This gives details of how to find details on the UKAS website of the Certification Bodies that provide services to the scheme. A summary list that is updated at quarterly intervals is contained in MCHW Volume 1 Appendix A www.standardsforhighways.co.uk/mchw/vol1/pdfs/appendix_a.pdf

Appendix G - The role of the certification bodies and assessor competence.

The Certification Body must be able to demonstrate to UKAS that it possesses and can maintain the necessary assessor experience and technical understanding of process covered in the scope of the relevant Sector Scheme. However auditors are expected to



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have knowledge of a very wide range of activities to keep them fully employed. They will not therefore be experts in the particular field but will, to an extent, depend upon the supplier/contractors quality plan and method statements. Assessor training modules have now been prepared to assist with providing adequate knowledge and UKAS have appointed consultant expertise to help them. An Assessor would normally be a graduate and/or have an NVQ level 4 or equivalent experience.

The scheme contains a list of the principal points within the process that an auditor should check and comment upon, this can also be used to guide internal audits.

Appendix H - Organization acceptance and guidelines for new entrants.

This states that only NHSS Certificated companies can carry out the function on the HA Network. For other customers it may be a contractual requirement. From its inception CSS as made it its policy that its members will implement Sector Schemes in contracts, as they come up for review.

Appendix J - Feedback.

Feedback is important on how the scheme is delivering the required customer quality. However, almost no feedback is being received by the NHSS Committees. This makes continual improvements and targeting customers’ particular concerns very difficult.

Supervisory staff are strongly urged to bring to the attention of the relevant NHSS Chair when they observe things on site that suggest that the scheme cannot a have been complied with, e.g. clearly incompetent /untrained staff or with no knowledge of the specified requirements or without CSCS Cards, a repeated need to do remedial works.

Appendix K: The interpretation of certificates issued by Certification Bodies.

This ensures that Certificates show the scope of accreditation of the company and the locations, both offices and depots from where it is supplied.

Appendix L: Guidance to Clients

This is a new section where the NHSS Committee can explain matters pertaining to Client implementation of the scheme

Role of Certification Body and UKAS

CBs are organisations assessed by UKAS as competent to carry out the process. They do this using staff with the minimum competencies listed in Appendix F, who carry out independent audits of the company, normally so that the every aspect of the quality system is inspected over a 3 year period. They pay particular attention to the internal audit reports and test results as these are the main link to actual works. They inform the company of the minor and major non-conformities they find; these must be addressed promptly.

UKAS carry out a review of the paperwork produced by CBs, to ensure that it is thorough and that appropriately qualified auditors have been used. They also carry out surveillance audits with the CB.

System Certification

System Certification can only be effective if it is adequately robust and is implanted within the culture of the company. However these are all overheads at a time when every aspect of a contractors operations is being scrutinised to reduce costs. The proper planning of the site works, production of contract specific documentation, the training and re-training of staff, carrying out testing as required at the frequency specified



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in the scheme or specification, the maintenance of Quality Assurance audit teams and payment to Certification Bodies are all essential activities to demonstrate a quality installation.

Health and Safety legislation impinges on the need for trained and competent staff and Corporate Manslaughter legislation can lead to extensive and intrusive police activity if a road death is contributed to by negligent activities. Absence of the documentation that a NHSS provides could become a serious matter.

Certification is contractual requirement for most contractors to the Public Sector and experienced, reputable contractors recognise the benefits in terms of reduced risk and costs of poorly planned work and remedial works a good system will provide.

A major fear still expressed by certified firms is that some Clients still prefer to buy the cheapest product even if it has no QA pedigree, or depend on a main contractor’s QA to ensure quality. These solutions do not provide any assurance of quality and will not therefore enable authorities to demonstrate Best Value.

System Certification has also changed the role of Clients supervisory staff. Whilst watching what operatives do for a short time gives a snapshot of performance, it does not necessarily ensure work is done well when they are not there. The records taken as part of the QA system provides this traceability and should be inspected.

Notwithstanding the chain of internal audit, certification audit and overall supervision by UKAS is still only a sampling exercise and faults, deliberate or inadvertent can still occur

It is important that client supervisors know what are the key activities that affect the performance and attend site to see that these have been carried out. Assistance with what these are, is provided un the Checklists in the Sector Scheme Documents available from UKAS. For asphalt some are listed below. Supervisors should also consider their role as a Second Party auditor of the quality system, checking that the key elements have been and have been addressed. Particular attention needs to be paid to the correct implementation of the Method Statement and the competency of sub-contractors’ operatives (if they are not already known).

Key aspects for asphalt installation include:

• The material specified has been delivered

• Accuracy of layer thickness, taken from painted dips but including local irregularities

• Staff available monitoring temperatures of materials delivered and during rolling

• A clean substrate with correct rate of spread of bond coat for the bond coat used

• Clean cut edges to previous layers painted with bitumen

• Covers set to level prior to laying surface course if at all possible

• Materials around covers properly compacted

• All rollers on site, with water and working close up behind the paver and rolling hand laid material promptly.

• Staff present to measure air voids, texture depth and rolling straight edge and keep the laying records up to date



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2.7 BBA Highway Authorities Product Approval Scheme (HAPAS)

The Highways Authorities Product Approval Scheme [HAPAS] was set up by the Highways Agency, the County Surveyors Society (CSS) and the British Board of Agrément (BBA) as a National Accreditation Scheme for innovative proprietary highways related products and systems. The first Certificates for Thin Surface Course Systems were issued in 1997. Work is currently ongoing for products for reflective crack control (SAMI).

HAPAS generally does not look after products that are the subject of British or European Standards. However where the quality of the delivered product involves a significant element of installation e.g. TSCS, BBA HAPAS can and does assess this at audit.

Unlike BS EN ISO 9001, it is a Product Certification Scheme not a system certification scheme. It is also particularly relevant for products that require a higher degree of certainty of performance either on safety or durability grounds. This includes High Friction Surfacing and Permanent Cold Lay Materials

For HAPAS to provide a nationally agreed method of assessment it wasstructured to ensure that any assessment and Certificate would satisfy key product performance requirements based on advice from a broad representation of the UK highways industry. A governing committee was set up, commonly referred to as HITAC (Highways Technical Advisory Committee), along with several sub-committees, known as Specialist Groups. SG1 covers High Friction Surfacing, SG2 Overbanding, SG3 Thin Surfacing, SG4 Bitumen Additives including Polymers Modified Binders, SG 8 Permanent cold-lay surfacing, SG9 Colour retention of pigmented surfacing, SG10 Coloured surface treatments, SG11 Grids and stress absorbing membranes. On occasion, HAPAS is presented with a unique ‘one-off application’. HiTAC decreed that the need for a Guideline in these circumstances is unnecessary although the route to approval is very similar. The only difference is that a bespoke Assessment Specification is drafted between the BBA, the manufacturer and ratified by HITAC. This helps to avoid the lengthy timescales and resource needed to create a Guideline through a Specialist Group.

HAPAS assessment stages A HAPAS assessment can be split into 3 key stages:

1 Manufacture and installation A review of, manufacturing and installation quality controls, generates documentation needed for Certification audits. Consistency of performance is one of the key attributes of the scheme. This is achieved by the ongoing post-Certification auditing using technically expert assessors and testing of samples

2 Performance trials All HAPAS assessments include both laboratory and site evaluations. The site performance trial remains a key element of the HAPAS assessment process. For example in the case of Thin Surfacing the product must show satisfactory performance for a minimum period of two years on at least 3 separate sites. If this is not available, a 2 year performance trial must be completed. In the absence of an agreed surrogate test to measure long term durability, this is considered to be the minimum necessary for HiTAC and Specialist Groups to support a claim on a products performance and durability.



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3 HAPAS Certificates

HAPAS Certificates contain information that reflects the findings of the BBA evaluation based on the assessment criteria from a Guideline or an Assessment Specification Guidance documents and all Certificates are available on the BBA website and Certificates should be read carefully. They should provide the potential customer with sufficient information to make an informed choice on whether the product is suitable for their purposes. Note: If a matter is not referenced in the Certificate then it is unlikely that the BBA have assessed it.

Specifying HAPAS Approved materials

For all innovative materials, the SHW requires BBA HAPAS certification. It is possible that a product required for highway maintenance does not have such a Certificate. A customer might accept the product provided it was contributing to the 2 year Assessment process as the underpinning Quality Assurance and Laboratory work will have been completed. There may be available a BBA Assessment report givingthe results of this work. 2.8 Specifying non-HAPAS Approved proprietary products

If the innovative product is unique but has no HAPAS Approval certificate, the customer has to carry out his own expert technical and quality management assessment, because if the product leads to an unsafe situation, the Local Authority is still at risk. This is in addition to the financial loss if premature failure occurs. The likelihood of being able to obtain redress from the original contractor/installer in the current climate is remote, despite the apparent rigidity of any guarantees offered. A typical technical assessment would include the following:

1. Evaluation of the process in theory and based on work elsewhere to see what added value it gives.

2. Laboratory work done on the material they propose to use in the Authority, with the parameters set by the Authority and agreed with the supplier. The Laboratory results provide ‘Type Approval' test data. A UKAS Accredited Laboratory should be used, even if they are not accredited for the particular test.

3. Trial site agreed to suit the worst case future use and check out the detailed method system provided.

4. Material from site tested as in 2 to see it the installed matches the Type Approval.

5. Site monitoring against the method statement for issues about installation.

6. Approval given by the Authority for its use more generally where the improved performance will be beneficial.

Experience has shown that it is essential, with a proprietary product without BBA HAPAS accreditation, to check out the references provided, and with others who may have used it but are not quoted, and to get an independent check on in-house data.

In accepting such a new product, time and budget must be allowed for the technical assessment and for monitoring the installations on site to ensure they conform with the method statements provided.



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3 Pavement Design

3.1 Introduction

The design of a maintenance treatment requires an evaluation of the

following

• Existing Pavement structure condition

• Traffic – volume, composition, speed particularly with reference

to commercial vehicle and bus flow

• Safety – surface characteristics

• Sustainability and the opportunities to reuse/recycle existing

pavement materials,

• Surface water and drainage requirements taking account of

climate change

• Aesthetics - surface type and characteristics

• Noise reduction

Whilst a complete pavement design guide is beyond the scope of this

Guidance Document, sufficient information has been provided directly

or by reference to enable commonplace treatment situations to be

designed.

3.2 Evaluating existing pavement structure and

condition

The structural design of new roads and areas of widening should be

based on the principles of DMRB Volume 7. This requires assessment

of ground conditions for the design of sub base thickness, with

thickness of bound (asphalt) layers being based on the traffic loading to

be carried.

The standard highway design document for carrying the process

leading to the sub base thickness is HD25/94 Foundations.

This is available in Volume 7 of Design Manual for Road and Bridge

works www.standardsforhighways.co.uk/dmrb/vol7/section2/hd2594.pdf

An Interim Advice Note IAN 73/06 has been published by Highways

Agency introducing a draft replacement to HD 25/94. County Surveyors

Society has agreed that this draft is inappropriate for use on a Local

Authority network and that HD25/94 should continue to be used.

Since the sub base thickness from this design document is designed to

take motorway construction traffic, it is very conservative for typical

road maintenance applications but this is offset by the difficulties of

achieving the same high level of compaction as major works.

The existing structural strength of the pavement should always be

assessed prior to maintenance works in order that the predicted design

life of the pavement can be achieved and value for money obtained.

TRAFFIC

GROUND CONDITION

SUB BASE

STRUCTURAL LAYERS

SURFACE CHARACTERISTICS

EXISTING

PAVEMENT

STRUCTURAL



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For example applying a single Thin Surfacing overlay to a road with observable

structural weakness, is unlikely to deliver bests value in the use of that surfacing

For strengthening existing roads, this is a significantly more complex procedure

which involves an identification of

a) the defect that the treatment is intended to solve and its cause,

b) the overall structural strength of the existing road.

It is extremely unlikely that a road will be scheduled for maintenance unless a surface defect is visible. Most County Councils now use the SCANNER device, which measures all the essential surface characteristics at traffic speed, to maintain an ongoing record of the state of their principal road network. Computer software is now available to take this data on a year-by-year basis to generate surface treatment and budget plans for future years. A typical output from a SCANNER Survey is shown below.

Red means intervention is critical, amber - likely to required shortly, green - the road is in good condition. For individual schemes identified from SCANNER or otherwise, e.g. the Detailed Visual Survey more commonly used in London, the type and extent of a defect will often give a very strong indication of the type of maintenance treatment likely to be necessary .

3.3 Defects

Common defects and suggested treatments are as follows:

3.3.1 Fretting

Deep potholes or fretted areas can present a real hazard to traffic and pedestrians.

Each Local Authority will have a policy a to when a pothole becomes a safety

hazard to traffic and pedestrians.

Fretting is the loss of material from the surface through the effects of trafficking

and/or weather, and is associated with a weakness in the surfacing such as a joint,



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thin layer or poorly compacted area, or material where the surface is oxidised due

to prolonged exposure to the weather. Fretting affects the ride and allows water

penetration through the surface, increasing the damage.

Fretting of the surface of roundabouts and sharp bends can be the result of too

large an aggregate size being used in the Thin Surfacing. Normally a 10mm

aggregate size material is recommended. Thin Surfacing laid in winter is more

prone to early fretting as the surface is more likely to have been insufficiently

compacted. The greater the texture depth, the more prone to fretting is the

surface.

It is strongly recommended that particular attention is given to cutting

back of sufficient material at joints during installation; particularly those

subject to trafficking All joints should be painted.

Fretting may be very discrete and localised, forming a pothole which

can be readily and cheaply patched, but when these are numerous or

when the fretting is more widespread, then resurfacing may be a more

economical and satisfactory solution.

Fretting is not necessarily a deep-seated problem, but can be a safety and political

issue. Depending on how deep it is and the basic causes, fretting can usually be

remedied by inlay of a surface course, with possible inclusion of a binder course

particularly in heavily trafficked or stressed areas.

In the case of Thin Surface Course Systems TSCS and SMA, the increase in

surface texture with time will not be at the same rate as fretting in macadam or loss

of chippings in Hot Rolled Asphalt. Notwithstanding, fretting of TSCS, particularly

near joints, can spread rapidly especially in winter and lead to a requirement for

pothole filling or even replacement.

Monitoring the increase in surface texture by SCANNER may give information on

incipient failure.

Prompt attention by Surface Dressing or Microasphalt should hold the surface and

help prevent further deterioration.

3.3.2 Deformation

Deformation may be broadly considered as two types: wheel track rutting and

general loss of profile by wear.

Wheeltrack rutting, as the name implies, is due to intense loading by traffic tyres in the wheelpaths, and occurs where there is heavy commercial vehicle traffic and especially where the vehicles are travelling slowly. Where traffic is channelled at locations of ‘gateways’, build-outs, pedestrian refuges or bus lanes this increases the risk of damage; when these are added the pavement strength/ rut resistance should be evaluated.



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It is often caused as the surfacing or binder course becomes softened by high

summer temperatures and is displaced in the wheelpaths, with consequent heave

to the offside and nearside which may not always be visible. South facing slopes,

which are in full sun in the summer months, can have very high

surface temperatures that soften the bitumen and increases the risk

of rutting. In an unshaded place the summer surface temperature

can be twice the air temperature. This problem will increase with

Climate Change predicting an air temperature increase of up to 5ºC

which can ,ad to a conseqien siurfce tempwrature increase of up to

10 ºC.

Deep ruts [>20mm ] can be a safety hazard for motorcyclists. Shallow

rutting may be tolerated provided that the texture is maintained on

high speed roads and water is not collecting in the ruts.

Deformation is readily measured and data is provided by SCANNER

surveys. It is the most important defect in determining best value

performance indicators.[BVPI].

It is important to determine the depth to which rutting has affected the road layers

in order to decide on treatment. This may be carried out by taking a number of

interlocking cores across the affected area and measuring the layer thickness.

Materials made with a hard, or suitable polymer modified binder and/or containing

a high percentage of aggregate, with good mechanical interlock, such as designed

Asphalt Concrete and particularly TSCS, are less prone to deformation than Hot

Rolled Asphalt. This has been taken account of in the recommended materials.

However further increased durability has been claimed by some suppliers of

proprietary products. Purchasers need to be sure the benefit is delivered sufficient

to justify the additional cost.

Increased temperatures make the deformation of binder courses an increasing

probability; it is already clearly evident at many traffic light sites. For this reason it

is recommended that Asphalt Concrete with 100/150 bitumen is not used in binder

courses for Road Types 1 and 2. Rutted binder course can only be resolved by

its removal.

3.3.3 Cracking

Cracking results from overstressing asphalt in tension. The type of

cracking visible at the road surface can give useful clues as to its

cause and the underlying pavement construction and provides

information to assist with any maintenance works.

Cracking may be due to:

• a single or small number of load applications by a heavy vehicle e.g. overrun of an unsupported edge – edge cracking,



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• repeated load applications by heavy vehicles over an inadequate foundation e.g. longitudinal fatigue cracking or crocodile/ alligator crazing, generally associated with vehicle wheelpaths.

• thermal movements, as the asphalt contracts in cold weather – thermal cracking – this is uncommon in the UK,

• reflective cracking where the asphalt overlays a concrete base where the joints or cracks in the concrete/cement bound material below reflect through to the surface – these are typically regular spaced transverse cracks.

All cracking other than hairline cracking (very narrow width cracking) is detrimental to the structural condition of a road as it reduces the structural strength of the layer [ c.f. Table in Section 3.6] and lets in water. The water can freeze, expand and thus lead to damage ranging from fretting of the material around the crack to delamination and fragmentation of the pavement layers with, ultimately, complete structural failure. In severe cases where the cracking extends through the full depth of the bound layers, the water ingress can cause mud-pumping whereby fine material is removed from the sub-base or sub-grade and pumped to the surface, leading to poor support and instability to the bound road.

New asphalt is a relatively flexible material, the greater the bitumen content the better resistance to cracking. However as the bitumen ages under the effect of air and water, it gets harder, more brittle and more likely to crack. Less permeable materials and those made with softer binder and/or higher binder content, or a suitable polymer modified binder are generally more durable. However further increased durability has been claimed by some suppliers of proprietary products. Purchasers need to be sure the benefit is delivered sufficient to justify the additional cost. For asphalt roads on a concrete base, whether lean concrete or overlaid concrete slabs, it is hugely expensive and disruptive to reconstruct, and if at all possible the best and most suitable solution is to leave the concrete in place. Unless it is obvious, a site survey by coring is essential to identify the type of concrete and the thickness of asphalt overlying it. If cracked concrete is found in cores assessment of slab stability and strength may well be justified using Falling Weight Deflectometer and trial pits may be a useful means of assessing the condition of the concrete surface. There are many different types of repair available for cracked roads, ranging from the simplest and cheapest short-term solutions – e.g. sealing the cracks by overbanding – to the most comprehensive, but costly – complete reconstruction.

Suitable treatments for reflective cracking

Overbanding by poured or screed sealant.

A hot poured sealant can be poured from a can along the joint. Alternatively, and better because there is control of the finished width, an overbanding of hot ‘filled bitumen’ can be screeded out along the crack/joint with surface applied grit if necessary. Where the crack or joint is wide enough the material may flow down and partly fill the void, but this rarely happens to any significant extent . Overbanding should, if possible, be preceded by applying a hot lance to dry the crack/joint and



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warm it to assist with penetration of the liquid. The process should be limited to transverse joints or on longitudinal joints less than 50mm wide, unless the skid resistance has been verified, as the surface can be very slippery for motorcycles. This is a short term solution until the material has been worn by traffic. Overbanding is covered by a BBA HAPAS Certification Scheme and only products with a certificate should be used. These are uncommon as the requirements are onerous and few contractors can satisfy them Use of an inlay joint treatment.

The most effective material is a proprietary modified partly stone filled mastic asphalt with surface applied chippings - Permatrack H. This is BBA approved. Other products are under evaluation. The material is designed to be flexible but have sufficient deformation resistance to cope with even the heaviest traffic. It is inserted by hand into a milled trench over each joint, overnight if necessary, and can be trafficked when cool. For many situations it is the most effective solution although rather slow and very expensive.

Removal of all or part of the asphalt overlay and replacement with materials that will be more flexible and elastic. Appropriate Polymer Modified Binders (pmbs) in the asphalt should not only improve resistance to cracking but should cracks eventually appear, the material will be less prone to fretting along the crack. The current list of materials tested and their performance is given in Section 4.7.1 Not all Thin Surface Course Systems are designed to be crack resistance, some have been designed to be very rut resistant or retain their high texture depth under very heavy traffic. Different polymers impart different properties. In general the greater the binder content the more resistant to cracking is the material. In addition, cracks in lower layers e.g Cement Bound Bases or trench sides will inevitably reflect through to the surface. The length of time this takes is largely dependent on the thickness of overlay material installed, though this can be extended by the use of a SAMI (see below) and a more flexible binder course and surface course. Introducing a ‘stress absorbing membrane interlayer’ [SAMI] prior to overlay. This can help to delay the onset of reflective cracking. Evidence from installations suggests they are very effective for treating reflective cracking in overlays to jointed concrete where there is good load transfer between joint.

Clients should consider carefully the costs and practicality of installing such systems compared with the use of an increased thickness of asphalt that will have a similar effect.

SAMIs available in UK include:



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Sprayed polymer modified bitumen membrane system with an overlay of fibre reinforced microasphalt to protect the membrane from construction operations and use by light traffic - Flexiplast. This is a specialist proprietary system that requires sufficient area to justify the mobilisation costs

Non- woven Geotextile membranes These are specialist proprietary systems using Polyfelt PGM 14 Geotextile to protect a sprayed bitumen membrane from construction traffic. They are too slippery for use by normal traffic. They have been used in the UK for about 15years and there is some evidence of effectiveness at delaying reflective cracking

Geogrids, (glass fibre reinforcing meshes) These are systems of self adhesive meshes of glass fibre laid on a regulating course or a fine milled surface - Glasgrid. The grid may have an additional sprayed overlay. The grid needs to be slightly tensioned to be effective and permit construction traffic. They have been used in the UK for about 15years and there is some evidence of effectiveness at delaying reflective cracking.

Combination systems of membranes interlayered with grids are also available.

Crack and Seat If the concrete is in poor condition, it may be mechanically broken up in-situ to provide a granular foundation that can be overlaid using a process sometimes known as “Rubbleising”. Additional asphalt may be required to replace the lost structural strength If the concrete forms slabs of consistent high quality and is unreinforced, controlled cracking known as “crack and seat“ may be employed. This retains more of the concrete strength than rubbleising but requires a substantial size of job to justify plant mobilisation and testing by Falling Weight Deflectometer. There may also be issues regarding possible damage to underlying services.

Hot Mix In-situ recycling This is a system that reheats the joint to a depth of about 50mm with infra-red heaters, the area is raked to close the crack and a grit applied to the surface to complete the process (Rhinopatch ) The system in BBA AHAPS Approved.

3.3.4 Skid Resistance

Visual surveys, SCRIM or GripTester data or accident records can identify sites that may deficient in Skid Resistance and therefore present a safety hazard. What action to take in case of a safety hazard is discussed further in Section 3.6. The appropriate treatment, from those described in Section 4, will depend upon the presence/absence of other defects, and the causes of the poor skid resistance.



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If the cause is only due to excess bitumen on the surface; e.g. as a result of fatting up of surface dressing, loss of aggregate from microasphalt, excess bitumen on the surface of Thin Surfacing/ SMA, or polishing of inappropriately specified aggregate for the site, short term benefit may be achieved by water jetting or physical removal; these are proprietary systems. 3.4 Assessing the structural strength of the existing road

Where the surface defect observed is only within the surfacing layers themselves (as described in Section 2.2), removal of all or part of the affected area, followed by replacement or application of an overlay, may be carried out without carrying out an assessment of the overall structural strength.

When significant sums are to be spent on a road it is prudent to carry out an assessment, of appropriate complexity, to determine whether a strengthening overlay with or without milling, or a strengthening inlay, would provide improved durability and value for money.

In most cases where longitudinal wheel path cracking, and particularly alligator/crocodile cracking is present, it is likely that a full reconstruction or deep strengthening inlay will be required. Where the primary fault is surface deformation it may be necessary to confirm whether this is in the pavement layers alone or structural if this is not clear from visual assessment. In such circumstances, a site investigation, probably involving cores but possibly also supplemented by Falling Weight Deflectometer [FWD] and/or Ground Penetrating Radar [GPP], will more than justify the outlay in ensuring an appropriate, durable solution. In combination with cores the former measures pavement strength, the latter measures pavement thickness, including an estimate of depth to services. From cores the thickness and existing strength of asphalt pavement layers can be measured in the Laboratory using the Nottingham Asphalt Tester ( NAT), the sub base thickness measured and the sub grade strength assessed using MEXE Probe or Dynamic Cone Penetrometerer ( but NOT where services are suspected). This information can be used to determine the feasibility of strengthening within the same overall thickness or whether overlay or reconstruction is necessary. Where cracking has all the appearance of reflective cracking surface replacement alone may be cost effective as full reconstruction may be prohibitively expensive. However where the cracks suggest inadequate structural strength, for example by mid-bay or corner cracking, a site investigation as above is recommended, supplemented by 0.5m square trial holes to expose the concrete enable its condition and in particular the degree of cracking to be assessed. Tar Tar is a carcinogenic binder used in highway construction from the beginning of the last century to around 1965.

Millings containing tar cannot be reused as granular fill, sub base or in a hot mix asphalt plant



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Tar cannot be disposed of except to a specially licensed landfill site; this is expensive.

Where the defects analysis shows that an inlay or reconstruction will be necessary, a supplementary site investigation must be carried out to determine whether or not tar is present. This normally consists of two parts, taking cores and using a spray that changes colour in the presence of tar identify presence or absence. The spray can change colour for other reasons than tar, so if tar is suspected the relevant material needs to be sent to an environmental laboratory analysis of the Poly-Aromatic Hydrocarbons (PAH).

The results can significantly affect the treatment choices for the site and even the overall maintenance budget. Sufficient time and budget should be allowed for the site investigation process.

3.5 Traffic Volume

For the purpose of road surfacing design in accordance with this document the network has been classified using the Road Type described in the New Roads and Streetworks Act 1991 [NRSWA] prepared by the Highway Authorities and Utilities Committee [HAUC].

All roads are classified into one of 4 road types and these are available to staff by means of a Gazetteer. This is used by the Public Utilities [Statutory Undertakers] to carry out reinstatements to the appropriate technical standard.

The road categories are determined by the number of millions of standard axles [msa] that will use the road as follows:

Category Traffic Capability - Roads carrying

Type 1 Over 10 to 30 msa

Type 2 Over 2.5 to 10msa

Type 3 0ver 0.5 to 2.5msa

Type 4 Up to 0.5msa

Roads with more than 30msa are out-with this categorisation range and will need

scheme specific calculations.

Where a road on the network has not been placed into one of the above categories

a traffic count of commercial vehicles will need to be carried out over at least a few

hours on a typical day and scaling up the value to a whole day.

Different vehicle types should be translated into standard axles using the wear factor as shown in the table below, an allowance made for traffic growth over the design period and the length of the design period i.e. 20 years, or 40 years if appropriate. Total standard axles = ∑ ( number of vehicles per typical day x vehicle class x wear factor x growth factor ) x 365 x Design life



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Table 2.3 HD 24/06 Detailed information is provided in HD 24/06 Traffic Assessment. This is available in Volume 7 of Design Manual for Road and Bridge works www.standardsforhighways.co.uk/dmrb/vol7/section2/hd2406.pdf .

Where traffic counts are carried out and the traffic is believed to be channelled it is prudent to multiply the msa by a factor of 2 before placing the road in the appropriate category. A similar factor of 2 is recommended for slow speed vehicles (less than 10 mph). It is not necessary to use both factors for slow speed and channelled traffic. This is particularly relevant where constraints on width are introduced such as pedestrian refuges and build-outs. Slow traffic has a much greater effect on the deformation of asphalt than high speed traffic. This deformation commonly takes place with Hot Rolled Asphalt surfacing, but is infrequent with TSCS. It can also take place in the binder course as described above. The effect of slow moving traffic has been taken into account in the table of recommended materials in this Guideline. 3.6 Structural design and material selection

In 1984 TRRL published Report LR1132, ‘The Structural Design of Bituminous Roads Powell, Potter Mayhew and Nunn’. This research document still underpins current UK design guidance though further work has been carried out for the Highways Agency and published in the Design Manual for Roads and Bridges [DMRB] in Volume 7 as HD 26/06 www.standardsforhighways.co.uk/dmrb/vol7/section2/hd2606.pdf

HD26/06 is intended for the construction and maintenance motorways and trunk roads with an emphasis on heavily trafficked roads and thick pavements and where delay costs are a significant component of in the whole life costing of a pavement solution. This affects minimum pavement thickness where 200mm is required and design life where 40 years is demanded . This assumption is not necessarily the case on Local Authority roads.



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The new standard, as one would expect, gives pavement thicknesses about 20 mm thicker than the old, to provide the extra 20 years life, and this increases construction costs. However the HAUC reinstatement specification still used designs based upon HD26/01 and these reinstatements have a disproportionate effect on urban streets

It also includes a relatively new material, EME 2, which requires a very stiff base which may not be present in a Local Authority road. This requirement is to ensure good compaction and limit deflections in the EME2 that could cause cracking as the material embrittles with age. The material replaces HMB35 for HA roads however this material is still a cost effective material on Local Authority roads and will become even more useful with increased temperatures

County Surveyors Society guidance is that for Local Authority roads HD26/01 should continue to be used

NB HD26/01 is no longer available from the HA website as the Highways Agency has superseded HD26/01 by HD26/06: The principal design chart is shown as follows

There are many roads with less than 2.7msa, the traffic level that requires the minimum thickness of 200 mm of asphalt. It is possible to reduce the thickness for lightly trafficked roads below 200mm, using the design information in LR 1132, which has been used in UK since 1985. This is shown for AC dense bin/base 50 [DBM 50] by the line extrapolation in red down to 1msa, further reductions below this are possible to 110mm minimum.

The thickness in HD 26/01 are dependent upon the stiffness of the surfacing material used. The current issue of SHW has reduced these. To use the chart from HD26/01 with confidence it is necessary to use the underpinning minimum stiffness values for binder course and base. These are as follows [BS594987 Annex E].

DBM50 Smin1800 ‘ HDM Smin 2500 HMB35 Smin 5200.

These values should be inserted in Appendix 7/1 together with any other site specific performance requirements e.g. deformation resistance.



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These are initial stiffness values. With time, as the binder ages, the layer stiffness will increase. This is taken account of in the design process for layer thickness. Further information is contained in TRL Report 250.

Existing Pavement evaluation

There are many situations where maintenance schemes require strengthening as inlay or overlay or combinations of both.

A pavement investigation as described in Section 3.4 together with expert analysis using analytical pavement design techniques will provide the necessary information.

Put simply, the existing pavement layers have to be substituted with stronger ones and/or added to, to increase the overall strength of the pavement For example in-situ cold mix recycling changes a weak unbound granular/cohesive material into a stronger, bound material.

A cracked layer has considerably less strength than an intact layer, the loss depending upon the degree of aggregate interlock The remaining strength can vary between 20% and 80% of the original.

Designed asphalt base and binder course permits stiff and rut resistant products to be produced. The stiffness refers to the Characteristic Strength in GPa measured in the Nottingham Asphalt Tester [NAT].

The stiffness of the material is strongly related to the penetration of the bitumen as given below. However the actual stiffness achieved is also dependent on binder quantity, the properties of the aggregate used and full compaction being carried out. For example, one would expect that a mixture made with crushed rock fines would achieve a higher stiffness than one with sand fine aggregate. However the former will be harder to compact than the latter. It is also possible to reduce the binder content and increase stiffness but at the risk of reduced durability caused by moisture damage and increased problems of workability and segregation of the material. There are minimum binder content requirements in EN 13016-1 to prevent very low binder contents.

Layer equivalence

For standard combinations of materials i.e. with decreasing stiffness the closer to the surface, it is possible to substitute one layer of materials with another depending upon their stiffness. This concept was pioneered by Asphalt Institute in USA and is there used in a very sophisticated form

The table below based upon BS 7533-1 gives some equivalence factors that may be used for commonly experienced materials

For example. 100mm of AC100/150 may be replaced with AC30/45 pro rata as

follows 100/1.32 x 0.95 = 72mm



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3.7 Selection of surfacing types and thickness

In order to limit the number of possible materials the materials tabulated below have been selected. These should be used as described in the Sections 4, 5 and 6.

The layer thickness’ are as described in BS 594987 Table 6A Asphalt concrete, 6B Hot Rolled Asphalt and 6D SMA binder course

Thin Surface Course Systems can be laid in the thickness range specified in the BBA HAPAS Certificate for the particular product. The values below are typical ranges.

Materials laid greater than 50mm thick are no longer Thin Surfacing and are not included in HAPAS

Combinations of surface course and binder course

Layers can be combined together as necessary provided that the minimum and maximum layer thickness is not exceeded.

The thickness of layers selected for inlay will depend upon the existing layers present. It is good practice when milling either to take out a complete layer +5mm into the underlying layer to allow for previous laying tolerances, or to not mill within 15mm of the layer interface so as not to leave a layer of possibly fragmented material which is unbonded.

Category of Material Material equivalence factor

Suggested Value

Range

Cement bound material 3 and 4 0.7 0.5 to 0.9

Pavement quality concrete 1.7 1.5 to 1.9

AC 30/45 HMB Base / Binder Course 1.32 1.25 to 1.35

AC 40/60 Dense Base / Binder Course 1.12 1.10 to 1.2

AC 100/150 Dense and HRA Base /Binder Course 0.95 0.85 to 1.05

Thin Surfacing 1.0 0.9 to 1.1

HRA Surface Course 0.8 0.8 to 1.0

Cold Mix asphalt storage grade and insitu stabilisation 0.75 0.7 to 1.0

Type 1 [150Mpa] granular sub base material over material

with a CBR of ≥ 5%

0.3 0.15 to 0.4

Condition Factors for existing pavements The equivalence factors above should be multiplied by these to give current equivalence

As new

Slight Cracking

Substantial Cracking

Wide and frequent cracks and fretting

1.0

0.8

0.5

0.2



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Thickness (mm) Course Material

Nominal Minimum **

TSCS 14 35 – 50 30

TSCS 10 25 – 35 20

TSCS 6 18 – 22 15

HRA 35/14 50 45

HRA 30/14 40 35

AC 10 close 30 - 40 25

Surface Section 4

AC 6 dense * 20 - 30 15

SMA 14 bin 30 - 60 25

SMA 10 bin 25 - 50 15

HRA 60/20 bin/base 45 – 80 40

AC 20 HDM/dense bin 50 – 100 40

AC 14 close surf * 40 – 55 35

Binder Section 5

14mm cold mix 40 - 70 35

AC 32 HDM 70 – 150 55

AC 20 dense bin 50 - 100 40

Base

Section 6

20 mm cold mix 50 - 100 40

HRA 60/32 60 - 150 55

HRA 60/20 45 – 80 40

* Footway use only

** NB The minimum thickness at any point is to allow for surface tolerance and is not

available to designers.

Examples of some combinations to treat a typical existing 40mm Surface course and 60mm Binder course are given below.

For an inlay/overlay the use of a Thin Surface Course alone is not recommended, unless the existing surface is sound and reasonably strong; a minimum deflection under a wheel of 0.65mm has been found suitable, and has a reasonable surface profile so that the TSCS thickness is always within the

40mm

60mm

Existing TSCS

6

20mm

TSCS

10

25mm

TSCS 6 +

10 SMA

20mm

20 -50mm

TSCS 10 +

14 SMA

25-35mm

30 -60mm

TSCS 14 +

14 SMA

35-50mm

30 -60mm

TOTAL 100 40 - 70 55 - 95* 65 – 110*

* Beware of proximity to layer interface



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permitted range. If this is not the case the use of a binder course is strongly recommended to give the best chance of a durable surfacing

In cold windy weather thicker layers are recommended to help the contractor with compaction but even so durability is likely to be compromised

Information on appropriate and inappropriate sites for TSCS is given in Section 4.7.1.

3.8 Safety

The safety of a road is a complex combination of a number of factors, of which the road surface itself is only one. All crashes are caused by people, and the actions they took, or failed to take. To a significant extent, this is affected by the visual and tactile information presented to them. Excessive information, commonly known as clutter, can confuse, inadequate information leads to wrong decisions. Engineers can use colour to provide information on the presence of a hazard. They can also use appropriate surface types e.g. small element paving and edge details, to make it plain that the road is being shared between vehicle and pedestrian. Inappropriate speed can lead to crashes or pedestrian injury, as the driver has inadequate time to react to the unexpected event. In conjunction with signing, chicanes, humps, cushions, rumble strips, road markings and similar techniques on the road surface, can reduce traffic speeds. The decision as to whether a road surface is unsafe and should be treated, must be a conscious one, carried out in accordance with the Authority’s Skidding Policy and implemented in a systematic way that is fully recorded. The Policy should identify the records to be kept of all the monitoring carried out to identify the site, the prioritisation process, the surface treatment selection and the site records that demonstrate that the client’s instructions were carried out.

The use of a published policy and good quality record keeping will significantly help an Authority to defend itself from a potential Corporate Manslaughter charge should a fatality occur and where the road surface was deemed to be contributory.

Attention is drawn to the Road Death Investigation Manual published by ACPO. [www.acpo.police.uk/asp/policies/Data/rd_death_manual_v2_2004_updated_1

9x04x04.pdf ]

Appendix F of the 2004 version is helpful in describing the kind of information sought by the Police

Further useful information on how Highways Agency approaches this issue is contained in IAN 98, available from www.standardsforhighways.co.uk/ians/pdfs/ian98.pdf



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3.8.1 Obtaining adequate Skid Resistance

The skid resistance of a road surface is a combination of the texture depth (macrotexture) and the microtexture. The latter can be assessed by the Polished Stone Value [PSV] of the aggregates at the surface of the road. In the early life of a new surfacing, the PSV is masked by the bitumen film, which takes time to wear away. In addition the skid resistance is affected by the contact stress at the road/tyre interface that is affected by aggregate size and shape.

The texture depth, or surface roughness, helps the tyre tread to disperse the water away from the contact patch, so that the tyre can grip on a ‘dry’ road surface. This macrotexture is more important at higher speeds than at lower speeds. It is important not to incorrectly specify too high a texture depth because the layer durability can be adversely affected. This is not only as a result of the increased access to air and water to the surface but also the increased risk of loss of surface aggregate, or coated chippings in the case of HRA, in areas of high braking and turning stresses. SHW Clause 921 [08/08] contains a table, shown below for completeness,

that describes the minimum new and retained texture depth requirements for Hot Rolled asphalt and Thin Surfacing, the difference recognises that the loss of texture depth with time for a TSCS is slower than HRA and precoated chippings

The HAPAS Guideline for Thin Surfacing gives three levels of performance for the systems as shown below. This is used in accordance with the traffic figures on the demonstration sites given in the certificate to provide information on the performance of the system.

[1.3]



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Most systems achieve Level 3 even under the heaviest traffic, although this may not be appropriate for low speed urban streets where less than 1.0mm would be preferable, there is no mechanism at present to set a maximum texture depth. . The Polished Stone Value of the aggregate to be incorporated into bituminous materials must be selected for the appropriate number of commercial vehicles that use the road and the amount of braking and turning or the ‘Risk Rating’ of the site. Information should also be provided on the hardness of the aggregate in the surface to prevent damage during construction and ensure durability (e.g. at small radius mini roundabouts. The aggregates in Thin Surface Course Systems [TSCS] can be a little softer than in Surface Dressing or Hot Rolled Asphalt (HRA). The surfacing material aggregate selection should be carried out using HD36/06, Surfacing Materials for New and Maintenance Construction Tables 3.1 (PSV) and 3.2 (AAV). This is available in

Volume 7 of Design Manual for Road and Bridge Works [DMRB ] HD 36/06 at www.standardsforhighways.co.uk/dmrb/vol7/section5/hd3606.pdf

For each traffic description, a choice of minimum Investigatory Level [ IL] for the Characteristic SCRIM Coefficient is provided ranging from 0.30 for an easy site to 0.55 for a high risk site. The Authority’s Skidding Policy will define how these values are selected for a maintenance scheme, largely based upon wet skidding accent records from the police. For new schemes guidance including pictures of typical sites is provided in IAN 98, available from www.standardsforhighways.co.uk/ians/pdfs/ian98.pdf Recent work strongly suggests that TSCS provides a better Skid Resistance for the same aggregate source/level of PSV than Hot Rolled Asphalt. This may be because of the aggregate size or that a greater percentage of the road surface is covered with aggregate.

It is expected that further advice on PSV selection for TSCS should be available early in 2010

Where the fine aggregate in TSCS has a much lower PSV than the coarse aggregate e.g. limestone, this may be detrimental. Further work on these aspects is in progress.

It is recommended that TSCS should be specified with the coarse and fine aggregate having the same PSV

Early life Skid Resistance and Horses Concern has been expressed in the media about the early life skid resistance of TSCS. There is no evidence that this is inferior to HRA. However guidance has been published by the Highways Agency as IAN 49 Use of warning signs for new asphalt road surfaces. This is available from www.standardsforhighways.co.uk/ians/pdfs/ian49.pdf



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A number of Local Authorities do not follow Highways Agency advice but have published their own procedure in their Skidding Policy document, to overcome the possible proliferation of signing that may be of limited value.

A worthwhile enhancement of early life skidding resistance can be achieved by the addition of a small quantity of grit applied to the new surface whilst it is being compacted. This can readily be carried out by a gritting box on the vibrating roller Alternatively, the surface bitumen may be carefully removed by a proprietary mechanical or water jetting system to expose the aggregate. Some time may have to elapse before this can be done successfully; full aggregate exposure is not necessary.

The locations where grit is normally specified is on roads with traffic speeds in excess of 30mph where the risk rating shows that > 0.45 SFC is required e.g. approaches to and across junctions. It can be used prior to the installation of HFS.

Surface applied grit can also be used where a binder course must be trafficked prior to overlay. ‘Temporary Road Surface’ and ‘Slippery Road’ signs should be erected. In addition, there are situations particularly on hills where horses have been known to slip on new TSCS. The application of surface applied grit is effective in improving the resistance to slipping by horses and should be considered for any new TSCS on roads regularly frequented by horse riders. CSS/British Horse Society Guidance has been published to reduce the risk of this occurring. Available at http://www.bhs.org.uk/About_Us/Campaigns/Safety/Slippery_Road_Surfacing/Slippery_Road_Surfacing.aspx

In order to implement this requirement the following additional clause is necessary.

Appendix 0/2 Additional Clause 942.17 Surface applied grit Where required the surface shall be gritted with 0/4 dust free or very lightly bitumen coated crushed rock fines at a rate exceeding 600gms/m2 before final compaction is complete and rolled in. Excess material shall be removed by sweeping.

High Friction Surfacing The use of HFS can lead to damage to the underlying road surface. Guidance has been published by CSS on the Use of High Friction Surfacing In summary CSS recommends that whilst in the past all High Friction Surfaces have been 50m in length, more recent guidance has indicated that the High



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Friction Surface should be installed where braking takes place. Typical best practice guidance suggests the following based upon Highway Code braking distances

Speed limit length of HFS(1)

Km/h MPH (m)

32 20 15 (2)

48 30 25

64 40 40

80 50 55

96 60 75

112 70 100

Note 1. The length of HFS has been determined by adding both thinking and braking distances in the Highway Code on a normal road surface. It therefore already incorporates a safety factor to take account of the drivers exceeding the speed limit. Note 2. HFS should only be provided on 20mph sites when there is a very hazardous location and evidence of skidding accidents Note 3 Where tailbacks are commonplace engineering judgment should be used on the extent of the HFS Further information on types of High Friction Surfacing is in Section 4.3 Alternative solutions include use of TSCS with PSV >68; or use of Surface Applied Grit or physical removal of the bitumen as above, and monitor the surface skid resistance with a Griptester Mk2 within the first month and quarterly thereafter, depending on the results obtained. It may be that HFS need not be installed at that location subsequently, depending upon traffic, degree of braking and an evaluation of risk. 3.9 Sustainability

Sustainability in the context of highway construction and maintenance means minimising the use of primary materials and the reducing the amount of energy used in the site preparation, and in production, transportation and laying of the new material.

3.9.1 Minimising the use of primary materials

There are three ways of achieving this

a) by using less material in total b) replacing primary materials by recycled and secondary materials c) using the pavement designs and material with the longest possible

service lives

Using less material in total Using less materials involves not removing the existing road surfacing if this can be avoided and using stiffer materials for the maintenance treatment. Stiffer materials, within reason, can be used thinner as they are stronger, to provide similar structural contribution. Details of the relative strengths of various materials is given in Section 3.6 layer equivalence table.



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It should be noted that concrete whilst it is very strong in itself is only as strong as the joints or cracks in the slabs and this is reflected in the equivalence factors. Overlay can either be a thick overlay, leaving all the existing road in place, or a part overlay where for example a rutted surface course is replaced with a new binder course and surface course.

Where it is intended that pedestrians and vehicles share the carriageway, for example in streets where delivery trucks attend the shops at night, reducing the kerb face and overlaying with small element pavers or asphalt can be an effective way of strengthening in a sustainable way, provided safety is not compromised. Where the footway could as a consequence be overridden, measures need to be put in place with bollards, planters or other street furniture to prevent this.

A strengthening inlay is particularly appropriate as an alternative to reconstruction of a cracked carriageway, or where binder course rutting is present as a result of the soft bitumen or tar macadam used in the past. The strength of the existing cracked or rutted carriageway can be assessed by cores and Falling Weight Deflectometer surveys or by expert visual assessment . With the use of an appropriate polymer-modified binder and proprietary systems, it is not always necessary to plane down to the concrete where this material comprises the road base and the lower layers of the existing asphalt overlay are in sound condition. The use of Surface Dressing and Microasphalt involve application of only small quantities of primary materials to the surface and are therefore very sustainable solutions for the defects they can treat. Replacing primary materials by recycled and secondary materials The benefits of reduced energy usage are discussed in Section 3.9.2 Hot Mix Hot mix asphalt binder course and base can contain a significant percentage of recycled material; usually about 18% Recycled Asphalt Products [RAP](millings or crushed rejected or plant mixed material) by mass is added in summer. This percentage is generally reduced to approximately 10% in winter, as RAP addition can affect mixture workability.

Greater than 10% addition requires the supplier to increase his quality control by testing the penetration of the binder in the millings and possibly making subsequent adjustments to the mix. Up to 50% incorporation can be carried out without adverse effect, if the plant technology is available locally to process, heat and mix the millings.

The quality of recycled material in asphalt is codified in EN 13108-8 and called up in SHW [08/08] Clause 902.



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RAP addition into surface course ( up to 10% ) is possible but requires a large quantity of millings of known coarse aggregate PSV, as for example may be available from a motorway contract.

The performance of hot mix materials containing recycled asphalt is identical to material made with 100% primary aggregate and can be used in the same thickness.

Warm Mix There are now number of processes that produced ‘lower energy’ hot mix material. These may be based upon an additive with a different temperature /viscosity relationship to bitumen i.e. they solidify at a particular temperature so provide low viscosity for mixing but high viscosity at ambient temperature. An alternative technology involves incorporating a small quality of water into the hot mixture. As steam it lowers the viscosity for mixing but on cooling the water is insufficient to detrimentally affect the performance. This process must be very well controlled and the performance of the resultant mix checked. Particular attention is required to ensure that the time between the delivery at the lower temperature and completion of compaction is practicable for the weather conditions. A problem with these processes is that the energy saved does not outweigh the increased cost of the additive and changes to the plant required. The asphalt produced is therefore more expensive than standard hot mix.

Cold Mix Cold mix materials are particularly valuable as a sustainable solution as they are generally made from at least 95% recycled concrete or processed demolition waste or most commonly processed millings. They can be very sustainable in terms of energy used and CO2 emissions (c.f. Section 2.7.2).

The materials are described in Specification for Highway Works Clause 948. This specification encompasses binders of

• Portland cement ( quick setting – QH), • Hydraulic binders, pfa, slag, lime (slow setting - SH). • Bitumen with cement addition ( quick setting - QVE), also

known as ‘Structural Grade’. • Bitumen with optional lime addition (slow setting - SVE), also

known as ‘Storage Grade’.

The first two are rigid materials when cured, and are now readily available. As they comply with Clause 948 they may also be used for reinstatements without the need for a trial. Storage Grade contains foamed bitumen, water and possibly pulverised fuel ash [pfa]. As the name implies it may be stored for periods up to 3 months. This grade is particularly suitable for footway base / binder course and housing development carriageway base. It can also be used for HAUC Reinstatements It requires a increased thickness of 25% compared to the hot mix asphalt.



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Structural grade is manufactured from the same base material as storage grade with the addition of a small percentage of cement. It must be used within a few hours of mixing. Structural grade is suitable for base course on any road, including motorways and principal roads. With a suitable thickness of surfacing it may also be used for binder course on lightly trafficked roads. Clause 948 contains different grades of material. Class B4 can be used at the same thickness as Hot Mix material; The design of pavement thickness using cold mix materials may be carried out in accordance with TRL 611. In situ recycling There are a number of companies that specialise in hot mix in-situ recycling of surface courses and cold mix in-situ recycling of all surfacing and sub base layers. Hot mix in-situ recycling is particularly suited to closing cracks in a surface course prior to overlaying with a new Thin Surfacing, which can be hot bonded. Despite reusing 100% of the existing road pavement these processes may not be as energy efficient as conventional asphalt unless there are savings in haulage if the asphalt plant is some distance away. (c.f. Section 2.7.2).

Cold mix in-situ recycling is particularly effective as an alternative to full reconstruction and should always be considered where full reconstruction is required. In any road where the depth of material to be removed exceeds 70mm it is necessary to check for the presence of tar. (c.f.) Section 3.4 ). Cold mix in-situ recycling is an acceptable way of encapsulating the tar on site so that expensive removal to a contaminated material landfill site can be avoided.

To carry out cold mix in-situ recycling an enhanced site investigation is required to determine the thickness and types of materials present and the depths to services. This is normally done with coring and a Ground Penetrating Radar (GPR) survey. This permits the feasibility of the process at that site to be determined. It is followed by a trial pit evaluation, normally done by the specialist contractor, when the design has been finalised and prior to works commencing.

Using the pavement designs and material with the longest possible service lives

Standard pavement design processes in accordance with HD26/01 Volume 7 of Design Manual for Roads and Bridges had a 40 year design life with maintenance overlays after 20years. This design document is still the one recommended for use by Local Authorities. The thickness of the pavement construction is similar to those that are used by Public Utilities using the HAUC Specification of June 1992 as they both refer back to TRRL Report LR1132. However in urban streets, overlay is rarely possible so a longer life may be justifiable and is frequently used to accept pavement designs for developments for subsequent adoption.



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For existing streets the continual opening and reinstatement to the old standard by Public Utilities may negate the benefits to the Highway Authority.

Each Local Authority must take a view on what design life to use.

HD 26/06 does not include HMB35 as base or binder course e.g AC 20 HMB bin 30/45, which some Local Authorities find most useful. The document instead introduces EME2, e.g.AC20 EME2 bin 10/20. EME2 is a material similar to Hot Rolled Asphalt but with a special very hard binder to give it a similar stiffness to HMB35. It is very expensive but has the advantage of having low voids, not dissimilar to SMA 20 bin 40/60. It must, however be laid on a stiff receiving layer. There are concern about embrittlement with ageing leading to cracking problems similar to CBM base, and with the high carbon ‘footprint’

This guidance document has retained HMB for special cases and has not incorporated EME2

3.9.2 Reducing energy usage.

Energy is used in the transportation of aggregates and binder to the plant, heating, drying and mixing the hot aggregate with bitumen, transportation to the site and laying and compaction. There is also the energy used by staff transport. For many asphalt materials the typical greenhouse gas emissions from their use is shown in the chart below.



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A more detailed computation programme will shortly be available to more accurately predict the GHG Emissions (CO2e) from the manufacture, transportation and laying of asphalt. The quantity of CO2 in hot mix asphalt can be declared in accordance with an agreed method of evaluation. This will permit the relative efficiencies of various asphalt plants to be compared.

It may be seen from the chart that the use of cold mix asphalt with primary aggregate and either emulsion or foam bitumen is beneficial in reducing emissions. Cold mix in-situ recycling is by far the best minimum energy option and hence generator of CO2 for the base layer, as there is no transportation of materials and no quarry energy to consider There is an energy calculator available produced for the Environment Agency in the form of an Excel spreadsheet that calculates the embodied carbon dioxide (CO2) of materials plus the CO2 associated with their transportation. It also considers personal travel, site energy use and waste management. It may be downloaded free from the Environment Agency website www.environment-agency.gov.uk/business/444304/502508/1506471/1506565/1508048/

The Waste Recycling Action Programme, [WRAP] also have a calculator that simply considers the material up to and including installation. This maybe downloaded from www.aggregain.org.uk/sustainability/try_a_sustainability_tool/co2_emissions.html.

Asphalt manufacturers are rolling out improvements to the energy efficiency of plants, for example by better insulation, covered storage, reduced friction in belts and gearboxes, more efficient heating arrangements. However these are capital intensive and many plants are not currently making the tonnage required to justify the expense.

The declared value provides the opportunity for customers to select the source of their asphalt to minimise its carbon footprint

However what is of prime interest is that the asphalt as delivered, has the lowest CO2 ; transportation, particularly in trucks, is energy intensive. It may be better to use a local inefficient plant than an efficient plant further away. Manufacturers of other products; surface treatments such as HFS, microasphalt and surface dressing, concrete/stone paving products and road marking are being challenged to provide information consistently and transparently calculated

on the embedded CO2e

From April 1st 2010 construction products have to form part of the Carbon Exchange Trading Scheme. In simple terms, each producer must determine how much carbon he needs to purchase for the year and buy the credits. Excess unused credits may be sold, more can be purchased but at a higher price. The cost of these credits may or may not be passed on to the customer. They will add about £0.70 /tonne to the cost of asphalt. Local Authorities must also reduce the amount of CO2 generated by their operations. Until recently the electricity used in street lights has been a very major priority as well as that used in offices. This has beenfollowed by fuel usage in the Authority’s vehicles. As soon as accurate information is available, the maintenance activities themselves can be added and the CO2 involved is considerable.



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As Microasphalt and Surface Dressing generate perhaps only 10% of the CO2 of hot mix, a maintenance department can reduce its carbon footprint by amending their maintenance programme. Whilst this can be of short term benefit it is still necessary to consider if this is best value and whether it is in the Authority’s interest to defer more carbon intensive treatments to a time when the Cost of Carbon is likely to be significantly greater than now.

3.10 Surface water and drainage requirements

Hot Rolled Asphalt is almost completely impermeable when new, unlike Thin Surfacing [TSCS] or SMA which are designed to be porous so that water can move easily from beneath the tyre/road contact patch. This means that if excess water is to be prevented from reaching the more vulnerable base and foundation layers an impermeable layer must be introduced beneath the surface course. Current BS 594987 bond coat requirements are being and simplified but these are much more copious than the thin tack coats used in the past. Bond coats shall be used between all layers TSCS are laid on a bond coat that is part of the system. This rate of spread may not be sufficiently high for the binder film to act as an impermeable layer.

Clients are recommended to ask the Installer for a method statement that will incorporate the minimum requirements of BS 594987 for all layers including beneath TSCS

An SMA binder course is strongly recommended for use beneath TSCS and has been used in this document. This will have the added benefit of permitting a thinner surface course and will also contribute to improved transverse and longitudinal profile. Where resurfacing is to take place, it is very prudent to review the current drainage of the carriageway or area as part of the planning process.

Areas identified by the Environment Agency as likely to flood regularly and areas of water ponding, particularly in wheelpaths, are very detrimental both to the road surface and to the adjacent footway, boundary walls and fences as a result of spray from passing vehicles. These areas can be recognised by and included within the SCANNER survey interpretation.

Where these wet conditions cannot be otherwise alleviated it is recommended that a Hot Rolled Asphalt Surface Course is used to improve long term durability of the pavement

Gulleys need to be sited at the low places taking account of surfacing tolerances. If necessary linear drainage may be appropriate. Linear drainage also provides an opportunity to drain the TSCS. Climate change estimates state that road drainage will have to cope with 20% greater rainfall volume than currently experienced. Where new roads are being considered or major reconstruction works planned such increased volumes should be taken into account in storm sewer and gully design.



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SUDS continues to be a challenge for trafficked roads, as water penetrating the road surface will reduce the durability of asphalt. The foundation and sub base layers must be designed to be wet . As a result of the inevitable clogging, ongoing maintenance of SUDS and the liability for it must be addressed. Whilst Porous Asphalt is included in the European Standards, the porous materials used in SUDS applications are proprietary products that form part of the systems marketed by the companies and lengthy guarantees should be demanded. For highways (as against public and private car parks), methods of attenuating run- off which do not depend on permeable pavements are preferred.

3.11 Aesthetics - surface type and characteristics

In urban areas, aesthetics are particularly important and significant funds are often allocated to environmental improvements. Landscape architects and urban designers tend to prefer concrete pavers, bricks, stone setts and slabs rather than asphalt. These can be designed and used successfully by both vehicles and pedestrians. However it is strongly recommended that a knowledgeable pavement engineer provides advice on modular paving at as early a stage as possible, as inappropriate and unsafe materials selection and installation is very common. The BS 7533 Series provides best practice design and installation guidance for the whole range of these products. Using this guidance, and taking due account of Statutory Undertakers activities, an extremely durable surface can be achieved that can justify the initial high outlay. Red coloured asphalt is made with standard bitumen and red pigment, but a wide range of colours is available using clear binder and natural aggregate. This can look extremely attractive instead of, or in combination with paving units. The PSV of red aggregate may be less than desirable, but these have been used for many years without significant accidents occurring.

Microasphalt is a surface treatment that is available in a number of colours. It is particularly suited to footways, cycleways and lightly trafficked roads. Surface Dressing normally uses grey natural aggregate but it can be carried out using a red aggregate, provided the binder/aggregate affinity is checked. It can also make an important visual contribution to safety and by improving skid resistance. The binder/aggregate affinity should be checked by testing Coloured resin bonded surfacing is available, normally red but blue green and blue are also available. When it incorporates calcined bauxite aggregate this has a very good skid resistance. However the



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longevity of the coloured coating to the bauxite depends on traffic levels and can be very short.

Some products are available that use the resins as a binder incorporating natural aggregate to form a resin bound (encapsulated system). These can have the appearance of an asphalt concrete to create a layer up to 50mm thick and are made as hot mix or are laid cold as a surface treatment up to 3mm thick, in which case they have the appearance of a road marking product. Highway and

Footway grades are available Imprinted surface treatments are available that provide an acceptable alternative

ot concrete blocks and paving flags. These are thin layers so can overlay an existing sound base or better be applied to a HRA support course. These are especially valuable where the Client demands paving flags but vehicular overrun cannot be prevented . Guidance on streetscape design has been published by TfL available on http://www.tfl.gov.uk/businessandpartners/publications/4858.aspx

3.12 Noise reduction characteristics

The noise emitted by a vehicle travelling along the road is a combination of a range of factors; engine, transmission, exhaust, wind as well as tyre/ road interaction. As speeds increase the tyre / road interaction increases as a proportion of the total and becomes the largest factor above 25km/hr.

Tyre/ road surface noise is primarily generated by the tread distorting and by vibration of the tread and side walls as the tyre passes over the road surface Rough surfaces (high macrotexture] created by the use of large aggregate at the tyre/surface interface generate significant noise; small aggregates much less. In addition Thin Surface Course Systems have texture depth [macrotexture] generated by voids in the surface layer, these absorb some noise so they are quieter than equivalent non porous materials [e.g. Surface Dressing, Microasphalt and Hot Rolled Asphalt] for the same aggregate size.

The BBA HAPAS system quotes a number known as Road Surface Influence [RSI] This gives the number of decibels [dB(A)] that a road surfacing material is quieter than HRA. HRA was the standard product when BBA HAPAS for Thin Surfacing was developed. Typical values are -3 dB(A) to -5 dB(A). 3 dB(A is very noticeable to a bystander. There are also benefits in reduction of noise within the vehicle



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Recent work in an urban area has demonstrated and conformed that the use of a Thin Surface Course System with a 6mm aggregate laid 25mm thick generated a saving in noise of 5.9 dB(A) A programme has been developed based upon this and traffic figures that can be applied to any road treatment proposal to give the number of people that will benefit from such a surfacing . For presentation to Members this has been displayed visually as follows

3.13 Innovation

Innovation and innovative products have a significant role to play in improving best value to customers and public satisfaction with outcomes, whether in a surfacing’s aesthetics or its durability. . The core list of asphalt materials given in Section 3 sets the basic standards for the performance of a standard material for that location in the highway. There could nevertheless be opportunities for proprietary products that claim to provide some added benefit, although these will probably not have the track-record of the standard materials, nor should the claims be taken at face value. How these should be addressed is detailed in Section 2.6 and 2.7

5.5dBa quieter

Range reflects different surface porosity

Regression Equation:

Relative change in traffic noise level, RSIH = 11 Log10(Aggmax) - 16 dB(A)

R2 = 0.6722

-10.0

-9.0

-8.0

-7.0

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

0 5 10 15 20 25

Maximum aggregate stone size, Aggmax, (mm)

Re

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an

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in

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no

ise

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I H d

B(A

)



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4 Surfacing Materials selection

4.1 Introduction The surface course is the layer in the pavement with the most complex set of criteria to satisfy. It must

• resist rutting • resist cracking if overlaying a cracked but otherwise

structurally sound base • be skid resistant • be durable • be smooth • provide a quiet surface when used on higher speed roads • be aesthetically satisfactory • be capable of being laid safety in all localities • be able to be laid swiftly when necessary to reduce traffic

disruption • be suitable for new works and maintenance activities • offer value for money

This guidance is intended to provide information that can be used in conjunction with consideration of these and wider issues to assist engineers select the most appropriate surfacing option. The materials choices are arranged in order of increased thickness The information is also summarised in tabular form in Appendix 2

4.2 Slurry surfacing This is an extremely economical way of restoring the surface of footways, pedestrian areas and cycleways. With thicker versions, small defects e.g. shallow potholes, open texture, cracking, can be covered. Thinner versions are best considered as paint. Slurry surfacing is available in a wide range of colours and so can be used for delineation It can be laid by hand in small areas or by small machines that can lay narrow widths Since it is so thin, milling is not required. Durability in carriageways can be low therefore it is unlikely to provide value for money in these locations despite its cheapness. Microasphalt should be considered

The materials selected for the maintenance of a road will take account of the following

• the defect (s) to be rectified,

• priorities and funding,

• sustainability and durability,

• site traffic conditions,

• time of year,

• environmental considerations,

• value for money

• customer preferences.

Slurry Surfacing High Friction Surfacing Micro asphalt Surface Dressing Resin bound surfacing Hot mix asphalt



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4.3 High Friction Surfacing [HFS]

HFS is a veneer treatment applied at situations where high resistance to skidding is required.

The systems comprise a resin binder which also acts as an adhesive for the fine single-sized calcined bauxite aggregate. This is very hard and has a high Polished Stone Value. Cold applied resins include the traditional epoxy material, polyurethane and the more recent Methyl Methacrylate [MMA]. Hot applied thermoplastic resins include tall oil also used in road markings

Cold applied resins are installed as continuous film of glue sprayed by machine or squeegeed out, onto which the aggregate is broadcast. Cold and hot applied materials can be applied as a mixture of resins and aggregate screeded out in strips or squeegeed over the surface

If necessary the surface is swept of loose material and again after 24 hours.

The Client should agree with the installer the ongoing regime of sweeping to keep the road free of debris that could present a hazard to motorcyclists, normally this is at least 30 days.

Calcined bauxite aggregate has either a grey or buff natural colour.

HFS can be coloured through pigmentation of the binder and coating of the aggregate, but the colouration of the aggregate can be short lived as traffic action removes the pigment to expose the natural colour of the calcined bauxite.

All material should come with a BBA HAPAS Certificate as described in section 2.7 that demonstrates its performance

HFS should last at least 5 years; there is increasing evidence that the cold lay materials are more durable than the hot screeded mixtures.

HFS is relatively expensive and should only be applied to a sound road surface, not only as it would be uneconomical and wasteful if structural maintenance is required soon after, but also because HFS transmits high horizontal stresses to the underlying surfacing, which can quickly develop cracks particularly if it is aged or unsound.

Most Local Authorities have safety policies setting out where to use HFS, normally on approaches to pedestrian crossings, traffic lights and roundabouts. These should be kept under review so that the material is not used un-necessarily. The recommended length of HFS are given in Sections 3.8.1

It is now generally accepted that HFS can be applied soon after a new TSCS has been laid. Advice is being prepared by RSTA.



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Resin bonded surfacing

This type of surfacing uses similar resins and techniques to HFS but uses natural aggregates to provide a long lasting coloured surface even after wear.

The surface does not have the high friction characteristics of HFS but skid resistance more related to the PSV of the aggregate used.

It is very suitable for gateways, cycleways and other areas of carriageway or footway where colour is helpful for delineation or safety. A

wide range of colours is available.

The application in winter can be expensive as the road needs to be free from salt and dry. Curing times can be lengthy requiring traffic management.

4.4 Microasphalt

Microasphalt is a superior slurry surfacing that usually contains a polymer modified binder to improve cohesion of the mix and adhesion to the surface.

It may be specified using the parameters in EN 12273 shown in Section 2.3 using the guidance in PD 6689

It is mixture of bitumen emulsion, cement, aggregates and additives. It may contain coarser aggregate (6mm) to enable a thicker application, and fibres to improve wear and crack resistance. Some shedding of fine aggregate occurs and it should be swept after a few days.

It is available in a range of colours, typically green and red, using natural sands and aggregates.

It can be used for regulating of ruts, shallow potholes and trench reinstatements. Some adjustment to ironwork may be necessary for thicker applications.

It is well liked by the public on account of the speed of laying and smooth texture on completion.

It has an extended laying season from around March to October.

It is suitable for a wide range of traffic especially urban streets and the rural network, except in locations with very sharp turning and braking where wear and polishing could be a problem. Some materials are very stiff and are primarily designed for rutted heavily trafficked roads, whereas others are more flexible and crack resistant.

Clients should ensure they are aware of the strengths and weaknesses of the particular proprietary systems offered

4.5 Surface Dressing



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This is an extremely economical way of restoring skidding resistance and sealing the surface but, as with slurry surfacing and HFS, it is a purely cosmetic surface treatment that does not improve structural strength.

It was traditionally known as “tar and chip” due to the process being the successive application of chippings spread onto a previously sprayed binder. Tar is no longer permitted for Health and Safety reasons and has been replaced with bitumen emulsion. The new dressing is then rolled and the excess aggregate swept before opening to unrestricted traffic. The binder can be unmodified, or polymer modified in two grades; intermediate and premium. These have improved grip with the chipping adhesion and tensile strength.

Best practice means that windscreen and bodywork damage should no longer be significant issues. Traffic delay during installation and in early life can be reduced and good design can reduce tyre noise.

Designs should be based upon Road Note 39 [6th Edition] and the quality of installation covered by the National Highway Sector Scheme 13A; details of this can be downloaded from the UKAS website www.ukas.com/information_centre/publications.asp

Many Clients prefer to specify a ‘performance’ or proprietary Surface Dressing from their contractor, where a performance guarantee is provided, normally in the form of a maximum limit to loss of surface texture and/or chipping loss. Performance dressing is specified in Specification for Highway Works Clause 922. Design is then the Contractor’s responsibility.

From 2011 performance surface dressing shall be specified using the parameters in EN 12271 shown in Section 2.3 using the guidance in PD 6689 . However SHW Clause 922 contains similar requirements but it includes a requirement for a performance guarantee

Surface dressing can only be carried out in the suitable weather in the summer months, and therefore requires forward programming, including measuring the road hardness the season before and advance patching where necessary.

It is suitable for all road categories except those with high volumes of braking and turning traffic.

The availability of premium emulsion binders has now made the use Surface Dressing suitable for residential locations. Previously problems have been experienced due to the risk of bitumen being carried into adjacent properties by pedestrians.

The use of multiple surface dressings as a regular treatment can build up a thick layer of soft material. This issue will become more important as surface temperatures increase with climate change. It can on;ly be addressed by removal and replacement.

4.6 Resin bound surfacing

Resin bound surfacing is a mixture of clear or pigmented resin binder and natural aggregates. It can be manufactured cold on site, or off-site in a hot-mix asphalt plant. The colour of the aggregate gives the principal colour of the layer



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It is used as a decorative surface as an alternative to stone or clay paving, in areas where a high quality of surface finish is required especially where traffic

may be too heavy for rigid products.

Resin bound surfacing materials are all proprietary products with different characteristics. Some are soft and flexible for use on weak footpaths; others are very strong and some are brittle. Binders can be clear or pigmented to suit the aggregate and application.

They are very expensive and users should ensure they have seen real installations typical of the traffic loading anticipated. The amount of traffic in the company’s sales brochure gives an indication of the usage but not necessarily of the colour.

4.7 Hot mix asphalt surfacing

There are three types of surfacing products in use in the UK –Thin Surfacing, Hot Rolled Asphalt and Macadam (now known as Asphalt Concrete).

4.7.1 Thin Surfacing Course Systems

Research has shown that two different forms of thin surfacing are being used, HAPAS Thin Surface Course Systems (TSCS) and generic ‘Stone Mastic Asphalt’ (SMA).

‘Generic SMA’ is either delivered to no quoted specification or to one produced in the early 1990’s, before BBA HAPAS products became available. The principal problems with these concern the liability for failure and where skidding accidents occur, especially those leading to a fatality.

Some TSCS failures can be addressed during the contract maintenance period but this period should be far less than the life of a surfacing.

A good thin surfacing should be largely defect free after 5 years and for many HAPAS TSCS installations this can be over 10 years.

However where a TSCS is applied to a poor substrate or in cold, windy or wet weather durability will be compromised. Lives as little as 2 years have been experienced. Installers should identify such sites at Contract Review stage and make their concerns known to the Client

In a case with a fatality one of the questions asked during the police investigation under the Police Road Death Investigation Manual is whether ‘best practice’ was adopted. C.f. Section 3.8.

Generic SMA is not ‘best practice’ as controls on quality of supplied materials and on laying are less onerous than with BBA HAPAS products. For example, early life fatting up and loss of skid resistance and texture depth is more likely.

Better products come at increased cost, however this should be very small and more than offset by the transfer of risk to the Contractor with



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reduction of risk to the Authority, as well as improved consistency of performance and durability.

TSCS complies with Highways Agency Specification for Highway Works Clause 942 and has important safeguards compared with SMA.

In particular the performance, for example regarding loss of texture depth, which can directly relate to surface skid resistance, has been assessed on sites under strict controls over at least a two year period by BBA.

If specified by reference to the Specification for Highway Works Clause 942.14 using Appendix 7/1, the performance is subject to a guarantee period of 5years. This is strongly recommended

HAPAS Thin Surface Course Systems (TSCS) have to be installed in accordance with a strict Quality Assurance regime based upon a detailed method statement and supervision requirements.

The Client is recommended to ask for these and ensure for himself they are being followed. In addition, visual assessment of the retention of surface macrotexture, with tests in case of doubt will help ensure the material is performing as stated in the Certificate. This is particularly relevant on high speed roads where texture depth contributes to safety

It is strongly recommended that only TSCS should be specified in preference to generic Stone Mastic Asphalt [SMA].

TSCS is available in three nominal coarse aggregate sizes: 14mm, 10mm and 6mm. The smaller the aggregate size the quieter the tyre noise generated and the better the skid resistance for a given aggregate.

TSCS may be laid in thickness ranges as shown in the table below.

The table below also gives indications of appropriate and inappropriate locations.

Stone Size Laid thickness range [mm]

$

Appropriate sites Inappropriate sites

6mm 15 – 22 Medium and high speed roads

On a binder course

Slow speed sites

Sites with braking and turning

On an existing road surface

Sites requiring handlay

10mm 25 – 35* All sites

On a milled surface** or binder course

None

Sites at minimum thickness requiring handlay

14mm 35 – 50* All sites except as stated

On a milled surface** or binder course

Roundabouts and other sites with sharp turning traffic

$ Any thickness within the permitted range is acceptable



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* On sites with very heavy traffic the texture depth may not be retained sufficiently for high speed traffic when TSCS is laid at the maximum permitted layer thickness

** Additional bond coat may be required with the agreement of the installer

6mm TSCS material has not been included in the draft Bill of Quantities and has been left for users. On suitable sites it does offer significant noise reduction as described in Section 3.12.

The Polished Stone Value of the aggregate should be selected in accordance with HD 36/06 as outlined in Section 3.8 unless evidence of improved skid resistance performance can be provided.

For improvement in early life skid resistance and where the road is extensively used by horses, the use of surface applied grit is strongly recommended. Cf. Section 3.8.

As temperatures fall below 10ºC, and on a wet surface, it becomes increasingly difficult to lay and compact thin layers of material to form a durable surface particularly at joints. This should be considered by Clients when planning and ordering works in the winter months.

The deformation resistance of HAPAS TSCS has been evaluated as part of the approvals process and is acceptable for the traffic level without additional requirements being added into the contract. This would not be true for SMA surface course.

Some systems may be more prone to reflective cracking than others. This is also discussed in Section 3.3.3. Research work for CSS has provided the information in the table below on a number of proprietary TCSC, listed in descending order of resistance to cracking as measured by the Tensile Bending Test at 0ºC.

Systems not listed have not yet been evaluated. Text in italics denotes the use of fibres rather than a Polymer Modified Binder.

Rank Product

Aggregate

size (mm) Supplier

Toughness

[N/mm1.5

]

1 SuperFlex 14 Bardon 36

2 HRA SC SBS 30/14 35

3 Axophalt Compave 10 Lafarge 33

4 MasterPave 14 Tarmac 31

5 HRA SC 50pen 35/14 Ringway 29

5 MasterFlex 14 Tarmac 29



5 ULM - H 10 Ringway 29

10 SMATex 14 Bardon 27

11 SMATex 10 Bardon 26

11 SMA 10 Ringway 26

13 SMA 14 Ringway 25


15 ULM - U 10 Ringway 23

15 ULM - U 14 Ringway 23




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Clients wishing to have the improved racking resistance from TSCS designed for this purpose should insert an appropriate minimum toughness value in Appendix 7/1

Good Thin Surfacing performance is best achieved if the layer thickness is constant, and with no areas less than the minimum permitted thickness, as these will certainly delaminate or fret out.

If the existing road does not have a planar transverse profile across the lane i.e. is barrelled, milling to achieve a straight plane is most strongly recommended.

This substrate may be overlaid with TSCS directly on a suitable bond coat, or for better durability have a binder course/regulating course applied. Suitable thickness combinations are given in Section 3.6

Where red TSCS is required it is strongly recommended that the binder is pigmented and red aggregate is used to ensure a durable colour retention.

4.7.2 Hot Rolled Asphalt [HRA] surfacing

HRA Surfacing, with superimposed coated chippings, was the material of choice until the middle 1990’s when the poor rutting characteristics, price and difficulties of laying made it much less popular and HA prevented its routine use on their network.

Notwithstanding there are significant lengths still in existence and where a length of HRA has to be replaced some Clients prefer to replace like – with - like. In addition in areas prone to waterlogging or flooding HRA can provide a more durable surface. Lack of confidence in the perceived durability of TSCS is better addressed by improving the design and installation of TSCS rather than reverting to HRA in

The principal reason for the demise of HRA was the rut resistance of standard recipe mixes. These are still available in the European standard and are recommended but only for lightly trafficked roads. They tend to be more workable than designed mixtures.

In accordance with the Specification for Highway Works, implementing European Standards, design HRA surface course is no longer specified by Marshall Stability and Flow, but is specified using the UK Small Wheel Tracking Test. The test is carried out at 60ºC (WTR 2) for very heavy trafficked roads (Type 1 and heavier – c.f. Section 2.5) and 45ºC (WTR1) for medium trafficked roads (Type 2) . It is anticipated that the UK test will be superseded by the similar European Test shortly with a consequent change in specified values

It is unlikely that WTR 2 can be achieved with HRA without the use of a polymer modified binder.



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For normal and lightly trafficked roads a recipe design is sufficient.

The following table summarises this specification

Traffic Heavy Normal Light

NRSWA type 1 2 3 and 4

msa [cv/day] >10 [600] 2.5 to 10 <2.5 [220]

HRA 35/14 F surf des PMB WTR 2

35/14 F surf des 40/60 WTR 1

30/14 F surf 40/60

The conversion of msa to cv/day is approximate

In accordance with BS 594987 Table 6B

• HRA 30/14 F surface course can be laid 40mm thick (minimum thickness at any point 35mm)

• HRA35/14 F surface course can be laid 50mm thick (minimum thickness at any point 45mm)

NB The minimum thickness at any point is to allow for surface tolerance and is not available to designers.

Coated chippings must be applied to cover the surface. The rate of spread is given in Clause 7.2 of BS594987.

The Polished Stone Value of the coated chippings should be selected in accordance with HD 36/06

Where red HRA is required it is strongly recommended that the binder is pigmented, red aggregate is used and red coated red chippings are used to ensure a durable colour retention

The materials should be installed in accordance with a Quality Assurance regime using the National Highway Sector Scheme 16 based upon a detailed method statement

4.7.3 Asphalt Concrete surfacing

Close Graded [Dense] Asphalt Concrete surfacing (previously known as Close Graded macadam) will not give the durability of TSCS nor the ongoing retention of texture depth under heavy traffic

However it is much easier to lay by hand and to compact.

It has therefore been included for lightly trafficked roads (Types 3 and 4) and more particularly for footways

The recommended materials are

AC 10 close surf 100/150 (PSV XX) Type 3 and 4 carriageways

AC 6 dense surf 100/150 (PSV 50) Footways

PSV XX refers to the PSV of the coarse aggregate. In this application, PSV 55 minimum is probably a suitable default Limestone should not be used as a fine aggregate

In footways. PSV 50 minimum is probably a suitable default. Limestone should not be used as a coarse aggregate.



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Where red AC is required it is strongly recommended that the binder is pigmented and red aggregate is used to ensure a durable colour retention.

AC 10 material can be laid 30 to 40mm thick (minimum thickness at any point 25mm)

AC 6 material can be laid 20 to 30mm thick (minimum thickness at any point 15mm)

NB The minimum thickness at any point is to allow for surface tolerance and is not available to designers

Close graded/dense surfacing has been selected to give improved durability and prevent water ingress into the pavement structure that can adversely affect performance

Materials should be manufactured in compliance with National Highway Sector Scheme 14 and EN13108-21 c.f. Section 2.1.

The materials should be installed in accordance with BS 594987 and a Quality Assurance regime using the National Highway Sector Scheme 16 based upon a detailed method statement provided to the customer

AC10 close surf can also be used as a patching material for TSCS and SMA surfacing

For large flat areas such as school playgrounds and sports surfaces, an open surface course may be more acceptable, a number of proprietary products are available

For car parks the 100/150 grade binder used can often lead to problems with power steering scuffing the surface. A 10mm TSCS or 6mm SMA is recommended; a number of proprietary products are available.



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5 Binder Course Materials selection

5.1 Introduction

The binder course contributes the following to the pavement construction:

• an impermeable layer below the surface to provide pavement durability

• a well profiled support so that the surface course can be laid at constant

thickness, which ensures even compaction

• structural strength

• rut resistance

• be crack resistance if overlaying a cracked but structurally sound base • value for money

Three European Standards materials are available

• Stone Mastic Asphalt [SMA] to EN 13108-5

• Hot Rolled Asphalt to EN 13018-4

• Asphalt Concrete to EN 13108-1

Each has its strengths and weaknesses as outlined below

Materials should be manufactured in compliance with National Highway Sector Scheme 14 and EN13108-21 c.f. Section 2.1

The materials should be installed in accordance with BS 594987 and a Quality Assurance regime using the National Highway Sector Scheme 16 based upon a detailed method statement provided to the customer

In addition binder courses and bases should have the minimum necessary structural

strength and be water resistant.

The Specification for Highway Works [08/08] gives minimum stiffness values for materials for use in accordance with design guide HD 26/06.

It is recommended that HD 26/01 is used in which case the following stiffness values are inserted in Appendix 7/1

DBM50 Smin1800 HDM Smin 2500 HMB35 Smin 5200.

These values should be inserted in Appendix 7/

5.2 Stone Mastic Asphalt [SMA] binder course

SMA binder course has been specified in a Clause within the Specification for

Highway Works [Cl. 937] for a number of years. It is the preferred material for use

beneath TSCS as it can satisfy all of the criteria above provided it is correctly

specified.

The following SMA binder courses are recommended for the traffic levels shown Traffic Heavy Normal Light

NRSWA type 1 2 3 and 4 msa [cv/day] >10 [600] 2.5 to 10 <2.5 [220]

SMA 14 bin 40/60* des WTR 2

14 bin 40/60des WTR 1

10 bin 40/60

* polymer-modified binder may be necessary to achieve the wheel tracking class



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Increasing the resistance to loss of texture depth and/ or the crack resistance of the

material increases its cost, particularly if a polymer-modified binder is required, this

may be necessary for very heavily trafficked sites.

SMA 14 bin can be laid in thickness range 35 – 60mm (minimum thickness at any point 25mm)

SMA 10 bin can be laid in thickness range 25 – 50mm (minimum thickness at any point 15mm)

Both materials are very suitable for use as regulating layers

Where the surface has to be used by traffic for a short period the use of surface applied grit is strongly recommended c.f. Section 3.8 . It should be accompanied by ‘Temporary Road Surface’ and ‘Slippery Road’ signs.

Proprietary polymer modified binder courses based on SMA technology are available that have significantly improved resistance to cracking when laid on a cracked or weak base. These may be specified on a scheme specific basis. Evaluation of this characteristic can be carried out using the Tensile Bending Test as tabulated in Section 4.7.1 or the Indirect Tensile Fatigue Test EN

5.3 Hot Rolled Asphalt [HRA] binder course

HRA binder course complements HRA surface course.

The material is very impermeable as a result of its relatively high binder content and is easy to compact to low air voids. This also makes it the most crack resistant material. It is therefore likely that HRA will be also be the most durable type of binder course. For very heavy trafficked roads and particularly under Thin Surfacing, a lack of rut resistance is likely to be an issue; this can be mitigated by using a polymer-modified binder

HRA binder course may be more expensive than SMA and the decision on value for

money will be scheme dependent.

The following HRA binder courses are recommended for the traffic levels shown



msa [cv/day] >10 [600] 2.5 to 10 <2.5 [220]

HRA 60/20 bin 40/60* des WTR 2

60/20 bin 40/60 des WTR 1

60/20 bin 40/60

* polymer-modified binder may be necessary to achieve the wheel tracking class

HRA 60/20 bin can be laid in thickness range 45 – 80mm (minimum thickness at any point 40mm)

The material can be used for regulating within this thickness range.

5.4 Dense Asphalt Concrete binder course

Carriageways

AC binder course is the least satisfactory of the three options, being more prone to cracking, rutting if 100/150 binder is used for other than lightly trafficked sites (Roads Type 3 and 4) , and needs good compaction to achieve its full potential.



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Nonetheless for sites where the stresses on it will be relatively low, it can provide a cheaper alternative than those above.

AC binder course is not recommended for very heavy traffic.

‘Dense’ mixtures were the original mix designs, however research showed that increasing the amount of fine aggregate (material passing the 63micron sieve size) could improved the strength and rut resistance of the material. This ‘new’ material is called Heavy Duty Macadam [HDM]. Nowadays it should cost no more than ‘Dense’ material. Where the material is used with 30/45 grade bitumen rather than 40/60, the product is known as High Modulus Base [HMB] Despite the loss of the term ‘macadam’ in EN13108-1, these acronyms are still used in product titles.

The following AC binder courses are recommended for the traffic levels shown.



msa [cv/day] >10 [600] 2.5 to 10 <2.5 [220]

AC 20 HDM bin 40/60*

20 HDM bin 40/60

20 dense bin 100/150

* A proprietary mix with polymer-modified binder may be necessary to achieve the deformation resistance and stiffness required.

AC 20 HDM or dense bin can be laid in thickness range 50 – 100mm (minimum thickness at any point 40mm)

The material can be laid in variable thickness within the permitted range if necessary

Footways

The use of AC base/binder course in footway construction should comply with AC14 close surf 100/150.

A preferred alternative footway base/binder course is 14mm cold mix asphalt. This is a proprietary product made from asphalt millings and other recycled materials and has very low energy usage (c.f. Section 2.7)



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6 Base Materials selection

6.1 Introduction

As a result of severely constrained budgets, the use of base material for maintenance works is very small. It is largely limited to heavy patching and corner widening schemes.

The greatest use is in new housing and industrial developments, which are outside the scope of this document.

The Specification for Highway Works [08/08] gives minimum stiffness values for materials for use in accordance with design guide HD 26/06.

It is recommended that HD 26/01 is used in which case the following stiffness values are inserted in Appendix 7/1

DBM50 Smin1800 HDM50 Smin 2500 HMB35 Smin 5200.

Moisture sensitivity of asphalt

The moisture susceptibility of an asphalt mixture can be assessed by the Saturated Aging Tensile (SATs) Test. It is lengthy and expensive

CSS guidance makes the following recommendations

a. Where there is local evidence of good performance of mixtures with the same binder grade/content and with known sources of coarse and fine aggregate, there is no reason not to continue to use them with confidence. SATS testing is not required .

b. EME2, recipe mixtures, and design mixtures with adequate minimum binder content, are likely to be more durable. Depending upon aggregate source, SATS testing is not required.

c. Where an aggregate has known or suspected poor adhesion to bitumen, this will be resolved by the use of 2% lime or cement, as an adhesion agent. If this additive is incorporated, testing by SATS is not required

d. Asphalt containing igneous coarse and fine aggregate, quartzite, and flint gravel/sand mixtures, are most at risk. The use of recycled filler may also increase risk depending upon its composition. Where there is no local knowledge of the performance of the mixtures with such constituents and binder content, and where lime or cement is not added, it is recommended that a SATS test is used to provide evidence on suitability.

e. Guidance on achieving durability in a laid material is available in CSS Guidance Note ‘Guidance on Durability Requirements of Road Note 42’

6.2 Dense Asphalt Concrete base

This is the cheapest and strongest material and is preferred for very heavy and normal traffic loading:

The following AC base materials are recommended for the traffic levels shown



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msa [cv/day] >10 [600] 2.5 to 10 <2.5 [220]

AC 32 HDM base 40/60 * 14 cold mix

32 HDM base 40/60* 14 cold mix

14 cold mix

20 dense base 40/60

* 30/45 pen may be required on very heavily trafficked major projects on a scheme specific

basis

The preferred base for light traffic is 14mm cold mix asphalt. Structural grade should be used if available.

Structural Grade B4 may also be used for heavily trafficked roads if available.

Cold Mix asphalt is a proprietary product complying with Clause 948 made from asphalt millings and other recycled materials and has very low energy usage c.f. Section 2.7)

6.3 Hot Rolled Asphalt base

Hot Rolled Asphalt provides benefits in situations where its enhanced flexibility and reduced porosity can be an advantage.

For example

• as an overlay to a concrete base that may cracked/jointed

• on a weaker than average foundation but there is inadequate space for a full sub base layer,

• where there is concern that the sub base will be permanently wet as HRA is more water resistant than AC.

The following HRA base materials are recommended for the traffic levels shown



msa [cv/day] >10 [600] 2.5 to 10 <2.5 [220]

HRA 60/32 base 40/60

60/32 base 40/60

60/20 base 40/60



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7 Summary of selected asphalt layers by Road Type

Material reference Road Type 1

Surface Course

ST14 ST10 or ST6 14, 10 or 6 TSCS Macrotexture level 3, 2 or1

S1H HRA 35/14 F surf des PMB WTR 2 + PCC 14/20

Binder Course

Bi1S SMA 14 bin 40/60* des WTR 2

Bi1H HRA 60/20 bin 40/60* des WTR 2

Bi1A AC 20 HDM bin 40/60*

* a polymer modified binder may be required

Base

Ba1A AC 32 HDM base 40/60*


Material reference 7.2 Road Type 2

Surface Course

ST14 or ST10 14 or 10 TSCS Macrotexture level 3,2 or1

S2H HRA 35/14 F surf des 40/60 WTR 1 + PCC 14/20

Binder Course

Bi2S SMA 14 bin 40/60 des WTR 1

Bi2H HRA 60/20 bin 40/60 des WTR 1

Bi2A AC 20 HDM bin 40/60

Base

Ba2A AC 32 HDM base 40/60*


Material reference 7.3 Road Type 3 and 4

Surface Course

ST14 or ST10 14 or 10 TSCS Macrotexture level 3,2 or1

S3H HRA 30/14 F surf 40/60 + PCC 14/20

S3A AC 10 close surf 100/150

Binder Course

Bi3S SMA 10 bin 40/60

Bi3H HRA 60/20 bin 40/60

Bi3A AC 20 dense bin 100/150

Base

Ba3C 20 Cold mix


Ba3A AC 20 dense base 40/60

Footways

SFA AC6 dense 100/150

BiFC 14 Cold mix

BiFA AC14 dense bin 100/150

Road Type is as follows Road Type 1 >10msa [<600cv/day] Road Type 2 2.5 to 10msa Road Type 3 <2.5msa [{<220 cv /day ]

*30/45 pen may be required on very heavily trafficked major projects on a scheme specific basis Where required Surface Applied Grit shall be applied c.f. Section 3.6.2 For regulating, in addition to the above, HRA 50/10F rec may be used for Road Types 3 and 4



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8 Preferred options for materials selection

Option 1 Option 2 Option 3 Option 4

Road Type 1

Surface course

ST14, or ST10 or ST 6

ST14 or ST10 or ST6

S1H S1H

Binder course

Bi1S Bi1S Bi1S Bi1A

Base Ba1A Ba1H Ba1H Ba1A

preferred when overlaying /inlaying cracked material

When maximum stiffness is required

Road type 2 Option 1 Option 2 Option 3 Option 4

Surface course

ST14 or ST10

ST14 or ST10

S2H S2H

Binder course

Bi2S Bi2H Bi2H Bi2C

Base Ba2A Ba2H Ba2H Ba2C


When maximum stiffness is required

Road types 3 and 4

Option 1 Option 2 Option 3 Option 4 Option 5

Surface course

ST14 or ST10

ST14 or ST10

S3H S3H S3A

Binder course

Bi3S Bi3H Bi3H Bi3A Bi3A

Base Ba3C Ba3H Ba3H Ba3A Ba3C


when maximum stiffness is required with HRA surface

cheapest solution for low speed/low stress sites

Footways

Surface course

SFA SFA

Binder/base course

Base Materials may not be necessary

BiFC BiFA

For details of materials see Draft Appendix 7/1 in Section 8



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9 Draft Appendix 7/1 for preferred materials

9.1 Surface course materials

Material Ref Clause Description Special Requirements

ST 14 942 Thin Surface Course Systems

TSCS 14

Thickness: Insert [in range 35mm-50mm]

Traffic Count >600 cv/lane/day

Stress Level: 2

Minimum Declared PSV: PSVXX

[The minimum PSV to be inserted ]

Maximum Aggregate Abrasion Value AAV12

Minimum Toughness Value * (Optional )

Red colour: Both aggregate and binder shall be red to an approved mixture colour

Minimum Wheel Tracking level required on BBS HAPAS Certificate: Level 2

Road / Tyre Noise Level Relative to HRA TABLE NG 9/30: (08/08): Level 1

Minimum Compacted layer thickness: 35mm

Average Macrotexture depth value:

Level [3, 2, or 1 as required NG 942] Performance Guarantee Period: 5 years

Surface Macrotexture – Performance Guarantee [3, 2, or 1 as required NG 942]


TSCS 10

Thickness: Insert [in range 25mm - 30mm]


Stress Level: 2




Minimum Toughness Value * (Optional)




Minimum Compacted layer thickness: 25mm


Level [3, 2, or 1 as required NG 942]

Performance Guarantee Period: 5 years




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TSCS 6

Thickness: 20mm


Stress Level: 2




Minimum Toughness Value * (Optional)





Level [3, 2, or 1 as required NG 942]

Performance Guarantee Period: 5 years


SAG 942.19 Surface applied Grit

0/4 clean dry or lightly coated grit

Where required

S1H 911/943 Hot Rolled Asphalt

HRA 35/14 F surf des PMB WTR 2 + PCC 14/20

Thickness: 50mm

Grade of binder : a polymer modified binder to achieve the wheel tracking performance to PD 6691 Table C.3 Class 2 [ Wheel Tracking test temperature 60ºC ]

Coated chippings to PD 6618 C.8

Aggregate size 14/20

PSV xx [ XX PSV as required for site]

AAV 12

Deformation after installation: Required [Cl 943:10]




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S2H 911/943 Hot Rolled Asphalt

HRA 35/14 F surf des 40/60 WTR 1 + PCC 14/20

Thickness: 50mm

Grade of binder : 40/60 pen paving grade or a polymer modified binder to achieve the wheel tracking performance to PD 6691 Table C.3 Class 1 [ Wheel Tracking test temperature 45ºC ]



PSV xx [60 or 65 as required for site]

AAV 12

Deformation after installation: Required [Cl 943:10]


S3H 910 HRA 30/14 F surf 40/60 +

PCC 14/20

Thickness: 40mm



PSV xx [60 or 65 as required for site]

AAV 12


S3A 912 Close Graded Asphalt Concrete Surface Course

(AC10 Close Surf 40/60)

Thickness Insert [ in range 25mm-35mm]

Minimum declared PSV: PSV60

Maximum Aggregate Abrasion Value: AAV16

Binder Penetration: 40/60 pen

SFA None Dense Asphalt Concrete Surface Course

(AC6 dense 100/150)

Thickness Insert [ in range 20mm-30mm]

Conform to EN13108:1 and PD6691:Annex B

Minimum declared PSV: PSV50

Maximum Aggregate Abrasion Value: AAV16

Limestone fine aggregate shall not be used



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9.2 Binder course materials [also suitable for regulating]


Bi1S 937 SMA 14 bin 40/60 des

WTR 2

Thickness: Insert [ in range 35mm-60mm]

Grade of binder : 40/60 pen paving grade or a polymer modified binder to achieve the wheel tracking performance to PD 6691 Table D.2 Class 2 [Wheel Tracking test temperature 60ºC

Deformation after installation: Required 937.6

Bi2S 937 SMA 14 bin 40/60 des

WTR 1


Grade of binder : 40/60 pen paving grade or a polymer modified binder to achieve the wheel tracking performance to PD 6691 Table D.2 Class 1 [Wheel Tracking test temperature 45ºC

Bi3S 937 SMA 10 bin 40/60 Thickness: Insert [in range 25mm-50mm]

SAG 942.19 Surface applied grit Where required

Bi1H 943 HRA 60/20 bin 40/60*

des WTR 2


* Grade of binder : 40/60 pen paving grade or a polymer modified binder to achieve the wheel tracking performance to PD 6691 Table C.3 Class 2 [ Wheel Tracking test temperature 60ºC ]

Bi2H 943 HRA 60/20 bin 40/60*

des WTR 1


*Grade of binder : 40/60 pen paving grade or a polymer modified binder to achieve the wheel tracking performance to PD 6691 Table C.3 Class 1 [ Wheel Tracking test temperature 45ºC ]

Bi3H 943 HRA 60/20 bin 40/60 Thickness: Insert [in range 45mm - 80mm]

Bi2A 929 AC 20 HDM bin 40/60 Thickness: Insert [in range 50mm - 100mm]

S min 1800MPa

Composition PD 6691 Table B11

Volumetric properties after installation: Required [Cl 929.3]

Bi3A 906 AC 20 dense bin

100/150




BiFC 948 14 Cold Mix Thickness: Insert [in range 40mm - 70mm]

SVH or QVH as available Class B1

BiFA 906 AC14 dense bin

100/150



For regulating ( in addition )

BiRH 911 HRA 50/10 F reg 40/60 Thickness: Insert [in range 20mm - 40mm]



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9.3 Base materials


Ba1H 929 HRA 60/32 base 40/60*

Thickness : Insert [in range 60mm - 150mm]

*Grade of binder : 40/60 pen paving grade or a 30-45 depending upon stiffness required [Cl 929.6 ]

Volumetric properties after installation: Required [Cl 929.3]

Ba2H 904 HRA 60/20 base 40/60 Thickness : Insert [in range 45mm - 80mm]

Ba2A AC 32 HDM base 40/60

Thickness : Insert [in range 70mm - 150mm]


S min 2500MPa

Ba2C Ba3C

948 20 Cold mix Thickness: Insert [in range 50mm - 100mm]

QVH as available Class B4

Trafficking trial: Only if sand fines used [Cl 948.8 ]

Ba3A 906 AC 20 dense base

40/60 rec


Composition PD 6691 Table B.11

S min 1800MPa


BaFC 14 Cold mix Thickness: Insert [in range 40mm - 70mm]

SVH or QVH as available Class B1

BaFA AC14 dense base

100/150


Composition PD 6691 Table B.14



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10 Draft Bill of Quantities for preferred materials

Item No. Description Qty Unit Rate Amount

Surface Courses

900.01 ST14 PSV 65 Macrotexture level 3, 2 or 1

Thickness 35mm

m 2

900.02 ST14 Red Macrotexture level 3, 2 or 1

Thickness 35mm


Thickness 45mm thick

m 2

900.04 EO 900.2 for ±5mm thickness m 2


Thickness 35mm

m 2


Thickness 45mm thick

m 2



Thickness 25mm

m 2


Thickness 25mm

m 2

900.10 ST10 Red Macrotexture level 3, 2 or 1

Thickness 25mm

900.11 EO for 0/4 SAG m 2

900.12 S1H Thickness 50mm m 2


900.14 S2H red


900.16 EO for 14/20 PCC 65PSV Macrotexture level 3, 2 or 1

m 2

900.17 EO for 14/20 PCC 60PSV Macrotexture level 3, 2 or 1

m 2

900.18 EO for red chippings

900.19 S3A Thickness 35mm m 2



900.22 SFA Thickness 25mm m 2




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Binder courses

901.01 Bi1S Thickness 35mm m 2









901.10 EO for 0/4 SAG m 2

901.11 Bi1H Thickness 45mm m 2





901.16 EO 901.15 per 5mm thickness change m 2



901.19 EO 901.12 per 5mm thickness change ± m 2

901.20 Bi2A Thickness 60mm m 2








901.28 BiRH tonnes

Base Course

902.01 Ba2A Thickness 80mm m 2


902.03 Ba2H Thickness 65mm m 2

902.04 EO 902.03 per 5 mm thickness change ± m 2






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902.13 Ba2C Thickness 65mm m 2


902.15 Ba2C Thickness 90mm m 2


902.17 BaFC Thickness 55mm m 2


902.19 BaFA Thickness 90mm m 2

902. 20 BaFA Thickness 55mm m 2




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Appendix 1: Translations of all mixes notified from BS to EN Standards

SURFACE COURSE

Current Name European name

BS594 -1 BS EN 13108- 4

35%0/14 HRA F 4-8 HRA 35/14 F surf 40/60 des WTR 1

30%0/14 HRAF 6kn (6-10kN) HRA 35/14 F surf PMB des WTR 2

30% 0/14 HRA des HRA 30/14 F surf 40/60 des WTR 1

30% 0/14 HRA 50 HRA 30/14 F surf 40/60 rec

30% 0/14 HRA red HRA 30/14 F surf 40/60 red

55% 0/14 HRA design HRA 55/14 F surf 40/60 des WTR

55% 0/14 HRA 50 HRA 55 /14 F surf 40/60 rec

50% 0/10 HRA HRA 50 /10 F surf 40/60 rec

30% HRA PMB HRA 30/14 F surf PMB des WTR 2

0/2 Sand Carpet HRA 0/2 C 40/60 rec

BS4987 -1 BS EN 13018 -1

0/32 Close graded Surface Course none

0/20 Close graded Surface Course none

0/14 Close graded Surface Course AC14 close surf 100/150

0/10 Close graded Surface Course 125 AC10 close surf 100/150

0/6 Close graded Surface Course 125 AC10 close surf 100/150

0/4 Fine graded Surface Course 125 AC10 close surf 100/150

0/10 Close graded Surface Course A pen grade has to be put

0/6 Close graded Surface Course 190/300 AC 6 dense surf 160/220

0/10 Open graded Surface Course AC10 open surf 100/150

0/6 Dense s/c AC 6 dense surf 100/150

0/10 Medium graded Surface Course AC10 medium surf 100/150

0/6 Medium graded Surface Course AC6 medium surf 100/150

0/6 Medium graded Surface Course RED AC6 medium surf 100/150 red

0/6 Thin Surface Course system [TSCS] PSV 55

6 HAPAS TSCS PSV 55

0/10 TSCS PSV 65 /55/45 10 HAPAS TSCS PSV 65/55/45

0/14 TSCS PSV 68+/65 /60/55 14 HAPAS TSCS PSV 68+/65/60/55

RED TSCS 14 HAPAS TSCS all red

EN 13108-5

RED SMA SMA 14 surf 40/60 red

0/10 Gen SMA PSV 68+/65/55 SMA 10 surf 40/60 PSV 68+/65/55

0/14 Gen SMA PSV 65 SMA 14 surf 40/60 PSV 65

0/6 Gen SMA PSV 55 SMA 6 surf 40/60 PSV 55

Mastic Asphalt EN13108-6

6mm Red macamit Proprietary

Coarse Cold Asphalt (1973) Obsolete

Fine Cold Asphalt AC10 close surf 100/150

TSCS Red/Green Clear Binder Proprietary

Only those in bold are recommended WTR refers to wheel tracking Class in accordance with SHW Clause 952



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APPENDIX 1

BINDER COURSE


BS594 -1 BS EN 13108- 4

60% 0/32 HRA 35 HRA 60/32 bin 30/45

60% 0/32HRA 50 HRA 60/32 bin 40/60

50% 0/20HRA HRA 50/20 bin 30/45

60% 0/20 HRA HRA 60/20 bin 40/60 des WTR 1 or 2

HRA 60/20 bin 40/60

50% 0/14 HRA 35 HRA 50/14 bin 30/45

50% 0/14 HRA HRA 50/14 bin 40/60

50% 0/10 HRA HRA 50/10 bin 40/60

35% 0/14 HRA Not available

0/2 Sand Carpet HRA 0/2 C 40/60 rec

BS4987 -1 BS EN 13108- 1

EME2 AC 14 EME2 bin 15/25

0/32 HMB35 AC 32 HMB bin 30/45

0/20 HMB35 AC 32 HMB bin 30/45

0/20 HDM50 AC 20 HDM bin 40/60

0/20 HDM50 929 AC 20 HDM bin 40/60 des WTR 1

0/32 HDM50 AC 32 HDM bin 40/60

0/32 DBM50 AC 32 dense bin 40/60

0/20 DBM50 AC 20 dense bin 40/60

0/20 DBM50 929 AC 20 dense bin 40/60 des WTR 1

0/32 DBM125 AC 32 dense bin 100/150

0/20 DBM125 AC 20 dense bin 100/150

0/14 DBM125 AC 14 close surf 100/150

0/10 DBM 125 AC 10 close surf 100/150

0/6 DBM 125 AC 6 close surf 100/150

0/20 DBM 190 AC 20 dense bin160/220

0/10 DBM 190 AC 10 close surf 160/220

0/20 Open Graded 200 AC 20 open bin 160/220

0/14 Open Graded AC 14 open surf 160/220

0/10 Close Graded Surface Course AC 10 close surf 100/150

BS EN13108- 5

SMA 937 45C See below

0/14 SMA 937 SMA 14 bin 40/60 des WTR 1 or 2

0/10 SMA 937 SMA 14 bin 40/60 des WTR 1 or 2

cold lay macadam proprietary

Mastic Asphalt BS EN13108-6

Superflex Proprietary

Only those in bold are recommended WTR refers to wheel tracking Class in accordance with SHW Clause 952 WTR Class 2 may require the use of PMB.



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APPENDIX 1

BASE


BS594 -1 BS EN 13108- 4

60% 0/32 HRA HRA 60/32 base 40/60

60% 0/32 HRA 35 HRA 60/32 base 30/45

60% 0/20 HRA HRA 60/20 base 40/60

50% 0/14 HRA HRA 50/14 reg 40/60

0/32 HRA china clay Proprietary

BS4987 -1 BS EN 13108- 1

40mm DBM/HDM Obsolete

0/32 DBM 190 AC 32 dense base 160/220

0/32 DBM 125 AC 32 dense base 100/150

0/32 HDM50 AC 32 HDM base 40/60

0/32 DBM50 AC 32 dense base 40/60

0/20 DBM50 AC 20 dense base 40/60

0/20 HDM50 AC 20 HDM base 40/60 0/32 HMB35 AC 32 HMB base 30/45 Cold mix 948 Proprietary

Only those in bold are recommended



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Appendix 2 Summary of relative performance of surface courses

The more stars the better.

Surfacing Type Surface Dressing

Micro-asphalt

Thin Surfacing Course system

Hot Rolled Asphalt

Thickness 25-30mm 35-50 45-50

Structural nil nil *** **** ****

Rut resistance N/A ***** ***** **** ***

Crack resistance * * *** **** ****

Crack resistance with SAMI

N/A N/A ***** ***** *****

Ride improvement 1

nil ** **** **** ***

High texture2 ***** **** *** **** ****

Retained texture3 Variable ** *** **** ***

Skidding (Early) ***** ***** *** 4

*** 4 ***

(Normal) ***** *** **** **** ***

Typical Noise RSI 5

+2 -4 -3 -2.5 0

Spray 6

** ** *** **** **

Risk of failure * ** ** ** **

Durability/Life *** ** **** **** ****

Speed of application

***** **** ** ** *

Typical Unit Cost 1 1.5 3 4 5

Note 1 All systems can achieve **** if they are laid on a new substrate/binder course.

Note 2 See Section 3.8 for texture depth requirements. A TD above the recommendation for the traffic speed is

not advantageous. See HAPAS Certificate for the TD for a particular TSCS.

Note 3 Retained texture depth should be measured on all sites after 2 years to check compliance.

Note 4 All systems are adequate to satisfy HD36 if grit is applied here required as specified.

Note 5 See HAPAS Certificate for RSI of Microasphalt and Thin surfacing.