us 0609a continuous hot mixt production

Technical guide

Continuous hot mix productionThe French expertise

service d'Études

techniques

des routes

et autoroutes

Sétra march 2006

Blank p

age

Technical guide

Continuous hot mix productionThe French expertisePublished by Sétra and carried out by the French Road Engineering Committee (CFTR)

CFTR main actions:

• laying down of state-of-the-art handbooks,

• drawing-up technical assessments on fitness for purpose of processes, products and equipment, as well as qualification documents for equipment,

• issuing approvals for road laboratories,

• carrying out procedures of certification and compliance with standards.

CFTR is an association that brings together different members of the French road community to elaborate a technical doctrine shared by all and used as a reference for road professionals in the field of pavements, earthworks and road drainage.

Association ruled under the law of 1st july 1901. Since june 1998 Its Head office is located at:46, avenue Aristide BriandBP 100 – 92225 Bagneux Cedex – FrancePhone: 33 (0) 1 46 11 31 53 – Fax: 33 (0) 1 46 11 36 96Internet: http://www.cftr.asso.fr

2 Continuous hot mix production – The French expertise

• Robert Baroux, Central Laboratory for Roads and Bridges

• Jacques Bonvallet, Fayat group

• Jacques Chardon, Colas

• Michel Ducasse, Eurovia

• Luc Amaury George, Cofiroute

• Christine Leroy, Paris City

• Jack Oudin, Technical Study Centre for Civil Engineering, Road Material Test Centre

• Robert Tasky, Technical Centre for Civil Engineering, Road Material Test Centre

Within the framework of the sectorial committee « methodology » activities of CFTR, a working group including representatives of the scientific and technical network of the Ministry for transport, Infrastructure, tourism and the sea, contractors technical department and suppliers in the road field, has drawn up this technical guide.

After an assessment by various members of CFTR, its content has been validated.

SommaireSummary1. Brief history of the technique1970-197619791984-19881990199519972. The types of hot mix process3. Description of the equipment3.1 - Aggregate metering3.2 - Belt flowmeter (conveyor belt scale)3.3 - Feed bin sizing method3.4 - The drying and coating mixer: the heart of the system3.5 - Bitumen metering management3.6 - Handling dusting filler and foreign filler3.7 - Bitumen concrete storage3.8 - Automatic operation3.9 - The continuous process and the environment3.10 - Mobility4. Examples of possible strategies to satisfy the market 4.1 - High tonnage motorway construction in open country 4.2 - Motorway works in an urban area: maintenance work on the carriageways of the Paris «Boulevard Peripherique»4.3 - Production of recycled products: environmental considerations5. Guide for a road investor6. Bibliography: standards covering continuous hot mix production6.1 - Equipment standards6.2 - Equipment test standards6.3 - Equipment approval standards6.4 - Calibration standards6.5 - Manufacturing and implementation standards6.6 - Information bulletins6.7 - Main approved and experimental reference methods for gaseous emissions from fixed sources

december 2005 3

Summary

1. Brief history of the technique . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. The types of hot mix process . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3. Description of the equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.1 Aggregate metering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.2 Belt flowmeter (conveyor belt scale). . . . . . . . . . . . . . . . . . . . . . 93.3 Feed bin sizing method . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.4 The drying and coating mixer: the heart of the system . . . . . . . . . . . 113.5 Bitumen metering management. . . . . . . . . . . . . . . . . . . . . . . 133.6 Handling dusting filler and foreign filler . . . . . . . . . . . . . . . . . . 133.7 Bitumen concrete storage . . . . . . . . . . . . . . . . . . . . . . . . . . 143.8 Automatic operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.9 The continuous process and the environment . . . . . . . . . . . . . . . . 153.10 Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4. Examples of possible strategies to satisfy the market . . . . . . . . . . . . . . 174.1 High tonnage motorway construction in open country . . . . . . . . . . . 174.2 Motorway works in an urban area: maintenance work

on the carriageways of the Paris «Boulevard Peripherique» . . . . . . . . . 194.3 Production of recycled products: environmental considerations . . . . . . . 21

5. Guide for a road investor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

6. Bibliography: standards covering continuous hot mix production . . . . . . . . . . 236.1 Equipment standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236.2 Equipment test standards . . . . . . . . . . . . . . . . . . . . . . . . . . 236.3 Equipment approval standards . . . . . . . . . . . . . . . . . . . . . . . 236.4 Calibration standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236.5 Manufacturing and implementation standards . . . . . . . . . . . . . . . 246.6 Information bulletins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246.7 Main approved and experimental reference methods

for gaseous emissions from fixed sources . . . . . . . . . . . . . . . . . . 24


The French road network started to be structured and developed after the Second World War and this process was accelerated during the 1960’s. The 1970’s saw the emergence of large national programmes consisting of new works and maintenance, major motorway programmes, coordinated reinforcement of the trunk roads (main road network) to make them frost proof, and modern structuring of the carriageways. The main characteristic of these works was the production of high tonnages on every site and the limitation to one asphalt formula per layer of carriageway.

In November 1972, the « Quality control in road building » symposium brought together the various players in French road building and laid down the basis for a quality approach by the companies, within the framework of a cooperative approach between the promoters, the construction companies and the equipment manufacturers. the equipment commission was created to contribute to the development of carriageway construction techniques. Other changes in parallel with this were ever more accurate production of the aggregates in all quarries and changes to the composition of the asphalts to satisfy the durability requirements of road infrastructures. To face up to these requirements the road construction companies quickly directed a proportion of their investments toward large continuous mobile plants with high hourly production capacities. Environmental constraints forced the manufacturers to improve the equipment on offer in the marketplace.

In this way a “French school” has been developed. Thirty years on we can see that these techniques are very widely used and confirmed. 50% of the hot mix production is continuous. That is why the CFTR equipment commission has prepared this document; following on from the one is created in 1973, to reflect French experience.

december 2005 5

Figure 1.1: parallel flow drum mixerFigure 1.2: example of lengthening of the drum with a dryer drum mixer

Hot production of mixes with hydrocarbon binders was developed industrially in France around about 1930 and progre s s ed

spectacularly at the end of the 1960’s because of major road network development programmes.

Mixing techniques have always hinged around two types of production, continuous production and batch production.

Today, the French parc of hot mix plants, still called coating plants, is about 500 units, of which about 20% are mobile and the rest fixed. There are about 50% of each type.

The continuous mix plants are today mainly drum mix types. Drum mix technology was born in the USA in 1910 and started to develop in Europe as from the 1970’s.

Over the last three decades this development has been as follows:

1970-1976

The first parallel f low drum mixers (parallel flow = movement of the gasses inside the drying drum, parallel to that of the ingredients and in the same direction) were imported and later manufactured in Europe.

1979

T h e f i r s t E u r o p e a n recycling ring drum mixers enabled aggregate from recycled asphalt to be used in the composition of the hot mixes.

1984-1988

European, and particularly French drum mixers, were lengthened in order to distance the coating zone from the combustion zone to eliminate the risk of ageing the hydrocarbon binders by overheating them (blue smoke emission). In 1984, the drums were extended by 15%, and then 10% more in 1986, and finally 12% in 1988. In all, that makes nearly 40%. This technological advance resulted in gas temperatures about the same as those of the asphalt, 170°C.

During this period, other changes contributed to improv ing the qua l i t y o f the p roduc t s manufactured:• The creation of a zone of forced mixing, at the mixer outlet, by means of mixing paddles placed to oppose the flow of the materials,• The injection of foreign filler and dusting filler, in the coating zone by a screw or pneumatic nozzle entering by the rear of the mixers.

1. Brief history of the technique

The advent of the recycling ring was an

important development, and the star t of typically French technology with a

lengthening of the mixers, temperature control and

control of the fillers.

France is historically one of the centres of development

of the continuous mix technique.


Figure 1.3: counterflow drum mixer

1990

Drum mix technology was enriched by the counterflow type (counterflow = gas flow opposite the direction of movement of the materials in the drum). This technique makes it possible to obtain gas emissions within the most severe environmental standards while at the same time providing:• higher coating temperatures; up to 200 °C if necessary,• aggregate recycling capacities up to 50% of the final product,• possibility of using unfilled aggregate thanks to the effectiveness of the dusting.

1995

The parallel flow technique started using an elongated mixing zone (mixing paddles) at the drum outlet to perfect the homogeneity of the materials by optimising the heat exchanges.

1997

Improvements in parallel flow drum mixers were transposed into counterflow drum mixers.

At the same time as these improvements were taking place, progress in computer technology made it possible to improve the manufacturing process. They made it possible to include all the dephasing between the ingredients and their progress inside the drum throughout the whole of the manufacturing process, including during changes in flow or composition.

Nowadays mobile plants are mainly continuous, and within the fixed plant population in France 35% are continuous as against 90% in North America.

The American manufacturers suddenly stopped

developing the recycling ring because of patent

restrictions at the end of the 1980’s.

Temperature control has been mastered in parallel flow and counterflow since

the 1990’s.

december 2005 7

batch continuous

Figure 2.1: illustration of the operating principle

Photo 2.2: continuous production plant

Photo 2.1: batch production plant

T h e c o n t i n u o u s h o t mix process of asphalt production differs from the batch hot mix process principally by the type of mixing.

The continuous process is practiced in an open mixer where the flows of the granular ingredients, hydrocarbon binder and any additives, are continuous.

The batch process consists of production by batches made up of weighed quantities of ingredients successively introduced into a closed mixer.

Upstream of the mixer the granular composition can be determined with certainty by the aggregate distributors adjusted to respect the formula of the product. The operation can be done in the batch mode, screening and hot granular sorting if the ingredients do not have grain sizes in conformity with the standards. In this latter situation it is the screening operation that has to control the recomposition by weighing of the final product. Downstream from the mixer the delivery of hydrocarbon product can be done in a similar way for both modes. Either directly into lorries, or via storage silos. The continuous mode is especially suitable for sites of all tonnages with a single mix formula with granular ingredients in conformity with the standards.

Two production modes exist side by side.

2. The types of hot mix process


Figure 3.1: principle of feed control

Continuous industrial processes are based on constancy of the flows that make it possible to minimise adjustment operations. Consequently a great deal of attention is given to the metering systems and the interactions between them.

3.1 - Aggregate metering

3.1.1 - The precision of a cold feeder

Aggregate feeders are checked electronically several times per second and the results of this polling are compared with the flow setting. If the differences or tendencies do not correspond with the setting an actuator operates and adjusts the devices of the cold feeder or feeders, one after the other. Figure 3.1 illustrates the interactive regulation principle which may either be volume- or weight-based. The latter type is essential for sand.

Figure 3.2 is a continuous record of the actual flow from a feeder. The increase or reduction in flow is also monitored so that the parameters vary linearly in a ratio of the order of 1 to 10.

3.1.2 - Interaction between flows

The flow setting for each feeder changes jointly with that of the other feeders, in order to maintain the relative proportions of the ingredients fixed by the mix formula. figure 3.3 shows the interactive principle that makes it possible to obtain, on the one hand 100% consumption of the ingredients, and on the other proportional flow changes.

A cold safety scalper eliminates undesirable accidental material.

Granular metering has been mastered technically for a long time, but aggregate

quality is absolutely essential.

Changes in flow must be made with a controlled

speed gradient.

3. Description of the equipment

Figure 3.2: flow record

vibrator

coder

weighing

computer

december 2005 9

Figure 3.3: granular metering Photo 3.2: belt flowmeter

Photo 3.1: fixed feeding group

3.1.3 - The notion of homogenous layers

The result of a continuous metering process is the creation of homogenous layers of material placed on the collecting conveyor under the feed bins in the correct proportions according to the formula (wet formula, without binder). This is a considerable industrial advantage reducing the duration of the homogenisation process before the introduction of the binders (see photo 3.1: of a battery of aggregate feed bins).

3.2 - Belt flowmeter (conveyor belt scale)

The belt flowmeter makes it possible to measure the accumulated wet flow of aggregate entering the drier drum.

Photo 3.2 shows a belt flowmeter, built into the conveyor belt. The accuracy of the conveyor belt scales is similar to that of feeder belts.

Naturally the belt flowmeter is an essential tool and it is obligatory from the point of view of conformity with standards

warning light

wall vibrator

level indicator

no-flow blade sensor

weighing scale

speed sensor

weighing bin

volumetric bins

(x + y + z + t = 100) 100 % + bitumen

x % y % z % t %

The existence of homogenous granular

batches is a considerable industrial advantage,

shortening the time for the homogenisation process before the introduction of

the binders.

The wet flow is automatically corrected for water content by the PLC. A water content

probe is recommended.


Figure 3.4: sizing process

Figure 3.5: parallel flow process Figure 3.6: counter flow process

3.3 - Feed bin sizing method

The feeder regulat ion process must be monitored continuously to make sure the weighing systems are accurate. This check, done regularly for fixed plant, and after every movement for mobile plant, is known as feeder « sizing ». The method is standardised. It is normal in France to use a reversing loading conveyor, which makes it possible to remain in an actual supply situation and monitor the flows over a significant period of time. The reversing loading conveyor should allow a lorry to be positioned to load at least 5 t figure 3.4 illustrates this process. Once it is loaded, the lorry is weighed with its load on an approved weighbridge and the two quantities are compared.

This operation is repeated to establish the sizing curve for each feed bin. The curve is then used by the machine control system to ensure the accuracy of the flows from the feed bins.

This operation is specific to France and it requires special equipment, including the reversing conveyor able to load the lorry. The vast majority of equipment available on the world market does not have this possibility and is consequently not suitable for direct monitoring.

« Sizing » is done for various types of aggregate and

various flows.

december 2005 11

Photo 3.3: Rotomix

Figure 3.7: Retrobatch

3.4 - The drying and coating mixer: the heart of the system

Functions

The drying and coating mixer heats wet aggregate, generally up to 150°c, so that the residual water content is less than 0,5% (standard reference). It also mixes and homogenises the granular ingredients, at first, and then coats the dry aggregate with the hydrocarbon binder.

The two types of drying mixers are parallel flow and reverse flow (diagrams in figures 3.5 and 3.6).

The gas speed has to be controlled to prevent too much filler being carried away, especially in the reverse flow technique. One of the advantages of parallel flow is that it produces about 10 times less filler than reverse flow, as the particles are mostly stuck to the bitumen.

The lengthening of the drums is a specifically French feature, at least in these proportions. All manufacturers have lengthened the drums under pressure from construction companies wishing to eliminate blue smoke and other toxic components. The route explored in France has made it possible to avoid the temperature differential between the gas and the aggregate, and hence to eliminated the problem of bitumen cracking so much criticised in the USA.

The introduction of mixing paddles, in the coating zone of the drum and at the drum outlet, was a great advance in the quest for homogeneity of mixes. This device produces shearing of the same type as in conventional mixers (photo 3.3: shows an example of paddle installation at the end of the drum and in the coating zone).

Finally we must mention one last development, consisting of blocking the asphalt outlet door for a sufficient time at the beginning of the cycle to prevent uncontrolled production of waste. Figure 3.7 is a retention system (Retrobatch) that is typically present on French plants.

Drying, heating, mixing coating, and possibly

recycling; the mixer is real multipurpose tool.

Progress in the knowledge about bitumen has

considerably improved results.

There is no difference in quality between asphalts

produced by continuous or batch processes.

Control of the star ts and ends of cycles requires

retention doors.


Figure 3.8: means needed for recycling

Photo 3.4: recycling in drum mixers

Continuous recycling

The recycling ring is a device that is already old but which has greatly contributed to the growth of recycling. The principle consists of introducing asphalt aggregate into the drum far away from the flame and in any event in a zone where the gas temperature is not excessive. Lengthening of the drums has made this arrangement possible. It is obvious that reverse flow arrangements facilitate this introduction since the ring is situated downstream of the flame. This is why the levels of recycling achievable by reverse flow are normally higher than those obtained with parallel flows. The means needed for recycling are not expensive. They are shown on figure 3.8. photo 3.4 represents a typical recycling installation.

The continuous production technique is unquestionably an excellent solution for recycling at a high level, and for low cost. Normally 25% to 30% can be achieved in parallel flow and 35% to 40% in counterflow. Rates of 50% are possible but are only obtained in special conditions (With a limit on the water content of the materials and a reduction in the instantaneous flow)

Which solution for recycling reverse flow or parallel flow?

Parallel flow is economical, and it is possible to achieve 25% without difficulty. The method consisting of recycling at a low rate but continuously, at 10% to 15% for instance is becoming popular and presents the advantage of not requiring major laboratory checks on the asphalt aggregate reused, or formulation studies.

Counterflow is the safe and ecological solution par excel lence that i s to be recommended in both situations: If the recycling rates are high and permanently above 25%. We must remember that the notion of traceability is essential and is tending

Recycling in the continuous mode is the most

economical method, from both the investment and

operational points of view.

The traceability of asphalt aggregates during

deconstruction is essential and star ts at the first

application.

The precision of the binder content is guaranteed

within the framework of the variations allowed in the

standard.

december 2005 13

Figure 3.9: time-based metering: deviation management Figure 3.10: filler processing

to take on more importance within what is known as deconstruction.

3.5 - Bitumen metering management

Automated systems contain a battery of receivers and actuators (belt flowmeter, binder flowmeter and frequency variators) that enable the binder content to be corrected instantly by integrating not only the space and time deviation, but also variations in aggregate flow (starting phase, run-down phase and temporary stoppage).

Refer to figure 3.9 for the automated regulation system normally used.

The control of feed quantities in transient phases is fundamental to guaranteeing quality. Growth in automatic systems has greatly contributed to industrialising an existing technique.

3.6 - Handling dusting filler and foreign filler

Dusting filler is the result of the drying process and its quantity varies with the type of drum and the water content of the aggregate. The percentage can vary in a ratio 1 to 10,

the quantities being greater with reverse flow drums. In this case the controlled return of dusting filler is essential to satisfy the aims of the formula. This control takes into account the transient phases, increases and reductions in flow, as well as the permanent phases.

In some countries or regions filler has to be removed. This can easily be done using a by-pass on the filler return. Modern bag filters often have built-in reception and storage hoppers, which facilitate the process, especially during the transient phases.We call “foreign filler”, as opposed to dusting filler, exogenous fines added to the formula. These are stored in silos situated close to the drum.

The reintroduction of dusting filler and the introduction of foreign filler takes place directly into the drum after the introduction of the bitumen.

The foreign filler feed bin is optional and depends on the objectives, it is installed as shown on the diagram in figure 3.10.

Great importance is given to precision in the metering of foreign or dusting filler. This precision is justified because the action of the f i l lers i s fundamental to the behaviour of the asphalt on carriageway with trafic.

Whether dusting or foreign, fillers play a fundamental par t in the compactness and the void ratio. The

continuous process facilitates excellent

« in-line » monitoring.

Naturally the compactness and void ratio play an essential par t in the prevention of rutting.


Photo 3.5: mobile plant with storage for 60 t

3.7 - Bitumen concrete storage

Plants may have direct l o a d i n g d e v i c e s o r intermediate storage.

L o a d i n g d e v i c e s a r e always fitted with anti-segregation hoppers and are dimensioned to suit the plant’s flow volume. Again to avoid segregation, the height of the fall is reduced specially when loading lorries.

This storage may be long-term. In this case the storage silos are fitted with anti-oxidation systems (see photo 3.5: mobile plant with storage for 60 t).

In the mobile mode, storage units contain 1 or 2 compartments. In the fixed mode, there is no significant difference between these storage facilities and those used in batch production.

3.8 - Automatic operation

The great advances in computer t echno logy and multiplexing have transformed the control of the production process by incorporating parameters of offset, anticipation and modelling of the transient phases, allowing stopping and restarting under load.

Production traceability, and improvement in the quality and management of stocks are the main consequences of a revolution similar to that which characterises all modern production processes (see photo 3.6: Control cab).

The very high reliability of the processes, and traceability, will be remembered as two great advances made possible by computer technology.

Loading systems are usually of the continuous type (drag

elevator) and feed one or more silos.

The use of remote maintenance and assistance

enables construction companies to secure their

activities.

december 2005 15

Photo 3.6: control cab

3.9 - The continuous process and the environment

The most significant points are linked to emissions, noise, dust and smoke:• as far as noise is concerned the advances are spectacular. The linear, instead of “tower”, production concept avoids vertical transfers and noisy falls. The absence of screening, the reduction in installed capacity compared with batch production contributes to the reduction in noise. Enclosed burners fitted with silencers are becoming more generally used,• concerning dust emissions there is no difference between continuous and batch production, fixed or mobile. All units, including the largest mobile ones, (500 t/hr and more), are fitted with monobloc bag filters, mounted on a single semi-trailer and ensuring emissions that conform to the severest standards,


Photo 3.7: single pack hyper mobile plant Photo 3.8: high capacity, 550 t/hr, hyper mobile drum mixer

3.10 - Mobility

T h e r e a r e d i f f e r e n t versions of the concept: transferability, mobility, hyper mobility, etc.

All construction companies’ needs are covered by different solutions, where they compete with each in ingeniousness.

It should be noted that mobile plants can require a crane to install them, that super mobiles are self-erecting, and that hyper mobiles have quick-fit connections, both electrical and thermal.

The concept has been developed particularly in France and can consist of simply three or four prewired packs that are operational practically immediately.

See photo 3.7: single pack hyper mobile plant and photo 3.8: high capacity, 550 t/hr, hyper mobile drum mixer.

• finally, the problem of smoke observed during the 1980’s has long since been solved. A series of improvements has led to a solution based on various specialities,

– the type of bitumen is perfectly controlled and in conformity with a standard,– the long and closed burners have clearly controlled combustion conditions,– the increase in the length of the drums is undoubtedly the main factor. It allows a protective curtain of material to form, acting as a thermal shield.

The result is a very small difference between the temperatures of the gases and the asphalt, regardless of the process used.

The historic problem of blue smoke and other emissions is no longer a problem as long as the instructions are followed. Many tests prove it.

The technologies used enable clean and ecological

asphalt to be produced.

The continuous hot asphalt plant is the easiest to

transport because of its horizontal design.

december 2005 17

Photo 4.1: aerial view of the A85 motorway

4. Examples of possible strategies to satisfy the market

4.1.1 - Description of the geographical context with its special difficulties

This new motorway construction is part of the link from Vierzon to Tours, contracted to Cofiroute by the French state by decree on 26/9/1995. It a motorway financed by tolls.

Cofiroute, an entirely private company operating as a statutory motorway undertaker, has contracted the building of this section to its main contractors SCAO and SOCASO, under a fixed price design and construction contract.

This is a 32 km, 2 x 2 lane section opened on 12 december 2003 and of which the carriageways were built between october 2002 and 2003.

It is partly situated in a woodland area (Sologne) and partly in an agricultural area. The earthworks did not present any particular difficulties. The nature of the soil (mainly sandy clay) necessitated soil treatments and importation of earth from outside the area.

Specifications • Rubble: 2 800 000 m3 Incl. backfill: 2 500 000 m3 treated with lime or road binder • Production and implementation 250 000 tonnes of asphalt gravel 100 000 tonnes of road base asphalt• 16 overhead crossings incl. 3 wild animal crossings. • 13 underground crossings incl. 4 pedestrian tunnels and 1 for wild animals

In total:

30 water structures restoring the natural flows and 26 retention and treatment basins ensuring the protection of the natural environment.

The traffic is moderate (6 000 vehicles / day incl. 20% heavy goods vehicles) leading Cofiroute to specify an evolutive carriageway enabling investments to be made progressively with time.

4.1 - High tonnage motorway construction in open country

A 85, Section from Romorantin Lanthenay to Saint Romain-sur-Cher.


4.1.2 - Formulation

FormulationFoundation / Base

Bitumen gravelWearing course

Thin asphaltic overlay

LA Los Angeles; MDE Micro Deval Test with water presence; PSV Polish Stone Value

0/D particle size 0/14 0/10

Origin of aggregates Solid (large quarry) Solid (large quarry)

Mineralogical nature Blue Diorite Blue Diorite

Intrinsic characteristicsLA* 9 to 13 MDE* 9 to 12

Density = 2.85LA* 9 to 13 MDE* 9 to 12Density = 2.85 PSV* = 0.50

Sand cleanliness (blue value) 69 69

External inspection SCAO SCAO

Outside inspection CETE ANGERS CETE ANGERS

Bitumen category 35/50 35/50

Tests carried out Penetration – Ball & Ring Penetration – Ball & Ring

Table 4.1

4.1.3 - The standard carriageway structure

4.1.4 - Practical execution and quality monitoring

Production & InspectionFoundation & Base

Bitumen gravelWearing course

Thin asphaltic overlay

Formulae

Aggregate 10/14 30 % Aggregate 6/10 17 % Sand 2/6 22 % Sand 0/2 29 % limestone fines 2 % bitumen 35/50 4.4 %

Aggregate 6/10 68.5 %

Sand 0/2 29.0 % Limestone fines 2.5 % Bitumen 35/50 5.3 %

Company SCAO

Coating equipment mobile

Manufacturer / Type / Model Ermont TSM Major

Inspection body 550 t/h

Outside inspection CEBTP

Table 4.2

december 2005 19

Implementation & inspection Bitumen gravel & Thin asphaltic overlay

Company SCAO

EquipmentFRANEX feeder

1 Vögele 2500 finisher

Spraying mode 18 m beams

Road base asphalt compaction 2 heavy wheeled compactors & 3 vibrating compactors

Asphalt compaction 4 vibrating compactors

Hourly spraySprayed per day

550 t/hBitumen gravel between 2,500 & 3,400 t/d

Bitumen concrete between 2,000 & 3,000 t/d

Company inspection (Method) SCAO (Coring + Hydrostatic weighing)

Asphalt inspection by outside laboratory (Method) CEBTP (Coring + Gamma density meter)

Smoothness and average texture depth inspection (sand depth) French public works research laboratory

Table 4.3

4.1.5 - Conclusion

On a motorway construction like the one described above, it is clear that the use of a high flow continuous plant, operating with the minimum of parameter variations, provides the promoter with a bonus in terms of overall quality and duration of the works.

4.2 - Motorway works in an urban area: maintenance work on the carriageways of the Paris «Boulevard Peripherique»

4.2.1 - Context of the maintenance work

The Par i s «Boulevard Pe r i p h e r i q u e » i s a n exceptional road because of its traffic and its special f e a t u r e s ( 1 1 0 0 0 0 0 vehicles per day, incl. 12% heavy goods vehicles). 35 kilometres long, this circular highway has a carriageway area of 1 000 000 m2 spread over 2 to 6 traffic lanes, incl. 20% on engineering structures and 17% in cut and covers. To this must be added 380 000 m2 of slip roads comprising 147 ramps, 6 interchanges and 44 exit roads.

The Engineering structures and Peripherique Section (SOAP) of the road maintenance and traffic department of the Paris Town hall is in charge of surveillance and maintenance of the Boulevard Peripherique, which has the status of a by-road.

Any carriageway reinforcement or maintenance necessitates a special procedure giving precedence to the safety of road users and workers, as well as continuity of traffic flow, over the works themselves.

Work on the carriageways is done at night. The period worked must be respected in all circumstances by the contractors who must only be present on the site between 22h00 and 05h00 in the morning.

4.2.2 - Sequences of works

Carriageway maintenance on the Boulevard Peripherique consists of milling one or more lanes to a variable depth in passes of between 25 and 120 mm, and putting in place carriageways of the same thickness, using bitumen concretes corresponding with two standard structures:

B B M E s h a v e b e e n produced since 2000 by a 17 Major mobile drier drum mixer plant installed o n t h e L a g n y - l e - Se c parking area.

Before 2000, a fixed plant, also continuous and situated at Gennevilliers, supplied the asphalt.

The Paris “Boulevard Peripherique” is one of the

busiest roads in France, with 130 000 heavy goods

vehicles per day.

For the last 20 years, the bitumen concretes used on the Paris “Boulevard Peripherique” have been supplied by continuous

process plants.


4.2.3 - Bitumen concretes with specific performance

The bitumen concretes used on the Boulevard Peripherique are special.

In 20 years, the order has evolved from BBSG 0/14 to BBME 0/10. These asphalts are used on the heavy lanes of the BP, where the heavy goods vehicles usually travel. Excellent rutting resistance is necessary. The reduction in the grain size bracket is due to a contribution to noise reduction.

0/14 thin asphaltic overlay is used on the lanes used by light vehicles. This has now become 0/10 thin asphaltic overlay for the same reason.

BBME 0/10 (the most commonly used):

The aggregates used must be light in colour.

The CCTP sets threshold values for lightness within the meaning of NF standard NF X 08-000, to improve rutting resistance.

Hence the formulation of BBME 0/10 today is the following:Light quartz 6/10: 57 %Light quartz 2/6: 13 %Rhyolite 0/2: 27 %Foreign filler: 3 %Special multigrade bitumen: 5.9 ppc

0/10 type A BBM:

As in the case of 0/10 BBME, the aggregates used come from the same quarries.

The formulation of a 0/10 type thin asphaltic overlay is the following batch formula:Light quartz 6/10: 65 %Rhyolite 0/2: 32 %Foreign filler: 3 %Special multigrade bitumen: 5.8 ppc

4.2.4 - Prospect of use of coated aggregates

Within the framework of its market, the city of Paris states that it reserves the right to keep available the asphalt planings from the Boulevard Peripherique. It requires the contractor to store them in a depot within a maximum radius of 40 km from Paris. This procedure is covered by an Organisation and Monitoring of the Removal of Waste Materials Instruction (SOSED) within the site Quality Assurance Plan (QAP).

This organisation, that was operational in 2001, has enabled the promoter (the city of Paris) to solve the problem of the removal of planings from its roads without having to worry about their final destination.

Under the SOSED, the contractor had to make undertakings on a certain number of principles:• make available a storage area near to the coating plant reserved for planings f r o m t h e B o u l e v a r d Peripherique,• not to mix different planings to ensure the traceability of the materials,• to screen and calibrate the planings to 0/10 mm in order to obtain recyclable asphalt aggregate.

These aggregates are destined to be incorporated into materials making up future layers of the carriageway.

A formulation study with asphalt aggregates and new aggregates has made it possible to assess the mechanical performance of a mixture incorporating different levels of recycled materials.

The 17 Major drier drum mixer is fitted with a recycling ring, which enables us to envisage this type of operation on the current works site.

In September 2002, the first experiment was successfully carried out on a site on the Boulevard Peripherique, with a BBME 0/10 wear course.

All the tests and inspections are satisfactory and confirm the quality of the production

and the adherence to the formula specifications.

Site monitoring over the past 20 years and more gives good traceability.

Selective demolition, or deconstruction,

is a principle imposed by the Sosed.

december 2005 21

4.2.5 - Conclusion

The experience gained over the last 20 years is based on implementation of asphalts produced in the continuous mode, to the City of Paris’ satisfaction.

The prospect of an increase in the partial use of asphalt gives the contractor, as the promoter and the main contractor, the opportunity to progress in recycling techniques and to obtain new experience in this domain.

4.3 - Production of recycled products: environmental considerations

A hot continuous mix asphalt plant is a classified installation subject to regulations (in France, Decree of 2nd february 1998) covering environmental protection.

It is accepted that counterflow asphalt plants, with or without recycling, do not pose any particular environmental problems because of the special arrangements in relation to the drum.

In the case of parallel flow of drum mix plants the gaseous emissions include gases produced by the heating of the foreign bitumen, and organic compounds from the heating of asphalt aggregates during recycling.

Tests on a pilot site enabled us to study the changes in gas and particle ratios as the recycling rate increases.

4.3.1 - Emissions of solid particles into the atmosphere

Emissions of solid particles have been covered by regulations for many years. If the dust remover uses a filter and is in good condition the current limit of 50 mg/Nm3 for plants is respected. Usual results in this domain are below 20 mg/ Nm3.

In this field, recycling or otherwise has no significant effect on emissions into the atmosphere. We should point out that for parallel flow drum mixers, the quantity of solid particles to be processed by the dust remover reduces when the production contains asphalt aggregates and varies inversely with the recycling rate. However the particles to be treated include coated particles. This is the limiting factor for the recycling rate for this type of plant.

4.3.2 - Gaseous emissions into the atmosphere

In the event of hot recycling in a parallel flow drum mixer, the old binder contained in the asphalt aggregates can be subjected to temperature rises greater than those of the new binders used in the normal asphalt production cycle.

In this context, analyses were carried out on a 17 Ermont type drier drum mixer plant operating on natural gas, for tradition production and with asphalt aggregate recycling at various rates (≤ 30%). The binder used was always a traditional binder (35/50).

Investigations have been carried out on the following gases: Carbon dioxide (CO2), Nitrogen oxide (NOx), Volatile Organic Compounds (VOCs), and specifically Polycyclic Aromatic Hydrocarbons (PAHs) with elementary determination of these. The main approved and experimental reference methods for fixed source gaseous emissions are listed in chapter 7 with the standards.

The results showed:• changes in CO2 conditioned by differences in the water content between natural aggregates and asphalt aggregates,• nitrogen oxide emissions below the regulations limits,• that the PAHs found do not pose any particular problem. Moreover we did not detect the presence of the components considered to be the most dangerous,• that recycling or not does not make any significant difference to total VOC emissions or non-methanic VOC emissions. The strict interpretation of these pollutants remains conditioned by the harmonisation in oxygen content of the gaseous emissions (a parameter fixing the emissions dilution rate and normally specified in the authorisation ruling).

In conclusion; at our current level of knowledge these analyses and tests show that this type of plant satisfies the standards in force concerning pollutant emissions into the atmosphere.


On the basis of quality criteria to suit the various methods, we can give the following advice on orientation and choice:

Stationary plantsMobile

continuous plants (*)

Batch with screening

Batch without screening (by pass)

Continuous

Annual tonnageHigh - + + ++

Low = = + +

Instant flowHigh = = ++ ++

Low = = + +

Number of formula changes

High ++ - - -

Low + + + +

Recycling10 to 20 % = = + +

20 to 50 % =(***) - ++ ++

SavingIn investment - - = +

In operation - = + +

Inspection quality + - +(**) +(**)

(*) As the mobility of batch plants is very poor we have only considered continuous plants, as mobile plants in this table.(**) With a continuous mobile plant, because of the limited asphalt storage, the in-line quality control is direct, and consequently of a higher level.(***) Possible with an extra drum.

Table 5.1

Recent developments in continuous drum mix plant techniques (refer to previous paragraphs) have made them into environmentally friendly installations.

The advantages of continuous plants, confirmed by French practical experience, are mainly linked to:• high and very high instantaneous flows (50 to 100% above the average for batch plants,)• lower production costs for the same level of investment,• mobility, which is a decisive advantage both for building new carriageways and for maintenance,• very easily implemented possibilities for recycling, at various rates up to 50%.

5. Guide for a road investor

december 2005 23

6.1 - Equipment standards

Road construction and maintenance equipement. Material processing plants. Terminology and performances. NF P 98-701. Afnor, may 1993

6.2 - Equipment test standards

Road construction and maintenance equipement. Continuous batching. Equipment for aggregates Test bench and method for flow rate measurement. NF P 98-721. Afnor, june 1992

Road construction and maintenance equipment. Continuous batching equipment for products in powder form. Test bench and method of flow rate measurement. NF P 98-722. Afnor, june 1992

Road construction and maintenance equipment. Bituminous binder pumpes. Part 1: test bench and method. NF P 98-723-1. Afnor, july 1994

Road construction and maintenance equipement. Bituminous binder measuring devices. Test bench and methods. NF P 98-724. Afnor, december 1991

Road construction and maintenance equipment. Conveyor belt quantity flowmeter. Test Bench and method. NF P 98-725. Afnor, july 1994

6.3 - Equipment approval standards

Road construction and maintenance equipment. Hot-setting hydrocarbon materials production plants – Definition of components, of the levels and verification of initial settings. Part 1: Continuous bituminous mixing plants. NF P 98-728-1 Afnor, august 2004

6.4 - Calibration standards

Road construction and maintenance equipment. Calibration and verification of the on site setting of the continous dosing apparatus of material production units. Part 1: belt flow meter for belt conveyor. NF P 98-744-1. Afnor, november 2993

Road construction and maintenance equipment. On-site calibration and verification of the setting of the continuous dosing apparatus of material production plants. Part 2: aggregate weighing dosing machine. NF P 98-744-2. Afnor, october 1996

Road construction and maintenance equipment. On-site calibration and verification of the setting of the continuous dosing apparatus of material production plants. Part 3: aggregate volumetrique dosing machine. NF P 98-744-3. Afnor, october 1996

Road construction and maintenance equipment. On-site calibeation and verification of the setting of the continuous dosing apparatus of material production plants. Part 4: weighing pulverulent bin - Testing by sampling on conveyor belt . NF P 98-744-4. Afnor, october 1996

Road construction and maintenance equipment. On-site calibration and verification of the setting of the continuous dosing apparatus of material production plants. Part 5: dry bulk weighing dosing machine. Substance weighing test. NF P 98-744-5. Afnor, october 1996

Road construction and maintenance equipment. On-site calibration and verification of the setting of the continuous dosing apparatus of material production plants. Part 6 bitumen feeds - Testing by weighing the material. NF P 98-744-6. Afnor, 2003

6. Bibliography: standards covering continuous hot mix production


6.5 - Manufacturing and implementation standards

Asphalt - Wearing course and base course: thick layer asphalt concrete. Definition – Classification – Characteristics – Fabrication - Laying. NF P 98-130. Afnor, november 1999

Road construction and maintenance. Manufacture of mixtures. Part 1: production control of hot mix asphalts using a data acquisition system. XP P 98-142-1. Afnor, december 2003

Bituminous asphalt. Laying of base, binder and surface courses. Components – Mix contents - performance and checks. NF P 98-150. Afnor, december 1992

Road construction and maintenance. Data acquisition modules for granular mixt fabrication plants - Description and functional specifications. Part 1: continuous production module. NF P 98-772-1. Afnor, september 2004

6.6 - Information bulletins• (AQP) Quality Weighing Association. Information bulletin « Chaussées Dépendances », n° 106. Sétra, november 1998, 6 p.• Very thin and extra thin asphalt concrete. Information bulletin « Chaussées Dépendances », n° 94. Sétra, april 1997, 6p.• Smoothness and implementation. Information bulletin « Chaussées Dépendances », n° 90. Sétra, august 1996, 4p.• The CFTR and its publications (technical bulletin and CATM). Information bulletin « Chaussées Dépendances », n° 87, Sétra, february1996, 6p.• Road equipment standardisation. Information bulletin « Circulation Sécurité Équipement », n° 88, Sétra, december 1990, 6p.

6.7 - Main approved and experimental reference methods for gaseous emissions from fixed sources

Parameter measured Standards

Flow FD X 10 112

O2 FD X 20 377 to 379

Dust NF X 44 052

CO FD X 20 361 to 363

SO2 XP X 43 310 – FDX 20 351 to 355 & 357

PAH XP X 43 329

Total hydrocarbons NF X 43 301

Table 5

46 avenue

Aristide Briand

BP 100

92225 Bagneux Cedex

France

téléphone :

33 (0)1 46 11 31 31

télécopie :

33 (0)1 46 11 31 69

internet : www.setra.

equipement.gouv.fr

Sétraservice d'Études

techniques

des routes

et autoroutes

Le Sétra appartient

au Réseau Scientifique

et Technique

de l'Équipement

The document presents the French experience on the continuous manufacture of hot-coated materials. The technique is strong of thirty years of developments and concerns today half of the hot-coated materials production. This development has been made possible and easiness by a joint work between the plants manufacturers, the contractors of works, the awarding authorities and contract managers.

The bituminous mixing plants are on the whole one half - thousand of units, 20 % are mobile plants, in majority continuous, and 80 % are stationary plants, of which 35 % are continuous.

The expansion of the continuous technique is at once due to the large national programs of new and maintenance works towards 1970, to the formalization of the quality requirements on the production of aggregates and on the composition of materials, and to the successive technological improvements on the continuous plants. These last allow today the incorporation of some recycled aggregates until 50 % of the end product, and respect the strictest environmental standards dealing with release of gas.

After a brief recall of the two types of process: continuous and discontinuous, and a detailed description of the components and the working of a continuous plant, the document describes two real cases of sites: the one is a rural motorway, including a 0/14 bitumen-bound granular material in foundation-basis layer and a 0/10 bituminous concrete, and the other concerns the pavement maintenance of the Paris ring road with a high modulus asphalt layer, including since 2002 a fraction of the milled old material.

The document ends by giving to the road investors a table that situates the interest of the choice of the different plants according to the technical and economic operating criteria, and presents the French standards for the continuous manufacture of hot-coated materials.

Crédit photos : Fayat, except page 17 CofirouteConception graphique - mise en page : Philippe Masingarbe (Sétra)L’autorisation du Sétra est indispensable pour la reproduction, même partielle, de ce document© 2006 Sétra -

us 0609a continuous hot mixt production

Documents