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AP-T65/06

AUSTROADS TECHNICAL REPORT

Asphalt Paving

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Asphalt Paving

First Published November 2006

Austroads Inc. 2006

This work is copyright. Apart from any use as permitted under the Copyright Act 1968,no part may be reproduced by any process without the prior written permission of Austroads.

Asphalt PavingISBN 1 921139 62 5

Austroads Project No. TP1054

Austroads Publication No. APT65/06

Project Manager

Gary Liddle, VicRoads

Prepared by

John Rebbechi

Published by Austroads IncorporatedLevel 9, Robell House287 Elizabeth Street

Sydney NSW 2000 AustraliaPhone: +61 2 9264 7088

Fax: +61 2 9264 1657Email: [email protected]

Austroads believes this publication to be correct at the time of printing and does not acceptresponsibility for any consequences arising from the use of information herein. Readers should

rely on their own skill and judgement to apply information to particular issues.

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Austroads profile

Austroads is the association of Australian and New Zealand road transport and traffic authoritieswhose purpose is to contribute to the achievement of improved Australian and New Zealand roadtransport outcomes by:

undertaking nationally strategic research on behalf of Australasian road agencies and

communicating outcomes promoting improved practice by Australasian road agencies

facilitating collaboration between road agencies to avoid duplication

promoting harmonisation, consistency and uniformity in road and related operations

providing expert advice to the Australian Transport Council (ATC) and the StandingCommittee on Transport (SCOT).

Austroads membership

Austroads membership comprises the six state and two territory road transport and trafficauthorities and the Australian Department of Transport and Regional Services in Australia, the

Australian Local Government Association and Transit New Zealand. It is governed by a councilconsisting of the chief executive officer (or an alternative senior executive officer) of each of itseleven member organisations:

Roads and Traffic Authority New South Wales

Roads Corporation Victoria

Department of Main Roads Queensland

Main Roads Western Australia

Department for Transport, Energy and Infrastructure South Australia

Department of Infrastructure, Energy and Resources Tasmania

Department of Planning and Infrastructure Northern Territory

Department of Territory and Municipal Services Australian Capital Territory

Australian Department of Transport and Regional Services

Australian Local Government Association

Transit New Zealand

The success of Austroads is derived from the collaboration of member organisations and others inthe road industry. It aims to be the Australasian leader in providing high quality information, adviceand fostering research in the road sector.

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SUMMARY

In 2004, Austroads commenced a review of all technical publications with a view to compiling existinginformation into a series of publications using a common format. Part 4B of the Guide to Pavement

Technology provides an overview of asphalt materials, manufacture and placing. This technical reportis one of a series that supports Part 4B as follows:

Guide to Pavement Technology Part 4B: Asphalt

Appendix A Asphalt mix design procedures

Appendix B Framework specification for asphalt and asphalt recycling

Technical Reports

AP-T62/06 Introduction to asphalt mix design

AP-T63/06 Asphalt characterisation for pavement designAP-T64/06 Asphalt manufacture

AP-T65/06 Asphalt paving

AP-T66/06 Asphalt recycling

AP-T67/06 Maintenance of asphalt surfacings

This document is intended to provide readers with a working knowledge of paving operations and isconsidered best practice at the time of writing. Text used in this document is based primarily oninformation originally prepared for the Austroads Asphalt Guide(AP-G66/02) (2002).

A section on planning the paving operation provides information on the development of traffic controlplans and the need for paving trials particularly for large projects. The problems associated withworking in an urban environment are discussed with emphasis on night work.

The preparation of the existing surface can have a significant effect on the quality and durability of theasphalt laid. Advice is given on cleaning and correction of existing defects before placing the newasphalt. Cold milling and pre-treatment of granular and concrete surfaces are covered.

A brief discussion of the risks associated with paving in adverse weather is provided.

It is considered best practice to apply a tack coat to all but granular (or rock) surfaces prior to theplacement of fresh asphalt and a brief discussion on this topic is included.

The transport and transfer of asphalt to the paver is discussed with a view to achieving the bestoutcome whilst being aware that the scale of the project will influence some of the options. Materialstransfer vehicles have been shown to reduce the roughness of the asphalt layer but can substantiallyraise the price of the project.

An extensive section is provided on paver operation. The correct operation of the paver is critical inachieving the best outcome and the adjustments and procedures necessary to obtain an acceptableoutcome are discussed in detail.

Handwork and joints are examined as these often have a large impact on the overall quality of aproject.

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Compaction equipment is covered. Compaction temperature is an important factor in attaining anadequate level of compaction and guidance is provided on the number and types of roller required forvarious situations. Special mention of differences in compaction techniques for stone mastic asphalt,open graded asphalt and thin and deep lift asphalts is provided.

The finished properties of the asphalt mat are discussed and these cover tolerances on shape, matthickness, ride quality and compacted density.

Extensive checklists are provided at the rear of the document covering typical activities in an asphaltpaving operation. The document concludes with advice on identifying and rectifying problems.

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CONTENTS

1 PLANNING AND PREPARATION FOR ASPHALT PAVING ...............................................11.1 General...................................................................................................................................1 1.2 Planning..................................................................................................................................1 1.3 Paving Trials...........................................................................................................................21.4 Traffic Control Plans...............................................................................................................21.5 Night Work..............................................................................................................................31.6 Audit and Surveillance of Asphalt Paving Contract Work.......................................................32 PREPARATION OF PAVEMENT SURFACE........................................................................42.1 Cleaning .................................................................................................................................42.2 Correction of Defects in Bituminous Surfaces........................................................................42.3 Correction of Defects in Concrete Surfaces ...........................................................................52.4 Cold Milling.............................................................................................................................52.5 Pre-treatment of Granular Pavements....................................................................................72.6 Pre-treatment of Concrete Surfaces.......................................................................................82.7 Public Utilities .........................................................................................................................83 CLIMATIC CONDITIONS.......................................................................................................93.1 General...................................................................................................................................9 3.2 Pavement Temperature..........................................................................................................93.3 Moisture..................................................................................................................................9 3.4 Risk Management...................................................................................................................94 TACK COATING..................................................................................................................104.1 General.................................................................................................................................10 4.2 Application............................................................................................................................10 4.3

Precautions...........................................................................................................................11

5 TRANSPORT OF ASPHALT ...............................................................................................125.1 General.................................................................................................................................12 5.2 Vehicles................................................................................................................................12 5.3 Release Agents ....................................................................................................................135.4 Organisation.........................................................................................................................136 TRANSFER OF ASPHALT FROM TRUCKS TO PAVER ...................................................147 PAVER PERFORMANCE AND SCREED OPERATION.....................................................157.1 General.................................................................................................................................15 7.2 Tractor Unit...........................................................................................................................167.3 Screed Unit...........................................................................................................................17

7.3.1 Angle of inclination .................................................................................................187.3.2 Volume of material in front of screed......................................................................197.3.3 Paving speed..........................................................................................................207.3.4 Primary compaction by screed unit ........................................................................217.3.5 Crown adjustment of screed...................................................................................217.3.6 Screed extensions..................................................................................................217.3.7 Care of screed........................................................................................................22

7.4 Automatic Sensing and Levelling Equipment .......................................................................227.5 Paver Stoppages..................................................................................................................22

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8 SPREADING OPERATIONS ...............................................................................................228.1 General.................................................................................................................................22 8.2 Setting Out............................................................................................................................228.3 Spreading by Paver..............................................................................................................228.4 Spreading by Grader ............................................................................................................228.5 Spreading by Hand...............................................................................................................228.6 Layer Thickness ...................................................................................................................228.7 Joints ....................................................................................................................................22

8.7.1 Longitudinal joints...................................................................................................228.7.2 Wedge joints...........................................................................................................228.7.3 Transverse joints ....................................................................................................22

8.8 Paving Output.......................................................................................................................228.9 Automatic Level Control .......................................................................................................22

8.9.1 Joint matching shoe................................................................................................228.9.2 Levelling (or averaging) beam................................................................................228.9.3 Fixed wire ...............................................................................................................228.9.4 Crossfall control......................................................................................................228.9.5 Computerised level control .....................................................................................228.9.6 Laser control...........................................................................................................22

8.10 Service Fittings.....................................................................................................................228.11 Safety During Paving Operations .........................................................................................229 COMPACTION.....................................................................................................................22 9.1 General.................................................................................................................................22 9.2 Compaction Equipment ........................................................................................................229.3 Mix Temperatures for Placing...............................................................................................229.4 Determination and Use of Temperature Profiles ..................................................................229.5 Roller Numbers and Speed ..................................................................................................229.6 Rolling Procedures ...............................................................................................................229.7 Rolling of Transverse Joints .................................................................................................229.8 Rolling of Longitudinal Joints................................................................................................229.9 Initial Rolling .........................................................................................................................22

9.9.1 Unsupported edges ................................................................................................229.10 Intermediate Rolling..............................................................................................................229.11 Final Rolling..........................................................................................................................229.12 Special Techniques..............................................................................................................229.13 Rolling Pattern......................................................................................................................229.14 Hand Compaction.................................................................................................................229.15 Compaction of Open-graded Asphalt ...................................................................................229.16 Compaction of Deep Lift Asphalt..........................................................................................229.17 Compaction of Stone Mastic Asphalt....................................................................................229.18 Placing and Compaction of Ultra Thin Open-graded Asphalt Surfacing...............................2210 FINISHED PAVEMENT PROPERTIES................................................................................2210.1 General.................................................................................................................................22 10.2 Thickness and Level.............................................................................................................2210.3 Shape ...................................................................................................................................2210.4 Riding Quality .......................................................................................................................2210.5 Compacted Density ..............................................................................................................22

10.5.1 General...................................................................................................................2210.5.2 Testing of density using nuclear density gauge......................................................22

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11 FIELD OPERATIONS CHECK-LIST....................................................................................2212 TROUBLE SHOOTING GUIDE............................................................................................22FURTHER READING....................................................................................................................22

TABLES

Table 2.1: Guide to selection of profiler .......................................................................................7Table 8.1: Typical asphalt layer thickness .................................................................................22Table 9.1: Asphalt spreading temperatures ...............................................................................22Table 9.2: Typical temperatures for placing and compacting of

asphalt containing various binders............................................................................22Table 9.3: Number of rollers.......................................................................................................22Table 9.4: Typical rolling sequence............................................................................................22Table 10.1: Typical permissible tolerances in shape....................................................................22Table 10.2: Typical in situ air voids (dense graded asphalt).........................................................22Table 10.3: Typical relative compaction (bulk density) .................................................................22

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FIGURES

Figure 2.1: Rotary road broom ...................................................................................................4Figure 2.2: Shape correction......................................................................................................5Figure 4.1: Tack coat sprayer in operation...............................................................................10Figure 5.1: A Flocon non-tipping delivery truck.......................................................................12Figure 6.1: Materials transfer device ........................................................................................14Figure 7.1: Typical paver..........................................................................................................15Figure 7.2: Typical paver components .....................................................................................15Figure 7.3: Flow of material through paver...............................................................................16Figure 7.4: Components of screed unit ....................................................................................17Figure 7.5: Factors influencing vertical position of the free-floating screed..............................18Figure 7.6: Response to change in angle of attack ..................................................................19Figure 7.7: Screed response to a step-function disturbance....................................................19Figure 7.8: Head of material.....................................................................................................20Figure 7.9: Paver with hydraulic screed ...................................................................................22Figure 8.1: Handwork...............................................................................................................22Figure 8.2: Overlapping of longitudinal joints in successive courses .......................................22Figure 8.3: Overhang of outer edge .........................................................................................22Figure 8.4: Poor roller placement.............................................................................................22Figure 8.5: Poor roller place .....................................................................................................22Figure 8.6: Paving in echelon (hot joints) .................................................................................22Figure 8.7: Cutting disc attached to steel roller ........................................................................22Figure 8.8: Correct overlap of longitudinal joint........................................................................22Figure 8.9: Transverse joint construction .................................................................................22Figure 8.10: Mix deliveries required to match paving machine speeds

for various compacted depths ................................................................................22Figure 8.11: Joint matching shoe ...............................................................................................22Figure 8.12: Multiple skid beam .................................................................................................22Figure 8.13: Fixed wire...............................................................................................................22Figure 9.1: Vibratory steel wheeled roller.................................................................................22Figure 9.2: Pneumatic-tyred roller ............................................................................................22Figure 9.3: Vibratory plate ........................................................................................................22Figure 9.4: Asphalt temperature profile curve ..........................................................................22Figure 9.5: Rolling of transverse joint.......................................................................................22Figure 9.6: Compacting longitudinal joint .................................................................................22Figure 9.7: Operation of rollers.................................................................................................22Figure 9.8: Typical rolling pattern .............................................................................................22Figure 10.1: Laser profiler ..........................................................................................................22Figure 10.2: Nuclear density testing...........................................................................................22

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1 PLANNING AND PREPARATION FOR ASPHALT PAVING

1.1 General

Good organisation is required to ensure efficiency and smoothness of asphalt paving work.

Equipment must be suitable to the task and personnel trained and skilled to achieve the requiredstandards of workmanship. Surfaces must be adequately prepared. Transport, spreading andcompaction must be completed while materials are sufficiently hot to achieve the requiredstandards of density and surface finish.

1.2 Planning

Preliminary planning activities for an asphalt job should include:

site inspection to assess the site conditions and the basic requirements of the job

arrangement of contracts for supply of asphalt, where appropriate

arrangement of paving trials, if appropriate

planning of traffic control arrangements

advertising and advance warning to occupiers of adjoining properties, if necessary

issuing of instructions to supervisory personnel

assessment of plant requirements

assessment of field organisation required.

The site should be inspected well in advance of the proposed start date for the work to confirm:

the appropriate treatment:

type(s) of mix

nominal size(s) of mix

layer thickness(s)

any remedial treatment required to restore the pavement to a condition suitable for theasphalt treatment

profiling requirements

the manner of executing the work

staging of work

the traffic control requirements for the work

the need for public utility adjustments and treatment adjacent to the utility

tie-in to existing work.

The site should be inspected again a day or two before commencement to ensure the pavementhas been satisfactorily prepared.

Where possible, paving should be scheduled to take advantage of daylight and daytimetemperatures and to avoid peak hour traffic restrictions and early morning frosts. When paving atnight, adequate artificial lighting must be provided.

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Detailed site planning should include:

correct position of longitudinal joints

planning of optimum length of each run and minimisation of transverse joints; method oflevel control

optimum use of labour, equipment and delivery trucks

adoption of good practices in all aspects of work

sketches and/or plans of the work, if appropriate.

1.3 Paving Trials

For larger works, particularly project work using transportable mixing plants, it may be appropriateto carry out paving of trial areas. This can assist in assessing:

suitability of proposed mix in terms of workability, ease of compaction, and surface texture(including check for segregation)

adequacy of mixing plant to supply asphalt at the rate required for continuous paving

adequacy of the proposed transport to ensure mix arrives on site at the required temperatureand rate of supply

adequacy of spreading equipment, and associated techniques to achieve the required rate ofpaving and to produce the required quality of asphalt pavement

suitability of the spreading and rolling pattern including location of joints

suitability of compaction equipment and procedures

allowance in thickness to be made for roller compaction.

1.4 Traffic Control PlansThe work site should be adapted to minimise traffic constraints and serve the needs of road userswhile at the same time providing adequate safety for the work crew.

Where required, a traffic control plan should be prepared for each job. The plan should ensure thatcontrol of traffic is carried out in accordance with appropriate standards such as AS 1742.3 andassociated field guides, or Transit New Zealands Code of practice for temporary trafficmanagement 2004, as well as any specific requirements.

The traffic control plan elements include:

1. determination of the most appropriate method of traffic control, such as:

single lane for 2 way traffic

2 lanes for 2 way traffic

side track or detour around the site.

2. arrangements for the supply and use of all necessary signs, traffic control devices, lights andpilot vehicles where necessary

3. detailed layout of all signs and devices (with diagrams as necessary)

4. arrangements for the required number of traffic controllers

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5. informing the public of the work by letterbox drop, advertising, advance warning signs andother appropriate means well before the worksite

6. removal of parked cars

7. arrangements for site to be left in a safe condition overnight, especially if traffic has access to

partially finished work.

Wherever possible, the full width of roadway should be paved each day and a ramp provided at theend of each day's work for the smooth passage of traffic. If it is not possible to pave the full width,traffic should be prevented from crossing the exposed longitudinal edge.

1.5 Night Work

Asphalt paving at night can significantly reduce problems associated with traffic disruption.Diversion or restriction of traffic can also provide a safer work site by reducing the proximity oftraffic and improving site access. This can speed up the whole operation.

Disadvantages of night work can include: low pavement and ambient temperatures

difficulty in achieving the same quality of surface finish, joints, etc.

the need for good artificial lighting

noise and disruption to residents

additional labour costs

potential for errors to be undetected.

1.6 Audit and Surveillance of Asphalt Paving Contract Work

A guide to audit and surveillance of asphalt paving contract works is included in the asphaltmanufacture part of this series Austroads (2006b) and includes checklists for paving activity as wellas general guidelines for the preparation of quality plans, inspection and test plans andmanufacture of asphalt. Detailed checklists for asphalt paving activity and a troubleshooting guideare included in Sections 11 and 12 of this document.

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2 PREPARATION OF PAVEMENT SURFACE

2.1 Cleaning

Before the asphalt is placed, the existing surface should be dry, and thoroughly swept to remove

any loose stones, dirt and foreign matter. Sweeping should be carried out with a rotary road broomor suction cleaner (Figure 2.1). It should extend at least 300 mm beyond each side of the area tobe paved.

Any foreign matter adhering to the pavement and not swept off by broom should be removed byother means. Any areas affected by minor oil contamination should be cleaned by an approvedmethod. Any area significantly affected by oil, and which has softened to an appreciable degree orhas ravelled, should be removed and reinstated with asphalt.

Figure 2.1: Rotary road broom

2.2 Correction of Defects in Bituminous Surfaces

Prior to commencement of the paving operation, any defects should be corrected, as follows:

filling of potholes and depressions with asphalt or approved patching material. Cold-mixshould not be used as it may lead to bleeding or flushing

removal of excess binder from fatty patches

crack filling

repair of edge breaks

cleaning and repairing any joints

removal and replacement of unstable materials

removal and replacement of cold-mix patches

shape correction.

Where the surface is badly out of shape, a corrective (regulation) course of asphalt should beapplied first (Figure 2.2). This will reduce the effects of differential compaction of subsequentlayers and enable the best possible riding quality to be achieved. Alternatively cold milling may beused to correct surface shape, as well as remove any unsuitable or unstable materials.

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Figure 2.2: Shape correction

2.3 Correction of Defects in Concrete Surfaces

Remedial action may be required to ensure that slabs are firmly supported and that the joints are ingood condition. Joints and cracks in the slabs will be reflected in the asphalt overlay. Slabsshould be firmly supported by the sub-base, and if necessary corrected by mud jacking, groutinjection or other appropriate means.

Joints should be sealed with suitable hot bituminous filler. Techniques for control of reflectioncracking include the use of a bandage of fabric impregnated with bituminous materials over thejoints, or saw cutting of the asphalt overlay and formation of a sealed joint in the asphalt.

2.4 Cold Milling

Planing or milling of the surface is used to remove existing asphalt that is unstable, poorly shaped

or where the new asphalt must match existing road levels, kerb and gutter, etc.

Common cold milling applications include:

removal of surface that is uneven or rough

removal of rutted, unstable or fatty materials

restoring desired profile by removing excess crown or cross fall

excavation of areas to be patched

creation of tapers for smooth transition or matching of levels of adjoining work

texturing as a bonding technique or for improving surface texture depth.

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The benefits of cold milling include:

old pavement material is removed, eliminating build-up.

the need for levelling or regulating courses or material may be reduced or eliminated.

differential compaction problems from uneven bases are eliminated.

it may provide a source of recyclable Reclaimed Asphalt Pavement (RAP).

it can be done quickly with minimum inconvenience to the traffic flow.

it allows neat and speedy excavation for patching.

The depth of milling (removal of material) will depend on:

the purpose

the material in the existing pavement.

Depths of up to 150 mm are possible in one pass, except for the smallest machines (cutting width

less than 500 mm) that are generally limited to a maximum depth of 100 mm. If only the wearingcourse is to be replaced, the usual depth is in the range 25 to 50 mm, which corresponds to thelayer thickness for a 10/14 mm asphalt mix.

Milling used for functional purposes such as improving skid resistance, drainage, or rehabilitationof the wearing surface generally requires only minimal milling depth.

Where possible, the size of the profiler should be matched to the size and productivity of the job.Table 2.1 provides a general guide to suitable profiler size based on typical production rates for adepth of cut of up to about 80 mm and appropriate job size that is suited to the productivity of themachine.

Other considerations include: The depth of the existing asphalt layer should be determined so that unnecessary exposure

of the granular base to possible damage and moisture ingress, by removal of the wholedepth of asphalt, is avoided.

After milling, care should be taken to avoid leaving thin layers that are likely to be stripped offby traffic. The minimum thickness of asphalt in the old layer left in place should beapproximately 30 mm.

Good control of the milling is required to ensure a consistent finished profile and a smoothriding surface.

Care should be taken where there are numbers of service pits and fittings in the milling area.

The presence of geotextiles in the existing pavement can cause problems during milling.

Profilers with rear conveyor discharge can reduce traffic disruption by operating within anarrower width.

Ramping the ends of the work with temporary materials (e.g. cold-mix) may be required toreduce traffic hazard risk.

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A cold milling machine can be used as an alternative to ripping and crushing equipment, especiallywhere asphalt is to be removed for recycling. The particle size of the RAP obtained from coldmilling is determined by:

depth of cut

forward speed of the machine quality of material

age and condition of the pavement surface

ambient temperature.

Table 2.1: Guide to selection of profiler

Suitable job size (m2)Width of profiler(mm)

Production rate(m2/h) 0500 5001000 10002000 >2000

150 1030

350 4060

500 6080

600 70100

1000 200500

1900 300600

2000 400700

2100 500900

2.5 Pre-treatment of Granular Pavements

On crushed rock or natural gravel pavements, a sprayed bituminous prime or primerseal should beapplied before asphalt is placed.

Although desirable, a primer or primerseal is not always necessary where the asphalt thickness isin excess of 100 mm.

A prime is used to penetrate the surface to protect the base against weather and assist inachieving a bond between the granular pavement and the asphalt layer.

A primerseal is used where it is desired to run traffic on the granular pavement for a period of timebefore placing asphalt.

Sufficient time should be allowed for curing of primerseals prior to paving. A cutback bitumenprimerseal may require up to about 12 months curing to allow evaporation of the cutter oil.Bitumen emulsion primerseals contain little or no cutter and do not require extended curingperiods. Without proper curing, cutter oils may bleed though asphalt surfaces causing softening ofthe layer or carrying of binder to the surface.

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2.6 Pre-treatment of Concrete Surfaces

For overlays on concrete pavements the use of a primer is generally recommended to ensure abond is achieved with the asphalt. A tack coat may also be required, but by itself will often lack thepenetration into the concrete necessary to provide a good bond.

Concrete bridge decks require priming or sealing using a variety of treatments before overlayingwith asphalt. Cutback bitumen treatments must be left for sufficient time for cutters to evaporate.

2.7 Public Utilities

The levels of public utility surface fittings (covers, access points, etc.) should be adjusted prior topaving to match the proposed surface levels or masked and clearly marked and recorded forimmediate recovery after the asphalt work (see also Section 8.10).

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3 CLIMATIC CONDITIONS

3.1 General

Ideally, paving operations should be planned for the daytime when the weather is warm to hot and

when rain is not expected before completing the compaction.

Asphalt cools rapidly in thin layers and when pavement and ambient temperatures are low. Windand excessive moisture will also increase the cooling rate. Unless quickly and adequately rolled,these conditions will result in a low degree of compaction being achieved and a subsequentreduction in the service life of the asphalt.

3.2 Pavement Temperature

Generally, asphalt layers of less than 40 mm thickness should not be placed when pavement

temperatures are less than about 10C (15C for open graded asphalt and mixes containingpolymer modified binders). Higher minimum pavement temperatures are desirable where cooling

rates are increased by wind.

Paving at lower pavement temperatures will generally be satisfactory for layers of 40 mm andthicker. However, mix temperatures and/or compaction densities should be closely monitored toensure that compaction standards are achieved (see also Section 9).

3.3 Moisture

When paving, the pavement should be dry, except for granular surfaces that may be slightly damp.Work may be permitted on a slightly damp bituminous surfaced pavement, provided it waspreviously tack coated.

Paving should not proceed if rain appears imminent.

3.4 Risk Management

Ideal conditions do not always exist and at times decisions have to be made as to whether pavingshould proceed. In these instances a risk management approach should be adopted.

Paving under adverse conditions will involve some risk of poorer density and surface finish,particularly where handwork is involved. This can lead to a reduction in the life expectancy and theearly replacement of the asphalt pavement.

In such circumstances, particular attention must be paid to planning and execution of work to

ensure that required standards of density, joint construction and handwork are achieved.

The additional effort involved, and potential risks, should be balanced against the additionalbenefits to the community, from completing the work at that time.

Reasons for proceeding may include:

minimisation of disruption to road users

political or other time constraints

critical path constraints when part of a larger project.

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4 TACK COATING

4.1 General

A tack coat is a light application of bituminous binder that provides a bond between the existing

surface and the new asphalt layer.

Generally, rapid setting cationic bitumen emulsion is used for tack coating although medium settinggrades and anionic emulsions may be used in dry conditions.

Medium curing cutback bitumen may also be used for tack coating. A curing period for evaporationof the cutter is necessary.

Surfaced pavements require tack coating before commencing asphalt paving except that tack coatmay be omitted when placing asphalt over a freshly placed, untrafficked, asphalt or clean primedsurface.

A tack coat should not be applied directly to natural gravel or crushed rock surfaces because of itsinability to penetrate the surface and the likelihood of pick-up of tack coat and underlying granularmaterial by vehicles and paving equipment. These surfaces must be first primed or primersealed.

Tack coating should not be applied if the pavement surface is wet.

4.2 Application

The tack coat should be applied by a mechanical sprayer with a spray bar to ensure an evenapplication (Figure 4.1). Hand spraying or brushing may be used but this is undesirable andshould be limited to small irregular shaped areas inaccessible to a mechanical sprayer.

Figure 4.1: Tack coat sprayer in operation

All contact surfaces should be tack coated, including cold joints.

Generally, tack coat is applied at a rate of 0.15 to 0.30 L/m2 of residual bitumen.

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If it is necessary to reduce the viscosity of the emulsion, it may be diluted with water or warmed tonot more than 50C. Dilution must be performed with care to avoid premature breaking. Whendiluting, water must be added slowly to the emulsion.

Asphalt should not be placed until the emulsion has fully broken; i.e. the tack coat has turned from

its original brown colour to a shiny black.

Some tack coating material may be picked up on truck tyres. If the pick up is excessive, a lightapplication of coarse sand or 5 mm aggregate should be broadcast across the areas traversed byconstruction traffic.

4.3 Precautions

A number of precautions are required when tack coating:

Avoid over-application of tack coat. Surplus binder from tack coating may lead to flushing,shoving or instability of the finished work. Over-application may occur in surface depressionsand any excess should be removed or dispersed by brushing.

Protect adjacent property, kerbs and gutters, guard rails, bridge handrails, etc., againstsplashing by masking or screening.

The work area should be cordoned off, and pedestrians and vehicular traffic kept well clear,to protect against direct contact with tack coat material and over-spray which can be carriedsubstantial distances by wind.

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5 TRANSPORT OF ASPHALT

5.1 General

Asphalt should be transported in such a way as to minimise the loss of heat, segregation of the mix

or contamination by foreign matter.

The mix should be delivered at a uniform rate, within the capacity of the spreading and compactingequipment, to enable a continuous paving process. To reduce the cooling of the mix, deliveriesshould be made by the shortest practical route, and waiting time and delays on site should beminimised.

5.2 Vehicles

Delivery trucks should have clean, smooth, metal bodies and a minimum capacity of 8 tonnes. Thesize and number of trucks is important to both the smooth running of the job and the quality of thework.

Figure 5.1: A Flocon non-tipping delivery truck

Delivery trucks usually have tipping bodies and can include semi-trailers and dog trailers. Non-tipping, Flocon type bodies, may also be used (Figure 5.1).

Truck bodies should have sufficient overhang (about 0.5 m) to enable tipping into the paver hopperwithout spillage.

During transportation, the asphalt should be covered with canvas or other similar waterproof cover.Transporting asphalt over long distances may require heavy duty covers and, in some instances,

insulation of truck bodies using oiled plywood or other suitable material, to minimise heat loss.

Trucks should be driven by experienced personnel. Care should be taken when dumping the mixinto the paver hopper to avoid spilling mix onto the pavement in front of the paver, or jarring thepaver.

Trucks should reverse to a position just short of the paver to allow the paver to make contact withthe stationary truck and push it forward. Trucks should only apply brakes sufficiently to maintainthe truck in contact with the paver.

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5.3 Release Agents

Internal surfaces of truck bodies should be clean so as to prevent the mix from adhering. Releaseagents may be used sparingly to facilitate easy unloading of mix. Any excess release agent shouldbe removed before loading asphalt, particularly if it contains diesel or flux oil.

5.4 Organisation

Transport operations should be organised to ensure continuous paving operations, taking intoaccount:

the number of trucks required and their availability

meal breaks

haulage distance/travelling time

the times at which the mix can be placed, due to site availability

site conditions and access restrictions that may limit the size of truck that can be used (e.g.

overhead cables).

Suitable communications between the mixing plant and the site are essential for effective controland organisation. Preferably, each truck should be in radio contact with the mixing plant and thesite.

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6 TRANSFER OF ASPHALT FROM TRUCKS TO PAVER

For most applications, asphalt is dumped directly from trucks into the front hopper of the paver.

Where project circumstances are suitable, a materials transfer device may be used to improve

control over feeding asphalt materials to the asphalt paver. In this case, delivery trucks dumpasphalt into a materials transfer device that then feeds it into the paver hopper by means of aconveyor belt.

Materials transfer devices (Figure 6.1) generally hold about 20 to 25 tonnes of asphalt.

Figure 6.1: Materials transfer device

Use of materials transfer devices provides advantages in terms of:

minimising the paver being bumped by trucks

acting as a surge bin for asphalt delivery to minimise unplanned paver stops resulting frominterruptions to asphalt supply

reducing segregation of the asphalt in the paver hopper

the ability to incorporate remixing facilities to reduce influence of mix segregation andtemperature variation during loading and transport.

If used correctly, materials transfer devices can lead to improved uniformity and smoothness of the

paved finish.

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7 PAVER PERFORMANCE AND SCREED OPERATION

7.1 General

Pavers operate on the floating screed principle, spreading material in a uniform layer to a desired

thickness and longitudinal and transverse shape.

The paver also provides primary compaction of the mix (which is completed by subsequent rolling).

Figure 7.1: Typical paver

The principal components of a self-propelled paving machine (Figure 7.2) are:

tractor unit

screed unit

automatic sensing and levelling equipment.

Figure 7.2: Typical paver components

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7.2 Tractor Unit

The tractor unit provides the power to drive the paver and includes:

a traction unit (usually pneumatic tyred)

a receiving hopper

a feed (slat) conveyor system

lateral spreading augers

controls.

The asphalt in the hopper is transferred by slat conveyors, through adjustable flow gates, to thetwo individually controlled augers that spread the material laterally and evenly in front of the screed(Figure 7.3).

Figure 7.3: Flow of material through paver

The basic adjustments to components of the tractor unit that affect paver performance and outputare:

Paver speed (see Section 7.3.3).

Flow control gates. Ideally, the flow gates should be adjusted so that the augers andconveyors run for the entire operating time (and not less than 80% to 90%) to provide asconstant a head of material as possible.

Slat conveyor speed.

Auger height adjustment. Generally, the bottom of the augers should be about 50 mm to75 mm above the finished mat surface to allow for correct feeding of material.

Auger feed. Generally, auger feed is controlled automatically using paddle arms, whichsense the level of material at the augers. The paddle switches also regulate the conveyorspeed.

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Auger box size. On some pavers larger auger boxes can be used to increase the quantityof material for paving of deep lifts.

Overfeeding of augers can result in the following mat deficiencies:

ripples

auger shadow (variable texture)

short and long waves

other mat blemishes due to cooling of the mix

premature auger wear.

Underfeeding or a fluctuating feeding of augers will cause a poor quality riding surface.

7.3 Screed Unit

The screed unit consists of a screed plate, compaction device(s) (i.e. tampers and/or vibrators),

and thickness controls. It is connected to the tractor unit of the paver by towing (levelling) arms,which are pin-jointed.

Figure 7.4: Components of screed unit

The screed is supported by the mix and automatically rides up and down seeking the level that isparallel to the line of pull. This arrangement gives the screed a floating action and allows it to

spread to a relatively uniform surface despite irregularities in the underlying pavement.

Several factors such as paving speed, head of material, asphalt mix consistency, pre-compactionand screed angle of attack, all influence the vertical position of the screed. Variation in any ofthese factors will cause a change in mat depth, density and/or texture.

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The three primary factors that influence the vertical position of the free-floating screed (Figure 7.5)are:

Factor F1 angle of attack

Factor F2 head of material

Factor F3 paving speed.

Understanding the inter-relationship and controlling these three variable factors is essential toproducing high quality asphalt paving. Where possible, all other factors should be kept constant.

F3

F2

F1

PIVOT POINT

SCREED DEPTH CRANK

TOW POINT

Figure 7.5: Factors influencing vertical position of the free-floating screed

7.3.1 Angle of inclination

The thickness of the spread mix is changed by altering the angle of inclination (attack F1 in Figure7.5) of the screed plate.

Altering the angle of attack is effected by:

adjusting the angle of the screed plate in relation to the levelling arms, using the depth

adjustment control (e.g. turnbuckle, crank, winder etc.)

raising or lowering the tow (pivot) point of the levelling arms.

Changing the angle of attack allows more or less mix to pass under the screed plate. This causesan imbalance in the vertical forces and the screed plate rises or falls until a new equilibriumposition is reached when the vertical motion stops. A gradual change in thickness is thus achieved(Figure 7.6).

The response of the screed to a change in the angle of attack is not immediate. It takes a distanceof approximately four to six times the length of the levelling arm (i.e. the natural paving length) forthe screed to reach a new equilibrium position (

Figure 7.7).

Therefore, it is desirable that:

adjustments to the angle of attack, to produce changes in thickness, be made only as aresult of unusual conditions at the paver, and not indiscriminately by the screed operator

the natural paving length be allowed to reflect one change before making another.

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MANUAL CONTROL WITH SCREED DEPTH CRANKS

Tow point

AUTOMATIC CONTROL OF TOW POINT

Tow point

Figure 7.6: Response to change in angle of attack

Figure 7.7: Screed response to a step-function di sturbance

7.3.2 Volume of material in front of screed

The balance of forces on the screed, and hence the quality of the mat, is assisted by maintaining aconstant head of material in front of the screed (F2 in Figure 7.5, also see Figure 7.8). Control ofthe volume of material in front of the screed (i.e. in the auger chamber) is achieved by:

proper setting of the adjustable flow gates

uniform operation of slat conveyor system

operation of the augers (which are generally controlled by sensors on the surface of the mix).

The volume of material in the auger chamber should be maintained at 50% to 75% of the height ofthe auger. Increasing the volume increases resistance, which causes the screed to rise.Decreasing the volume allows the screed to fall. Similarly, changes in the consistency in the mixdue to changes in temperature or composition, also increase or decrease the resistance, resultingin changes to level, density and texture.

Screed path

Directionof paving

Step function disturbanceTransient response of screed

Tow point pathSTEP AMPLITUDE = 100%

L = LEVELLING ARM LENGTH

0 1L 2L 3L 4L 5L 6L

100%63%

87% 95% 98% 99%

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CORRECT HEAD OF MATERIAL

CORRECTDEPTH OF MATMAINTAINED

EXCESSIVE HEAD OF MATERIAL

SCREED RISES DUETO EXCESSMATERIAL FORCEDUNDER NOSE OFSCREED

SCREED SETTLESDUE TOINADEQUATESUPPORTINGMATERIAL

INSUFFICIENT HEAD OF MATERIAL

Figure 7.8: Head of material

7.3.3 Paving speedChanges in the forward speed of the paver (F3 in Figure 7.5) can significantly affect the matquality, in terms of:

the thickness of the mat

the compaction achieved by the screed.

Changes in paving speed directly affect the head of material and consequently, the angle of attack.Increasing paver speed will decrease mat depth. Decreasing paver speed will increase mat depth.

If the paver speed is increased, the mix flowing under the screed is exposed to compactive forcesfor a shorter period, producing a mat with reduced density and reduced compacted thickness.

Therefore, any interruption in the paver speed will be reflected in the quality of the finished ridingsurface, and should be avoided. Changes in the paver speed can be caused by:

poor planning of supply of asphalt to the paver

trucks bumping the paver when tipping loads

trucks holding their brakes while paver is attempting to push, resulting in loss of pavertraction.

The effect of trucks on paver progress can be avoided through experience and co-operationbetween truck driver and paver operator.

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7.3.4 Primary compaction by screed unit

The design of the screed enables primary compaction of the mix. This is achieved by incorporatingvertically oscillating tamper blade(s), immediately ahead of the screed plate, or vertical vibration ofthe screed plate.

The degree of primary compaction may be varied by adjusting either the amplitude and/orfrequency of vibration. To achieve consistent compaction, these screed variables should also beset to suit the layer depth.

Screed compaction of deep lifts requires:

low frequency vibration

high impact forces (high amplitude).

Screed compaction of thin layers requires:

high frequency vibration

low impact force (low amplitude).

The degree of compaction will vary with the speed of the paver, with higher densities achieved atlower paver speeds.

Pavers typically achieve compaction to about 85% of relative density although this will vary with thedesign and weight of the screed assembly. Screed assemblies using single or multiple tamperswill generally achieve higher densities than vibration alone.

7.3.5 Crown adjustment of screed

The crown adjustments at the centre of the screed enable control of the transverse profile of the

finished surface. Separate adjustment is provided for the leading and trailing edges of the screed.

The forward adjustment is the lead crown which controls the flow of material beneath the screed.The lead crown should always be slightly greater than the tail crown.

The rear adjustment or tail crown controls the finished contour of the mat.

The crown adjustments should be checked daily before paving. This can be carried out by raisingthe screed and using a string line to measure both the lead and tail crowns.

The measurements of the lead and tail crowns (of the raised, unsupported screed) will, throughexperience and familiarity with the particular paver, indicate the crown that will be produced in the

finished mat.

7.3.6 Screed extensions

The width of paving may be varied using extensions to the screed. These may be rigid boxes thatare bolted to the screed, or hydraulically operated extensions (Figure 7.9).

Paving widths of up to 8 m are possible using screed extensions, although widths greater than 5 or6 m are not commonly used due to the difficulty of maintaining a consistent head of material acrossthe full width of the screed.

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When using screed extensions, care should be taken to:

ensure alignment of extensions matches that of the main screed

ensure auger extensions are fitted to provide an adequate head of material in front of thescreed extensions

ensure tamping/vibration is consistent across whole width of mat.

7.3.7 Care of screed

The condition and operation of the screed will directly affect the quality of the finished pavement.

The screed should be lifted and checked before commencing paving each day for:

loose or worn screed plates

poor shape or distortion that can be a result of overheating of screed

misalignment of screed extensions and main screed

incorrect crown adjustments.

Figure 7.9: Paver with hydraulic screed

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7.4 Automatic Sensing and Levelling Equipment

This equipment is used to control the operation of the screed unit in a pre-determined relationshipto either:

the existing surface

an adjoining finished surface

a fixed reference line.

These controls are used to maintain levels, mat thickness and crossfall within required limits.

A sensor box controls the angle of attack by changing the vertical position of the tow point. Thesensor box may be used with a variety of devices for achieving the specified surface levels(Section 8.9).

7.5 Paver Stoppages

When the paver stops the equilibrium conditions of the screed can change due to: a slight settling of the screed

cooling of the material in front of the screed.

When the paver starts moving again, the screed will rise or fall to achieve a new equilibriumposition. These effects can be eliminated or minimised if the paver moves continuously.Sometimes it is not practical to keep the paver moving continuously. In these cases the stoppingand accelerating of the paver should be achieved quickly but smoothly.

During prolonged paving stoppages, the settling of the screed may cause a permanent depressionof unacceptable depth in the pavement surface. In such circumstances the mat should be cut back

to remove the depression and a transverse joint constructed as described in Section 8.7.

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8 SPREADING OPERATIONS

8.1 General

Asphalt should be spread and compacted uniformly in order to:

limit segregation

produce a homogeneous product

achieve a density that delivers the intended design performance of the asphalt

provide the specified thickness of asphalt

achieve the specified riding quality.

Spreading may be carried out by self-propelled paver, grader or hand methods. Whereverpossible self-propelled pavers should be used as they provide greater control during spreading anda superior surface finish. Paver operations are also quicker and more economical. The use of

such equipment forms the main focus of this Chapter.

8.2 Setting Out

The work should be set out in advance with the order of runs and the position of joints for eachlayer clearly defined.

Setting out will be influenced by the desirable location of joints, minimisation of handwork, levelcontrol procedures and provision for traffic.

8.3 Spreading by Paver

Spreading is designed to be a continuous operation. The rate of delivery of the asphalt should be

arranged so that the paver can operate at a uniform speed. Paving should not commence untilsufficient asphalt is on site to ensure continuous operation.

At the start of each paving run, and at each cold transverse joint, the paver operation should be asfollows:

check crown adjustment

position the screed on wooden blocks at the height of the uncompacted layer

set the tow points at the required uncompacted mat thickness

heat the screed plate to the temperature of the mix

set hopper gates to ensure constant flow of mix.

After laying a short length of mat, the paver set up should be checked as follows:

flow gates delivering suitable flow of material

screed heat sufficient to avoid dragging of surface

settings of tamper(s) and/or vibrators

screed depth control and thickness of uncompacted asphalt

functioning of automatic controls.

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A 3 m straight edge should be used at frequent intervals to check surface shape and smoothness,particularly at joints and paver stops.

The spread material should be examined constantly for faults in texture. Any faults such assegregation or tearing of the surface should be corrected before compaction.

To increase output and eliminate or reduce cold joints, two or more pavers may be operated inechelon. The pavers should work close enough so that the temperature of the uncompacted edge

behind the advance paver is not less than 100C (120C for PMBs) when the following pavermatches the longitudinal joint.

8.4 Spreading by Grader

Spreading by grader may be used only in special circumstances. It should be discouragedbecause of difficulty in achieving compaction and ride quality requirements and promotessegregation of the asphalt. The method should only used for applications such as:

temporary access roads

patching work where it is not practical to operate a paver.

Points to be observed in placing asphalt by grader include:

prompt spreading is essential to avoid cooling and loss of workability

placing of thin layers may be difficult

grader operation is helped by uniform spreading from trucks; a slight excess of materialallows a head of material in front of the blade

handling of asphalt should be kept to a minimum to avoid segregation, more rapid cooling,and the effect of partial compaction by the grader wheels.

8.5 Spreading by Hand

Hand spreading should always be kept to a minimum. Hand placing of open graded asphalt, ultrathin mixes and asphalt containing PMBs is particularly difficult and requires extra care.

Shovelling, raking or other disturbances of the surface after machine spreading should be kept tothe minimum and completed quickly, before the mix cools below the minimum temperature foreffective compaction.

Asphalt should be placed in full shovelfuls and not cast or thrown over the new mat or area to bepaved. Generally, a slight excess of material is placed that is then screeded to level.

Wooden lutes are most commonly used for hand screeding. Their light weight enables smoothscreeding of hot materials. Where practicable, the screeding should be done with a head ofmaterial in front of the lute, and using a single pass that leaves a uniform surface of fresh asphalt.Excessive working of the surface leads to separation of coarse materials, and should be avoided.The mix should never be thrown, scattered or loosely raked.

Coarse segregated materials resulting from handwork must be completely removed from thesurface along with any other excess material. Attempting to avoid wastage and clean-up of surplusasphalt is false economy if it results in inferior quality in the finished work.

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Handwork should be carried out as quickly as possible to avoid excessive cooling of the asphalt.All surface correction should be completed prior to commencing compaction.

The only exception to hand broadcasting or scattering of asphalt material is in correcting minortearing or isolated areas of open texture in paver spread asphalt. A shovelful of asphalt, skilfully

broadcast over the unrolled asphalt, can provide additional material to correct open textured areas.Such hand broadcasting should not be undertaken indiscriminately. If spreading texturedeficiencies persist, the source of the problem should be determined and corrected. Possiblecauses include incorrect paver screed temperature, front and rear settings of paver crown, andsegregation of asphalt mixes as a result of deficiencies in mixing, loading or spreading practices.

Walking on the surface of the uncompacted mix should be avoided at all times.

Figure 8.1: Handwork

8.6 Layer Thickness

The thickness of asphalt layer(s) within a pavement should normally be determined by thestructural requirements of the pavement. For initial treatments, the determination of thickness ispart of the structural design. For retreatments, the thickness will depend on the amount of surfacecorrection and structural strengthening required. If this is considerable, it may be necessary to layone or more corrective courses before the final course.

The thickness and type of course will determine the nominal size of the asphalt mix. The nominalsize of an asphalt mix is an indication of the maximum particle size present and is usuallyexpressed as a convenient whole number above the largest sieve size to retain more than 0% andless than 10% of the aggregate material.

The selected nominal size of mix will be determined by:

location of asphalt course in pavement

proposed compacted thickness of layer

functional requirements of asphalt layer.

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Table 8.1 provides a guide to appropriate mix sizes for ranges of course thickness.

Table 8.1: Typical asphalt layer thickness

Nominal mix size (mm) Compacted layer thickness (mm)1

5 15 to 207 20 to 30

10 25 to 40

14 35 to 55

20 50 to 80

28 70 to 110

40 100 to 160

Notes:

1 The minimum thickness may need to be increased when placing thin layers in cool conditions or using less workable mixes.

Minimum thickness may not apply to some ultra-thin asphalt applications.

Maximum thickness may be exceeded provided that asphalt surface shape requirements can be adequately achieved.

Generally, asphalt should be placed in layers with a compacted thickness of not less than 2.5 timesthe nominal size of mix in order to:

prevent the mix tearing during laying

assist the compaction process by allowing the aggregate particles to mechanically interlock.

The minimum thickness may need to be increased when placing thin layers in cool conditions orusing less workable mixes.

Some ultra-thin asphalt surfacing types can be successfully laid with a layer thickness as little as

1.5 times the nominal mix size provided that they are combined with a suitable seal coat or tackcoat to effectively bond the asphalt to the underlying pavement.

In wearing and intermediate course applications the maximum compacted layer thickness isgenerally limited to around 4 times the nominal mix size. Greater thicknesses may be used toachieve practical placing thickness; for example a requirement for 50 mm of 10 mm asphalt isbetter achieved with one 50 mm layer than two 25 mm layers. Where the layer thickness exceedsfour times the nominal size, it may be more cost effective to use a larger nominal size mix althoughlarger sized mixes are also more prone to segregation and may not necessarily provide the surfacefinish required.

Base course applications may involve multiple layers with the maximum layer thickness being

largely determined by practical placing considerations taking into account the total asphaltthickness and ability to achieve the required finished shape and riding qualities. For mostapplications, 20 mm is selected as the largest nominal sized mix.

The thickness of asphalt layer placement may be specified in a number of ways, including:

a required average or nominal thickness

a minimum compacted depth

a rate of kilograms per square metre

a rate of square metres per tonne

placement to fixed levels.

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The thickness of the uncompacted mat depends on the degree of compaction achieved by tampersand screed. It may be up to 20 to 25% thicker than the required compacted thickness. Fieldexperience will determine the required uncompacted thickness.

The thickness of the uncompacted and compacted layers should be checked at 10 to 15 m

intervals at the start of each run. The screed can be adjusted to give the desired thickness. Theuncompacted layer should be measured directly by probing the mix in the body of the run or bymeasuring adjacent to the outside edge. The compacted layer thickness may be measured at theoutside edge of the run using a straight edge, if the underlying crossfall is uniform.

When paving to specified levels, regular checking is required after compaction.

8.7 Joints

Construction joints in an asphalt layer are potential planes of weakness and imperfection that canbe the first locations to deteriorate. Poorly constructed joints that are more permeable than therest of the asphalt mat can lead to the ingress of moisture into the pavement, and also cracking

and ravelling.

The number and extent of joints in asphalt layers should be kept to a minimum and the pavingpattern should be designed accordingly in advance of the work.

Correct jointing technique will ensure that the two mats are joined in such a way as to minimisedifferences in density, texture, shape and level and also minimise the amount of deterioration atjoints caused by traffic.

Longitudinal joint

Longitudinal joint

Base course

Intermediate course

Wearing course

150 150mm mm

Figure 8.2: Overlapping of longit udinal joints in successive courses

8.7.1 Longitudinal joints

Longitudinal joints are construction joints in an asphalt layer parallel to the paving run.

The following procedures should be adopted to ensure satisfactory longitudinal joints:

For wearing courses, longitudinal joints should be continuous and parallel to the road centreline. They must always be located away from traffic wheel paths. Where possible theyshould coincide with proposed lane markings. If this is not possible, the wearing course jointshould be located in the centre of the lane.

Good alignment of longitudinal joints is achieved by following a paving line marked on theroad, and with pointers attached to the paver as a guide to the operator. Poor or unevenalignment of the first lane makes it difficult to evenly match the next pass of the paver.

Joints in successive courses should be offset or staggered by at least 150 mm (Figure 8.2) tominimise the possible occurrence of reflective cracking.

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All excess material or segregated particles should be removed and discarded and notincorporated into the mat (as this can increase the roughness of the finished surface).

Work should be arranged to avoid longitudinal joint faces being left exposed overnight.Where this is not practical, traffic should be excluded or temporary ramps used and trimmedback the next day.

Compaction of the unconfined edge of the first lane is important. It is critical that the roller makethe same number of passes over the edge of the first lane as are made over the rest of the width ofthe lane. Generally, the edge of the roller drum should extend over the free edge by about150 mm (Figure 8.3). This ensures vertical compaction of the unconfined edge and reduces anytendency for the asphalt to shove sideways during the compaction operation.

Overhang150mm

Double drumvibratory roller

Lane 1

Figure 8.3: Overhang of outer edge

Operating the steel roller inside the unsupported edge (Figure 8.4) tends to cause the asphalt tospread. Longitudinal cracks may also open up along the edge of the drum. Placing the edge ofthe roller directly over the unsupported edge (Figure 8.5) will avoid cracking but will still cause theunsupported edge to move sideways.

Figure 8.4: Poor roller placement

Figure 8.5: Better roller placement


Lane 1


Lane 1

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Hot joints are preferable to cold joints but are usually only possible when using two pavers inechelon, e.g. on large construction works (Figure 8.6). The distance between pavers, operating inechelon, should not exceed 80 m.

A hot joint is one where both the new mat and the adjacent mat are still workable and have not

been compacted. The hot joint should be constructed by leaving an uncompacted stripapproximately 150 mm wide along the edge of the first placed lane. Both sides of a hot jointshould be rolled simultaneously.

Figure 8.6: Paving in echelon (hot joints)

Figure 8.7: Cutting disc attached to steel roller

When constructing cold longitudinal joints, the first lane should be compacted as described above.

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In some cases, before the longitudinal joint between two adjacent paver lanes is constructed, theedge of the previously placed mix is cut back to remove material that may have a lower densitythan the main portion of the mat. This is accomplished with a cutting wheel that is usually attachedto a roller (Figure 8.7). The cut face should be lightly tack coated before the adjacent lane isplaced.

Cutting back of the exposed edge is generally not necessary if adequate joint constructionprocedures are followed as described in this section. Tack coating is generally not required forclean, untrimmed edges.

Lane 1 Lane 2

Overlap25 - 40 mm (max)

Figure 8.8: Correct overlap of longitudinal joint

The key to the construction of good longitudinal joints between adjacent paving lanes is theamount of overlap between the new and previously placed mats. The typical overlap is not morethan 25 to 40 mm (Figure 8.8). The height of the new mix above the compacted mix is alsoimportant and should be about 6 mm for each 25 mm of compacted mix ( of thickness).

If the right amount of mix is put in the right place, little, if any, hand raking is required. Overlappingmaterial may be pushed back with a lute to form a bump on the new mat. When rolled, thismaterial is pinched against the vertical face of the first mat to increase density at the joint. If toomuch material is left over the joint, however, the roller will tend to leave a bump that cannot beremoved by further rolling. If there is an excess mix, it should be pulled away from the joint, pickedup and discarded. It should not be thrown across the new mat.

Excess raking of the joint is highly detrimental to the long term performance of the joint with apotential for lower density and poor appearance from segregated materials.

Rolling of longitudinal joints is undertaken in accordance with procedures described in Section 9.8.

8.7.2 Wedge joints

New techniques are being developed to improve the construction of longitudinal joints usingdevices such as a plate attached to the paver that forms an inclined face at the edge of the mat sothat the following adjoining mat forms an overlapping wedge. Such techniques are not commonly

used in Australia but continued improvement in this area could result in higher standards oflongitudinal joint construction.

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8.7.3 Transverse joints

Transverse joints are construction joints in the asphalt paving, at right angles to the direction ofpaving, and are formed:

at the start and finish of each paving run

when the work is disrupted causing

cooling of the asphalt and/or settlement of the screed

when resuming on the next day.

Transverse joints can be a common cause of poor riding qualities in a finished asphalt wearingsurface. The importance of correct transverse joint preparation and formation techniques cannotbe over-emphasised.

Transverse joints should be approximately at right angles to the direction of paving. They shouldbe staggered by at least 1 m between successive layers and between adjacent runs to avoidplanes of weakness and possible water entry through the whole asphalt thickness.

A paving run may be finished against a timber bulkhead to ensure a straight, vertical, wellcompacted edge, or may be feathered out (ramped) and compacted.

For ramped material, the transverse joint is formed by the subsequent trimming back to a linewhere the minimum layer thickness exists (Figure 8.9).

When finishing flush against an existing surface, the paver should maintain sufficient material infront of the screed to pave to the end of the run. It is poor practice to finish machine spreadingseveral metres before the end of the run, lifting the screed, dumping asphalt from the paver, andthen hand spreading the remaining material to finish the run. This hand spread material rarelymatches the surface finish and uniformity of the machine laid material.

Trimming of joints, and edge cutting, may be carried out using:

a cutting disc attached to a steel wheel roller (Figure 8.7)

a concrete saw

a jackhammer with spade attachment

milling machine.

To facilitate subsequent trimming of a joint, a short section at the end of the run may be removedbefore rolling, and re-laid on paper or sand to prevent adhesion of the asphalt to the lower layer.

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