New Seal Design Guide

AP-T68/06

AUSTROADS TECHNICAL REPORT

Update of the Austroads Sprayed Seal Design Method


First Published September 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.

Update of the Austroads Sprayed Seal Design Method ISBN 1 921139 65 X

Austroads Project No. TT1132

Austroads Publication No. APT68/06

Project Manager Gary Liddle, VicRoads

Prepared by Allan Alderson, ARRB Group

Published by Austroads Incorporated Level 9, Robell House 287 Elizabeth Street

Sydney NSW 2000 Australia Phone: +61 2 9264 7088

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

www.austroads.com.au

Austroads believes this publication to be correct at the time of printing and does not accept responsibility 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.


Sydney 2006

Austroads profile Austroads is the association of Australian and New Zealand road transport and traffic authorities whose purpose is to contribute to the achievement of improved Australian and New Zealand road transport 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 Standing

Committee on Transport (SCOT).

Austroads membership Austroads membership comprises the six state and two territory road transport and traffic authorities 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 council consisting of the chief executive officer (or an alternative senior executive officer) of each of its eleven 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 in the road industry. It aims to be the Australasian leader in providing high quality information, advice and fostering research in the road sector.

ACKNOWLEDGEMENTS This document was prepared by a Working Group from the Bituminous Surfacing Research Review Group comprising:

Mr Kym Neaylon Department for Transport, Energy and Infrastructure South Australia (Convenor)

Mr Walter Holtrop Australian Asphalt Pavement Association

Mr Ray Gaughan Roads and Traffic Authority, NSW (to October 2004)

Mr Sai Yin Roads and Traffic Authority, NSW (from October 2004)

Mr John Esnouf VicRoads, Victoria

Mr Russell Spies Department of Main Roads, Queensland

Mr Allan Alderson ARRB Group (Technical secretary) Technical Writers Mr Walter Holtrop

Mr John Rebbechi

Mr Allan Alderson

PREFACE This document replaces previous Austroads guides for the design of binder rates of application and aggregate spread rates for sprayed seals, including:

Austroads Design of Sprayed Seals, Austroads 1990. Austroads Provisional Sprayed Seal Design Method: Revision 2000, AP-T09/01, Austroads

2001.

Practitioners Guide to the Design of Sprayed Seals Revision 2000 method, AP-T17/02, Austroads 2002.

The document has been based on AP-T17, but has been considerably extended, and incorporates selection criteria not included in the earlier document.

This design of sprayed seal surfacing method has been prepared for use in conjunction with the Austroads Sprayed Sealing Guide (Austroads, 2004). It provides a guide to the determination of rates of application of binder and aggregate spread rates for most commonly encountered conditions. Designers are reminded that provision of a surfacing treatment that provides the desired performance characteristics also relies on selection of an appropriate treatment and adequate preparation of surfaces prior to treatment.

Key Points are highlighted throughout the document to draw to the attention of designers, particularly those who may be new to or have limited experience in seal design, items such as: good practice, advice on interpretation of data, the influence of traffic, and potential problems or risks associated with the treatment selected or the design being considered. These Key Points are enclosed in a lightly shaded box.


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SUMMARY

In 1992, Austroads provided funding for a project to investigate variability in the performance of sprayed seals. The aim of the project was to improve reliability of design by measuring existing pavement conditions and their influence on the design process and sprayed seal performance. The outcome of the project was the provisional Revision 2000 design method (Austroads 2001).

This updated document is based on the Austroads practitioners guide to the design of sprayed seals Revision 2000 Method (Austroads 2002) but has been considerably extended and now also includes a brief section on selection of treatments. To design suitable rates of application of binder and aggregate for the service conditions, it is essential that, as a first step, an appropriate treatment is selected. Failure to do so may result in a treatment that cannot provide the surfacing characteristics and performance expected.

The importance of traffic and the average least dimension (ALD) to the design of a sprayed seal is emphasised with new sections covering these topics.

The life of sprayed seals are highly dependent on the quality of granular base materials and the standard of surface preparation of pavements prior to resealing. When embedment of aggregate into soft base materials or poorly prepared maintenance patches occurs, there is a possibility of subsequent flushing and loss of surface texture and, consequently, unsatisfactory levels of skid resistance.

The design philosophy follows previous Austroads methods that are loosely based on the concept, as originally proposed by Hanson (1935), that to achieve a satisfactory sprayed seal, the voids within the sealing aggregate mosaic should be filled to about one-half to two-thirds with binder. Adjustments for differing aggregate shape and traffic are applied to develop a basic binder application rate. To this, further allowances are applied to cater for the surface texture of the underlying substrate, embedment of the seal into the underlying substrate, and any binder absorbed by either the sealing aggregate or the underlying substrate.

Individual sections cater for the design of:

single/single seals with C170, C320 or multigrade single/single seals with polymer modified binders single/single seals with emulsion binders double/double seals with C170, C320 or multigrade double/double seals with polymer modified binders geotextile reinforced seals fibre reinforced seals scatter coat (sometimes referred to as a rack-in coat).

The design sections are intended to be self sufficient within each section. This has resulted in duplication of many tables and figures throughout the document. However, this should make the document easier to use in that designers will not be required to leaf through the document to locate important tables and figures that may have been introduced in earlier sections.


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Throughout the document Key Points are included to draw to the attention of designers, particularly those who may be new to or have limited experience in seal design, items such as: good practice, advice on interpretation of data, the influence of traffic, and potential problems or risks associated with the treatment selected or the design being considered.

A brief section has been included describing the main materials used in sprayed seals. This information should help users decide what materials and applications are likely to be successful for a given situation.

Worked examples have been added in Appendix A.


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CONTENTS

1 INTRODUCTION ................................................................................................................... 1 1.1 General .................................................................................................................................. 1 1.2 Selection of treatment type and materials ............................................................................. 2 1.3 Application of seal design procedure to various seal types ................................................... 2

1.3.1 Single/single seals ................................................................................................... 2 1.3.2 Double/double seals ................................................................................................ 3 1.3.3 Geotextile reinforced seals and fibre reinforced seals............................................. 3

1.4 Design philosophy ................................................................................................................. 3 1.4.1 Single/single seals size 10 mm aggregates and larger ........................................ 3 1.4.2 Single/single seals size 7 mm and smaller aggregates ........................................ 5 1.4.3 Other seal types....................................................................................................... 5

1.5 Calculation of design traffic.................................................................................................... 5 1.5.1 General .................................................................................................................... 5 1.5.2 Single carriageway - two way traffic ........................................................................ 7 1.5.3 Dual carriageway - one way traffic........................................................................... 7 1.5.4 Large heavy vehicles (LHV)..................................................................................... 8 1.5.5 Short term traffic variations...................................................................................... 9 1.5.6 Access roads to quarries, mining locations, etc....................................................... 9

1.6 Average least dimension (ALD) ........................................................................................... 10 2 SINGLE/SINGLE SEALS SIZE 10 MM AND LARGER AGGREGATES ........................ 12 2.1 Design binder application rate ............................................................................................. 12

2.1.1 Abbreviations ......................................................................................................... 12 2.1.2 General .................................................................................................................. 12 2.1.3 Basic Voids Factor (Vf) .......................................................................................... 14 2.1.4 Adjustments to the Basic Voids Factor .................................................................. 15 2.1.5 Design Voids Factor (VF) ...................................................................................... 16 2.1.6 Basic Binder Application Rate (Bb)........................................................................ 16 2.1.7 Allowances applied to basic binder application rate .............................................. 17 2.1.8 Design Binder Application Rate (Bd) ..................................................................... 23

2.2 Aggregate Spread Rate ....................................................................................................... 23 3 SINGLE/SINGLE SEALS SIZE 7 MM AND SMALLER AGGREGATES ........................ 25 3.1 General ................................................................................................................................ 25 3.2 Binder application rate ......................................................................................................... 26

3.2.1 Basic binder application rate (Bb).......................................................................... 26 3.2.2 Design Binder Application Rate (Bd) ..................................................................... 26

3.3 Aggregate Spread Rate ....................................................................................................... 27 4 SINGLE/SINGLE SEAL WITH POLYMER MODIFIED BINDER ........................................ 28 4.1 General ................................................................................................................................ 28 4.2 Design for size 10 mm and larger aggregate....................................................................... 28

4.2.1 PMB binder application rate................................................................................... 28 4.2.2 SAMI treatments .................................................................................................... 31 4.2.3 Aggregate Spread Rate ......................................................................................... 31

4.3 Size 7 mm and smaller aggregates ..................................................................................... 32 4.3.1 Binder application rate ........................................................................................... 32 4.3.2 Aggregate Spread Rate ......................................................................................... 32


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5 SINGLE/SINGLE SEALS WITH BITUMEN EMULSION BINDER...................................... 33 5.1 General ................................................................................................................................ 33 5.2 Single/single seals aggregates size 10 mm and larger .................................................... 34

5.2.1 Binder application rate ........................................................................................... 34 5.2.2 Aggregate Spread Rate ......................................................................................... 35

5.3 Single/single seals aggregates size 7 mm and smaller .................................................... 36 5.3.1 Binder application rates ......................................................................................... 36 5.3.2 Aggregate Spread Rate ......................................................................................... 36

6 DOUBLE/DOUBLE SEALS ................................................................................................ 37 6.1 General ................................................................................................................................ 37 6.2 Both applications with little or no trafficking between applications ...................................... 38

6.2.1 General .................................................................................................................. 38 6.2.2 First application...................................................................................................... 38 6.2.3 Second application ................................................................................................ 40 6.2.4 Varying surface texture of finished seal ................................................................. 41

6.3 Second application delayed................................................................................................. 41 6.3.1 General .................................................................................................................. 41 6.3.2 Aggregate Spread Rate ......................................................................................... 41

7 DOUBLE/DOUBLE SEAL WITH PMB................................................................................ 43 7.1 General ................................................................................................................................ 43 7.2 Both applications with little or no trafficking between applications ...................................... 43

7.2.1 First application using a PMB ................................................................................ 43 7.2.2 Second application using a PMB ........................................................................... 43 7.2.3 Second application using C170/320, multigrade ................................................... 44

7.3 Second application delayed................................................................................................. 44 8 DOUBLE/DOUBLE SEALS WITH BITUMEN EMULSION BINDER .................................. 45 9 GEOTEXTILE REINFORCED SEALS (GRS) ..................................................................... 46 9.1 General ................................................................................................................................ 46

9.1.1 Applications ........................................................................................................... 46 9.1.2 Geotextile fabric..................................................................................................... 46 9.1.3 Design procedure .................................................................................................. 46

9.2 Binder application rate ......................................................................................................... 47 9.2.1 Preliminary Design Binder Application Rate .......................................................... 47 9.2.2 Binder fabric retention allowance........................................................................... 47 9.2.3 Final Design Binder Application Rate .................................................................... 47

9.3 Aggregate Spread Rate ....................................................................................................... 47 10 FIBRE REINFORCED SEALS ............................................................................................ 48 10.1 General ................................................................................................................................ 48 10.2 Binder application rate ......................................................................................................... 48 10.3 Design Aggregate Spread Rate........................................................................................... 48


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11 SELECTION OF TREATMENT TYPES .............................................................................. 49 11.1 General ................................................................................................................................ 49 11.2 Specialty seals/treatments................................................................................................... 49

11.2.1 Inverted seal .......................................................................................................... 49 11.2.2 Dry matting ............................................................................................................ 49 11.2.3 Cape seals............................................................................................................. 51 11.2.4 Variable spray rates............................................................................................... 51 11.2.5 Surface enrichment................................................................................................ 51 11.2.6 Rejuvenation.......................................................................................................... 52

11.3 Binders................................................................................................................................. 52 11.3.1 Conventional bitumen ............................................................................................ 52 11.3.2 Multigrade bitumen ................................................................................................ 53 11.3.3 Polymer modified binder (PMB)............................................................................. 53 11.3.4 Bitumen emulsion .................................................................................................. 54

11.4 Geotextiles........................................................................................................................... 54 11.5 Aggregates .......................................................................................................................... 54

11.5.1 General .................................................................................................................. 54 11.5.2 Aggregate properties ............................................................................................. 54 11.5.3 Selection of aggregate size ................................................................................... 55

12 PRIMING AND PRIMERSEALING...................................................................................... 57 12.1 Introduction.......................................................................................................................... 57 12.2 Prime ................................................................................................................................... 57

12.2.1 Function of a prime ................................................................................................ 57 12.2.2 Selection and design for priming ........................................................................... 57 12.2.3 When to prime ....................................................................................................... 58 12.2.4 Life expectancy of prime........................................................................................ 59

12.3 Primerseals.......................................................................................................................... 59 12.3.1 General .................................................................................................................. 59 12.3.2 Selection of primerbinder....................................................................................... 59 12.3.3 Primerbinder application rates ............................................................................... 60 12.3.4 Selection of aggregate size for primerseals........................................................... 61 12.3.5 Aggregate spread rates for primerseals ................................................................ 61

REFERENCES ............................................................................................................................. 62 APPENDICES ...............................................................................................................................65


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TABLES

Table 1.1: Estimation of Design Traffic from AADT for single carriageways ............................... 7 Table 1.2: Estimation of Design Traffic from AADT for dual carriageways.................................. 8 Table 2.1: Adjustment to Basic Voids Factor for aggregate shape (Va).................................... 15 Table 2.2: Adjustment (Vt) to Basic Voids Factor for traffic effects ........................................... 16 Table 2.3: Surface texture allowance for existing surfacing, As (L/m2)..................................... 19 Table 2.4: Design Aggregate Spread Rates for single/single seals (Class 170 bitumen,

Class 320 bitumen, multigrade)................................................................................ 24 Table 3.1: Basic Binder Application Rates for size 7 mm and smaller aggregates ................... 26 Table 3.2: Design Aggregate Spread Rates for single/single seals with 7 mm aggregate........ 27 Table 4.1: PMB factors (PF)...................................................................................................... 30 Table 4.2: Design Aggregate Spread Rates for single/single seals using PMB........................ 32 Table 5.1: Emulsion factor......................................................................................................... 34 Table 5.2: Aggregate spread rates for single/single seals using bitumen emulsion.................. 35 Table 5.3: Aggregate spread rates for 7 mm single/single seals using bitumen emulsion........ 36 Table 6.1: Amendment of Design Voids Factor for the first application of a double/double seal38 Table 6.2: Aggregate Spread Rates for first application of double/double seal ........................ 39 Table 6.3: Aggregate Spread Rates for second application of a double/double seal................ 40 Table 9.1: Typical binder retention allowance for geotextile reinforced seals ........................... 47 Table 10.1: Typical binder allowances for glass fibre.................................................................. 48 Table 11.1: Guide to the selection of sprayed seals ................................................................... 50 Table 11.2: Generally recommended aggregate sizes for sprayed seal treatments ................... 56 Table 12.1: Guide to grade and rates of application of primer .................................................... 58 Table 12.2: Selection of type and grade of primerbinder ............................................................ 59 Table 12.3: Basic primerbinder application rates (total volume of binder) .................................. 60 Table 12.4: Embedment allowances for primer seals ................................................................. 61


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FIGURES

Figure 1.1: Single/single seal (single application of binder & single application of aggregate) .... 2 Figure 1.2: Double/double seal (double application of binder & double application of aggregate)3 Figure 1.3: Flow chart for design of binder application rates for a single/single seal ................... 4 Figure 1.4: Three dimensional shape of a sealing aggregate particle........................................ 10 Figure 2.1: Design process for single/single seals ..................................................................... 13 Figure 2.2: Basic Voids Factor (Vf) traffic volume 0 to 500 vehicles/lane/day......................... 14 Figure 2.3: Basic Voids Factor (Vf) - traffic volume 500 to 10,000 vehicles/lane/day................. 14 Figure 2.4: Embedment allowance for initial treatments............................................................. 21 Figure 3.1: Design method for size 7 mm and smaller aggregate.............................................. 25 Figure 9.1: A single/single geotextile reinforced seal ................................................................. 46 Figure 11.1: Dry matting technique .............................................................................................. 50 Figure 11.2: Cape seal ................................................................................................................. 51 Figure 12.1: Prime ........................................................................................................................ 57 Figure 12.2: Primerseal ................................................................................................................ 59


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1 INTRODUCTION

1.1 General A single application of binder and single application of aggregate, termed a single/single seal, is the most common form of sprayed seal used in Australia. The design of rates of application of binder and aggregate for single/single seals forms the basis of the design procedures for all other sprayed seal types including modified binders or multiple applications of binder and/or aggregate.

The use of single/single seals on unbound granular base materials has been at the heart of the ability of road agencies in Australia to provide all weather roads over great distances and remote areas at relatively low cost. Increases in traffic volumes, particularly the increase in the size and number of heavy vehicles used for the movement of freight in rural areas, has placed greater demands on the performance of sprayed seals. The continued success of sprayed seal surface treatments requires care in both the selection of surfacing type and the design process.

ARRB conducted a National Sprayed Sealing Workshop for Austroads in February 2005. This was attended by representatives from state road authorities, local government and industry. Issues raised and discussed at the workshop included:

The importance of selection of an appropriate seal type. This is necessary in order to have confidence in the design of rates of application of binder and aggregate. Poor selection often results in a lower than expected standard of performance of sprayed seals.

Concern with the quality of granular base materials and standards of surface preparation as well as concern with the standards of preparation of existing pavements prior to resealing. Embedment of aggregate into soft base materials or poorly prepared maintenance patches has a major impact on subsequent flushing and loss of surface texture of sprayed seals and, consequently, unsatisfactory levels of skid resistance.

This procedure for the design of sprayed seal surfacings is an update of the Practitioners guide to the design of sprayed seals (Austroads 2002). It also supersedes the design guidelines provided in Austroads Provisional sprayed seal design method (Austroads 2001).

This update is derived from a combination and consolidation of the two earlier guides, and monitoring data obtained from subsequent validation trials. In addition, the opportunity has been taken to address some of the issues raised at the national workshop, and other feedback, and the document includes a brief guide to selection of sprayed treatments as well as guidance on selection and design of primes and primerseals.

Monitoring of the validation trials has revealed that there are still several aspects of the seal design method that need to be investigated and require collection of further data. These aspects include matters such as:

potential embedment of aggregate determination of a more accurate design allowance and development of a simpler and quicker method of measurement

the effect of large heavy vehicles on the rolling/packing of aggregates in sprayed seals and therefore adjustments that may be required to be applied in the design as well as defining limits for the practical use of different sprayed seal types.

This document is, for convenience, divided into a number of separate sections for each type of sprayed sealing treatment. Although the basic design philosophy applies to all treatments, they are sufficiently different to warrant being separated. The design philosophy is based on the design of a single/single seal, and this design is explained in detail.


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The design process is outlined for the other treatments (including reference to the appropriate tables/figures contained in the single/single design section), plus additional information required in order to complete the design of the particular treatment.

Designers should continue to apply their own judgement based on proven performance of sprayed seals in the application being considered, and take into account local practices and procedures that may apply to the design of application rates. It is requested that feedback be provided to Austroads on any anomalies detected, or problems encountered, in using this sprayed seal design method.

1.2 Selection of treatment type and materials The importance of selecting the right surfacing for the conditions at the site is of primary importance. It is also necessary to consider the practicality of a sprayed seal being able to provide a reasonable level of service. Enhancements to sprayed seal performance can be made with multigrade and polymer modified binders, double/double seals and specialty treatments. Some situations may necessitate a more substantial treatment such as hot mix asphalt. There are no quantitative measures available to define where a seal will perform and where it will quickly exhibit distress, and designers must rely on experience and, if necessary, seek expert advice on the practicalities of using a particular surface treatment.

Sprayed seals involve the use of bituminous binders, additives, modifiers, aggregate and other materials according to the type of treatment, performance expectations and the prevailing application conditions.

Section 11 of this guide provides a brief guide to selection of sprayed seal surfacing type and the main materials used. Further guidance on selection of surfacing type and materials used in sprayed seals is provided in the Austroads Sprayed Sealing Guide (Austroads 2004) and Guide to selection of roads surfacings (Austroads 2003).

1.3 Application of seal design procedure to various seal types 1.3.1 Single/single seals Single/single seals (see Figure 1.1) consist of one layer of binder covered with a single layer of aggregate. It is the most common treatment used, particularly on very low to medium trafficked rural roads.

Base

Uniform-sized aggregateSealing binder

Primer penetration into base

Figure 1.1: Single/single seal (single application of binder & single application of aggregate)

Small differences apply to the design of the rates of application of binder and aggregate spread rates for single/single seals using aggregates 10 mm and larger, and those using aggregates 7 mm and smaller. Separate sections are provided for the design for seals with:

10 mm and larger aggregate 7 mm and smaller aggregate.


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Further separate sections are provided for variations to the single/single design procedure applied to:

polymer modified binders bitumen emulsion binders.

1.3.2 Double/double seals Double/double seals (see Figure 1.2) consist of two applications of binder, each followed by an application of aggregate. The design procedure for double/double seals is based on the procedure for single/single seals with particular allowances and variations applied to binder and aggregate application rates. Further allowances are made for polymer modified binders and bitumen emulsions and these variations are also described in separate sections.

Base

First (larger) aggregateFirst binder

Second binder

Second (smaller) aggregate

Prime/primerseal

Figure 1.2: Double/double seal (double application of binder & double application of aggregate)

1.3.3 Geotextile reinforced seals and fibre reinforced seals Separate sections are provided for the design of geotextile reinforced seals and fibre reinforced seals. Seal reinforcement is used to improve waterproofing and resistance to cracking of seals placed over cracked or weak pavements. The design of reinforced seals is also based on the design of single/single seals with appropriate allowances for additional binder retained by the geotextile fabric or fibreglass reinforcing material.

1.4 Design philosophy 1.4.1 Single/single seals size 10 mm aggregates and larger The design philosophy adopted applies principally to the design of the most common type of sprayed seal, the single/single seal using conventional bitumen as the binder. Assumptions used in the design of single/single seals are:

aggregate is single-sized and of appropriate quality average least dimension (ALD) of the aggregate is an important input into the design method

and must be representative of the aggregate being used

design traffic volume is expressed in vehicles/lane/day (v/l/d) and based on Average Annual Daily Traffic (AADT)

aggregate is spread in a uniform layer of one stone thickness, with particles in continuous, partly interlocked contact and the least dimension near vertical

there is no separate allowance to be made for whip-off in the design aggregate spread rate aggregate spread rate determines the inter-aggregate void space in the seal layer, and

hence the amount of binder required. Failure to achieve, within practical limits, the design aggregate spread rate will result in the design binder application rate being incorrect


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a single layer of aggregate particles settles with, typically, 4060% voids after orientation and packing of the aggregate by rolling and trafficking

binder rise should be a minimum of about 3540% up the height of the aggregate particle after initial rolling and trafficking, increasing to between 5065% (i.e., 1/22/3) about two years after construction

aggregate particles may penetrate (embed) into the base reseals interlock with the existing surfacing binder may be absorbed into the base and, sometimes, by the aggregate the proportion of voids to be filled with binder may be varied to optimise requirements such

as surface texture, maximum seal life, and for specific applications such as non-traffic areas. A minimum texture is generally required for skid resistance

preliminary treatments such as primes and primerseals have been correctly designed and applied. If this has not been achieved, remedial work should be undertaken prior to, and well in advance of, the commencement of sealing.

all application rates determined by this method are expressed in L/m2 of residual binder at the standard reference temperature of 15C.

Sprayed seals are a system, and sealing trials and subsequent work have shown that the design of the rates of application of binder and aggregate spread rates are both of major importance in achieving a satisfactory performance for the service conditions.

A general schematic of the process for determination of binder application rates for single/single seals is shown in Figure 1.3.

Figure 1.3: Flow chart for design of binder application rates for a single/single seal

Aggregate shape adjustment

Traffic adjustment

Embedment allowance

Existing surface condition allowance

Absorption allowance

Basic voids factor

Design voids factor

Traffic volume

ALD Basic binder

application rate

Design binder application rate


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1.4.2 Single/single seals size 7 mm and smaller aggregates The design method for seals with aggregate size 7 mm or smaller, where the aggregate layer may vary between one and up to three aggregate particles in thickness, differs from the method for seals with larger aggregate in that:

small sized sealing aggregates are not generally tested to determine the average least dimension

small aggregate seals are often used as correction courses to provide an interim, even surfacing, with uniform texture prior to the placement of a more durable seal treatment

small aggregate sizes are appropriate on low to medium traffic roads, particularly over existing seals with large aggregates and high surface texture

small aggregate seals are used in situations that can tolerate, or only require, a reduced surfacing life, such as where a temporary surfacing is required.

1.4.3 Other seal types The design philosophy adopted applies principally to the design of the most common type of sprayed seal, a single/single seal using conventional bitumen as the binder.

Various alternatives were considered for the design of other types of seals (e.g. double/double seals and use of modified binders). Based on various sealing trials and observations of existing treatments that have given satisfactory performance, the approach most appropriate is to base the design of other seal types on the design procedure for single/single seals, with appropriate amendments in the procedure, and additional information as required.

It is therefore strongly recommended that designers of sprayed surfacing treatments familiarise themselves with the required information and tables/charts used in the design procedure for single/single seals in Section 2, prior to designing other seal types.

1.5 Calculation of design traffic 1.5.1 General Accurate traffic volumes are an essential requirement for the determination of appropriate rates of application of binder. The traffic volume data should be expressed in terms of the total number of vehicles, and the composition in terms of light and heavy vehicles (heavy vehicles are those over 3.5 tonne gross mass). Worked examples have been included in Appendix A.

Failure to determine the Design Traffic as accurately as possible is a common problem and this may (and often does) result in an inappropriate seal design leading to reduced service life because of early loss of aggregate or flushed seals with low texture.

It is important to determine the volume and composition of the design traffic as close as possible to the work site. If traffic volumes provided are considered to be not representative, a traffic count should be determined for the site using automatic or manual traffic counts.

When the total count is considered to be representative, but the traffic distribution is uncertain, a site investigation should be conducted to provide a reliable estimate of traffic distribution for each lane. For example, this may be the case where heavy traffic does not travel predominantly in the left hand lane as commonly accepted/observed due to interference from turning traffic, stop/start traffic, parking lanes etc., such as on roads through urban areas, rural towns, tourist areas, etc.


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Traffic data is generally provided as the total traffic volume on the road and not for individual lanes, shoulders etc. Traffic volume may be given as:

Annual Average Daily Traffic (AADT), which is the most common method used by state road authorities

12 hour or 24 hour count at a particular date or time. State road authorities can generally provide factors to convert the 12 and 24 hour counts to AADT. For example, on medium to low traffic roads, a factor of the order of 1.25 to 1.30 is typically used to convert 12 hour counts to AADT. For a freeway or other very busy urban road, with a large percentage of traffic travelling at night, the factor is generally 1.45 to 1.50, and can be as high as 2.0 in some instances

vehicles per lane per day (v/l/d), generally on multiple lane urban and rural roads where the traffic count is taken for individual lanes.

Design Traffic, when determined from AADT, must take into account the following:

the number of carriageways (generally single or dual) the direction of traffic (one-way or two-way) number of lanes percentage of the total traffic travelling in each lane.

Design Traffic should be the best estimate of traffic using each lane. On multi-lane roads, the proportion of heavy vehicles should be calculated separately for each lane, based on the total mix of light and heavy vehicles estimated to use each lane. Adopting, for each lane, an overall heavy vehicle percentage given as part of AADT (e.g. 28%) will often result in an incorrect Design Traffic and/or Traffic Adjustment being applied.

A separate design is required for each lane of traffic having either a different traffic volume (v/l/d) and/or different proportion of heavy vehicles.

It is important to use a traffic count taken as close as possible to the location of the proposed sealing work. This particularly applies to rural roads connecting townships where the traffic counts are often taken at or near the town limits where the traffic volume is higher than elsewhere on the road.

It is usually assumed that traffic in each direction is equal to about half the AADT for the facility, unless it is evident that distribution of traffic, in both volume and proportion of heavy vehicles, is not uniform.

In some locations, the proportion of heavy vehicles in each lane may not be uniform or may not be equal in both directions because of restrictions, specified routes, specified lanes such as bus lanes, overtaking/climbing lanes, or roads with a third lane in the centre used as passing lanes by traffic in both directions.


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For the purpose of this design method, where general references are made to typical traffic volumes, the following descriptions apply:

very low: 200 v/l/d

low: 201750 v/l/d

medium: 7512000 v/l/d

high: >2000 v/l/d

1.5.2 Single carriageway two way traffic A single carriageway is the most common sealed road pavement in rural areas and traffic needs only to be apportioned to each lane. The width of sealed pavement influences the traffic pattern. Assuming that traffic is equal in both directions, Table 1.1 provides a guide to estimating the Design Traffic.

Table 1.1: Estimation of Design Traffic from AADT for single carriageways

Width of seal (m) Estimated Design Traffic (v/l/d) Comment

3.7 - 5.6 AADT Seal width is considered too narrow for 2 lanes

6.2 - 7.4 AADT Traffic is considered to predominantly travel in distinct lanes on seals of this width, especially if the centre line and/or lanes are line marked Sealed shoulders, parking lanes, identified by edge line marking to be separate from the traffic lanes

adopt < 50 If not line marked, some of the traffic may wander onto the shoulder and < 50 v/l/d may not be appropriate. If in doubt, a traffic count should be conducted.

Overtaking lanes (in one direction) left hand lane (3.7m)

6080% of AADT

right hand lane (3.7 m) 2040% of AADT

Determine % of HV for each lane as a proportion of the total traffic volume in that lane.

Single lane in opposite direction AADT %HV same as in AADT

If in doubt, arrange a traffic count for each lane

On and off ramps on freeways or urban road systems

Traffic volumes (AADT) before and past the ramp, may provide a good indication of AADT on ramp. Otherwise, arrange a traffic count. Traffic volume on the road connected to the ramp may also provide additional useful information to determine AADT on the ramp.

Service roads to major roads For one-way traffic, the Design Traffic is equal to the AADT For two way traffic use AADT

AADT refers to traffic using the service road only. If not available arrange a traffic count..

1.5.3 Dual carriageway one way traffic AADT is usually defined as the total traffic carried by both carriageways, but this should be confirmed. Where it is the total traffic for both carriageways, the first step is to determine the traffic on each carriageway, and this is generally assumed to be AADT.

For heavily trafficked roads, with more than two lanes in each direction, an actual traffic count may be available for each lane and this should be the traffic volume used in the design.

For rural freeways and highways, or duplicated roads into rural townships (classed as urban type location) with medium to high traffic volumes, Table 1.2 provides a guide to estimating the Design Traffic from AADT.


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The traffic volumes used throughout the seal design procedures are based on the general mix of light and heavy vehicles (HV), with the heavy vehicle proportion assumed to be between 5 and 10% of the total. If heavy vehicles make up more than 10% of the total, the actual percentage should be determined. This is particularly important where the road may be an access to an industrial estate, a quarry access road, a road connecting major industrial centres, etc. It is also important to note in these instances whether the heavy vehicles are evenly loaded/unloaded in both directions, or predominantly travel loaded/empty in one direction only. Generally the heavy vehicles use the left hand lanes on multi-lane carriageways, and the climbing/passing lane conditions provided that the additional lane is of sufficient length to allow the heavy vehicles to change lanes without undue interference.

Table 1.2: Estimation of Design Traffic from AADT for dual carriageways

Lane (assumed 3.7m wide)

Estimated Design Traffic (v/l/d) Comments

Multi lane, heavily trafficked

AADT divided by the number of lanes in the carriageway

OR AADT x % traffic in each lane

These roads are usually in urban areas or linking major centres. Traffic volume is often > 2000 v/l/d in all lanes but the % heavy vehicles may vary between lanes.

2 lane carriageway left hand (outer) lane

60 to 80% of AADT

60% for urban / 80% for rural

right hand (inner) lane 40 to 20% of AADT 40% for urban / 20% for rural Each carriageway = AADT

Sealed shoulders, Parking lanes identified by edge line marking to be separate from the traffic lanes

adopt < 50 On some busy roads, trucks may tend to travel partially on the shoulder, and this must be taken into account. A traffic count should be conducted, and/or traffic pattern determined.

Where two lanes merge into one (at end of a duplicated section) AADT

Merged traffic is AADT, but design of binder application rates and layout of sprayer runs within the merge area require particular care.

Off and on ramps % of x AADT If actual traffic counts are not available for ramps, traffic on the side road, before and past the ramp, may provide an indication of the traffic volume using the ramp.

1.5.4 Large heavy vehicles (LHV) Since the initial development of the Austroads (2001) seal design method there has been a national increase in the number of large heavy vehicles (LHV), particularly in rural areas of NSW, QLD and WA. Based on data collected in rural areas, the traffic adjustment for heavy vehicles has been amended and updated to reflect this change.

An investigation is currently being conducted into the effect of these large heavy vehicles, compared to a standard two axle truck with a combined load of around 15 tonne. As an interim measure for this seal design method, it has been agreed to determine a design traffic volume and proportion of equivalent heavy vehicles based on the following:

Equivalent Heavy Vehicles (EHV)% = HV% + LHV% 3

where:

HV and LHV are as obtained from annual traffic count or on-site counts.

LHV includes B-Doubles and other heavy truck/trailer combinations with seven or more axles (Austroads vehicle class 10 and above - see Appendix B).


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The value of EHV calculated by this procedure is used solely for the determination of adjustments to the basic voids factor for the effects of traffic (Table 2.2) and does not alter the design traffic volume.

Designers must apply caution when designing binder application rates for seals used by these large heavy vehicles. They should monitor and compare their design against actual seal performance to provide additional information in order to be able to make appropriate additional amendments for traffic adjustments in future designs. Refer Appendix A for some worked examples on converting LHV to EHV.

1.5.5 Short term traffic variations

Short term traffic variations may occur as a result of a range of factors including:

seasonal variation on roads in tourist areas school holidays grain harvest specific events (e.g. local show days, race days, etc.) staging of construction or rehabilitation work.

Designers need to be aware of the impact of undertaking sprayed seal work at a time when the traffic conditions vary from that applicable to normal use. Where possible, the impact of short term variation should be minimised by avoiding undertaking work during, or shortly before, abnormal events. Generally, the traffic volume used in seal design should be that estimated to apply at the time, or within the first few months, of sealing. The influence of anticipated weather conditions coinciding with the expected higher traffic volumes should also be considered in determining design application rates.

It is suggested a design is carried out for both traffic conditions (normal and short term), and final design rates of application determined taking into account risk factors such as potential loss of aggregate (low binder rates) and potential flushing (high binder rates).

1.5.6 Access roads to quarries, mining locations, etc. Traffic in these locations often consists predominantly of heavy vehicles and large heavy vehicles (HV and LHV) with only a few light vehicles and cars. In such circumstances, the determination of an appropriate traffic volume for selection of the Basic Voids Factor at the start of the design process, can be difficult.

Adjustments to binder application design rates for proportions of heavy vehicles greater than 15% and up to 45% of total traffic are provided in Part 2.1.4 and Table 2.2 of the design procedure for single/single seals. Where the proportion of heavy vehicles is greater than 45% of the total traffic, the following procedure may be used for selection of an alternative Basic Voids Factor.

The procedure is based on the assumption that the Basic Voids Factors shown in Figure 2.2 and Figure 2.3 of Section 2.1.3 have been developed around a mixture of light and heavy vehicles where the proportion of heavy vehicles is typically around 10% of the total. Multiplying the number of heavy vehicles by 10 provides a nominal design traffic volume for selection of an alternative Basic Voids Factor.


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The procedure is as follows:

1. determine Equivalent Number of Heavy Vehicles (HV + 3.0 LHV)

2. multiply Equivalent Number of Heavy Vehicles x 10 + actual number of light vehicles, to determine a nominal design traffic volume

3. select a Basic Voids Factor based on this nominal traffic volume.

When using this procedure, the voids factor reductions for the proportion of heavy vehicles in normal, flat conditions (Table 2.2) do not apply, but additional reductions in voids factor of up to 0.02 L/m2/mm should still be made for channelised or slow moving vehicles.

1.6 Average least dimension (ALD) The concept of an aggregate particle tending to lie with its least dimension vertical is central to the volumetric design of a sprayed seal.

The least dimension is defined as the smallest dimension of a particle when placed on a horizontal surface (see Figure 1.4). The shape is most stable when lying with its least dimension (A) vertical. If placed with the width (B) or the depth (C) of the shape vertical, it would require less energy to knock the aggregate particle over so that the least dimension (A) was again vertical, particularly if the particle is other than cubic. Thus in a seal, the final orientation of most particles is such that the least dimension is near vertical, providing that there is sufficient room for the particles to re-align.

Figure 1.4: Three dimensional shape of a sealing aggregate particle

The least dimension may be only marginally smaller than the other two dimensions, as in the case of almost cubical aggregates, or can be much less in the case of flaky aggregates.

ALD can be determined by:

direct measurement (AS1141.20.1 for 10 mm or larger nominal size or AS1141.20.2 for 5 mm and 7 mm nominal sizes)

AS1141.20.3 involving calculating (or using a nomograph) the ALD from the grading, median size, and flakiness index.

ALD determined by either method can be used in this design method.

A

B

C


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ALD is the critical parameter in the Austroads sprayed seal design procedures. It is used to calculate both the aggregate spread rate and the design binder application rate. The design procedures assume that, for 10 mm and larger, only a single layer of aggregate particles adheres to the binder film, but for 7 mm and smaller aggregates, the aggregate layer can often be two (or more) aggregate particles in thickness.

Particles rearrange during construction rolling into a more stable position with the least dimension tending towards vertical. This can only happen if there is sufficient space (provided by the aggregate spread rate) for the aggregate particles to move.

At the design spread rate, with an interlocked mosaic, particles provide mutual support and can thus provide greater resistance to the shearing and plucking action of traffic. If the spread rate is too heavy, the contact to contact mosaic may form in a more random orientation. The void volume in this random orientation is considerably higher (up to 25% more) than is the case where a large percentage of the particles lie with the least dimension vertical. If the aggregate spread rate is too light, the particles will not be able to form a fully interlocked mosaic resulting in a lower binder rise and possible reduced seal life.

Aggregate particles in a sprayed seal continue to reorientate under traffic. The rate of reorientation and amount of change in void volume is dependent on the traffic volume and, in particular, the number of heavy vehicles. This reorientation occurs mainly during the first one or two years of service. High traffic volumes result in the least dimension of nearly all particles being near vertical and interlocking with each other. The extent of reorientation is less at low traffic volumes resulting in greater random orientation of aggregate particles and greater void volume.

For the binder application rate to fill the voids in the aggregate mosaic to a depth of about two thirds up the aggregate, it is essential that the aggregate is spread at the design rate.

The importance of using a representative ALD cannot be overemphasised. Poor sampling techniques and/or inaccurate testing procedures to determine ALD will result in incorrect aggregate design spread rates and inaccurate design binder application rates.

It is poor practice to use assigned or nominal values of ALD for a particular nominal size of aggregate. ALD of individual aggregate samples can vary by up to 17% within normally specified ranges of grading and flakiness index, resulting in an equivalent variation in the design rates of basic binder application and aggregate spread rate. It is thus important to monitor the ALD of aggregate stockpiles regularly within a sufficiently comprehensive sampling scheme to progressively evaluate whether seal design changes are warranted.


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2 SINGLE/SINGLE SEALS SIZE 10 MM AND LARGER AGGREGATES

2.1 Design binder application rate 2.1.1 Abbreviations The following terms and abbreviations are used in the procedures for the design of the binder application rate:

Vf = Basic Voids Factor

Va = Voids factor adjustment applied to aggregate shape

Vt = Voids factor adjustment applied to traffic effects

VF = Design Voids Factor

Bb = Basic Binder Application Rate (before application of allowances)

PF = Polymer modified binder factor (applied to Basic Binder Application Rate)

Bbm = Modified Basic Binder Application Rate (for PMB)

EF = Emulsion factor (applied to Basic Binder Application Rate)

As = Allowance for surface texture

Ae = Allowance for embedment

Aba = Allowance for binder absorption

Bd = Design Binder Application Rate (after application of allowances).

2.1.2 General The design objective is for the residual binder to be about 50% to 65% of the height of the aggregate layer two years after construction. The quantity of binder required will depend on the size, shape and orientation of the aggregate particles, embedment of aggregate into the base, texture of surface onto which the seal is being applied, and absorption of binder into either the pavement or aggregate.

All application rates determined by this method are expressed in L/m2 of residual binder at the standard reference temperature of 15C. Orientation and aggregate penetration into the binder are mainly functions of construction rolling, traffic compaction and substrate properties. It is essential that adequate, timely rolling is carried out, particularly at very low traffic volumes (


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a traffic mix with 10%, or less, heavy vehicles. If the actual traffic mix includes a higher percentage of heavy and large heavy vehicles, a reduction in the required binder quantity will most likely be necessary due to additional reorientation and aggregate embedment. A further reduction in the required binder quantity may be necessary in situations where the traffic is channelised, or on climbing grades.

Allowances for existing surface texture conditions, aggregate and pavement absorption, and for hardness of the existing surface of the base (as determined by the ball penetration test, Austroads, 2003) are added to or subtracted from the basic binder application rate.

Further modifications are made to basic binder application rates for polymer modified binders and bitumen emulsions as described in Sections 4 and 5.

A flow chart for determination of aggregate design spread rates and design binder application rates for single/single sprayed seals is shown in Figure 2.1.

Figure 2.1: Design process for single/single seals

Traffic volume (v/l/d)

Aggregate, Va shape and size

Traffic effects, Vt composition untrafficked areas short term effects climbing lanes curvature intersections narrow lanes

Basic Voids Factor, Vf(L/m2/mm)

Design Voids Factor, VF(L/m2/mm)

Design aggregate spread rate

Aggregate ALD Basic binder application rate, Bb (L/m2) = VF x ALD

Allowances (L/m 2 )

Surface texture, As

Binder absorption, Aba Design binder

application rate, Bd (L/m2)

Seal intentions road environment asset management criteria treatment type

Void factor adjustments (L/m2/mm)

Embedment, Ae


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2.1.3 Basic Voids Factor (Vf) The Basic Voids Factor, Vf (L/m2/mm), is related to traffic level and is determined from Figure 2.2 or Figure 2.3 (depending on traffic volume) and should be read to the nearest 0.01 L/m2/mm.

The central target line is used to determine the Basic Voids Factor in all cases.

The volume and composition of traffic has a direct effect on the performance of a sprayed seal. It is critical that the traffic volume used in the design is representative of the actual traffic on the area being considered.

If traffic is given in AADT, this must be separated into vehicles/lane/day for each lane/section of the road being considered (see Section 1.5).

Figure 2.2 and Figure 2.3 also contain upper and lower limits that represent indicative confidence limits for the Design Voids Factor, VF, after applying aggregate and traffic adjustments to the Basic Voids Factor, Vf.

0.15

0.20

0.25

0.30

0 100 200 300 400 500


Bas

ic v

oids

Fac

tor,

Vf (L

/m2 /m

m)

Upper limitTargetLower limit

Figure 2.2: Basic Voids Factor (Vf) traffic volume 0 to 500 vehicles/lane/day

0.05

0.10

0.15

0.20

500 2500 4500 6500 8500


Bas

ic V

oids

Fac

tor,

Vf (

L/m

2 /mm

)

Upper limitTargetLower limit

Figure 2.3: Basic Voids Factor (Vf) - traffic volume 500 to 10,000 vehicles/lane/day


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The upper limit indicates the Design Voids Factor beyond which the resultant binder level may be too high and texture depth too low, with an increased potential risk of flushing/bleeding.

The lower limit indicates the Design Voids Factor beyond which the resultant binder level may be too low and texture depth too high, with an increased potential of early loss of aggregate.

Designers must exercise caution if adopting Design Voids Factors outside these limits.

2.1.4 Adjustments to the Basic Voids Factor The Design Voids Factor, VF (L/m2/mm), is determined by adjusting the Basic Voids Factor (Vf) to account for abnormal aggregate shape (Va) and effect of traffic (Vt). These factors may be positive or negative and are cumulative.

(a) Adjustment for aggregate shape (Va)

An adjustment, Va, is made to the Basic Voids Factor (Vf) to account for variation in aggregate shape in accordance with Table 2.1.

Table 2.1: Adjustment to Basic Voids Factor for aggregate shape (Va)

Aggregate type Aggregate shape Flakiness index (%) Shape adjustment Va

(L/m2/mm) Very flaky > 35 Considered too flaky and not

recommended for sealing Flaky 26 to 35 0 to - 0.01

Angular 15 to 25 Nil Cubic < 15 + 0.01

Crushed or partly crushed

Rounded n.a 0 to + 0.10 Not crushed Rounded n.a + 0.01

(b) Adjustment for traffic effects (Vt)

The Basic Voids Factors, Vf, described in section 2.1.3, have been developed for an average mix of light and heavy vehicles in a free traffic flow situation. Where this assumption is not correct, an adjustment, Vt, needs to be made to compensate for variations in the traffic composition, in particular for non-trafficked areas, overtaking lanes with few heavy vehicles or for large proportions of heavy vehicles, channelisation or concentration of traffic, and slow moving heavy vehicles in climbing lanes or stop/start conditions (refer Table 2.2).

Traffic normally wanders within traffic lanes resulting in wheelpath travel up to 1.2 m wide. Where traffic is constrained (channelled) from wandering such as on single lane bridges, tight radius curves or narrow lane widths, an appropriate adjustment to the Basic Voids Factor (Vf) must be made to reduce the risk of the seal bleeding. For example, a narrow single lane bridge may increase the effective traffic loading in the wheel path by as much as threefold when the cumulative effects of combining lane volumes and constraining traffic to a confined path are taken into account.

Possible short increases in traffic volumes such as during grain harvest, local field days, etc. may occur early in the life of the seal. Designers should take this into account and may need to make some adjustment to the traffic volumes and Design Voids Factor adopted in the design procedure.

Where a short term traffic increase is only for a few days, it is preferable to defer the sealing work, for example to avoid a local annual field day or race meeting.


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Seasonal variation, particularly an increase in large heavy vehicles such as large truck and trailer combinations, B-doubles or larger combinations during hot summer periods, can affect the performance of a seal for up to two summers after construction. This applies mostly to annual crops harvested during the hotter weather conditions, stock transport etc.

Consideration should be given to changing the type of treatment and/or binder if the increase is relatively large compared to the Average Annual Daily Traffic.

If unsure, design the rates of application for the normal and worst traffic cases before deciding on deferral of work, selection of an alternative treatment or selection of a final design.

Table 2.2: Adjustment (Vt) to Basic Voids Factor for traffic effects

Adjustment to Basic Voids Factor (L/m2/mm) Flat or downhill Slow moving climbing lanes Traffic

Normal Channelised* Normal Channelised* On overtaking lanes of multi-lane rural roads where traffic is mainly cars with 10% of HV +0.01 0.00 n.a. n.a.

Non-trafficked areas such as shoulders, medians, parking areas +0.02 n.a. n.a. n.a.

0 to 15% Equivalent Heavy Vehicles (EHV) Nil -0.01 -0.01 -0.02 16 to 25% Equivalent Heavy Vehicles (EHV) -0.01 -0.02 -0.02 -0.03 26 to 45% Equivalent Heavy Vehicles (EHV) - 0.02 - 0.03 - 0.03 - 0.04** > 45% Equivalent Heavy Vehicles (EHV) - 0.03 - 0.04** - 0.04** - 0.05**

N/A Not applicable EHV Equivalent Heavy Vehicles, includes both Heavy Vehicles and Large Heavy Vehicles 3 (See Section 1.5.4). * Channelisation - a system of controlling traffic by the introduction of an island or islands, or markings on a carriageway to direct traffic into predetermined

paths, usually at an intersection or junction. This also applies to approaches to bridges and narrow culverts. ** See Key point below.

If adjustments for aggregate shape and traffic effects result in a reduction in Basic Voids Factor of 0.4 L/m2/mm or more, special consideration should be given to the suitability of the treatment and possible selection of alternative treatments. Note that the recommended MINIMUM Design Voids Factor is 0.10 L/m2/mm in all cases.

2.1.5 Design Voids Factor (VF) The Design Voids Factor is now calculated as shown below.

VF = Vf+ Va + Vt

Selection of an alternative type of treatment should be considered where the Design Voids Factor is at, or close to, the minimum recommended value of 0.10 L/m2/mm. For example, use of a polymer modified binder to aid aggregate retention or a double/double seal to provide a more robust treatment.

2.1.6 Basic Binder Application Rate (Bb) The procedure for the determination of the Basic Binder Application Rate, Bb (L/m2), for the proposed seal is as follows (see also Figure 1.4):

determine the Design Voids Factor, VF as described above.


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determine the Basic Binder Application Rate, Bb, to the nearest 0.01 L/m2 by multiplying the Design Voids Factor (VF) by the ALD, as shown in the following equation:

Bb = VF x ALD (L/m)

For example: VF = 0.16 L/m2/mm and ALD = 5.8 mm

Bb = 0.16 x 5.8 = 0.928 = 0.93 L/m.

If multigrade bitumen is used for high stress seals or in place of conventional bitumens in high temperature areas, a multiplication factor may be applicable (see Table 4.1). Research is being conducted to determine the applicability of multigrade bitumen factors.

2.1.7 Allowances applied to basic binder application rate The following allowances need to be considered to complete the design. Allowances are determined to the nearest 0.1 L/m2 and are cumulative. They must be added to or subtracted from the Basic Binder Application Rate, Bb (L/m), to determine the Design Binder Application Rate, Bd (L/m2).

Allowances in L/m2 are made for the following:

surface texture of existing surface, as shown in Table 2.3 potential aggregate embedment into the existing surface potential binder absorption into the existing pavement potential binder absorption into the sealing aggregate.

(a) Surface texture allowance (As)

Measurement of surface texture Surface texture allowance is based on measurement of the existing surface texture using the sand patch method Austroads Test Method AG:PT/T250.

Texture measurements should be taken at least every 400 to 500 m or where there is a visual change in texture, such as a change to a seal of different aggregate size.

It is recommended the texture depth be measured both in the wheel paths and between/outside wheel paths. This will assist in deciding if separate design rates of binder need to be considered across the lane. If the difference in texture allowance is 0.3 L/m or greater, one of the following alternatives may assist in achieving optimal performance across the full width of the seal.

Regulate the surface with a 5 mm or 7 mm seal. Pre-spray the coarse textured areas using the techniques described in Pavement Work Tip

No 36.

Use a bitumen sprayer with a variable rate spray bar.

Surface texture allowance for existing seals

Table 2.3 provides a guide to binder application rate allowances for different sizes of aggregate for a seal over various existing seal sizes and textures. The allowances are based on an assumption of satisfactory interlock between aggregates. Aggregates that have unusual (atypical) shape or size may require minor variations from the tabulated values.


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Texture allowance for asphalt

For an asphalt surface, the sand patch test is usually not appropriate. Based on experience, the texture allowance for hardened and aged asphalt surfaces is typically between +0.0 to +0.3 L/m2. Embedment into freshly placed asphalt or asphalt that is slick with fatty patches, may also need to be considered (see sub section (c), below).

Texture allowance for slurry surfacing For slurry surfacing, the sand patch test is, again, usually not appropriate. Similar to asphalt, a typical allowance is between +0.0 to +0.3 L/m2.

Texture allowance for concrete surfaces

The concrete must be primed and, in order to get a satisfactory seal over a well-primed concrete surface, the allowance should be +0.2 to +0.4 L/m2, even on smooth surfaces, to compensate for the lack of aggregate embedment and interlock into the texture of the concrete surface. For broom dragged or tyned surfaces, the allowance can be as high as +0.4 to +0.5 L/m2.

Some aggregate sizes will not be readily compatible with existing seal sizes and texture depths. For example: small-sized reseals will generally not give good results over flushed large-sized seals, and 10 mm reseals may sometimes not interlock well with existing hungry coarse textured 16, 14 and 10 mm seals.

Allowances to be applied for existing surface texture may be substantial, and require a degree of judgement by the designer.

Consideration should be given to changing the size of aggregate and/or the treatment if surface texture allowances required become excessive, say exceeding 0.5 L/m.

On surfaces with low texture depths (e.g.


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Table 2.3: Surface texture allowance for existing surfacing, As (L/m2)

Aggregate size of proposed seal

Measured texture depth (mm)

Surface texture allowance (L/m2)

Aggregate size of proposed seal

Measured texture depth (mm)

Surface texture allowance (L/m2)

Existing: 14, 16 or 20 mm seal Existing: 5 or 7 mm seal 0 to 0.3 Note 1 0 to 0.3 Note 1

0.4 to 0.6 Note 2 0.4 to 0.9 +0.1 0.7 to 0.9 +0.1 1.0 to 1.5 +0.2 1.0 to 1.3 +0.2 1.6 to 2.2 +0.3 1.4 to 1.9 +0.3 2.3 to 3.2 +0.4 2.0 to 2.9 +0.4

5 or 7 mm

>3.2 +0.5

5 or 7 mm

>2.9 +0.5 0 to 0.3 Note 1 0 to 0.3 -0.1 0.4 to 0.7 +0.1

0.4 to 0.5 0 0.8 to 1.1 +0.2 0.6 to 0.7 +0.1 1.2 to 1.8 +0.3 0.8 to 0.9 +0.2

10 mm

>1.8 Note 3 1.0 to 1.3 +0.3 0 to 0.2 Note 1 1.4 to 1.8 +0.4 0.3 to 0.6 +0.1

10 mm

>1.8 Note 3 0.7 to 0.9 +0.2 0 to 0.3 -0.1 1.0 to 1.4 +0.3

0.4 to 0.5 0 1.5 to 2.0 +0.4 0.5 to 0.6 +0.1

14 mm

>2.0 +0.5 0.6 to 0.7 +0.2 Existing: asphalt/slurry surfacing 0.8 to 0.9 +0.3 0 to 0.1 0 1.0 to 1.3 +0.4 0.2 to 0.4 +0.1 1.4 to 1.8 +0.5 0.5 to 0.8 +0.2

14 mm

>1.8 Note 3 0.9 to 1.4 +0.3 Existing: 10 mm seal

All

>1.4 +0.4 0 to 0.3 Note 1

0.4 to 0.9 +0.1 1.0 to 1.4 +0.2 1.5 to 2.0 +0.3 2.1 to 2.7 +0.4

5 or 7 mm

>2.7 +0.5 0 to 0.3 Note 1

0.4 to 0.7 +0.1 0.8 to 1.1 +0.2 1.2 to 1.7 +0.3

10 mm

>1.7 Note 3 0 to 0.2 Note 1

0.3 to 0.6 +0.1 0.7 to 0.9 +0.2 1.0 to 1.2 +0.3 1.3 to 1.7 +0.4

14 mm

>1.7 Note 3

Notes:

1. Embedment considerations dominant

2. Specialised treatments necessary

3. This treatment might not be advisable depending on the shape and interlock of aggregates so alternative treatments (surface enrichment, small size seal or others) should be considered

4. For application of aggregate sizes greater than 14 mm, adopt allowances applicable to 14 mm aggregate.

Texture allowance for timber surfaces

Timber may be untreated, primed, coated or impregnated. Similar to concrete, and as a guide, an allowance of between +0.2 to +0.4 L/m2 may be appropriate.

Texture allowance for primes or primerseals

In addition to texture allowance, the ball penetration test (see embedment allowance (c)) should be carried out to determine if an allowance for embedment is also required, particularly on areas trafficked by heavy and large heavy vehicles:


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primerseals - a texture allowance is determined similar to existing sealed surfaces primes some pavement materials present a coarse textured surface and it may be possible

to measure surface texture. If not, and based on experience, the texture allowance is generally in the order of +0.0 to +0.3 L/m2.

Texture allowance for regulation or patched areas

Shape correction of pavements and maintenance patching prior to sealing is often carried out using asphalt or premix. Allowance may need to be made for patches that are much smoother in texture than the surrounding seal, particularly if the affected area is substantial.

In addition, if the regulation/patching has not had time to cure, there is an increased risk of aggregate embedment, with resulting flushing of the seal over those areas. The regulation/patching should be allowed to cure to minimise the risk of flushing/bleeding. Recommended minimum curing times are three months in hot weather and six months in cooler weather (see also Austroads & AAPA Pavement Work Tip No. 9).

(b) Embedment allowance (Ae)

General

Embedment allowance compensates for loss of voids in the seal under traffic due to the aggregate being forced into the surface of the substrate. This depth of embedment will depend on the volume and mass of traffic and the condition (hardness) of the surface being sealed.

Embedment problems can generally be recognised by the fact that the wheel paths will fill up with binder in a very short time period (weeks), while the remainder of the seal remains coarser textured. Long term, very slow reduction in texture is a separate issue and not part of this step in the design process.

Initial treatments

Embedment of aggregate may occur in initial treatments applied over:

a soft base primed or primersealed surfaces.

Typical embedment allowances (in L/m2) are shown in. Pavement surface hardness should be determined in accordance with the Ball penetration test, Austroads Test Method AG:PT/T251.


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0

1

2

3

4

0 1000 2000 3000 4000 5000

Traffic volume (vehicles/lane/day)

Bal

l pen

etra

tion

(mm

)

Nil

-0.1 L/m2

See note

Figure 2.4: Embedment allowance for initial treatments

It is recommended that following alternatives be considered where the ball embedment value exceeds 3 mm:

(a) If due to moisture, defer sealing to allow the surface to harden as it dries back. The surface should be retested once it has dried sufficiently.

(b) Apply a small aggregate seal as the first seal to act as an armour-coat and minimise the amount of embedment of the larger aggregate applied at a later date, say after about 12 months.

To minimise potential risk of flushing/bleeding it is recommended that:

(c) Primerseals with cutback bitumen primerbinder should not be sealed for at least 12 months after placement. If a primerseal must be sealed sooner, it should not be covered within six months, including at least three months of HOT weather. A shorter curing period applies to primerseals using bitumen emulsion.

(d) A surface primed with cutback bitumen should be allowed to cure for a minimum period of three days prior to sealing. Otherwise, the possibility of absorption of binder and the potential cutting back effect of the cutter in the primer must be taken into consideration. Bitumen emulsion primers (specialty grades) can often be sealed after one or two days curing depending on prevailing drying conditions.

Reseals

Embedment of aggregate may occur in reseals:

if there is free binder on the surface being resealed when applying a reseal over fresh asphalt or slurry surfacing when applying a reseal over fresh maintenance patching. Patches that are soft and/or porous

can cause problems with embedment and/or binder absorption. Maintenance patches should be allowed to cure for a minimum of two to six months depending on type of patching material (see Pavement Work Tip No 9).


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Where the binder in the existing seal is relatively soft, some embedment may occur. The ball penetration test, referred to above, has been found to provide poor correlation with field performance for flushed bitumen surfaces and further research is required to determine appropriate allowances. In the meantime, designers must apply their own judgement in providing suitable allowances. Where surfaces are severely flushed, alternative treatments may need to be considered. Alternative treatments include:

specialty treatments (Section 11.2) surface correction using solvent and aggregate (see Pavement Work Tip No. 7) removal of excess bitumen by high pressure water (see Pavement Work Tip No. 44) selection of a surfacing type other than a sprayed seal.

(c) Binder absorption allowance (Aba)

General

It will be necessary to increase the binder application rate to allow for any binder absorption by pavement and/or aggregate, Aba, but it is not possible to give a general allowance.

Binder absorption by pavement

Initial treatments

Binder from a seal may drain into voids in the surface of the base course if these have not been adequately filled by the prime or primerseal. This is most likely to occur in sandy or silty rubble base materials (sandstone, limestone or silty gravels) in a hot dry climate. For unusually absorptive pavement surfaces, particularly in hot climates, long-term absorption of the binder into the base course can occur. The allowance for this will generally be between +0.1 to +0.2 L/m2. Where more than 0.2 L/m2 is required, an alternative treatment should be considered.

Alternative treatments may comprise:

use of a different class of binder, including PMB modification or stabilisation of the base course use of a 5 or 7 mm initial seal, followed by a larger aggregate seal one or two years later.

In extreme cases, binder absorption into base materials may lead to the need for surface enrichment or a small aggregate reseal being required within one or two years.

As previously stated, it is strongly recommended that all new pavement surfaces should be primed or primer-sealed. However, in some areas a seal is applied directly to the prepared granular pavement and the following binder absorption allowances provide a guide for use in these situations:

granular unbound pavements allow +0.2 to +0.3 L/m2

pavements using cementitious binders allow +0.1 to +0.2 L/m2

bitumen stabilised pavements allow -0.2 to 0.0 L/m2

pavements using chemical binders For the use of chemical binders, refer to Austroads publication Series Part 4D.


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Reseals

Binder absorption into the existing surface will seldom be a problem unless the existing surface is visibly open and porous.

Binder absorption by aggregate

Absorptive aggregates may fall into two general categories:

porous, e.g. sandstone, rhyolite etc. vesicular (full of cavities), e.g. scoria, slags etc.

In general, binder absorption into aggregate is not applicable, but if an allowance is required, it does not usually exceed 0.1 L/m2.

2.1.8 Design Binder Application Rate (Bd) The design is based on using conventional bitumen such as Class 170, 320 or multigrade bitumen as the binder. Guidance on determination of design binder application rate for polymer modified binders and bitumen emulsion binders is provided in Sections 4 and 5.

The Design Binder Application Rate, Bd, is determined by the following equation:

Design Binder Application Rate (Bd) = Basic Binder Application Rate (Bb) + Allowances (L/m2)

where:

Design Binder Application Rate (Bd) is in L/m2, rounded to nearest 0.1 L/m2

Basic Binder Application Rate (Bb) is in L/m2, rounded to nearest 0.01 L/m2 (refer 2.1.6)

Allowances are in L/m2, as determined in Section 2.1.7 (see also Table 2.3 and Figure 2.4).

For example: Bb = 0.97 L/m2 and surface texture allowance is + 0.3 L/m2

Bd = 0.97 + 0.3 = 1.27 = 1.3 L/m2 (rounded to nearest 0.1).

2.2 Aggregate Spread Rate The amount of 10 mm or larger aggregate required in single/single sprayed seals is based on the Average Least Dimension (ALD) of the aggregate.

Traffic will influence the packing of the aggregate (and hence the void space to be filled with binder) and some adjustm

Documents

New Seal Design Guide