Austroads Spray Seal 2000

AP-T09

AUSTROADS

AUSTROADS PROVISIONAL SPRAYED SEAL DESIGN METHOD REVISION 2000

Austroads Provisional Sprayed Seal Design Method

Revision 2000

First Published 2001

© Austroads Inc. 2001

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.

National Library of Australia Cataloguing-in-Publication data:

Austroads Provisional Sprayed Seal Design Method Revision 2000

ISBN 0 85588 593 9

Austroads Project No. N.T&E.9902

Austroads Publication No. AP–T09/01

Project Manager Lance Midgely, VicRoads

Prepared By

Sprayed Seal Design Project Group Ray Gaughan, Roads and Traffic Authority, NSW (Convenor)

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.

AUSTROADS PROVISIONAL SPRAYED

SEAL DESIGN METHOD REVISION 2000

Sydney 2001

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 transport related outcomes by:

♦ developing and promoting best practice for the safe and effective management and use of the road system

♦ providing professional support and advice to member organisations and national and international bodies

♦ acting as a common vehicle for national and international action ♦ fulfilling the role of the Australian Transport Council’s Road Modal Group ♦ undertaking performance assessment and development of Australian and New Zealand standards ♦ developing and managing the National Strategic Research Program for roads and their use.

Within this ambit, Austroads aims to provide strategic direction for the integrated development, management and operation of the Australian and New Zealand road system — through the promotion of national uniformity and harmony, elimination of unnecessary duplication, and the identification and application of world best practice.

AUSTROADS MEMBERSHIP

Austroads membership comprises the six State and two Territory road transport and traffic authorities and the Commonwealth 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 ♦ Transport South Australia ♦ Department of Infrastructure, Energy and Resources Tasmania ♦ Department of Transport and Works Northern Territory ♦ Department of Urban Services Australian Capital Territory ♦ Commonwealth Department of Transport and Regional Services ♦ Australian Local Government Association ♦ Transit New Zealand

The success of Austroads is derived from the synergies of interest and participation of member organisations and others in the road industry.

Executive Summary The sprayed seal design project was undertaken by an Austroads Seal Design Project Group in response to concerns raised by practitioners in regard to the inconsistent performance of sprayed seals designed using the current sprayed seal design method (Austroads 1990).

In 1991 to 1993 a series of 47 sealing road trials were constructed throughout Australia aimed at comparing the Austroads (1990), the local State Road Authority (SRA) and a modified National Institute for Transport and Road Research (NITRR) South African sprayed seal design methods. The local State Road Authorities monitored the performance and properties of the trial sections at predetermined intervals. After two years in service, the field trials were inspected by an Expert Team to provide an objective assessment of their relative performance.

Analysis of the trial data was approached in two ways. The first approach was based on a rigorous regression analysis. Correlations were sought between design input parameters such as Average Least Dimension (ALD) of the aggregate, binder application rate (BAR), traffic, texture depth, embedment, etc., and field parameters such as field layer thickness, voids filled with binder, embedment voids, voids in the aggregate layer, etc. The method derived using this approach is known as the Draft 7A method.

The second approach used the current Austroads design method format with some input from regression analysis and practitioners’ experience. The second approach was seen as an incremental improvement on the previous Austroads (1990) sprayed seal design method. This approach to seal design is reported in this document as the Austroads Provisional Seal Design Method - Revision 2000.

It is likely that a future, final method will be a consolidation of the two approaches so as to ensure the most favourable outcome. The Provisional method and the Draft 7A method are being validated by field performance trials. Meaningful information from the validation trials can be expected in 2002.

Details of the validation program, including trial site selection criteria and design and performance data record sheet, are discussed in the Commentary Section of the report.

The remaining work to complete the project involves:

• completing the monitoring of the validation field trials

• reviewing the Provisional Revision 2000 method with regard to the findings of the validation program

• Publishing a final Austroads seal design method with a strategy for dissemination and implementation.

Acknowledgments

The work described in this report was funded by Austroads through the National Strategic Research Program. The project was managed by an Austroads Sprayed Seal Design Project Group that drew on members from Austroads Member Authorities, Australian Asphalt Pavement Association members and ARRB Transport Research.

The Sprayed Seal Design Project Group has had involvement from numerous individuals through the ten or so years of the Project but the following members made significant, sustained contributions.

L. Midgley VicRoads (Project Manager)

R. Gaughan Roads & Traffic Authority of NSW (Convenor)

E. Booth formerly of Transport South Australia

R. Leach formerly of Main Roads Western Australia

P. Baburamani formerly of ARRB Transport Research

W. Holtrop Australian Asphalt Pavement Association

I. Cossens VicRoads

S. Hogan Main Roads Queensland

S. Walton Main Roads Western Australia

K. Neaylon Transport South Australia

B. Walker Department of Infrastructure, Energy & Resources Tasmania

J. Bethune Australian Asphalt Pavement Association

J. Rebbechi formerly CSR Emoleum

J. Oliver ARRB Transport Research

A. Alderson ARRB Transport Research (Technical Secretary)

Any comments or feedback on the Austroads Provisional Sprayed Seal Design Method should

be forwarded to: Ray Gaughan (Convenor)

Ph: (02) 9662 5891 Fax: (02) 9662 5123 email: [email protected]

or

Allan Alderson (Technical Secretary)

Ph: (03) 9881 1555 Fax: (03) 9886 4870 email: [email protected]

Contents SECTION A — COMMENTARY ON THE DEVELOPMENT OF THE AUSTROADS PROVISIONAL SPRAYED SEAL DESIGN METHOD — REVISION 2000 1. INTRODUCTION 1 1.1 BACKGROUND 1 2. SPRAYED SEAL DESIGN METHOD TRIALS 2 2.1 BACKGROUND 2 2.2 OBJECTIVES 2 2.3 TRIAL RESEARCH PLAN 2 2.4 DATA ANALYSIS 3 2.5 OUTCOMES 3 3. STRUCTURE OF THE REVISED METHOD 4 3.1 GENERAL 4 3.2 DESIGN INFORMATION REQUIRED 4 3.3 REVISION 2000 DESIGN PROCEDURE 4 3.3.1 Aggregate Spread Rate 5 3.3.2 Binder Application Rate 5 4. VALIDATION TRIAL PROGRAM 7 5. PROGRAM FOR FURTHER WORK 8 SECTION B — AUSTROADS PROVISIONAL SPRAYED SEAL DESIGN METHOD - REVISION 2000 1. OVERVIEW OF THE DESIGN PROCESS 10 1.1 GENERAL 10 1.2 INPUTS REQUIRED TO DESIGN A 10 MM OR LARGER SPRAYED SEAL 10 1.3 DESIGN OVERVIEW 10 2. LOOSE AGGREGATE SPREAD RATE 12 3. BINDER APPLICATION RATE FOR SINGLE/SINGLE APPLICATION SEALS 13 4. BASIC VOIDS FACTOR 13 5. ADJUSTMENTS 16 5.1 GENERAL 16 5.2 AGGREGATE ADJUSTMENT FACTOR 16 5.3 ADJUSTMENT FOR TRAFFIC EFFECTS 16 6. BASIC BINDER APPLICATION RATE 17 7. ALLOWANCES 17 7.1 SURFACE ALLOWANCES 17 7.1.1 Retreatment of Existing Seals 17 7.1.2 Resealing Over Asphalt 17 7.1.3 Resealing Over Primed Concrete Surfaces 17 7.1.4 Resealing Over Timber Surfaces 17 7.1.5 Sealing Treatments for New Pavements 17 7.1.6 Bituminous Slurry Surfacing 19 7.2 BINDER ABSORPTION 19 7.2.1 Binder Absorption by Aggregate 20 7.2.2 Binder Absorption by Pavement 20 7.2.2.1 New Pavements 20 7.2.2.2 Existing Pavements 20

Contents (continued) 7.3 EMBEDMENT 20 7.3.1 New Pavements 20 7.3.2 Exiting Pavements 21 8. DESIGN BINDER APPLICATION RATE 22 9. DESIGN APPLICATION RATES FOR SIZE 7 MM AND SMALLER 23 9.1 OVERVIEW OF THE DESIGN PROCESS 23 9.1.1 General 23 9.1.2 Inputs required to design a 7 mm or smaller sprayed seal 23 9.2 LOOSE AGGREGATE SPREAD RATE 23 9.3 BINDER APPLICATION RATE 24 9.3.1 Basic Binder Application Rate, BB, (L/m2) 24 9.3.1.1 ALD Known 24 9.3.1.2 ALD Unknown 24 9.3.2 Design Binder Application Rate 24 10. BINDER APPLICATION RATE FOR DOUBLE/DOUBLE SEALS OR RESEALS 27 10.1 GENERAL 27 10.2 FOR THE SECOND APPLICATION DELAYED 27 10.2.1 First application 27 10.2.2 Second Application with 7 mm or Smaller Aggregate 27 10.2.3 Second Application with 10 mm or Larger Aggregate 27 10.3 BOTH APPLICATIONS ON THE SAME DAY 28 10.3.1 First Application 28 10.3.2 Second Application with 7 mm or Smaller Aggregate 28 10.3.3 Second Application with 10 mm or Larger Aggregate 28 SECTION C — GUIDE TO THE AUSTROADS PROVISIONAL SPRAYED SEAL DESIGN METHOD — REVISION 2000 1. INTRODUCTION 29 1.1 GENERAL 29 1.2 ASSUMPTIONS 29 1.3 TYPES OF SPRAYED SEALS 30 1.3.1 Single/Single Seal 30 1.3.2 Single/Single Reseal 30 1.3.3 Double/Double Seal 30 2. DESIGN PHILOSOPHY 31 2.1 SINGLE/SINGLE SEALS 31 2.2 DOUBLE/DOUBLE SEALS 31 2.2.1 Double/Double Seals and Reseals - Delay of Second Application 32 3. EXISTING CONDITIONS AND CONSTRAINTS 33 3.1 DELAYED OPENING TO TRAFFIC 33 3.2 USE OF SMALL AGGREGATE SIZES (SIZE 7 OR SMALLER) ON COARSE

TEXTURED SURFACES 33 3.3 FACTORS AFFECTING THE BINDER APPLICATION RATES 34 4. SELECTION OF BINDER AND AGGREGATE 35 4.1 BINDER 35 4.2 AGGREGATE 35

Contents (continued) 5. DESIGN DATA 35 5.1 TRAFFIC 35 5.1.1 Introduction 35 5.1.2 Single carriageway - two way traffic 36 5.1.3 Dual carriageway - one way traffic 36 5.1.4 Heavy vehicles 36 5.1.5 Special conditions 37 5.2.1 Average Least Dimension 37 5.2.2 Absorption 37 5.2.3 Angularity 38 5.2.4 Shape 38 5.3 EXISTING SURFACE TO BE RESEALED 38 5.3.1 Surface Texture 39 5.3.2 Variations in Surface Texture 39 5.3.3 Influence of Surface Texture with Aggregate Size 39 5.3.4 Absorption of Binder by the Pavement 40 5.4 EMBEDMENT 40 5.5 ROAD GEOMETRY 41

SECTION D — REFERENCES & APPENDIX A APPENDIX A — SELECTION CRITERIA AND DATA RECORD SHEETS FOR VALIDATION OF THE REGRESSION APPROACH TO SPRAYED SEAL DESIGN 43

Austroads Provisional Sprayed Seal Design Method - Revision 2000

Preface

This report is in four sections:

Section A: Commentary on the development of the Austroads Provisional Sprayed Seal Design Method – Revision 2000

Section B: The Austroads Provisional Sprayed Seal Design Method – Revision 2000

Section C: A Guide to the Austroads Provisional Sprayed Seal Design Method – Revision 2000

Section D: References and Appendix

It is intended that each of the Sections A, B and C can be read separately and this has necessarily led to some duplication of information.

The commentary provides background information on the research that has led to the development of the provisional Revision 2000 sprayed seal design method. Additional discussion highlights the further work necessary to develop a new Australian/New Zealand sprayed seal design method.

The provisional sprayed seal design method Revision 2000 is contained in Section B of the report. The design method is released as a provisional method since it is expected that a further revision will take place in the year 2002. The design method provides procedures for designing both small sized (7 mm and smaller nominal size) and typical sized (10 to 20 mm nominal size) seals and reseals as well as strategies for double/double sprayed seal applications.

The Guide provided in Section C offers a greater insight into the application and development of the Revision 2000 design method. This is provided for both experienced and inexperienced designers of sprayed seals to gain a deeper understanding of how sprayed seals behave and the steps necessary to ensure in-service performance.

Section D contains relevant references and the data record worksheets developed to assist with characterising the validation trial sites.


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SECTION A COMMENTARY ON THE DEVELOPMENT OF THE

AUSTROADS PROVISIONAL SPRAYED SEAL DESIGN METHOD – REVISION 2000

1. INTRODUCTION

1.1 IMPORTANCE OF SPRAYED SEALS Sprayed seals are used on over 80% of the length of Australia's all weather road network to provide a safe, low cost running surfacing. A sprayed seal pavement can carry up to 10,000 vehicles per lane per day with a significant proportion of heavy commercial vehicles. In recent years, increased axle loads and tyre pressures and other environmental factors have imposed greater demands on sprayed seal surfacings, affecting their performance. Greater incidence of early distress, such as bleeding (reduced skid resistance) and stripping (reduced service life) has reduced the safety of road users and is a major concern. In response to these concerns with the current sprayed seal design method (Austroads 1990), this project was undertaken by the Austroads Sprayed Seal Design Project Group to improve the Austroads sprayed seal design method, construction practices and delivery systems.

1.2 PREVIOUS DESIGN METHODS The Austroads Design of Sprayed Seals procedure (Austroads, 1990) replaced the NAASRA (1975) Seal Design Method, based on methods developed by Hanson in 1935. A survey into the use of the NAASRA design method revealed that the basic binder application rate was determined in accordance with the NAASRA method but that local practitioners then made substantial alterations based on local knowledge of materials and pavement types. In effect, the success of a seal or reseal was overly reliant on the competence of the practitioner and this was a seen to be a major problem.

Whilst the Austroads (1990) sprayed seal design method represented a definite improvement over the previous version (NAASRA, 1975), concerns expressed by practitioners regarding a number of areas of deficiency indicated that the method required further refinement. The Austroads (1990) sprayed seal design method was based on collective experience of practitioners and introduced the use of simple tests to quantify surface hardness and existing surface texture depth. However, there were still a number of problems with sprayed seal designs at both the low and high traffic volumes that needed to be addressed.


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2. SPRAYED SEAL DESIGN METHOD TRIALS

2.1 BACKGROUND After a thorough review and assessment of the problems with the Austroads (1990) sprayed seal design method, the Project Group decided to carry out a number of field trials throughout Australia to compare three different methods of designing sprayed seals under various conditions of climate, traffic, etc. The following methods were trialled:

• Austroads 1990 method • a modified seal design method of the National Institute of Traffic and Road Research, South Africa

(NITRR) (Jordan and Gaughan 1994) • the local State Road Authority’s (SRA) method.

The road trial sections included new seals over primerseals, reseals and primerseals placed over a range of substrate strengths, with aggregate sizes 7, 10, 14, 16 and 20 mm, and traffic volume ranging between 50 and 6,000 vehicles/lane/day (v/l/d). A total of 47 sites were established in Western Australia (20), New South Wales (16), Victoria (6) and South Australia (5). Thirty seven of the sites were established in 1991/92 and the remaining ten sites during the 1992/93 sealing season.

2.2 OBJECTIVES The objective of the trials was to develop a performance based seal design model. Accordingly, the analysis of the trial data was based on building on current Australian and overseas concepts of seal design, i.e. the aggregate in a seal is orientated approximately one layer thick and contains a percentage of air voids. It is necessary to fill to a nominated level of the percentage of voids available with the binder to hold the aggregate in place. The minimum binder application rate required for this can be expressed as follows:

Binder application rate (L/m2) = percentage of voids to be filled × total available voids (%) × layer thickness (mm)

Adjustments or allowances must be made to this basic formula for factors such as traffic volume and composition, aggregate and pavement characteristics, surface texture, embedment, etc.

2.3 TRIAL RESEARCH PLAN The Austroads seal design trials monitoring data included the parameters measured from laboratory and field testing of samples from the 47 trial sites, during pre-construction and design, at placement of trial sites, and monitoring by SRAs and the Expert Team two years after placement.

Inputs used in the data analysis were:

• design traffic volume, T (vehicles/lane/day ), based on Annual Average Daily Traffic (AADT); • aggregate ALD obtained at the design stage; • binder application rate measured in the field; and • voids and recovered aggregate spread rate measured from seal behaviour testing.


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2.4 DATA ANALYSIS Analysis of the data and the development of the seal design model were approached in two ways:

1. application of rigourous statistical analysis to field and laboratory data, and 2. an approach based on the current Austroads design method format with some input from regression

analysis and practitioners’ experience based adjustments and allowances (commonly referred to as the incremental approach).

The outcomes of both the statistical and incremental approaches were compared against the Expert Team’s assessment of the performance of the trial sites. The success rate of the two approaches was measured by the design binder application rate obtained being within ± 0.2 L/m2 of the Expert Team’s ‘best section’ binder application rate.

2.5 OUTCOMES The analysis of the data from the sprayed seal design trials showed that the measured field layer thickness was greater than a single layer of average least dimension by 10 to 40%, depending on the size of the aggregate used. The measured aggregate voids fraction in the two year old, trafficked seal layer was also higher than the theoretically estimated value of 45 to 50%. The smaller the aggregate average least dimension, the higher the measured aggregate voids fraction.

In addition, the trials confirmed that there was a national tendency to overspread aggregate, and that the aggregate spread rate influenced the field layer thickness and voids in the aggregate layer. As a general indication, the recommended aggregate spread rate in the revised method is 10% lower than the current practice, i.e., a lighter aggregate spread rate. This is considered as one of the significant outcomes of the trial data analysis. The loose aggregate spread rate (m2/m3) adopted in the Austroads Provisional Seal Design Method – revision 2000 is:

Loose Aggregate Spread Rate (m2/m

3) =

900ALD

It was believed that neither the statistical approach nor the incremental approach was correct in all instances. The design method developed from the statistical analysis was seen as a radical shift from earlier methods of designing seals and would require significant effort to implement. It was believed that it would be unwise to release the statistically based seal design method prior to commissioning validation trials.

However, the seal design method based upon the incremental approach was seen as an incremental but definite improvement over previous methods. Users familiar with the previous Austroads method of seal design should not be unduly troubled by the design philosophy in the revised method. The incremental design method is released as a provisional update of the 1990 “Austroads Design of Sprayed Seals” document until the results of the validation trials can be assessed and incorporated into a final seal design method. Meaningful information from the validation trials can be expected in 2002

It is believed that the final sprayed seal design method will be a consolidation of the statistical and incremental approaches so as to ensure the most favourable outcome.


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3. STRUCTURE OF THE REVISED METHOD

3.1 GENERAL The revised design procedure (Revision 2000) has been produced for use in conjunction with the NAASRA Technical Report “Bituminous Surfacing - Sprayed Work (NAASRA 1989)”, and replaces:

• Section 3.3.3 - Aggregate Application Rate, (NAASRA, 1989) • Section 3.3.5 - Binder Application, (NAASRA, 1989) • Design of Sprayed Seals (Austroads 1990). Design procedures for seals and reseals using Polymer Modified Binders (PMBs), bitumen emulsions and geotextiles reinforced seals are under development.

The Revision 2000 differentiates between:

• single/single seals and reseals (single application of binder and a single application of aggregate) with 10 mm or larger aggregates

• single/single seals and reseals with 7 mm or smaller aggregates • double/double (two applications of binder and two applications of aggregate) seals and reseals.

3.2 DESIGN INFORMATION REQUIRED The following information is required to determine the aggregate spread rate and the design binder application rate:

• aggregate angularity (crushed, partly crushed or rounded) and if a crushed aggregate is used, one of the following aggregate characteristics must be known: aggregate shape (flaky to cubic) or the flakiness index.

• design traffic volume and composition in vehicles/lane/day (v/l/d) including the total for the lane/area, the percentage of heavy vehicles (% HV) for the lane/area

• road geometry • average least dimension of aggregate (mm) (optional for 7 mm or smaller aggregate) • binder absorption by aggregate and/or pavement (L/m2) • substrate texture depth (mm) or a visual assessment of the existing surface texture • embedment (mm), for seals only • existing surface condition.

3.3 REVISION 2000 DESIGN PROCEDURE The Revision 2000 procedure for the determination of the aggregate spread rate and the binder application rate requires progression through a sequence of operations.

The design philosophy is based on the following:

• use of single sized aggregate as described in NAASRA (1989), Chapter 4 • single layer of aggregate particles has typically 40 to 60 % voids • binder should be 50 to 60% up the height of the aggregate particle • aggregate particles may penetrate (embed) into the base • reseals interlock into the substrate • surface texture is required for skid resistance


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• binder may be absorbed into the base and aggregate • binder filled voids may be varied to optimise surface texture requirements and seal life.

3.3.1 Aggregate Spread Rate

It is important to note that, in the sprayed seal design method trials, only the design binder application rate was varied according to the design method used. At the time of the trial, manually operated box spreaders were used and it was decided that the aggregate spread rate would conform to existing SRA practice.

The aggregate spread rate established both the layer thickness of the seal and the voids to be filled with binder (subject to allowances for aggregate wear, embedment and minimum texture depth requirements). In view of the importance of aggregate spread rate to seal design, and with the more recent availability of improved and automated aggregate spreaders, a study of aggregate spreading was also undertaken.

The testing of seal behaviour samples taken from the trial sites after two years of trafficking generally indicated that an aggregate spread rate of approximately 900/ALD, had produced a satisfactory mosaic. This compares with an aggregate spread rate of 625/ALD to 800/ALD in the current method and a saving of at least 10% of the aggregate quantity used has been shown to be achievable, within the limits of accuracy of manually operated and properly maintained box and automatic spreaders.

3.3.2 Binder Application Rate

The procedure for determining a binder application rate varies depending upon whether the proposed surfacing is:

• a seal • a reseal • 7 mm and smaller, or 10 mm and larger • single/single seal • double/double seal.

Many of the concepts in the design of each seal type are identical. The first step for all 10 mm or larger sprayed seals is to determine a basic voids factor and this is related to the expected traffic levels. Adjustments for aggregate characteristics (flakiness, angularity) and traffic (composition of light and heavy vehicles, channelisation, short term abnormal traffic loading) are added to derive a design voids factor. This is multiplied by the ALD to determine the basic binder application rate.

With 7 mm or smaller sprayed treatments, there are two approaches dependant upon whether the ALD is available. In the simplest case where the ALD of the aggregate has not been measured, the basic binder application rate is established from a table at the appropriate the traffic level (vehicles/lane/day). If the ALD is available, a basic voids factor is determined from the appropriate chart and then multiplied by the ALD to derive a basic application rate, regardless of whether the proposed treatment constitutes a seal or reseal.

The basic binder application rate is then modified with allowances to cater for the type of surface being treated (surface texture, porosity), aggregate porosity and embedment into the underlying substrate, except where a 7 mm aggregate is the second application in a double/double seal or reseal (in which case, only the basic application rate is used). The allowances system is the same for all seals and reseals though there are separate surface texture allowances for the 7 mm and smaller sprayed treatments and the 10 mm and larger sprayed treatments.


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The design binder application rate is calculated by adding all the allowances to the basic binder application rate. It should be noted that some of the allowances may be negative and thus the design binder application rate may be lower than the basic binder application rate.

For double/double seals there are some differences dependant upon whether the second treatment is applied immediately or whether the first treatment is opened to traffic for a short period (months).

When it is planned that both treatments in a double/double seal will be placed on the same day, the first treatment is designed as a single/single seal but with a reduction in the design voids factor. Adjustments are as per normal for the first treatment and the second treatment is designed as a reseal but without allowances for surface texture or embedment.

When it is planned to delay placing the second treatment for a short period, the design procedure is the same as for a single/single reseal. The second treatment is designed with the binder application based upon the minimum and the aggregate application rate reduced by as much as 30%.


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4. VALIDATION TRIAL PROGRAM The Project Group commissioned a number of field trials with the specific aim of validating the models developed from regression analysis of the sprayed seal design method trial data. The first validation trials were placed in 1998 and sites have continued to be established through to 1999. The validation trial sites have been established with the following objectives:

• selection of a final seal design method • identification and refinement of any inconsistencies, e.g., over or under prediction, bias towards low or

high traffic, etc., in design application rates • review of the bleeding and stripping criteria proposed in the statistical approach design method • gaining of confidence in the final design approach • in the longer term, ensuring that the final seal design will provide longer lasting and better performing

sprayed seals. The validation program was designed to include a minimum of ten seal and reseal trial sites in each of six Australian States, however not all States were able to commission this number of trials. Site conditions such as surface texture and embedment, and traffic volume, were to cover as wide a range as possible depending on local conditions. Details of trial site selection criteria and design and a performance data record sheet are given in Appendix A of this report.

From the analysis of the sprayed seal design method trial data it was noted that surface texture steadily decreased over the first two years or so of seal life. After about two years the decrease in surface texture dramatically slowed and it was believed that the surface texture at this stage was more representative of the seal over its life. This meant that the validation trial sites will yield meaningful data after about two years service.

The structure of the validation program included the following:

• selection of test methods for field and laboratory testing • selection and establishment of validation trial sections • field and laboratory testing as part of monitoring of validation trial sites at predetermined intervals by

SRAs • inspection of validation trial sections by an Expert Team, two years after placement of the trial seals


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5. PROGRAM FOR FURTHER WORK Further work will be undertaken as part of a review of Austroads sprayed sealing design practices. Based on the outcomes of the project to date, further work in the following areas has been identified:

• evaluating Austroads Provisional Sprayed Seal Design Method - Revision 2000 • publishing an Austroads Sprayed Seal Design Method and Guide • workshops and seminars in all States to implement the final sprayed seal design method • seeking feedback on use of the final sprayed seal design method • continuing to monitor long term and validation trial sites to intervention or failure to obtain a history of

field performance • verifying and updating the final sprayed seal design method as appropriate.


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SECTION B AUSTROADS PROVISIONAL SPRAYED SEAL DESIGN

METHOD — REVISION 2000

FOREWORD

This Design Procedure has been prepared for use in conjunction with the NAASRA Technical Report “Bituminous Surfacing - Sprayed Work (NAASRA 1989)”, and replaces the design procedures in Section 3.3.3 - Aggregate Application Rate and Section 3.3.5 - Binder Application Rate of that document. The Design Procedure also replaces the Austroads document “Design of Sprayed Seals” published in 1990 (Austroads 1990).

Polymer Modified Binders (PMBs) and their aggregate application rates are outside the scope of this document. Refer to the Austroads Guidelines for the selection and use of PMBs.

This procedure has been produced as the result of an Austroads review involving 47 sealing trials and extensive monitoring work. The road trials compared the Austroads (1990), the local State Road Authority (SRA) and modified National Institute for Transport and Road Research (NITRR), South Africa design methods for use in Australia. As a result of this study, two approaches to seal design were considered based on:

1. a statistical analysis of field and laboratory data

2. an incremental improvement of the Austroads (1990) design method based upon the assessment of the seal design trials by experienced practitioners.

It is believed that the final method will be a consolidation of the two approaches so as to ensure the most favourable outcome. The method based upon the statistical approach is being fully validated by field performance trials.

The seal design method based upon an incremental improvement to the existing design method (Austroads, 1990) is believed to be a step forward and it is released as a provisional update of the 1990 “Austroads Design of Sprayed Seals” document until the results of the validation trials can be assessed and incorporated into a final seal design method and can be expected in 2002.

Designers should continue to apply their own judgement to the design application rates. It is requested that feedback be provided to the Austroads Sprayed Seal Design Research Project Group on any anomalies observed with regard to the Design Method given in this document.

This design procedure document describes the design rates of application for various seals and reseals in three parts as follows:

PART I — applicable to size 10 mm and larger aggregates, given in Sections 1 to 9

PART II — applicable to size 7 mm and smaller aggregates, given in Section 10, and

PART III — applicable to double/double seals, given in Section 11.


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PART I

1. OVERVIEW OF THE DESIGN PROCESS

1.1 General The design of sprayed seals has been divided into three distinct types as indicated in the foreword at the beginning of Section B of this report and these are:

1. Sprayed seals using an aggregate with a nominal size 10 mm or greater (see Figure 2),

2. Sprayed seals using an aggregate with a nominal size 7 mm or smaller (see Figure 5), and

3. Double/double sprayed seals.

A Guide (see Section C) has been prepared for those who are not familiar with the design of sprayed seals. This provides background, design philosophy, assumptions and discussion to the development and interpretation of the design method.

1.2 Inputs required to design a 10 mm or larger sprayed seal In each of the three seal types listed above, the design of a sprayed seal involves the determination of an aggregate spread rate and a binder application rate. To derive these quantities the following data are required:

• Average least dimension (ALD) of the aggregates.

• Traffic, in vehicles per lane per day, the percentage of heavy vehicles and whether the pavements are subjected to higher volumes of seasonal traffic,

• The binder absorption of the aggregate,

• Aggregate angularity (crushed partly crushed or rounded) and if a crushed aggregate is used, one of the following aggregate characteristics must be known; aggregate shape (flaky and/or elongate to cubic) or the flakiness index.

An assessment of the surface to be sealed will need to be undertaken and the assessment parameters will vary depending on whether there is an existing pavement or the work involves a new pavement. It will be necessary for the following items to be known before a sprayed seal can be designed:

• The type of existing pavement surface (e.g. sprayed seal, asphalt, concrete, timber, etc).

• The size of the existing seal (for reseal applications)

• The existing surface condition or the surface texture (i.e. flushed through to very coarse or measurements of the surface texture)

• The expected amount of binder that will be absorbed by the existing surface and the aggregate.

• The expected depth of aggregate embedment into the underlying substrate as determined by the ball penetration test.

1.3 Design overview The aggregate spread rate is calculated from the ALD of the aggregate. No other calculation is necessary and the only exception to this is in the provision of double/double seals and this is discussed in greater detail in section 10.

The design of the binder application rate begins with determining the amount of voids that need to be filled with binder for a given traffic level. This relationship has been developed over time from observations of sprayed seal performance. The ideal is for the binder to be about one half to two thirds the height of the aggregate (after about two years trafficking). This will ensure a satisfactory texture and durable life.


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The voids value is adjusted to cater for variations in aggregates and to cater for traffic situations that are not typical. The voids value is in litres per square metre per millimetre and is multiplied by the ALD of the aggregate to derive a base binder application rate.

Allowances are then determined to cater for variations in substrate surface properties, the capacity for the aggregate to absorb binder and the capacity of the substrate to absorb binder. The final allowance adjusts the binder application rate for situations where the sealing aggregate penetrates the substrate and becomes embedded and thus effectively reducing the ALD of the aggregate.


— 12 —

2. LOOSE AGGREGATE SPREAD RATE The previous sprayed seal design method (Austroads, 1990) calculated an aggregate spread rate based upon a theoretical relationship and suggested that in practice the spread rates needed to be increased above the theoretical rate to about 625/ALD to ensure a satisfactory coverage. Examination of field trial data established a practical relationship to calculate the loose aggregate spread rate using the following equation:

The practical spread rate of loose aggregate (m2/m3) = 900ALD

equation (1)

The aggregate spread rate shown in equation (1) and Figure 1 are less than those derived from the theoretical relationship. Aggregate spread rate is expressed in the number of square metres of coverage from a cubic metre of loose aggregate. A higher number in the numerator results in a lighter application rate (i.e. more square metres covered per cubic metre of loose aggregate).

50

100

150

200

250

4 5 6 7 8 9 10 11 12

Average Least Dimension (mm)

Aggr

egat

e Sp

read

Rat

e (m

2/m

3)

Fig. 1 Loose aggregate spread rate for seals and reseals

Note: The above spread rates do not include allowances for stockpile wastage. A typical allowance for stockpile wastage is 5 to 10 %.


— 13 —

3. BINDER APPLICATION RATE FOR SINGLE/SINGLE APPLICATION SEALS

The design of single/single application seals (i.e. one application of binder and one application of aggregate) involves:

• Determination of a basic voids factor (Vf) (Section 4) based upon the traffic (see section 5.1 of the Guide for a detailed discussion on derivation of traffic values).

• Adjustments to the basic voids factor (Vf) for aggregate (Va) and traffic (Vt) characteristics to derive a design voids factor (VF) (Sections 5 and 6).

• Conversion of the design voids factor (VF) to a basic binder application (BB) rate by multiplying with ALD.

• Allowances are then made to cater for absorption by the aggregate (AA) and the pavement (AP) and to cater for embedment (AE) into the underlying substrate to give the design binder application rate (BD) (Sections 7 and 8). An allowance (AS) is also required to compensate for the variety of surfacings that are to be sealed.

A flow chart for determination of aggregate and binder application rates for single/single sprayed seals is shown in Figure 2.

4. BASIC VOIDS FACTOR A basic voids factor, Vf (L/m2/mm) is determined from either Figure 3a or 3b depending on traffic level, and should be read to the nearest 0.01 L/m2/mm. The designer should use the central target line as the basic voids factor in all cases unless experience with specific situations suggests otherwise.

A stripping limit (upper bound) and bleeding limit (lower bound) are included in Figs. 3a and 3b. These limits represent zones where potential stripping of bleeding of seals may occur.


— 14 —

Seal Intentions * Road environment * Asset management criteria * Treatment type

Traffic Volume(vehicles/lane/day)

Basic Voids Factor, Vf

(L/m2/mm)Fig. 3

Traffic Effects, Vt

* Composition* Untrafficked areas* Short term effects* Climbing lanes* Passing lanes* Curvature* Intersections* Narrow lanes Table 2

VoidsFactor

Adjustments

Aggregate, Va

shape and sizeTable 1

Design VoidsFactor, VF

Basic BinderApplication Rate, BB

(L/m2) = VF x ALD

AggregateALD

Surface Texture, Aof existing seal

Table 3

Binder Absorption* by aggregate, A* by pavement, A Table 4

Embedment, A(seals only)

Fig. 4

Allowances(L/m2)

Design BinderApplication Rate, BD

(L/m2)Traffic Volume(vehicles/lane/day)

AggregateApplicationRate , Fig. 1

S

A

P

E

Fig. 2 — Determination of aggregate and binder application rates for single/single sprayed seals or reseals and the first application in a double/double seal.


— 15 —

0.15

0.20

0.25

0.30

0 100 200 300 400 500Traffic Volume (vehicles/lane/day)

Basi

c Vo

ids

Fact

or V

f (L/

m2/

mm

)

Bleeding Limit Target Stripping Limit

Fig. 3a — Basic Voids Factor (Vf) –Traffic Volume 0 – 500 vehicles/lane/day

0.05

0.10

0.15

0.20

500 1500 2500 3500 4500 5500 6500 7500 8500 9500Traffic Volume (vehicles/lane/day)

Basi

c Vo

ids

Fact

or V

f (L/

m2/

mm

)

Bleeding Limit Target Stripping Limit

Fig. 3b — Basic Voids Factor (Vf) -Traffic Volume 501 – 10,000 vehicles/lane/day


— 16 —

5. Adjustments

5.1 General Adjustments to the basic voids factor (Vf) are made to account for aggregate characteristics (Va) and for traffic effects (Vt) and this then becomes the design voids factor, VF (L/m2/mm). The design voids factor should lie within the limits shown in Figs 3(a) or 3(b). These factors are cumulative as shown in equation (2).

Design Voids Factor, VF = Vf + Va + Vt equation (2)

5.2 Aggregate Adjustment Factor An adjustment, Va, is made to the basic voids factor to account for the variation in aggregate characteristics in accordance with Table 1.

Table 1 — Aggregate Characteristic Adjustment Factor (Va)

Aggregate Type

Aggregate Shape

Flakiness Index (%)

Va

(L/m2/mm)

Crushed Flaky

Angular Cubic

26 to 35 15 to 25

< 15

-0.010 to +0 +0 to +0.005

+ 0.010 Partly crushed Not applicable Not applicable + 0.005

Rounded Not applicable Not applicable + 0.01

5.3 Adjustment for Traffic Effects Where traffic is channelled into confined wheel paths such as on single lane bridges, tight radius curves or pavements with confined lane widths, a traffic adjustment factor (Vt) should be made in accordance with Table 2.

Terrain and a higher than normal proportion of heavy vehicles will affect the performance of a sprayed seal and this is accounted for by using the traffic factors in Table 2. In flat or downhill terrain, where there is very low traffic volumes moving at high speed a traffic adjustment is also required as shown in Table 2.

Table 2 — Traffic Adjustment Factor (Vt)

Flat or downhill Slow moving – climbing lanes TRAFFIC EFFECT Normal Channelised* Normal Channelised*

15 to 30 % HV -0.01 -0.02 -0.02 -0.03 > 30% HV -0.02 -0.03 -0.03 -0.04

Fast moving cars only (overtaking lanes of multi-lane rural roads)

+0.01 0 N/A N/A

Untrafficked areas (shoulders, medians)

+0.02 N/A N/A N/A

* Possible short increases in traffic volumes such as during grain harvest, local field days, etc. that may occur early in the life of the seal or reseal should be allowed for by an increase in the design traffic volume. The road geometry also needs to be considered as this will affect traffic flow and ultimately the performance of the seal or reseal. The adjustment for road geometry has been include in the traffic effects adjustment in Table 2.


— 17 —

6. BASIC BINDER APPLICATION RATE The upper and lower lines in Figures 3a and 3b represent indicative limits for the design voids factor, VF. Practitioners must exercise caution if adopting design voids factors outside these limits. Significant risk of bleeding or stripping may be encountered above the upper limit and below the lower limit respectively. The basic binder application rate, BB (L/m2) is determined by multiplying the design voids factor (VF) by ALD as shown in equation (3).

BB = VF x ALD equation (3)

7. ALLOWANCES The following allowances are cumulative and must be added to the basic binder application rate (BB) to determine the design binder application rate, BD (L/m2).

Allowances in L/m2 are made for the following:

• surface texture of existing surfacing, the surface texture determined by the sand patch method in accordance with Austroads Test Method SDT 02 (Austroads, 1997b), for reseals and seals over primerseals (Table 3, Section 7.1)

• binder absorption by the aggregate and/or the existing pavement (Table 4, Section 7.2) • aggregate embedment into existing surface (for sealing treatments only) (Figure 4, Section 7.3)

7.1 Surface Allowances Allowances (AS) for existing surface texture may be substantial, and require a degree of judgement by the designer (see section 5.3 of the Guide).

7.1.1 Retreatment of Existing Seals

The allowances (AS) to be made for different sizes of resealing aggregate over various existing seal sizes and textures assumes satisfactory interlock between aggregates. There may be some aggregates which have unusual (atypical) shape or sizes, which require minor variations from the tabulated values given in Table 3a.

7.1.2 Resealing Over Asphalt

For an asphalt surface the sand patch test would not usually be appropriate. In this case, a surface allowance (AS) based on a visual assessment may be necessary, see Table 3c. Based on experience, AS should be between +0.0 and +0.3 L/m2. Where the asphalt is slick with fatty patches, the ball embedment test may be appropriate (see section 7.3).

7.1.3 Resealing Over Primed Concrete Surfaces

For a well primed concrete surface, the sand patch test may not be appropriate. In this case, a surface allowance, AS, based on a visual assessment may be necessary. Based on experience, AS should be between +0.2 and +0.4 L/m2 .

7.1.4 Resealing Over Timber Surfaces

For a timber surface, the sand patch test is not appropriate. Timber may be untreated, primed, coated or impregnated. A surface allowance, AS, based on experience and visual assessment may be necessary. As a guide, AS should be typically between +0.2 and +0.4 L/m2.

7.1.5 Sealing Treatments for New Pavements

Sealing treatments on aggregate primersealed surfaces will be treated as for reseals in 7.1.1 above for surface texture effects except that an additional embedment allowance is included (section 7.3).


— 18 —

For a seal over a primed surface, the sand patch test is not appropriate. In this case, a surface allowance, AS, based on a visual assessment may be necessary. Based on experience, AS should be between +0.0 and +0.2 L/m2. In addition, a ball penetration allowance will need to be measured or estimated (see section 7.3).

TABLE 3a — Surface Texture Allowance, AS (L/m2) For Existing Seals

Existing Seal Proposed Reseal Size Condition Texture Depth 5 mm 7 mm 10 mm 14 mm

5 mm Flushed a b -0.2 -0.2 -0.2

Black < 0.7 mm b -0.1

Smooth 0.9 mm

Well Textured 1.0 mm +0.1 +0.1 +0.1

Coarse 1.4 mm +0.2 +0.2 +0.2 +0.2

Very Coarse > 1.8 mm +0.3 +0.3 +0.3 +0.3

7 mm Flushed a b -0.2 -0.2 -0.2

Black < 0.7 mm -0.1 -0.1 -0.1

Smooth 1.0 mm

Well Textured 1.2 mm +0.1 +0.2 +0.2

Coarse 1.7 mm +0.2 +0.2 +0.3 +0.3

Very Coarse > 2.0 mm +0.3 +0.4 +0.4e +0.4

10 mm Flushed a b -0.2 -0.2 -0.2

Black < 0.7 mm -0.1 -0.1 -0.1

Smooth 1.0 mm +0.1 +0.2

Well Textured 1.4 mm +0.1 +0.2 +0.3 +0.4e

Coarse 1.9 mm +0.2 +0.3 +0.4e +0.5e

Very Coarse > 2.2 mm +0.3 +0.4 +0.5d +0.6d

14 mm Flushed a c b -0.3 -0.3

Black < 0.7 mm b -0.1 -0.1 -0.1

Smooth 1.0 mm + 0.1 +0.2

Well Textured 1.6 mm +0.1 +0.2 +0.4e +0.4e

Coarse 2.4 mm +0.2 +0.3 +0.5e +0.6d

Very Coarse > 3.2 mm +0.3 +0.4 +0.6d +0.7d

20 mm Flushed a c b -0.3 -0.3

Black < 0.7 mm c -0.1 -0.1 -0.1

Smooth 1.0 mm +0.1 +0.2

Well Textured 1.8 mm +0.1 +0.2 +0.4e +0.4e

Coarse 2.9 mm +0.2 +0.3 +0.5e +0.6d

Very Coarse > 3.5 mm +0.3 +0.4 +0.6d +0.8d

Notes a Embedment considerations dominate

b Not recommended

c Specialised treatments necessary

d Consider alternative treatments (fog coat or whatever, see text above)

e This treatment might not be advisable depending on the shape and interlock of aggregates.


— 19 —

7.1.6 Bituminous Slurry Surfacing

Table 3b provides surface texture allowances, AS, for bituminous slurry surfacings. This includes slurry seal surfacing and micro surfacing treatments. Visually, a slurry seal surfacing or a micro surfacing are similar and unless records indicate the surfacing type, the lower allowance should be adopted.

Table 3b — Surface Texture Allowance, AS (L/m2) For Bituminous Slurry Surfacing

Age (months) Type Thickness (mm) Appearance Allowance (L/m2) ≤ 3 SS

Micro ≤ 10 > 10

Smooth – black matt Smooth – black matt

- 0.1 - 0.2

3 to 12 SS

Micro

≤10

> 10

Some minor texture due to loss of fines Some minor texture due to loss of fines

Nil

Nil, + 0 to + 0.1

12 + SS

Micro

≤10

> 10

a) smooth, fine texture b) ravelling, coarse texture generally, would have some more texture than SS - may be similar to an asphalt

+ 0.1 + 0.2 + 0.2

Notes:

1. SS = Slurry Seal; Micro = Micro Surfacing

2. For flushed or bleeding surfaces: allowance of -0.2 to -0.3 L/m2

3. For badly ravelled surfaces - allowances should be checked by sand patch (refer Table Austroads Sprayed Seal Design Method Document)

Table 3c — Surface Texture Allowance, AS (L/m2) For Dense Graded Asphalt

Category Appearance Recommended Allowance New Asphalt, Age - up to 2 years

Black and smooth, with a large percentage of soft material, fines and binder, near the surface. Asphalt relatively soft and easily dug into with a screw driver, particularly when very new and low traffic. Small size asphalt is usually softest.

Embedment is to be expected, and is related to traffic volume/type, size and age of asphalt Heavy/high traffic - deduct 0.2 to 0.1 L/m2 Medium/low traffic - deduct 0.1 to 0.0 L/m2

Aged Asphalt, Age between 2 years and 5 years

Lost the blackness, there are less fines and the asphalt has hardened and is not easy to dig into with a screw driver.

Embedment is not expected, some allowance for texture and minor absorption. Heavy/high traffic - add 0.0 to 0.1 L/m2 Medium/low traffic - add 0.1 to 0.2 L/m2

Old Asphalt, Age - over 5 years

No longer black in appearance due to binder hardening and loss of binder, surface may still show fines near the top but generally more of the larger aggregate is showing, surface hard and difficult to dig into. Texture rated fine and smooth but too small or difficult to measure reliably.

Some absorption expected into the relatively dry asphalt surface and some texture allowance required. Heavy/high traffic - add 0.1 to 0.2 L/m2 Medium/low traffic - add 0.2 to 0.3 L/m2

7.2 Binder Absorption It will be necessary to increase the binder application rate to allow for any binder absorbed by the aggregate and/or the pavement, but it is not possible to give a general factor (See section 5.2.2 of the Guide for additional information).


— 20 —

7.2.1 Binder Absorption by Aggregate

Absorptive aggregates may fall into two general categories, i.e., those which are:

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

An aggregate should be tested for binder absorption in accordance with Austroads Test Method SDT 03 (Austroads, 1997c). Generally, the allowance for binder absorption by aggregate, AA, does not exceed 0.1 L/m2. Precoating alone will not usually compensate for absorption. The appropriate allowance to be added should be made in accordance with Table 4. However, allowances of up to +0.3 L/m2 may be needed in some circumstances.

7.2.2 Binder Absorption by Pavement

No test method has been devised at this time to measure the quantity of binder absorbed by a pavement.

7.2.2.1 New Pavements

For new pavements, the binder may drain into voids in the base course if a prime or primerseal has not adequately filled these. This is most likely to occur in sandy or silty rubble base courses (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 pavement allowance, AP, for this will generally be between +0.1 and +0.2 L/m2. Where AP is estimated to be more than +0.2 L/m2, an alternative treatment should be used.

7.2.2.2 Existing Pavements

Binder absorption into the substrate will seldom be a problem in reseals, unless the existing surface is visibly porous.

TABLE 4 — Allowances for Binder Absorption by Aggregate, AA (L/m2) (Austroads Test Method SDT 03)

Binder Absorption

(%)

AA

(L/m2) ≤ 1 +0 to +0.1

> 1 to 3 + 0.1 to +0.3

≥ 3 Do not use unless performance is proven

7.3 Embedment Typical embedment allowances, AE (in L/m2) for sprayed seals are shown in Figure 4. Existing pavement surface hardness should be determined by the Ball Penetration Test, in accordance with the Austroads Test Method SDT 04 (Austroads, 1997d). (See section 5.4 of the Guide for additional information.)

7.3.1 New Pavements

Embedment of aggregate may occur:

• in an initial treatment applied over a soft base • in a sealing treatment applied over a primed or primersealed surface.


— 21 —

1

2

3

4

5

6

7

8

0 1000 2000 3000 4000 5000Traffic Volume (vehicles/lane/day)

Bal

l Pen

etra

tion

(mm

)

-0.4 L/m2

-0.3 L/m2

-0.2 L/m2

-0.1 L/m2

NIL

Fig. 4 — Embedment allowance for seals (AE)

Note: Where embedment allowances of -0.3 L/m2 or more are indicated, consideration should be given to alternative treatments. Alternatives such as armour-coating with higher quality materials rolled into the surface of the base or the use of a primerseal/prime and seal with a small aggregate in order to provide a platform on which a larger aggregate seal may be placed.

7.3.2 Exiting Pavements

An embedment allowance, AE, may be required for sealing over an existing pavement:

• if there is free binder on the surface being resealed • when applying a reseal over fresh asphalt or slurry surfacing.


— 22 —

8. DESIGN BINDER APPLICATION RATE The equation for the determination of the design binder application rate, BD (L/m2), is as follows:

BD = BB + AS + AA + AP + AE equation (4) Where

BB = basic binder rate determined in accordance with equation (3) AS = Surface allowance (section 7.1) AA = Allowance for aggregate absorption (section 7.2.1) AP = Allowance for pavement absorption (section 7.2.2) AE = Allowance for aggregate embedment (section 7.3)


— 23 —

PART II

9. DESIGN APPLICATION RATES FOR SIZE 7 mm AND SMALLER

9.1 Overview of the Design Process

9.1.1 General

The design philosophy for size 7 mm and smaller aggregates is the same as for size 10 mm and larger aggregates. That is, adjustments and allowances to the basic voids factor and basic binder application rate need to be considered. A flow diagram (see Figure 5) illustrates the design method for the 7 mm and smaller seals.

9.1.2 Inputs required to design a 7 mm or smaller sprayed seal

The following information is required to design a sprayed seal with a nominal size 7 mm or less:

• ALD (optional) • Traffic, in vehicles per lane per day, the percentage of heavy vehicles and whether the pavements

are subjected to higher volumes of seasonal traffic • The binder absorption of the aggregate • Aggregate angularity (crushed partly crushed or rounded) and if a crushed aggregate is used, one

of the following aggregate characteristics must be known; aggregate shape (flaky and/or elongated to cubic) or the flakiness index.

An assessment of the surface to be sealed will need to be undertaken and the assessment parameters will vary depending on whether there is an existing pavement or the work involves a new pavement. It will be necessary for the following items to be known before a sprayed seal can be designed:

• The type of existing pavement surface (e.g. sprayed seal, asphalt, concrete, timber, etc.) • The size of the existing seal (for reseal applications) • The existing seal surface condition or the surface texture (i.e. flushed through to very coarse or

measurements of the surface texture) • The amount of binder that will be absorbed by the existing surface • The amount of aggregate embedment likely as determined by the ball embedment test.

9.2 Loose Aggregate Spread Rate In general, a typical loose aggregate spread rate for size 7 mm and smaller aggregates is about 200 to 250 m2/m3. The broad ranges of typical spread rates for 7 mm and smaller aggregates take into account different seal objectives. Lighter spread rates are applied where the aggregate is being used in conjunction with light binder application rates to fill the spaces in a coarse textured surface, e.g. correction seals. Heavier spread rates are applied where a complete interlocked aggregate matrix is required. With 5 mm aggregates and sands, this may even result in more than one thickness of aggregate particles.


— 24 —

9.3 Binder Application Rate Derivation of a binder application rate depends upon whether the ALD of the sealing aggregate is known. The design process is shown diagrammatically in Figure 5.

9.3.1 Basic Binder Application Rate, BB, (L/m2)

9.3.1.1 ALD Known

A basic voids factor is determined from Figure 3 and adjustments for aggregate (Va, Table 1) and traffic (Vt, Table 2) are added to the basic voids factor to derive the design voids factor, BD, which is multiplied by the ALD to derive a basic binder application rate, BB.

9.3.1.2 ALD Unknown

A basic binder application rate, BB (L/m2), can be selected from Table 5 based upon the traffic, taking into account the notes at the conclusion of the table.

9.3.2 Design Binder Application Rate

Determine the design binder application rate, BD, by adding allowances for surface texture (AS, Table 6),

binder absorption by aggregate (AA Table 4, section 7.2.1), binder absorption by pavement (AP, section 7.2.2) and embedment (AE, Figure 4) to the calculated basic binder application rate, BB.

TABLE 5 — Basic Binder Application Rates, BB (L/m2) For Size 7 mm and Smaller Aggregates

Vehicles/lane/day |

(v/l/d)

BB

(L/m2) < 100 0.8 to 1.0

100 to 600 0.7 to 0.9 601 to 1200 0.6 to 0.8 1201 to 2500 0.5 to 0.7

> 2500 0.5

Notes:

a. The lower of the basic binder application rates should be selected for use with flaky aggregates. The higher of the basic binder application rates should be selected for use with more cubically shaped aggregates.

b. The lower of the basic binder application rates should be used where traffic includes 10% HV or higher.

c. If not certain of the conditions and traffic composition, it is recommended the mid-point basic binder application rate be selected.

d. If the smaller aggregate is part of the second application of a double/double seal, applied within a short time after the first application, then it is recommended that the lower of the basic binder application rates be selected and no allowances added.


— 25 —

Basic BinderApplication

Rate, BB

Table 5

ALD

Basic VoidsFactor, Vf

(L/m2/mm)

Fig. 3

NO ALD


Allowances L/m2

* Surface texture (Table 7)* Binder absorption (Table 5)* Embedment (Fig. 5)

Basic Binder ApplicationRate, BB (L/m2)

BB = ALD x VF


Design Voids Factor,VF L/m2/mm

VF = Vf + Vt + VaFig. 3, Table 1 & Table 2

Design Binder ApplicationRate, BDBD = BB + Allowances

(L/m2)

Fig. 5 — Determination of binder application rate for 7 mm and smaller single/single sprayed seals


— 26 —

Table 6 — Surface Texture Allowances, AS (L/m2) For Size 7mm and Smaller Aggregates

Existing Seal Proposed Seal Size Condition Texture Depth 5 mm 7 mm 5 mm Flushed a b -0.2

Black < 0.7 mm b -0.1 Smooth 0.9 mm Well Textured 1.0 mm +0.1 Coarse 1.4 mm +0.2 +0.2 Very Coarse > 1.8 mm +0.3 +0.3

7 mm Flushed a b -0.2 Black < 0.7 mm -0.1 -0.1 Smooth 1.0 mm Well Textured 1.2 mm +0.1 Coarse 1.7 mm +0.2 +0.2 Very Coarse > 2.0 mm +0.3 +0.4

10 mm Flushed a b -0.2 Black < 0.7 mm -0.1 -0.1 Smooth 1.0 mm Well Textured 1.4 mm +0.1 +0.2 Coarse 1.9 mm +0.2 +0.3 Very Coarse > 2.2 mm +0.3 +0.4

14 mm Flushed a c b Black < 0.7 mm b -0.1 Smooth 1.0 mm Well Textured 1.6 mm +0.1 +0.2 Coarse 2.4 mm +0.2 +0.3 Very Coarse > 3.2 mm +0.3 +0.4

20 mm Flushed a c b Black < 0.7 mm c -0.1 Smooth 1.0 mm Well Textured 1.8 mm +0.1 +0.2 Coarse 2.9 mm +0.2 +0.3 Very Coarse > 3.5 mm +0.3 +0.4

Notes:

a Embedment considerations dominate

b Not recommended

c Specialised treatments necessary


— 27 —

PART III

10. BINDER APPLICATION RATE FOR DOUBLE/DOUBLE SEALS OR RESEALS

10.1 General A double/double seal or reseal consists of two applications of binder each followed by an application of aggregate. Double/double seals may be laid in two ways:

• the second application delayed • both applications placed on the same day.

Typically the aggregate in second application is designed to fit into the spaces in the surface texture of the first application. This will generally result in the aggregate in the second application being no more than half the nominal size of the aggregate in the first application.

10.2 For the Second Application Delayed When the second application is to be applied some time after the first, e.g. after several months of trafficking, both applications should be designed as single/single seals, except that the design binder and aggregate application rates for the second application may be reduced to the minimum basic rate, to fill the void spaces in the first application only, i.e. no surface texture or embedment allowances are applied.

10.2.1 First application

Design as for a single/single seal or reseal. (See Sections 2, 8 and 9.)

10.2.2 Second Application with 7 mm or Smaller Aggregate

The basic binder application rate (BB) is determined using the procedures in Section 9.3.1. The design binder application rate (BD) is determined by adding allowances for aggregate and pavement absorption (AA and AP respectively) to the basic binder application rate. However, it is unlikely that there will be any binder absorption by the pavement.

The aggregate spread rate is determined using the procedures in sections 2 and 9.2 and then reduced by up to 30% (use 30% less aggregate). This should fill the void spaces in the first application and avoid excessive aggregate loss.

10.2.3 Second Application with 10 mm or Larger Aggregate

The basic binder application rate (BB) is determined using the procedures in Section 6. The design binder application rate (BD) is determined by adding allowances for aggregate and pavement absorption (AA and AP respectively) to the basic binder application rate. However, it is unlikely that there will be any binder absorption by the pavement.

The aggregate spread rate is determined using the procedures in section 2 and reduced by up to 30% (use 30% less aggregate). This should fill the void spaces in the first application and avoid excessive aggregate loss.


— 28 —

10.3 Both Applications on the Same Day When the second application is to be applied immediately after the first, with little or no trafficking between applications, the following design procedure may be used. It should be noted that the first application designed using the principles outlined in this section, is very vulnerable to traffic damage, and the second application must be applied on the same day.

To retain more of the second layer of aggregate in the final mosaic, the total binder application rate for both layers can be calculated. If the traffic volume allows, the binder application rate for each layer may be proportioned more evenly (e.g. 55% of the total binder in the first layer and 45% in the second). In some circumstances, the lower binder application rate may be placed on the bottom to ensure there is sufficient binder to hold the second aggregate in place.

10.3.1 First Application

The design voids factor is determined using the procedures in section 5 and this is reduced by the factor in Table 7. The design binder application rate (BD) can then be calculated using the procedures in section 8 based upon the reduced design voids factor. The design binder content should be at least 0.1 x ALD.

The aggregate spread rate is reduced by 10% from that calculated using the procedures in sections 2 or 9.2.

10.3.2 Second Application with 7 mm or Smaller Aggregate

The basic binder application rate (BB) is determined using the procedures in Section 9.3.1. The design binder application rate (BD) is determined by adding allowances for aggregate and pavement absorption (AA and AP respectively) to the basic binder application rate. However, it is unlikely that there will be any binder absorption by the pavement.

The aggregate spread rate should just fill the void spaces in the first application and avoid excessive aggregate loss.

10.3.3 Second Application with 10 mm or Larger Aggregate

The basic binder application rate (BB) is determined using the procedures in Section 6. The design binder application rate (BD) is determined by adding allowances for aggregate and pavement absorption (AA and AP respectively) to the basic binder application rate. However, it is unlikely that there will be any binder absorption by the pavement.

The aggregate spread rate should just fill the void spaces in the first application and avoid excessive stone loss.

Table 7 — Modification To Design Voids Factor for the First Seal of a Double/Double Seal

Traffic Volume (vehicle/lane/day)

Modification to VF (%)

≤500 -25 501 to 1000 -21 1001 to 1500 -17 1501 to 2000 -13

> 2000 -10


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SECTION C GUIDE TO THE AUSTROADS PROVISIONAL SPRAYED SEAL

DESIGN METHOD – REVISION 2000

This Guide document has been prepared to supplement the information in the Austroads Provisional (Revision 2000) Seal Design Method. The information within this Guide will assist both experienced seal designers and those less familiar with the design of binder and aggregate application rates for sprayed seal surfacings.

1. INTRODUCTION

1.1 General Sprayed sealing is the application of a thin surface layer of bituminous binder into which aggregate is incorporated.

The functions of a sprayed seal are:

• to protect the underlying pavement and subgrade from water and other damaging effects of the environment

• to provide a wearing surface resistant to abrasion by vehicles; and • to provide an economical, durable and skid resistant surface on which it is safe and comfortable to

travel under normal weather conditions and reasonable driving practices. Selection of an appropriate sprayed sealing treatment, and the design of the binder application rate and the aggregate spread rate, requires careful consideration (NAASRA 1985, 1989). The following factors affecting the selection and design should be taken into account:

• existing surface conditions • road alignment and grades • traffic composition • availability of materials • weather and moisture conditions • expected life • occupational health and safe working practices • economy • safety and environment

1.2 Assumptions The Austroads sprayed seal design method for size 10 mm or larger aggregate is based on the following assumptions:

• the average least dimension of the aggregate is determined by direct measurement • correct prime/primerseal design and application. Where this has not been achieved, remedial work

should be undertaken prior to commencement of sealing. • the aggregate is sound and single-sized • aggregate is spread in a uniform layer of one stone thickness, with particles in continuous, partly

interlocked contact, with the least dimension near vertical • the aggregate spread rate determines the inter-aggregate void space in the seal layer, and hence the

amount of binder required


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• failure to achieve the correct aggregate spread rate will result in the designed binder application rate being incorrect.

• That appropriate work practices have been adhered to in the placement of the seal or reseal and this will include the use of precoating (see APRG Pavement Work Tip No. 23) and appropriate rolling practices (see APRG Pavement Work Tip No. 24).

The design method for seals with aggregate size 7 mm or less differ from the coarser seals in that:

• the sealing aggregate is not generally tested to determine the average least dimension • they are commonly used as a correction courses to provide an interim even surfacing prior to the

placement of a more durable surface treatment • they are used in situations that can tolerate a reduced surfacing life, such as where a temporary

surfacing is required.

1.3 Types of Sprayed Seals There is a large range of sprayed seal types possible but in Australia the majority of sprayed seal work utilises a single/single seal or reseal and less commonly a double/double seal or reseal. Other types of seals are being researched but are beyond the scope of the Revision 2000 design method.

1.3.1 Single/Single Seal

A single/single seal consists of one application of binder and one application of aggregate over a base, primed or primersealed surfacing to provide a waterproof, and skid resistant riding surface.

1.3.2 Single/Single Reseal

A reseal is the utilisation of a single/single seal to an existing bituminous surface to restore a previously sealed surfacing to a satisfactory condition. It may also apply to resealing over a primed concrete surface or timber bridge deck.

1.3.3 Double/Double Seal

A double/double seal consists of two applications of binder and aggregate. The aggregate in the second application is normally no more than half the size of the first, and spread rate is just sufficient to fill the voids in the first application


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2. DESIGN PHILOSOPHY The design objective is for the residual binder to be about 50 to 60% of the height of the aggregate layer two years after construction. The residual binder comprises bitumen, flux oil and adhesion agent, but does not include cutter oil or water. The amount 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 stated in L/m2, of residual binder at a temperature of 15°C. In determining the actual field application rate, allowances must be made for proportion of the cutter oil or water (emulsions) and the volume corrected for the spraying temperature.

2.1 Single/Single Seals The general aim of the design of single/single sprayed seal or reseal is to achieve a single layer of aggregate particles in continuous, interlocked contact, with sufficient binder to hold the aggregate in place leaving sufficient surface voids to ensure adequate surface texture.

The design philosophy is based on the use of single-sized aggregate in accordance with AS 2758.2 - Aggregate for Sprayed Bituminous Surfacing. Aggregates not complying with this Standard may result in inappropriate design. The following summarises the findings of recent Austroads sprayed seals trials:

• single layer of aggregate particles has typically 40 to 60 % voids • for a seal, the binder should be 50 to 60% up the height of the aggregate particle after two years of

service • aggregate particles may penetrate (embed) into the base • reseals interlock into the substrate • surface texture is needed for skid resistance (desirable surface texture should exceed 1.2 mm) • binder may be absorbed into the base and aggregate • binder filled voids may be varied to optimise surface texture requirements and seal life.

2.2 Double/Double Seals In certain circumstances, such as at intersections, high stress areas, etc., double/double seals may be used. The general aim of the design of double/double seals is for the aggregate in the second application to occupy the spaces between the aggregate particles in the first application. The second layer improves interlock and modifies the surface texture of the first layer. It is usual for the aggregate for the second application to be half the size of the first, or smaller. Generally, the rate of application of binder and aggregate between the two applications may be varied to produce the desired surface characteristics.

The design philosophy of a double/double seal is such that:

• the first layer is designed as per single/single seal or reseal (as appropriate) and the rate of application of binder and aggregate spread rate may be reduced if the second application is done within few days of the first

• the design of the second layer is based on single/single seal or reseal (as appropriate), with reduced binder and aggregate application rates

• the total design binder and aggregate application rates are less than the sum of two single/single seals.

Both layers of a double/double seal are designed as for single/single seals except that for the first layer the basic voids factor is reduced (in accordance with Table 7 in the Design Method).

The second layer is designed without any surface texture or embedment allowances.

As general rule, the total binder required for both layers will be about 70% of that required for the two layers designed as separate reseals. The total binder may be divided in halves, and the resultant application rate, applied for each layer.


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2.2.1 Double/Double Seals and Reseals - Delay of Second Application

Where the second application is to be applied after 1 week and up to several months after the first application, and the seal will be trafficked during this delay:

• The first application should be designed as a single/single seal or reseal (as appropriate). • For the second application, the binder application rate may be reduced to a minimum and the

aggregate spread rate reduced by up to 30% (use 30% less aggregate). This should fill the void spaces in the first seal and avoid excessive loss of aggregate particles. a) For 7 mm and smaller aggregates: the basic binder application rate is given in Table 5, b) For 10 mm and larger aggregates: The basic binder application rate is calculated by adding

adjustments (Tables 1 & 2) to the basic voids factor (Fig.3a or 3b) and then multiplying by the ALD of the aggregate (i.e. no adjustments).

Note: the traffic adjustment factor and the basic voids factor will be the same as for the first seal or reseal application.


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3. EXISTING CONDITIONS AND CONSTRAINTS

3.1 Delayed Opening to Traffic Primerseals and seals which are left for some time prior to opening to traffic present difficulties with aggregate retention and flushing, particularly in cold, wet weather. Where some doubt exists in regard to the application, seek specialist advice before proceeding. On new freeways and bypass roads where it is not feasible to run traffic on each stage of seal construction as it is completed, larger size seals should be deferred until just before, or shortly after, opening. Where circumstances dictate that the larger size seals must be applied well in advance of opening, an enrichment or small sized aggregate seal should be applied just prior to opening. Primerseals or prime and seals using 7 mm or smaller aggregates should be used to protect each completed section of pavement until the whole length of road can be trafficked.

3.2 Use of Small Aggregate Sizes (Size 7 or Smaller) on Coarse Textured Surfaces

A small aggregate seal is a versatile treatment. It can provide a result ranging from a uniform small aggregate seal appearance to the old aggregate being visible with the small aggregate locked into the voids. Binder application rates for small aggregates applied on coarse textured seals will vary according to the end result required (Refer Design Method Section 9). This may be achieved by applying the full surface texture to provide a high design binder application rate, to applying a nil allowance resulting in a base design binder application rate. See section 5.3.2. A flow diagram (see Figure 5 of the Design Method) illustrates the design method for the 7 mm and smaller seals and it allows two approaches to the design of these seals.

3.2.1 ALD not measured

The basic binder application for 7 mm and smaller seals and reseals is based predominantly upon the traffic and can be determined from Table 5 of the Design Method. Attention is drawn to the Notes of Table 5. As the ALD of 7 mm and smaller aggregates has not been determined, a simpler design procedure has been adopted. In the simpler design procedure the basic binder application rate is determined directly from Table 5 requiring only a knowledge of the traffic . This simpler procedure does not require any adjustments to be added. Allowances are applied to the basic binder application rate to derive a design binder application rate.

3.2.2 ALD measured

Where the ALD of the aggregates is known, the design procedure for size 7 mm and smaller aggregates is similar to that for size 10 mm and larger aggregates. A basic voids factor is determined from Figure 3. Adjustments for aggregate (Table1 of the Design Method) and traffic (Table 2 of the Design Method) are added to the basic voids factor to derive the design voids factor which is multiplied by the ALD to derive a basic binder application rate. Appropriate allowance are then applied to the basic binder application rate to derive the design binder application rate.

3.2.3 Aggregate spread rates

In general, a typical loose aggregate spread rate for size 7 mm and smaller aggregates is about 200 to 250 m2/m3. The broad ranges of typical spread rates for 7 mm and smaller aggregates take into account different seal objectives. Lighter spread rates are applied where the aggregate is being used in conjunction with light binder application rates to fill the spaces in a coarse textured surface, e.g. correction seals. Heavier spread rates are applied where a complete interlocked spread is required. With 5 mm aggregates and sands, this may even result in more than one thickness of aggregate particles.


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3.3 Factors Affecting the Binder Application Rates Orientation and embedment are mainly functions of rolling, traffic compaction and substrate properties. It is essential that adequate, timely rolling is carried out, particularly at low traffic volumes, < 100 vehicles/lane/day (v/l/d), to achieve initial aggregate interlock, orientation and embedment. Increasing volumes of traffic will cause the reorientation of the aggregate and increase aggregate embedment, and hence, reduce the binder quantity required. Consequently the seal layer volume to be filled with binder will decrease with an increase in traffic volume.


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4. SELECTION OF BINDER AND AGGREGATE

4.1 Binder Binder types, and conditions for their use, are given in NAASRA (1989).

4.2 Aggregate The aggregate size is selected as part of the selection of surface treatment (NAASRA 1989).

5. DESIGN DATA The following design input parameters are required:

• traffic volume and composition (this should be determined separately for each lane) • aggregate Average Least Dimension (ALD) and aggregate shape • surface texture depth • binder absorption by aggregate and pavement • embedment (seals only) • road geometry.

5.1 Traffic

5.1.1 Introduction

To determine the appropriate rates of application of binder to use in a seal design, it is essential to base the design on accurate traffic volumes. The traffic volume data used should be expressed in terms of total number of vehicles and composition in terms of light and heavy vehicles (heavy vehicles are those over 3.5 tonne gross mass).

Traffic volumes are generally provided as the total volume on the road and ignore the number of traffic lanes, shoulders, etc. In addition, the traffic volume may be based on a 12 hour or 24 hour count at a particular date or time, or be given as the Annual Average Daily Traffic (AADT), expressed as vehicles per lane per day (v/l/d).

The 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, to convert from 12 hour counts to AADT, the factor to multiply by is of the order of 1.25 to 1.30. For a freeway or for some 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.

Converting the AADT to the Design Traffic, in vehicles per lane per day, must take into account the following:

• the number of carriageways (single or dual) • the direction of traffic (one-way or two-way) • number of lanes • percentage of the total traffic that uses each lane.

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


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5.1.2 Single carriageway - two way traffic

The traffic needs only to be apportioned to each lane. The width of sealed pavement influences the traffic pattern. Based on the general design criteria of pavement widths for various traffic volumes, and that traffic is equal in both directions, the following is a guide to estimating the design traffic:

Table C1 — Apportioning Traffic for Single Carriageway - Two Way Traffic

Width of Seal (m) Estimated Design Traffic (v/l/d) 3.7 to 5.6 AADT 6.2 to 7.4 ½ x AADT

sealed shoulders (line marked) adopt < 50 overtaking lanes (in one direction)

left hand lane (3.7m) right hand lane (3.7m)

80% of ½ x AADT 20% of ½ x AADT

5.1.3 Dual carriageway - one way traffic

The Average Annual Daily Traffic (AADT) is the total traffic carried by both carriageways, but this should be checked. If it is the total for both carriageways, the first step is to determine the traffic on each carriageway, and generally this can be assumed to be ½ AADT.

For heavily trafficked roads, with more than 2 lanes in each direction, the actual traffic count is generally available for each individual lane and this should be the traffic volume used in the design. If the actual lane traffic count is not available, then based on normal road design criteria, the traffic may be assumed usually to be in excess of 2000 v/l/d.

For rural freeways and highways, or duplicated roads into rural townships (classed as urban type location) etc., with medium to high traffic volumes, Table C2 provides a guide to estimating the design traffic from the AADT:

5.1.4 Heavy vehicles

The traffic volumes are based on the general mix of light and heavy vehicles, with the heavy vehicle proportion assumed to be less than 10% of the total. If the 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 in one direction only. Generally the heavy vehicles use the left hand lanes on multi-lane carriageways, and the left hand climbing or passing lanes.


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Table C2 — Apportioning Traffic for Dual Carriageway - One Way Traffic

Lane (assumed 3.7m wide) Estimated Design Traffic (v/l/d) Comments multi lane heavily trafficked ½ AADT divided by the number of lanes

in the carriageway OR ½ AADT x % traffic in each lane

usually urban or linking major centres (generally traffic > 2000 in all lanes)

2 lane carriageway left hand lane right hand lane

60 to 80% of ½ AADT 20 to 40% of ½ AADT

60% for urban / 80% for rural 40% for urban / 20% for rural

Shoulders assume < 50 Where two lanes merge into one (at end of the duplicated section)

½ AADT

off and on ramps % of ½ x AADT often the traffic on the side road, before and past the ramp, may provide an indication of the traffic volume using the ramp

Note: On some busy roads, trucks may tend to travel on the shoulders, and this must be taken into account.

5.1.5 Special conditions

Special traffic conditions may apply on roads in tourist areas where the traffic volume may vary considerably during the year. In such cases, the designer should base the design on the traffic estimated at the time of sealing work plus the traffic in the following three months.

Quarry access roads and roads carrying a very high commercial vehicles, say over 30%, will require special consideration.

5.2 Aggregate Characteristics

5.2.1 Average Least Dimension

The design requires the use of the average least dimension (ALD) of the actual aggregate to be used for the work when the nominal size of the aggregate is greater than 7 mm. ALD of 7 mm or smaller aggregates are not generally measured. However, in some instances the ALD of 7 mm or smaller aggregates are measured and the ALD can be used in the design process. The ALD is determined in accordance with Austroads Test Method (1997).

The sprayed seal design method has evolved based upon ALD determined from direct measurement. ALD determined from nomograph procedures based upon grading should not be used.

5.2.2 Absorption

Some aggregates will absorb part of binder over time (porous aggregates [such as sandstone, rhyolite, etc], and vesicular aggregates [such as scoria, slags, etc.] most commonly exhibit this tendency), resulting in the decrease of effective binder and a possible loss of aggregate from the seal under traffic. Adding allowances (L/m2) to the basic binder application rate compensates for this characteristic. A guide to allowances for binder absorption is given in the design method (Table 4).

An aggregate should be tested for binder absorption in accordance with Austroads Provisional Test Method SDT 03 (Austroads 2000c). Absorption values can range from nil to > 3% by mass of dry aggregate and different aggregates absorb bitumen over different lengths of time. Typically, the allowance for binder absorption is about 0.1 L/m2. The appropriate allowance to be added should be made in accordance with Table 4 in the Design Method.

Precoating alone will not usually compensate for absorption. For further information on precoating practice, the reader is referred to APRG Work tip No. 23


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5.2.3 Angularity

The number of aggregate crushed faces influences the binder application rate. Rounded or partly crushed aggregates require more binder to hold the aggregate firmly in the seal. Crushed aggregates will form a stronger interlocking mosaic and may actually need a reduction in the binder application rate.

5.2.4 Shape

The shape of crushed aggregate influences the binder application rate. Aggregate shape is determined in accordance with AS 2358.2.

5.3 Existing Surface to be Resealed Surface allowance can be broadly separated into the following three distinct types:

• bleeding surface - where texture measurement is not applicable but ball embedment may be determined by a standard test

• textured surface - where measurement of the texture can be performed by a standard test method • flat surface - where surface texture measurement is not applicable.

For a bleeding surface, which comprises free bituminous binder, a ball embedment test may be used to determine an allowance (see Fig. 4), in the order of -0.1 L/m2 to -0.4 L/m2. If in doubt, an allowance of -0.2 L/m2 is a good starting point.

For a textured surface, appropriate surface allowances are given in Table 3a. This is applicable for existing primersealed, sealed or resealed surfaces, and takes account of the measured existing surface texture, existing seal size, and the nominated seal size to be applied.

For a flat surface, e.g. primed base, slurry surfacing, asphalt, cement concrete and timber bridge deck, only broad guidelines can be provided as this relies on a preliminary site inspection by the designer prior to determining the magnitude of the allowance to be used.

Note: Practitioners are sometimes over-cautious when selecting a surface allowance for a flat surface, and typically they tend to underestimate the allowance by up to + 0.2 L/m2. In most circumstances, values of 0.0 to + 0.1 L/m2 are selected and this results in a stripping failure.

Table 6 of the Design Method shows the allowances for surface texture for size 7 mm and smaller aggregates. It should be noted that there are a number of warnings built into the table to alert users where a small seal or reseal is inappropriate or where a specialised treatment should be considered. In a number of instances embedment needs to be checked as it is likely that in these instances the allowance for embedment will predominate the design.

5.3.1 Selection of allowances for flat surfaces

It should be appreciated that, on a flat surface, there is no underlying texture into which the seal can lock, i.e. no friction key. It is essential therefore that sufficient binder is applied to secure (stick) the seal to the surface. Providing this is achieved, the aggregate will then become interlocked under rolling and traffic, and a satisfactory seal will result. The recommended surface allowances for flat surfaces are as follows:

(a) seal over primes +0.2 to + 0.3 L/m2

(b) seal over primed cement concrete + 0.2 to + 0.3 L/m2

(c) seal over primed timber bridge deck + 0.2 to + 0.3 L/m2

(d) seal over slurry surfacings Refer Table 3b

(e) seal over asphalt Refer to Table 3c

Asphalt surfaces can either be hard (aged asphalt) or soft (new asphalt), depending on the age of the asphalt, and would require a different surface allowance as indicated in Table 3c.

As a good sealing practice, cement concrete and timber bridge deck surfaces need to be primed (or primer sealed) before the application of a sprayed seal.


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For primed cement concrete and timber bridge decks, the surface is essentially rigid, and therefore the application of additional binder is required to bond the aggregate effectively to the existing surface. When in doubt, use an allowance of at least + 0.2 L/m2.

5.3.2 Surface Texture

Texture depths of existing surfacing are to be measured using the sand patch method in accordance with Austroads Provisional Test Method SDT 02 (Austroads 2000b). The condition, appearance and texture depth ranges of existing seals have been described in Table C3 (see also Tables 3a, 3b and 3c) as follows:

Table C3 — Condition, appearance and texture depth of existing seals

Description of Condition Texture Depth Range (mm)

Appearance

Bleeding/Flushed Not applicable Free binder on surface completely covering aggregate/near top of aggregate

Black < 0.7 Binder near top of aggregate Smooth 0.7 to 1 Worn aggregate, minimal texture depth Well Textured 1.1 to 1.8 Textured seal, binder 50 to 60% up the aggregate particle Coarse 1.9 to 2.9 Binder 30 to 50% up the aggregate particle Very Coarse > 2.9 Binder < 30% up the aggregate particle (binder not visible between the

aggregate particles)

5.3.3 Variations in Surface Texture

Assessment of surface texture for design of binder application rates is based on measurements taken in the wheel path. However, the variability of surface texture across the pavement surface must be considered. If the difference between design application rates for the wheel path and other areas is about 20%, this is likely to result in an unsatisfactory seal, and one of the following techniques may be considered;

• change the treatment, e.g. apply a small aggregate reseal as an interim measure, which may act as a corrective treatment to the coarser textured areas, either followed soon after by another reseal, or left for some years.

• vary the binder application rates, according to the texture, by using a transversely variable spraybar or additional selective spray passes.

• apply localised corrective treatments, e.g. dry matting, slurry, hand patching, etc.

5.3.4 Influence of Surface Texture with Aggregate Size

When a reseal is placed on a seal, the aggregate particles may either interlock or bridge the underlying surface texture. The design method provides for the influence of surface texture.

The user should note that large aggregate reseals on coarser surface texture will require high binder application rates to retain the aggregate and it may be preferable to select a smaller sized aggregate.

Some aggregate sizes will not be readily compatible with existing seal sizes and texture depths, e.g. small sized reseals will generally not give good results over flushed large sized seals and 10 mm reseals sometimes do not interlock well with hungry 14 mm and 10 mm seals.

Allowances for existing surface texture may be substantial, and require a degree of judgment by the designer. Table 3 gives a guide to the selection of an appropriate allowance based on surface texture measurements.

Where the surface texture cannot be determined by the sand patch method, refer to Tables 3b and 3c in the Design Method for guidance.


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5.3.5 Absorption of Binder by the Pavement

The factors that affect the binder absorption into pavement are:

• base material type • base preparation method (e.g. moisture, inadequate compactive effort) • presence of porous or soft patches The allowances (L/m2) for these factors should be made based on experience. A guide to allowances for binder absorption is given in the design method (Section 7.2.2).

Binder absorption into the substrate will seldom be a problem in reseals, unless the existing surface is visibly porous. Where the pavement absorption allowance is more than +0.2 L/m2, or where the base material is known to have a continuous long term absorption, particularly in hot climates, one of the following treatments should be considered:

• use of different grade or class of binder including PMBs or • modification or stabilisation of the base • use of a small nominal size seal • design at a higher binder application rate for the conditions or in extreme cases, an early surface

enrichment might be necessary Porous or soft patches, which can cause absorption or flushing of binder, should be corrected by pretreatment or removal prior to sealing.

5.3.4.1 Seals

For seals, the binder may drain into voids in the base course if these have not been adequately filled by a prime or primerseal. This is most likely to occur in sandy or silty rubble base courses (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 used as indicated in the dot points above..

5.3.4.2 Reseals

Binder absorption into the substrate will seldom be a problem in reseals, unless the existing surface is visibly porous and/or known to contain absorptive aggregate(s).

5.4 Embedment Embedment is the term used to describe the intrusion of the sealing aggregate into the underlying substrate. This is likely to occur when the underlying substrate has free binder on the surface or when the substrate is soft. The Austroads Provisional ball penetration test SDT 04 Austroads 2000d) was devised to assess the embedment so that an allowance can be made to the binder application rate. The test method includes a temperature correction.

Larger size aggregates are less sensitive to reductions in application rate for embedment into flushed surfaces. To ensure sufficient binder for initial adhesion and retention of aggregate a minimum application rate (in L/m2) of 0.1 x ALD is desirable. Flushed surfaces may be pretreated (corrected) by spraying with cutter oil or proprietary material to soften the binder, then covered with a size 5 or 7 mm aggregate and rolled. In hot weather, it may not be necessary to apply cutter oil or proprietary product. Alternatively, hot aggregate from a nearby asphalt plant may also be used.

Embedment of aggregate may occur:

• when applying an initial treatment to a soft base. • when applying an sealing treatment over a primed or primersealed surface.


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The embedment allowance, which compensates for loss of voids in the seal under traffic, is determined from Figure 4 in the Design Method. It is added to the basic application rate. High ball penetration values (5 to 8 mm) indicate that bleeding may occur in subsequent seals. Where ball penetration and traffic volume are both high, alternative treatments should be considered (see Austroads 2000e).

5.5 Road Geometry The geometry of the road can affect the design of a seal and it is necessary to make adjustments to the binder application rate. Geometric factors include

• narrow lanes which cause a channelised traffic flow • climbing lanes which are likely to cater for the majority of heavy vehicles travelling at a reduced

speed • untrafficked or lightly trafficked areas such as shoulders, turning slots, etc.


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SECTION D

REFERENCES APRG (1997). Provisional Guide to the Design of Sprayed Seals - Draft 7A, October 1997, Draft APRG Report.

APRG (1999a) Pavement Technology – Glossary of Terms, APRG 99/12 (MA) [unpublished]

APRG (1999b) Development and validation of the provisional guide to the design of sprayed seals (draft 7A) - A commentary for the Austroads Pavement Reference Group APRG 99/08 (MA)

APRG (1999c) A summary of Austroads sprayed seal design method draft 7A- October 1997 APRG 99/09 (MA)

APRG (2000a) Sprayed Sealing – Aggregate Precoating APRG Pavement Work Tip No. 23

AUSTROADS (1990). Design of Sprayed Seals, Austroads, Sydney Australia, 6p.

AUSTROADS (2000a). Average least dimension of aggregate by direct measurement (nominal size 10 mm and greater), Austroads Provisional Test Method SDT 01.

AUSTROADS (2000b). Surface texture depth (Pestle method), Austroads Provisional Test Method SDT 02.

AUSTROADS (2000c). Absorption of bituminous binder into aggregate, Austroads Provisional Test Method SDT 03.

AUSTROADS (2000d). Ball penetration test, Austroads Provisional Test Method SDT 04.

AUSTROADS (2000e). Guide to the Selection of road Surfacing, Austroads AP-63/00, Sydney, Australia, 82p.

JORDAN, J. and GAUGHAN, R.L. (1994). Modified NITRR Design Method for Sprayed Sealing, Paper No. 44, Proc. 9th AAPA International Conference, Brisbane.

NAASRA (1975) Principles and Practice of Bituminous Surfacings Vol 1 - Sprayed Work, National Association of Australian Road Authorities, Sydney, Australia.

NAASRA (1989). Bituminous Surfacing - Sprayed Work, Technical Report, NTR-07, National Association of Australian State Road Authorities, Sydney, Australia, 75p.

STANDARDS AUSTRALIA (1982). Methods for Sampling and Testing Aggregates - Part 20, Average Least Dimension by Direct Measurement, AS 1141.20, Standards Australia.

STANDARDS AUSTRALIA (1996). Aggregate and Rock for Engineering Purpose - Part 2, Aggregate for Sprayed Bituminous Surfacing, AS 2758.2, Standards Australia.


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APPENDIX A Selection Criteria and Data Record Sheets for

Validation of the Regression Approach to Sprayed Seal Design

PROPOSED TRIAL SITE SELECTION CRITERIA

1. Number of Trial Sections 10 in each State (Western Australia, South Australia, Victoria,

Tasmania, New South Wales, and Queensland).

2. Seal Types Four seals and six reseals.

3. Traffic (v/l/d)

Commercial Vehicles, (%)

Road trains, B - Doubles

100 to 5,000

10 and 40

4. Aggregate Size Two. 10 mm and 14 mm.

5. Existing Substrate (Surfacing) For seals (Selection based on Ball embedment):

Prime/primerseals of different hardnesses, hard, medium and soft.

For Reseals (Selection based on existing surface texture):

Seals (hungry and bleeding), Asphalt and Concrete.

6. Proposed Treatment (Surfacing)

6.1 Seals (Four) on primerseals

Traffic (v/l/d) 100, 600, 1,000 and 2,000.

Size 10 mm on 7 mm (1)



6. Proposed Treatment (Surfacing)

6.2 Reseals (Six) on seals, concrete and asphalt

Traffic (v/l/d) 100, 300, 600, 1,000, 2,000 and 5,000.

On Seals (4):

Size 10 mm and 14 mm on size 7 mm, 10 mm and 14 mm hungry and bleeding seals.

On Concrete (1)

On Asphalt (1)


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DATA RECORD SHEET

1 GENERAL AND DESIGN DATA

1.1 Section Identification

1.1.1 State

1.1.2 Location - Road Name or No.

1.1.3 Distance in km

1.1.4 Geometry

1.1.5 Site No. (ARRB TR Id)

1.1.6 Design Traffic (v/l/d)

1.1.7 Commercial Vehicles (%)

1.1.8 Other (Road trains, B - doubles)

1.2 Surfacing Type

1.2.1 Proposed

1.2.2 Existing

1.2.3 Base (for seals only)

1.2.4 Surface Texture (mm)

1.2.5 Ball Embedment (mm)

1.3 Aggregate (Pre trial)

1.3.1 Aggregate Type

1.3.1 Aggregate Size - Nominal (mm)

1.3.2 Average Least Dimension (mm)

1.3.3 Bulk Density (t/m3)

1.3.4 Loose Unit Mass (t/m3)


— 45 —

2 FIELD DATA

2.1 General

2.1.1 Date Sprayed

2.1.2 Weather Conditions

2.1.3 Air and Pavement Temperatures (°C)

2.1.3.1 Air

2.1.3.2 Pavement

2.2 Binder Application Rate (L/m2)

2.2.1 Design

2.2.2 Actual (field) - Sprayer Dipstick

2.2.3 Carpet Tile

2.2.4 Cutter Oil

2.2.4.1 Type and parts or (%)

2.3 Aggregate Spread Rate (m2/m3)

2.3.1 Design

2.3.2 Actual (field)


— 46 —

2.4 Surface Texture Depth, TD1 (mm) OWP BWP

2.4.1 Initial (1 to 3 months)

2.4.2 6 months

2.4.3 12 months

2.4.4 24 months

2.5 Ball Embedment (mm) OWP BWP


2.5.2 6 months

2.5.3 12 months

2.5.4 24 months

2.6 Lower Surface Texture Depth, TD2 (mm) OWP BWP


2.6.2 6 months

2.6.3 12 months

2.6.4 24 months

2.7 Recovered Aggregate Spread Rate (kg/m2) OWP BWP


2.7.2 6 months

2.7.3 12 months

2.7.4 24 months

INFORMATION RETRIEVAL

Austroads (2001), Austroads Provisional Sprayed Seal Design Method Revision 2000, Sydney, A4, 58pp, AP-T09/01

KEYWORDS: Surfacing; Sprayed seal; Research and development; Pavement design; Pavement performance; Pavement testing; Bituminous pavement; Aggregate; Data collection ABSTRACT: This report gives an overview of the Austroads Sprayed Seal Design Research Project which was initiated to develop a reliable, accurate national seal design method. The project involved the establishment, monitoring and review of trial sections in five states and culminated in the issue of a new sprayed seal design method, Revision 2000. The report is in three parts: ♦ A commentary on the development of the Austroads provisional sprayed seal

design method – Revision 2000. ♦ The provisional sprayed seal design method. ♦ A guide to the design method giving a deeper understanding of how sprayed seals

behave and the steps necessary to ensure in-service performance.

AUSTROADS PUBLICATIONS

Austroads publishes a large number of guides and reports. Some of its publications are:

AP-1/89 Rural Road Design AP-8/87 Visual Assessment of Pavement Condition Guide to Traffic Engineering Practice

AP-11.1/88 Traffic Flow AP-11.9/88 Arterial Road Traffic Management AP-11.2/88 Roadway Capacity AP-11.10/88 Local Area Traffic Management AP-11.3/88 Traffic Studies AP-11.11/88 Parking AP-11.4/88 Road Crashes AP-11.12/88 Roadway Lighting AP-11.5/88 Intersections at Grade AP-11.13/95 Pedestrians AP-11.6/93 Roundabouts AP-11.14/99 Bicycles AP-11.7/88 Traffic Signals AP-11.15/99 Motorcycle Safety AP-11.8/88 Traffic Control Devices

AP-12/91 Road Maintenance Practice AP-13/91 Bridge Management Practice AP-14/91 Guide to Bridge Construction Practice AP-15/96 Australian Bridge Design Code AP-17/92 Pavement Design AP-18/00 RoadFacts 2000 AP-22/95 Strategy for Pavement Research and Development AP-23/94 Waterway Design, A Guide to the Hydraulic Design of Bridges, Culverts & Floodways AP-26/94 Strategy for Structures Research and Development AP-29/98 Austroads Strategic Plan 1998–2001 AP-30/94 Road Safety Audit AP-34/95 Design Vehicles and Turning Path Templates AP-36/95 Adaptions and Innovations in Road & Pavement Engineering AP-38/95 Guide to Field Surveillance of Quality Assurance Contracts AP-40/95 Strategy for Ecological Sustainable Development AP-41/96 Bitumen Sealing Safety Guide AP-42/96 Benefit Cost Analysis Manual AP-43/00 National Performance Indicators AP-44/97 Asphalt Recycling Guide AP-45/96 Strategy for Productivity Improvements for the Road Transport Industry AP-46/97 Strategy for Concrete Research and Development AP-47/97 Strategy for Road User Cost AP-48/97 Australia at the Crossroads, Roads in the Community — A Summary AP-49/97 Roads in the Community — Part 1: Are they doing their job? AP-50/97 Roads in the Community — Part 2: Towards better practice AP-51/98 Electronic Toll Collection Standards Study AP-52/97 Strategy for Traffic Management Research and Development AP-53/97 Strategy for Improving Asset Management Practice AP-54/97 Austroads 1997 Bridge Conference Proceedings — Bridging the Millennia AP-55/98 Principles for Strategic Planning AP-56/98 Assessing Fitness to Drive AP-57 & 58/98 Cities for Tomorrow — Better Practice Guide & Resource Document AP-59/98 Cities for Tomorrow — CD AP-60/98 Guide to Stabilisation in Roadworks AP-61/99 Australia Cycling 1999-2004 — The National Strategy AP-62/99 e-transport — The National Strategy for Intelligent Transport Systems AP-63/00 Guide to the Selection of Road Surfacings AP-64/00 Austroads 4th Bridge Conference Proceedings — Bridges for the New Millenium These and other Austroads publications may be obtained from: ARRB Transport Research Ltd Telephone: +61 3 9881 1547 500 Burwood Highway Fax: +61 3 9887 8144 VERMONT SOUTH VIC 3131 Email: [email protected] Australia Website: www.arrb.org.au or from road authorities, or their agent in all States and Territories; Standards New Zealand; Standards Australia & Bicycle New South Wales.

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Austroads Spray Seal 2000

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