BS594.1-2003

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BRITISH STANDARD
BS 594-1:2003
Hot rolled asphalt for roads and other paved areas —

Part 1: Specification for constituent materials and asphalt mixtures

ICS 93.080.20

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BS 594-1:2003

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This British Standard was published under the authority of the Standards Policy and Strategy Committee on 27 August 2003

© BSI 27 August 2003

First published April 1985Second edition September 1992Third edition December 2002Fourth edition August 2003

The following BSI references relate to the work on this British Standard:Committee reference B/510/1

ISBN 0 580 42384 0

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Committees responsible for this British StandardThe preparation of this British Standard was entrusted by Technical Committee B/510, Road materials, to Subcommittee B/510/1, Coated macadam and hot asphalt, upon which the following bodies were represented:

British Civil Engineering Test Equipment Manufacturer’s Association

County Surveyors’ Society

Institution of Civil Engineers

Institution of Highways and Transportation

Mastic Asphalt Council Ltd.

Ministry of Defence — UK Defence Standardization

Department for Transport — Highways Agency

Quarry Products Association

Refined Bitumen Association

Road Surface Dressing Association

Scottish Office — Roads Directorate

Society of Chemical Industry

TRL — Transport Research Laboratory

United Kingdom Accreditation Service

Amendments issued since publication

Amd. No. Date Comments

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BS 594-1:2003

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ContentsPage

Committees responsible Inside front coverForeword ii

Introduction 1

1 Scope 12 Normative references 13 Terms and definitions 24 Constituent materials 35 Hot rolled asphalt mixtures 46 Mixing 117 Coated chippings for application to surface course surfaces 128 Sampling and testing 13

Annex A (informative) Guidance on the selection of materials and mixtures 14Annex B (informative) Recommendations for the application of design test criteria 16Annex C (informative) Specifying hot rolled asphalt 17Annex D (informative) Guidance on the selection of performance related design criteria for surface course mixtures 18Annex E (normative) Specifying performance specified hot rolled asphalt 22

Bibliography 23

Table 1 — Designation of binders and recommended storage temperatures 3Table 2 — Composition of base (roadbase), binder course and regulating course mixtures 6Table 3 — Composition of design type F surface course mixtures 7Table 4 — Composition of design type C surface course mixtures 7Table 5 — Table deleted 8Table 6 — Composition of recipe type F surface course mixtures 9Table 7 — Maximum temperatures of mixed asphalt 12Table 8 — Grading of chippings 12Table B.1 — Criteria for the stability of laboratory design asphalt 16Table D.1 — Limiting wheel-tracking requirements for site classifications 20Table D.2 — Classification of sites by traffic and stress condition 21

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Foreword

This British Standard has been prepared by Subcommittee B/510/1. It supersedes BS 594-1:2002, which is withdrawn.The previous edition of BS 594-1 introduced the following changes:

— bitumen grade references in accordance with BS EN 12591;— terminology which will be used in future European asphalt standards to familiarize UK users with the new terms; — reference to the in-plant blending of bitumens;— requirements for the specification of surface course mixtures based on their resistance to deformation;— the design type R surface course mixtures were deleted.

This edition introduces the following changes. The requirements for aggregates, the sieve sizes used for the definition of mixtures and the size designations of mixtures have been amended to align with BS EN 13043, which is being implemented in the UK on 01/01/2004. The introduction of BS EN 13043 implies the use of both different size designations and test methods. Detailed guidance and advice on the changes may be found in PD 6682-2 and PD 6682-9.BS 594 comprises two parts:

— Part 1: Specification for constituent materials and hot rolled asphalt mixtures;— Part 2: Specification for the transport, laying and compaction of hot rolled asphalt.

This part includes requirements for asphalt mixtures and their constituent materials and for coated chippings applied to the surface of some asphalt surface courses.The requirements and recommendations for transporting asphalt and for site work are given in BS 594-2.Over the years, a considerable number of hot rolled asphalt mixture compositions have evolved. During the preparation of this revision, some rationalization of the previous range has been undertaken by omitting the type R enriched mixtures. The limited range of preferred mixes introduced in the previous edition and identified in bold type in Table 2, Table 3, Table 4 and Table 6, is maintained. As mixtures suitable for most uses can be selected from this reduced range, the use of a preferred mixture is encouraged wherever possible.Further guidance on the selection of mixtures, the application of design test criteria and recommendations for stability related to traffic conditions, and information to be provided by the purchaser and the supplier is given in Annex A, Annex B, Annex C, Annex D and Annex E.The requirements for the composition of all asphalt mixtures are based on testing the constituents and the mixture by methods described in BS 598 and other British Standards (see Clause 2). Adjustment values for soluble binder content and material passing the 0.063 mm test sieve are given in BS 598-102. Methods of test to determine the condition of the binder on coated chippings and their rate of spread, the texture of finished surfaces, the density of cores drilled from asphalt surfacing and a method for assessing the compaction performance of other rollers by comparison with the performance of a non-vibrating 8 t roller are included in other parts of BS 598 (see Clause 2).It has been assumed in the drafting of this part of BS 594 that the execution of its provisions is entrusted to appropriately qualified and experienced people.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.

Compliance with a British Standard does not in itself confer immunity
from legal obligations.Summary of pagesThis document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 23 and a back cover.The BSI copyright notice displayed in this document indicates when the document was last issued.
© BSI 27 August 2003

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BS 594-1:2003


Introduction

This part of BS 594 specifies the properties of materials used to make hot rolled asphalt and of the mixtures manufactured from those materials.

Base (roadbase), binder course and regulating course mixtures are specified by conventional recipe methods in 5.1.

Surface course mixtures are specified in three ways. In 5.2 design mixtures are specified, based on the mechanical testing of the asphalt mixture to determine a design binder content. This binder content is of particular value when dealing with aggregates of previously unknown performance. Design mixtures are recommended for use on heavily trafficked roads.

Since the previous revision of this standard, mixtures have been developed which are suitable for use on very heavily trafficked sites. These are now specified in 5.4 (performance specified mixtures). No mix design method is specified. Instead, the as-laid asphalt mixtures are specified in terms of their resistance to deformation under varying degrees of traffic stress, from moderate to the most severe.

The recipe type of surface course mixture specified in 5.3 is the conventional mixture which has proved satisfactory, except under heavy traffic, for most applications for many years.

Where hot rolled asphalt surface course mixtures, of nominal 35 % coarse aggregate content or less, are used in trafficked areas it is usual to apply coated chippings to provide a suitable level of skidding resistance to the finished road. The properties of such chippings and the requirements for their manufacture are specified in Clause 7.

1 ScopeThis part of BS 594 specifies requirements for mixtures of hot rolled asphalt to be laid as surface course, regulating course, binder course or base (roadbase) on roads and other paved areas, excluding heavy duty airfield pavements.

It also specifies requirements for coated chippings, but excludes requirements for site-specific properties such as polished stone values and abrasion values of aggregates.NOTE The terms “base (roadbase)”, “binder course” and “surface course” are used throughout this standard in place of the traditional terms “roadbase”, “basecourse” and “wearing course” respectively to encourage use of the new terminology which will be used in European asphalt standards to be introduced in the near future.

2 Normative referencesThe following normative documents contain provisions which, through reference in this text, constitute provisions of this British Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the publication referred to applies.

BS 410-1:2000 (ISO 3310-1:2000), Specification for test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth.

BS 410-2:2000 (ISO 3310-2:2000), Specification for test sieves — Technical requirements and testing — Part 2: Test sieves of perforated metal plate.

BS 594-2:2003, Hot rolled asphalt for roads and other paved areas — Part 2: Specification for transport, laying and compaction of hot asphalt.

BS 598-100:1987, Sampling and examination of bituminous mixtures for roads and other paved areas — Part 100: Methods for sampling for analysis.

BS 598-101, Sampling and examination of bituminous mixtures for roads and other paved areas — Part 101: Methods for preparatory treatments of samples for analysis.

BS 598-102:1996, Sampling and examination of bituminous mixtures for roads and other paved areas — Part 102: Analytical test methods.

BS 598-107:1990, Sampling and examination of bituminous mixtures for roads and other paved areas — Part 107: Method of test for the determination of the composition of design wearing course rolled asphalt.

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BS 598-108:1990, Sampling and examination of bituminous mixtures for roads and other paved areas — Part 108: Methods for determination of the condition of the binder on coated chippings and for measurement of the rate of spread of coated chippings.

BS 598-109, Sampling and examination of bituminous mixtures for roads and other paved areas — Part 109: Methods for the assessment of the compaction performance of a roller and recommended procedures for the measurement of the temperature of bituminous mixtures.

BS 598-110, Sampling and examination of bituminous mixtures for roads and other paved areas — Part 110: Methods of test for the determination of wheel-tracking rate and depth.

BS 812-2, Testing aggregates — Part 2: Methods for determination of physical properties.

BS 3195-3 (EN 58), Methods for sampling petroleum products — Part 3: Method for sampling bituminous binders.

BS 3690-3, Bitumens for building and civil engineering — Part 3: Specification for mixtures of bitumen with pitch, tar and Trinidad lake asphalt.

BS 6100, Glossary of building and civil engineering terms.

BS EN 197-1, Cement — Part 1: Composition, specifications and conformity criteria for common cements.

BS EN 932 (all parts), Tests for general properties of aggregates.

BS EN 933 (all parts), Tests for geometrical properties of aggregates.

BS EN 1097 (all parts), Tests for mechanical and physical properties of aggregates.

BS EN 1367 (all parts), Tests for thermal and weathering properties of aggregates.

BS EN 1744 (all parts), Tests for chemical properties of aggregates.

BS EN 12591, Bitumen and bituminous binders — Specifications for paving grade bitumens.

BS EN 13043:2002, Aggregates for bituminous mixtures and surface treatments for roads, airfields and other trafficked areas.

HIGHWAYS AGENCY, Specification for Highway Works (SHW). London: The Stationery Office.

3 Terms and definitions

For the purposes of this part of BS 594 the terms and definitions given in BS 6100 and the following apply.

3.1 stabilitymaximum resistance to deformation, in kilonewtons, of a moulded asphalt specimen made and tested in accordance with BS 598-107

3.2 flowdeformation of moulded asphalt specimen, in millimetres, at the point of maximum resistance, when made and tested in accordance with the requirements of BS 598-107

3.3 design binder contentbinder content of a surface course design mixture determined in accordance with the procedure described in BS 598-107

3.4 target binder contentnominal soluble binder content of a surface course design mixture specified in 5.2 and which is equal to or greater than the design binder content and the specific requirements given in Table 3 and Table 4

3.5 added fillermaterial, a substantial proportion of which passes a 0.063 mm test sieve, added to the mixture in excess of that present in the coarse and fine aggregates

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3.6 test sievesieve conforming to BS 410-1 (ISO 3310-1) or BS 410-2 (ISO 3310-2)

3.7 commercial vehiclevehicle with an unladen weight exceeding 1.5 t

4 Constituent materials

4.1 Binder

The binder used in hot rolled asphalt mixtures shall be one of the binders designated in Table 1. Paving grade bitumen shall conform to BS EN 12591. Lake asphalt-bitumen mixtures shall conform to BS 3690-3. NOTE 1 Guidance on the selection and use of different grades of binder is given in Annex A. Improved performance characteristics may be achieved by the use of modified bitumens but these are outside the scope of this standard. Guidance is available in the Design Manual for Road and Bridgework, Volume 7 (HD 37/99) [1].

70/100 and 100/150 pen grade bitumen may be produced by blending in the mixer at the asphalt plant. The grades used for blending shall be no harder than 30/45 pen nor softer than 160/220 pen and shall conform to BS EN 12591. The producer shall be able to demonstrate that the plant is capable of adequately blending the bitumens. Measures for ensuring consistency of proportioning of the blend shall be included in plant quality management systems. These shall include evidence of type tests carried out on a laboratory blend of the bitumens to demonstrate conformity to BS EN 12591. The quality assurance/management systems shall also include the steps to be taken to demonstrate the continuing adequacy of the process following significant changes being made to those parts of the plant involved in the process of bitumen blending.

No grades of bitumen harder than 70/100 pen shall be blended in the mixer. NOTE 2 Other grades may be in-plant blended provided that the resulting bitumen can be sampled and tested before it is added to the aggregate and to ensure it conforms to BS EN 12591.

Table 1 — Designation of binders and recommended storage temperatures

4.2 Coarse aggregate

4.2.1 Type of coarse aggregate

Coarse aggregate shall be material substantially retained on a 2.36 mm test sieve and shall conform to all appropriate requirements of BS EN 13043 and consist of one of the following.

a) Crushed rock of one or more of the following groups: basalt, gabbro, granite, gritstone, hornfels, limestone, porphyry or quartzite.

b) Gravel of one or more of the groups in a) or flint.

c) Blastfurnace slag conforming to BS 1047.

d) Steel slag, either electric-arc furnace or basic oxygen slag, with a compacted bulk density between 1.60 Mg/m3 and 1.80 Mg/m3 when tested in accordance with BS 812-2.

Binder number Type Grade Recommended storage temperature

°C

1 Bitumen 30/45 pen 1702 Lake asphalt-bitumen 35 pen 1753 Bitumen 40/60 pen 1654 Lake asphalt-bitumen 50 pen 1705 Bitumen 70/100 1606 Lake asphalt-bitumen 70 pen 1657 Bitumen 100/150 150NOTE Prolonged storage of binders at elevated temperatures may result in hardening. To reduce this risk, binders should be delivered to coating plants at temperatures below 200°C and prolonged subsequent storage above the temperatures given in this table should be avoided. (It should be recognized that binder deliveries may result in short-term storage temperatures above those recommended in this table.)



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NOTE 1 Some aggregates other than those referred to in a) to d) have been found to be suitable for hot rolled asphalt. Guidance is available on the use of secondary and recycled aggregates, e.g. Specification for Highway Works (SHW).

NOTE 2 This British Standard does not include requirements for site-specific properties of aggregates, such as the polished stone value or the aggregate abrasion value, that may be required to assist skid-resistance, or the 10 % fines value which indicates aggregate strength.

4.2.2 Particle shape

The coarse aggregate shall conform to flakiness category FI35.

4.2.3 Fines content

The coarse aggregate shall conform to fines category f4.NOTE 1 Some aggregates other than those referred to in 4.2.1a) to d) have been found to be suitable for hot rolled asphalt. Guidance is available on the use of secondary and recycled aggregates, e.g. Specification for Highway Works (SHW).

NOTE 2 This standard does not include requirements for all the properties of aggregates, for example polishing resistance, abrasion resistance and resistance to fragmentation. Guidance on the specification of such requirements in accordance with BS EN 13043 and the relationship between the new European aggregate test methods and those previously used in the UK can be found in PD 6682-2. Specification should be in terms of the categories recommended in PD 6682-2. Further guidance is given in B.5.2.

4.3 Fine aggregate

4.3.1 Type of fine aggregate

Fine aggregate shall substantially pass a 2 mm test sieve and shall be one of the following types:

a) sand;

b) fines produced by crushing coarse aggregate conforming to 4.2.1;

c) a blend of a) and b).NOTE Advice on the selection of asphalt mixtures containing various types of fine aggregate is given in Annex A.

4.3.2 Fines content

The fines content shall conform to the appropriate fines category specified in 5.1.1.2, 5.2.2.2 or 5.3.2.2.NOTE For guidance on fines quality see PD 6682-2.

4.4 Added filler

Added filler shall be Portland cement conforming to BS EN 197-1 or limestone.

The grading of added filler shall be in accordance with BS EN 13043:2002, 5.2.1.

The loose bulk density in kerosene of added filler shall be in accordance with BS EN 13043:2002, 5.5.5.NOTE For all other properties specified in BS EN 13043:2002, Clause 5 it is recommended that the “No Requirement” category is used.

5 Hot rolled asphalt mixtures

5.1 Group 1: base (roadbase), binder course and regulating course mixturesNOTE 1 Adherence to the requirements of this clause will generally give mixtures of satisfactory performance. However, it is impossible in a general specification to cover all suitable aggregates a few of which might necessitate binder contents other than those in Table 2.

NOTE 2 The requirements for composition are based on testing the constituent materials and the mixture in accordance with methods referred to in Clause 4, Clause 5 and Clause 8. The values of binder content are those for the soluble binder content on analysis.

5.1.1 Aggregate

5.1.1.1 Coarse aggregate

Coarse aggregate shall conform to 4.2.

5.1.1.2 Fine aggregate

Fine aggregate shall conform to 4.3 and fines category f22 of BS EN 13043.



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5.1.1.3 Added filler

When added filler is required to achieve the composition given in Table 2, it shall conform to 4.4.

5.1.2 Binder

The grade and type of binder shall conform to 4.1.

5.1.3 Composition of the mixture

The results of a mixture analysis shall be adjusted in accordance with BS 598-102:1996, Clause 6. The adjusted results shall conform to Table 2, appropriate to the particular mixture designation and coarse aggregate, and within a tolerance of ±0.6 % (m/m) of the total mixture on the values for binder content.

5.2 Group 2: surface course design mixtures

5.2.1 General

Design mixtures shall either be type F or type C conforming to Table 3 or Table 4.NOTE Type F is characterized by a gap grading typical of traditional hot rolled asphalt surface course mixtures usually associated with the use of a fine sand, although other fine aggregates conforming to the grading limits may also be used.

Type C is characterized by a coarser grading usually associated with the use of crushed rock or slag fine aggregates. However, natural sand may be used in part or in total.

The designation F reflects a finer grading of the fine aggregate used in this type of mix. A coarser grading of the fine aggregate is used in type C mixes. The distinction between types F and C mixtures is in grading only; no restriction should be placed on the source and type of fine aggregate.

5.2.2 Aggregate




Fine aggregate shall conform to 4.3.

For type F mixtures, fine aggregate shall be 0/2 mm conforming to grading category GA 90 and fines category f10.

For type C mixtures, fine aggregate shall be 0/4 mm conforming to grading category GA 85 and fines category f16.


When added filler is required to achieve the composition given in Table 3 or Table 4 it shall conform to 4.4.

5.2.3 Binder

The grade and type of binder shall conform to 4.1.NOTE Guidance on the selection and use of different grades of binder is given in Annex A.

5.2.4 Target binder content

The target binder content shall be determined by adjusting the design binder content, determined in accordance with the procedure in BS 598-107 (see 3.3), where required, to allow for such properties as workability and durability.

The target binder content shall be not less than either the design binder content or the appropriate minimum value in Table 3 or Table 4 and shall be such that the values for stability and flow, tested in accordance with BS 598-107, at the target binder content are within the specified range selected from Table B.1.NOTE 1 Design proposals should be verified in accordance with Annex B.

NOTE 2 The factors incorporated in the design method of BS 598-107 are such that for most type F mixtures, the design binder content is satisfactory as the target binder content. Addition of extra binder improves workability and durability and is acceptable as long as the resultant mixture properties conform to Table B.1. As there is less knowledge of the design of type C mixtures using this method, greater care is needed to ensure the specified binder content is adequate as regards workability and durability.



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5.2.5 Composition of mixtures

The results of a mixture analysis shall be adjusted in accordance with BS 598-102:1996, Clause 6. The adjusted results shall conform to the appropriate column in Table 3 or Table 4 for aggregate grading. The soluble binder content shall conform to the target binder content within a tolerance of ±0.6 % (m/m) of the total mixture.NOTE Guidance on the information to be provided at the time of enquiry or order is given in Annex B.

Table 2 — Composition of base (roadbase), binder course and regulating course mixtures

Column number 2/1 2/2a 2/3 2/4 2/5a

Designationb 50% 0/10c 50% 0/14c 50% 0/20c 60% 0/20 60% 0/32

Nominal layer thickness (mm) 25 to 50 35 to 65 45 to 80 45 to 80 60 to 150

Percentage (m/m) of total aggregate passing test sieve

31.5 mm — — 100 100 90 to 100

20 mm — 100 90 to 100 90 to 100 50 to 80

14 mm 100 90 to 100 65 to 100 30 to 65d 30 to 65

10 mm 90 to 100 65 to 100 35 to 75 — —

6.3 mm — — — — —

2 mm 30 to 50 30 to 50 30 to 50 25 to 39 25 to 39

0.500 mm 13 to 50 13 to 50 13 to 50 8 to 39 8 to 39

0.250 mm 6 to 31 6 to 31 6 to 31 4 to 26 4 to 26

0.063 mm 1 to 8 1 to 8 1 to 8 1 to 7 1 to 7

Binder content percentage (m/m) of total mixture for:

Crushed rock or steel slag 6.5 6.5 6.5 5.7 5.7

Gravel 6.3 6.3 6.3 5.5 5.5

Blastfurnace slag: bulk density

1.44 Mg/m3 6.6 6.6 6.6 5.7 5.7

1.36 Mg/m3 6.7 6.7 6.7 5.9 5.9

1.28 Mg/m3 6.8 6.8 6.8 6.0 6.0

1.20 Mg/m3 6.9 6.9 6.9 6.1 6.1

1.12 Mg/m3 7.1 7.1 7.1 6.3 6.3

NOTE For mixtures containing crushed rock fine aggregate, and in some instances sands or blends of sand and crushed rock fines, the binder contents given in Table 2 may be reduced by up to 0.5 %, where experience shows this to be advisable to avoid an over-rich mixture (see Annex B).

a Preferred mix (see Foreword).b The mixture designation numbers (e.g. 50% 0/10 in column 2/1) refer to the nominal coarse aggregate content of the mixture and

size of the course aggregate in the mixture respectively.c Suitable for regulating course.d The value of 65 can be extended to 85 where evidence is available that the mixture so produced is suitable. To ensure consistency

of finish of the laid mixture, supplies from any one source should be controlled within a 35 % band within this permitted range.



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Table 3 — Composition of design type F surface course mixtures

Table 4 — Composition of design type C surface course mixtures

Column number 3/1 3/2a 3/3a 3/4 3/5

Designationb 0% 0/2c 30% 0/14 35% 0/14 55% 0/10 55% 0/14

Nominal layer thickness (mm) 25 40 45 or 50 40 45

Percentage (m/m) of total aggregate passing test sieve20 mm — 100 100 — 10014 mm — 85 to 100 87 to 100 100 90 to 10010 mm — 60 to 90 55 to 88 90 to 100 35 to 706.3 mm 100 — — 35 to 70 —2 mm 90 to 100 59 to 71 55 to 67 35 to 47 35 to 470.500 mm 75 to 100 44 to 71 40 to 67 25 to 47 25 to 470.250 mm 30 to 85 18 to 62 15 to 55 5 to 35 5 to 350.063 mm 12.0 to 16.0 7.0 to 11.0 6.0 to 10.0 4.0 to 8.0 4.0 to 8.0Maximum percentage of aggregate passing 2 mm and retained on 0.500 mm test sieves

— 15 14 10 10

Minimum target binder content percentage (m/m) of total mixture

9.0 6.5 6.4 5.5 5.5

a Preferred mix (see Foreword).b The mixture designation numbers (e.g. 35% 0/14 in column 3/3) refer to the nominal coarse aggregate content of the mixture and

nominal size of the course aggregate in the mixture respectively.c Suitable for regulating course.

Column number 4/1 4/2 4/3 4/4 4/5

Designationa 0% 0/2 30% 0/14 35% 0/14 55% 0/10 55% 0/14

Nominal layer thickness (mm) 25 40 45 or 50 40 45

Percentage (m/m) of total aggregate passing test sieve20 mm — 100 100 — 10014 mm — 85 to 100 87 to 100 100 90 to 10010 mm — 60 to 90 55 to 88 90 to 100 35 to 706.3 mm 100 — — 35 to 70 —2 mm 90 to 100 59 to 71 50 to 62 32 to 44 32 to 440.500 mm 30 to 65 25 to 45 20 to 45 15 to 35 15 to 350.250 mm 20 to 50 20 to 40 15 to 35 5 to 35 5 to 350.063 mm 12.0 to 16.0 7.0 to 11.0 6.0 to 10.0 4.0 to 8.0 4.0 to 8.0Minimum target binder content percentage (m/m) of total mixture

9.0 6.5 6.4 5.5 5.5

NOTE There is no preferred mix for design type C.

a The mixture designation numbers (e.g. 35% 0/14 in column 4/3) refer to the nominal coarse aggregate content of the mixture and nominal size of the course aggregate in the mixture respectively.

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5.3 Group 3: surface course recipe mixturesNOTE Adherence to the requirements of this clause will generally give mixtures of satisfactory performance. However, it is impossible in a general specification to cover all suitable aggregates a few of which might necessitate binder contents other than those in Table 6.

5.3.1 General

Only type F mixtures, conforming to 5.2.1, shall be used for recipe mixtures. The values of binder content shall be those for the soluble binder content on analysis.

5.3.2 Aggregates




Fine aggregate shall conform to 4.3.

Fine aggregate shall be 0/2 mm conforming to grading category GA 90 and fines category f10.


When added filler is required to achieve the composition given in Table 6 it shall conform to 4.4.

5.3.3 Binder

The grade and type of binder shall conform to 4.1.NOTE Guidance on the selection and use of different grades of binder is given in Annex A.

5.3.4 Composition of mixture

The results of a mixture analysis shall be adjusted in accordance with BS 598-102:1996, Clause 6. The adjusted results shall conform to the requirements given in Table 6 appropriate to the particular mixture designation, type of coarse aggregate and schedule. A tolerance of ±0.6 % (m/m) of the total mixture shall be permitted on the values for binder content.NOTE 1 Advice on mixture schedules is given in Annex A.

NOTE 2 Guidance on the information to be provided at the time of enquiry or order is given in Annex C.

Table 5 — Table deleted

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Table 6 — Composition of recipe type F surface course mixtures

Column number 6/1a 6/2a 6/3 6/4 6/5

Designationb 0% 0/2c 15% 0/10d 30% 0/10 30% 0/14 35% 0/14

Nominal layer thickness (mm) 25 30 35 40 45 or 50

Percentage (m/m) of total aggregate passing test sieve20 mm — — — 100 10014 mm — 100 100 85 to 100 87 to 10010 mm — 95 to 100 85 to 100 60 to 90 55 to 886.3 mm 100 75 to 95 60 to 90 — —2 mm 90 to 100 75 to 87 59 to 71 59 to 71 55 to 670.500 mm 75 to 100 55 to 85 44 to 71 44 to 71 40 to 670.250 mm 30 to 85 25 to 75 18 to 62 18 to 62 15 to 550.063 mm 12.0 to 16.0 10.0 to 14.0 7.0 to 11.0 7.0 to 11.0 6.0 to 10.0Maximum percentage of aggregate passing 2 mm and retained on 0.500 mm test sieves — 20 15 15 14Binder content percentage (m/m) of total mixture for:Crushed rock or steel slagSchedule 1A 10.3 8.9 7.8 7.8 7.4Schedule 1B 10.8 9.4 8.3 8.3 7.9GravelSchedule 2A 10.3 8.9 7.5 7.5 7.0Schedule 2B 10.8 9.4 8.0 8.0 7.5Binder content percentage (m/m) of total mixture for:Blastfurnace slag: bulk densitySchedule 3A

1.44 Mg/m3 — 9.0 7.9 7.9 7.6

1.36 Mg/m3 — 9.0 8.0 8.0 7.7

1.28 Mg/m3 — 9.2 8.1 8.1 7.8

1.20 Mg/m3 — 9.3 8.2 8.2 7.9

1.12 Mg/m3 — 9.4 8.3 8.3 8.0

Schedule 3B

1.44 Mg/m3 — 9.5 8.4 8.4 8.1

1.36 Mg/m3 — 9.6 8.5 8.5 8.2

1.28 Mg/m3 — 9.7 8.6 8.6 8.3

1.20 Mg/m3 — 9.8 8.7 8.7 8.4

1.12 Mg/m3 — 9.9 8.8 8.8 8.5a Preferred mix (see Foreword).b The mixture designation numbers (e.g. 35% 0/14 in column 6/5) refer to the nominal coarse aggregate content of the mixture

nominal size of the course aggregate in the mixture respectively.c Sand carpet.d Suitable for footpaths.

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5.4 Group 4: performance-specified surface course design mixtures

5.4.1 General

Performance-specified surface course design mixtures shall conform to 5.2 (except 5.2.4) and shall be chipped type F mixtures conforming to column 3/3 of Table 3, 35 % stone, with a nominal thickness of either 45 mm or 50 mm.

Mixtures shall conform to a target mixture designed to deliver the specified performance properties. The conformity of the target mixture shall be established by means of a job mixture trial and this shall constitute the required type testing procedure.

The job mixture trial shall comprise a sufficient area on which plant mixed asphalt is laid by a paver and compacted in accordance with BS 594-2. This area shall be sampled in accordance with D.4 and tested in accordance with D.5 to determine conformity to the following performance requirements:

a) binder volume (as defined in 5.4.2.1) not less than 15.5 % by volume;

b) void content (as defined in BS 594-2:2003, 9.4) not more than 7.5 % for a pair and not more than 5.5 % for the mean of any six consecutive determinations;

c) wheel tracking to classification 0, 1 or 2 as defined in Table D.1 and as specified.NOTE 1 Guidance on the selection of site-specific requirements is contained in Annex D.

NOTE 2 The use of performance-specified surface course design mixtures, including the full sampling and testing of laid material in the permanent works as described in BS 594-2:2003, Clause 9, is only appropriate for major works contracts. The use of these mixtures in minor works, and in particular those mixtures suitable for the category 2 sites (see Table D.2), is likely to result in very significant cost penalties. However, if either site category mixture is used in minor works, purchasers are advised to accept mix designs which have been approved in previous job mixture trials or in previous applications of the mixtures, as long as there have been no consequent significant changes in the mix constituents or production processes. This acceptance will obviate the relatively frequent sampling and testing from the laid material which is a requirement on the major works, so that only routine audit samples of loose material are taken to check the compositional analysis.

5.4.2 Binder

5.4.2.1 General

The binder shall constitute not less than 15.5 % by volume of the mixture at the target binder content. The binder content by volume (BVol, %) shall be calculated as follows:

Information concerning bitumen processed during refining to provide a binder with enhanced properties without the addition of a modifier shall be provided in accordance with the requirements in Annex E (see E.2), unless it has a British Board of Agrément1) HAPAS (BBA/HAPAS) Roads and Bridges certificate. This information shall include advice on early trafficking of asphalts made with the binder.

5.4.2.2 Binder modifiers

Binder modifiers, if required, shall either be combined with the base binder prior to mixing or blended with the other component materials of the mixture at the mixer. Information concerning binder modifiers or pre-blended modified binders shall be provided and approved unless they have a BBA/HAPAS Roads and Bridges certificate1) (see E.2). This information shall include advice on early trafficking of asphalts made with the binder in accordance with the requirements in Annex E (see E.2).NOTE Guidance on the information usually provided on the properties of modified binders and mixtures utilizing modified binders is given in the Notes for Guidance to the Specification for Highway Works [2].

BVol = Bmass ×

where

Bmass is the binder content as a proportion of the total mixture by mass (%) added at the mixer;

Ôb is the density of the binder at 25 °C in kilograms per cubic metre (kg/m3);

Ômix is the bulk density of the compacted mixture without pre-coated chippings in kilograms per cubic metre (kg/m3).

1) British Board of Agrément, P.O. Box 195, Bucknalls Lane, Garston, Watford, Herts WD25 9BA. www.bbacerts.co.uk.

ÔmixÔb-----------

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5.4.3 Job mixture

5.4.3.1 For each asphalt mixing plant where the mixture is produced, details of the proposed mixture design shall be obtained from either a job mixture trial or from a previous use of the mixture, and shall include all the following particulars:

a) bitumen grade; b) quantities of binder and aggregate;c) aggregate source and grading;d) proprietary name and generic type of any binder modifier or binder modified by processing;e) quantity of any binder modifier added at the mixer;f) modified binder and any site-specific mixture data requirements.

5.4.3.2 If a modified binder including any proportion of the modifier, is not fully recovered on analysis for determination of binder content, details of alterations to the test method and/or the correction necessary to the results together with any supporting data and the proposed mixture design shall be identified (see E.2).

5.4.3.3 The mixture shall be designated the job standard mixture provided that:

a) the mixture design proposed conforms to 5.4.1;

b) test results submitted demonstrate that the binder content by volume of the mixture compacted without pre-coated chippings conforms to 5.4.2;

c) information submitted in accordance with 5.4.3.1 on the mixture design proposed is complete;

d) information submitted in accordance with 5.4.3.2 has been provided;

e) when a density gauge is used to monitor compaction rather than cores:

1) test results submitted demonstrate that the density gauge has been calibrated for the compacted mixture with pre-coated chippings, using sand to fill surface depressions;

2) test results submitted establish the correlation between the air voids content, as measured from cores in accordance with BS 594-2:2003, 9.2.6, and density determined using the calibrated density gauge;

f) test results submitted demonstrate conformity to BS 594-2:2003, 9.4.2, 9.4.3 and 9.4.4.

5.4.3.4 If the mix design or constituent materials of a job standard mixture are changed, details of the revised mixture shall be submitted for approval in accordance with 5.4.3.1 and 5.4.3.2. Although job mixture trials may be carried out on- or off-site, material laid for a job mixture trial on site may or may not be considered unsuitable as part of the surface course in permanent work, depending on the number of core holes. However, the material may be retained as part of the permanent binder course if laid at a suitable level.NOTE If job mixture trials are carried out off-site, they may be arranged independently or in conjunction with other works.

5.4.4 Mixing, transporting, laying and determining the performance characteristics

The hot rolled asphalt shall be mixed in accordance with Clause 6, then transported and laid in accordance with BS 594-2. The material shall be sampled and tested as described in BS 594-2:2003, Clause 9 to determine its conformity to the site-specific requirements.

6 Mixing

6.1 General

Hot rolled asphalt shall be mixed either by the batch process or in a continuous or drum mixer. The moisture content of the asphalt mixture, measured by the method given in BS 598-102, shall not exceed 1.0 % (m/m) of the mixture. On discharge from the mixer the aggregate shall be completely coated with binder with no evidence of balling of the fine aggregate.

6.2 Temperature of mixed asphalt

Whichever method of mixing is adopted, the appropriate maximum temperature given in Table 7 shall not be exceeded, to avoid the risk of undue binder hardening. Temperatures shall be measured in accordance with BS 598-109.



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Table 7 — Maximum temperatures of mixed asphalt

7 Coated chippings for application to surface course surfaces

7.1 Chippings

The chippings to be coated shall be coarse aggregate conforming to 4.2.1.NOTE The polished stone value and aggregate abrasion value of the chippings are site specific and outside the scope of this standard.

7.2 Binder coating

7.2.1 General

Binder used to coat the chippings shall be 40/60 pen paving grade bitumen conforming to 4.1. Except in the situation described in 5.4.2 (see Note), the amount of binder used shall yield a binder content on analysis of (1.5 ± 0.3) % (m/m).NOTE A higher binder content may be specified for chippings to be used in the situation described in BS 594-2:2002, 7.3, but any such higher binder content is still subject to a tolerance on analysis of ±0.3 % (m/m).

7.2.2 Quality of binder coating

The coated chippings, when tested for the condition of the binder in accordance with BS 598-108:1990, Clause 3 shall have a mass of sand retained of not less than 40 g/kg for 20 mm chippings or 50 g/kg for 14 mm chippings. Not more than 7.5 % (m/m) chippings shall fail the visual assessment of sand-cover.NOTE 1 Before the chippings are coated with binder, they should be dried and fed into a mixer at a maximum temperature of 170 °C. The maximum temperature of the coated chippings on discharge from the mixer should be 160 °C.

NOTE 2 In order to minimize formation of insoluble material in the binder the coated chippings should, on discharge from the mixer, be cooled quickly to ambient temperature by the application of clean water or by spreading in a layer not thicker than 1.0 m.

7.3 Size, shape and grading of chippings

The aggregate recovered from the coated chippings on analysis shall:

a) conform to the appropriate grading given in Table 8 when tested in accordance with BS EN 933-1; and

b) have a flakiness index not exceeding 20 when tested in accordance with BS EN 933-2.

Table 8 — Grading of chippings

Binder number

Type Grade Maximum temperature at any stage

Base (roadbase) or binder course Surface course

°C °C

1 Bitumen 30/45 175 1952 Lake asphalt-bitumen 35 pen — 1953 Bitumen 40/60 170 1904 Lake asphalt-bitumen 50 pen — 1905 Bitumen 70/100 165 1856 Lake asphalt-bitumen 70 pen — 1857 Bitumen 100/150 — 175NOTE Minimum delivery and rolling temperatures given in BS 594-2 should be considered when determining mixing temperature.

Test sieve Percentage (m/m) passing test sieve

14/20 mm size 8/14 mm size

31.5 mm 100 —20 mm 90 to 100 10014 mm 0 to 25 90 to 10010 mm 0 to 4 0 to 25

6.3 mm — 0 to 40.063 mm 0 to 2 0 to 2

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8 Sampling and testingNOTE The tolerances and ranges specified in this part of BS 594 are intended to provide for errors in sampling and testing when carried out by a skilled operator and for variations in the asphalt due to plant variations and fluctuations in gradings of aggregates. Attention is drawn to the difficulties inherent in obtaining representative samples of asphalt for analysis and to the further (usually smaller) errors in the reduction of the sample and its analysis in the laboratory. It should be realized that, whenever any sampling and testing procedure is used, complete conformity to the specification may not always be achieved with every sample tested even when the material is satisfactory (see BS 598-102).

8.1 Binders

Paving grade bitumens and lake asphalt-bitumen blends shall be sampled and tested in accordance with BS 3195-3 (EN 58), BS EN 12591 and BS 3690-3.

8.2 Aggregates and fillers

Coarse and fine aggregates and fillers shall be sampled and tested in accordance with the appropriate parts of BS EN 932, BS EN 933, BS EN 1097, BS EN 1367 and BS EN 1744 (see Clause 2).

8.3 Asphalt mixtures

Asphalt mixtures shall be sampled and tested in accordance with BS 598-100, BS 598-101 and BS 598-102.NOTE The grading of the mineral aggregate fraction of the mixture is determined by means of wet sieving. The fraction passing 0.063 mm as obtained by this method is reported without wet/dry correction.

8.4 Coated chippings

Coated chippings shall be sampled in accordance with BS 598-100, when their temperature is below 130 °C, and tested in accordance with BS 598-102.

The condition of the binder on the chippings shall be determined in accordance with BS 598-108:1990, Clause 3.

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Annex A (informative)Guidance on the selection of materials and mixtures

A.1 General

The selection of an asphalt mixture for a particular site depends upon many factors, particularly traffic, climate and layer thickness.

A.2 Aggregate

As there are no satisfactory tests for determining the amount of deleterious materials in aggregates, any obviously degraded or dirty stone together with contamination, such as by roots, vegetation or particles of lignite, should be avoided.NOTE Where experience indicates that an aggregate is prone to stripping, addition of an adhesion agent or 1 % to 2 % (m/m) of Portland cement or hydrated lime might be beneficial.

A.3 Base (roadbase) mixtures

A.3.1 Thickness

No specific recommendations for the total thickness of hot rolled asphalt bases (roadbases) are included in this standard as thickness is dependent upon a number of factors including the strength of the sub-base or formation and the traffic loading. Guidance can be obtained from publications dealing with pavement design.

A.3.2 Composition of mixtures

Base (roadbase) mixtures should be selected from Table 2 to suit the nominal layer thickness. A 40/60 pen bitumen is normally suitable for most applications but the softer 70/100 pen bitumen may be used where traffic loading is unlikely to be intense.

A.4 Binder course and regulating course mixtures

A.4.1 Binder

Reference should be made to Table 1. The use of 40/60 pen grade bitumen is generally satisfactory for most applications. In areas of intense canalized traffic in southern England, 30/45 pen grade bitumen may provide greater resistance to deformation. In Scotland and northern England 70/100 pen grade bitumen may be satisfactory for less heavily trafficked roads.

A.4.2 Thickness

Binder course and regulating course mixtures should be selected from Table 2 to suit the required nominal layer thickness.


The choice of coarse aggregate content depends largely upon the thickness of material laid. For general applications, 60 % (m/m) of coarse aggregate is recommended; 50 % (m/m) of coarse aggregate is recommended when a mixture is to be laid as a regulating course.

A.5 Surface course mixtures

A.5.1 Binder

The physical properties of an asphalt mixture are generally determined by the type of fine aggregate and bitumen. Traditional mixtures for normal traffic have been made with sand fine aggregate and 40/60 pen grade bitumen. If crushed fines or harsh sands are used, softer bitumen may be suitable, even on heavily trafficked roads.

For sites with more intense traffic, the use of harder (e.g. 30/45 pen) grade bitumen or crushed fine aggregate may be considered. For sites with very intense traffic, modified bitumens may by considered. On lightly trafficked roads and other lightly stressed areas, softer binders, e.g. 70/100 pen grade or 100/150 pen grade, may be used, even with sand fine aggregate.



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A.5.2 Aggregate

The choice of coarse aggregate and of coated chippings depends primarily on their suitability for the traffic and site conditions. In all circumstances on public roads and in certain off highway applications it is essential that the required level of skid resistance is maintained. To achieve this an aggregate with suitable resistance to the polishing effect of traffic should be used.

The resistance to polishing of coarse aggregate should be specified in terms of the appropriate category from BS EN 13043. In most cases this should be done using the category PSVdeclared and quoting the required minimum PSV value.

The rate at which exposed aggregate is abraded by heavy vehicular traffic is important in determining the retention of texture by the surface course. The resistance to surface abrasion should be specified in terms of the appropriate category from BS EN 13043. In most cases this should be done using the category AAVdeclared and quoting the required maximum AAV value. NOTE Guidance on the selection of appropriate polished-stone value and aggregate abrasion value for carriageways is published by the Highways Agency in Departmental Standard HD 36/99 (1999) [2].


A.5.3.1 General

Clause 5 of this standard gives specifications for three groups of surface course mixtures. The groups are of equal status and it is not intended that preference be given to any group.

The traditional recipe type surface course mixtures (see 5.3) have been successfully used in most applications. However, on some roads where traffic loadings have reached unprecedented levels, and as the range of constituent materials proposed for use has greatly widened, recipe mixtures have generally failed to perform well, and have been replaced by design mixtures and performance-specified design mixtures. Purchasers having proven materials sources and experience of the satisfactory use of recipe mixtures under the conditions applicable to their areas may wish to continue with their use, possibly with the additional resource of harder binders for roads where deformation may become a problem.

A.5.3.2 Group 2 mixtures: design method

When there is little or no experience of the use of the proposed constituent materials (especially the fine aggregate), or where severe traffic loadings exist or are anticipated, the design method is more suitable than the recipe method, particularly for major contracts involving high tonnage of surface course material.

The mixture derived from the laboratory procedure described in BS 598-107 should satisfy the traffic related criteria given in Table B.1. If the criteria are not met, alternative sources of constituent materials should be sought; normally a different fine aggregate and/or grade of binder should be chosen.

It is not yet possible to give specific guidance on minimum flow values for each traffic category in Table B.1.

The mixtures derived from the use of the design method in BS 598-107 are the result of tests on laboratory prepared specimens, undertaken well in advance of the works to determine an agreed composition. Adequate time should be allowed for this work. The laboratory design mix should be checked using aggregate from the plant bins, or the aggregate feed in the case of a continuous plant.

In normal circumstances the laboratory design procedure is undertaken whenever a new source of fine aggregate is used or proposed. It may also need to be carried out if the aggregate grading changes materially during production. When little or no variation has been indicated, a measure of consistency may be obtained by testing specimens, using plant-produced mixture compacted in accordance with the procedure in BS 598-107. As the results obtained using such material are not directly comparable with those obtained on laboratory prepared specimens, the values given in Table B.1 will not directly apply.

Periodic checks on the design should, therefore, be carried out at mixing plants, even when fine aggregate known to be reasonably consistent is used, to enable a producer to supply, with confidence, asphalt to a recent mix design conforming to this British Standard, even when the quantity of asphalt required is too small to justify the full design procedure being carried out.

Attention is drawn to the limited experience with type C design mixtures. Problems may occur in obtaining durable material of low permeability because the harshness of this type of mixture makes compaction more difficult. The problem may be overcome by increasing the binder content by up to 1 % (m/m) of total mixture above the design binder content, provided the criteria given in Table B.1 are satisfied.



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In the case of 55% 0/10 mm and 55% 0/14 mm surface course mixtures, which are not chipped, 100/150 pen grade bitumen is normally used where the mixes are laid on secondary roads, housing estate roads, play areas and similar sites. However, the use of 40/60 pen grade bitumen is advised on high-stress sites used by heavy goods vehicles; this material may not be suitable for hand laying. Mixtures containing 100/150 pen grade bitumen have traditionally been known as medium-temperature asphalt (MTA), in view of their lower handling temperatures compared with mixtures containing 40/60 pen grade bitumen.

A.5.3.3 Group 3 mixtures: recipe method

As indicated in Clause 5, this British Standard does not cover all suitable aggregates, a few of which require binder contents other than those given in Clause 5. If there is little experience with a particular aggregate, and particularly a fine aggregate, the recipe method should be used with caution. If the mixture obtained using the recommended recipe is unsuitably brittle or soft, the use of either a softer or harder binder, or the design method (group 2), should be considered.

The soluble binder contents used should be related to the climatic conditions and the volume of traffic at the specific site. In the majority of cases mixtures conforming to schedules 1A, 2A and 3A should be used. In cold, elevated, wet conditions, or for more lightly trafficked roads, mixtures conforming to schedules 1B, 2B and 3B are more appropriate.

A.5.3.4 Group 4 mixtures: performance-specified design mixtures

Performance-specified design mixtures should be considered where severe or very severe traffic conditions or traffic loadings exist or are anticipated (see Annex D, Table D.1 and Table D.2).

A.6 Cold weather working

The use of some modified binders can facilitate the laying of mixtures in cold weather conditions. The advice of the asphalt supplier should be sought if laying in these conditions is unavoidable.

A.7 Storage of mixed materials

It is not possible at the present time to give specific guidance on extended storage of bituminous mixtures. Conditions of storage affect the maximum storage period.

Annex B (informative)Recommendations for the application of design test criteria

B.1 Consideration of traffic conditions

When a hot rolled asphalt surface course with chippings is specified in accordance with 5.2, the properties of the asphalt should be suitable for traffic conditions at the site on which it is to be used. Table B.1 gives suggested test criteria, measured at the target binder content, for various levels of traffic.

Table B.1 — Criteria for the stability of laboratory design asphalt

Traffic is categorized in terms of the estimated average number of commercial vehicles per lane per day during the year of laying.

Where intense canalization of commercial vehicles occurs, such as at approaches to traffic lights, where heavy vehicles are continually braking and restarting, and where the rate of growth of traffic is expected to be abnormally high, the design test criteria should be based on the next higher traffic category.

Traffic (in commercial vehicles per lane per day) Stability of complete mix

kN

Less than 1 500 3 to 8a 1 500 to 6 000 4 to 8Over 6 000 6 to 10NOTE 1 For stabilities up to 8.0 kN the maximum flow value should be 5 mm. For stabilities in excess of 8.0 kN a maximum flow of 7 mm is permissible.

NOTE 2 The stability values referred to should be obtained on laboratory mixes.

NOTE 3 The stability and flow values are those pertaining to the target binder content.

a It may be necessary to restrict the upper limit where difficulties in the compaction of materials might occur.

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B.2 Verification of design proposals

The routine submission of design proposals required in the previous edition of this standard is not considered necessary for designs produced in UKAS accredited laboratories. If a purchaser intends to verify design proposals these should be specified to be submitted in accordance with BS 598-107:1990, Clause 11. This verification may be done by supervision or by further testing. An exception may be made for small contracts using material from a particular source where there is sufficient experience of the mixture for there to be confidence in the design submitted.

Annex C (informative)Specifying hot rolled asphalt

C.1 Information to be provided by the purchaser with the enquiry or order

When the purchaser wishes to select the constituent materials and mix composition from the options given in this part of BS 594, the following information should be agreed between the purchaser and the supplier at the time of the enquiry or order:

a) description of course(s) (see Annex A);

b) thickness of layer (see Table 2, Table 3, Table 4 and Table 6);

c) coarse aggregate content for each course (see Table 2, Table 3, Table 4 and Table 6);

d) type of coarse aggregate (see 5.2);

e) type of fine aggregate (see 5.3);

f) type and grade of binder for each course (see 5.1);

g) composition for each course and design method, recipe method or performance specified mixture for surface course (see Table 3, Table 4 and Table 6);

h) any additional requirements, e.g. coated chippings (see Clause 7), minimum polished stone value of coarse aggregate or chippings;

i) any additional relevant information (see BS 594-2).

C.2 Information to be provided by the supplier with the quotation

The following information should be provided by the supplier with the quotation, particularly when the purchaser, after providing the details of the construction to be carried out, has left the choice of the options given in this part of BS 594 to the supplier:

a) description of course(s) (see Annex A);

b) type, source and size of coated chippings (see Clause 7);

c) coarse aggregate content (see Table 2, Table 3, Table 4 and Table 6);

d) type of coarse aggregate (see 5.2);

e) type and source of fine aggregate (see 5.3);

f) type and grade of binder (see 5.1 and Note to Table 2);

g) composition for each course and design method or recipe method for surface course (see Table 2, Table 3, Table 4 and Table 6);

h) any additional relevant information (see BS 594-2).



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Annex D (informative)Guidance on the selection of performance related design criteria for surface course mixtures

D.1 General

Wheel-track rutting in the surface course may result from deformation in the surface course itself but also in lower pavement layers, particularly the binder course and, to a lesser extent, the base (roadbase). The purchaser should not consider using these performance related surface course mixtures unless he/she is satisfied that the binder course and base (roadbase) will provide the necessary support without undue deformation. To provide adequate resistance to deformation, it may be prudent to specify binder course and base (roadbase) macadams that are designed in accordance with BS 4987-1:2003, 4.7 using 40/60 pen grade binder for the sites in Table D.1.

The aim of 5.4.1 of this British Standard is to specify 35 % stone content hot rolled asphalt in terms of:

a) the component materials (other than binder modifiers) conforming to Clause 5 of this British Standard;

b) a maximum wheel-tracking rate in the laid mat to limit permanent deformation;

c) a maximum wheel-tracking rut depth to avoid mixtures with a tendency for significant early rutting but whose rutting subsequently stabilizes;

d) a maximum air voids content in the laid mat to ensure durability; and

e) the surface characteristics (such as texture depth and surface profile) to be as required for the materials specified in BS 594-2.

D.2 Binder modifiers

Modified binders, where shown to be necessary, are used to enhance the properties of the mixture over those provided by the available aggregate mixed with unmodified bitumen. In the absence of the Highways Authorities Product Approval Scheme (HAPAS), details of specific binder modifiers or process modified bitumens need to be provided (see E.2).

The need for approval of binder modifiers and modified binders is to minimize the possibility of adding anything to the mixture that may have harmful long-term effects. If there is evidence of successful use of a binder modifier/modified binder in similar conditions, the presumption should be of approval; if there is knowledge of the binder modifier/modified binder having had deleterious effects on mixtures, the binder modifier/modified binder should be rejected. The need for the modifier and the extent of its concentration are the responsibility of the producer in ensuring that the mixture conforms to the performance requirements and is durable. This should be especially noted if no data is available.

It is possible that producers may wish to seek approval for more than one modified binder and/or binder modifiers. Arrangement should be made so that approval for specific modified binder(s) and/or binder modifier(s) can be given in due time so that those tendering for works can submit tenders based on approved binders; if all binders submitted by a producer are rejected, there should be sufficient time to allow for the producer to submit alternative binders for approval.

As analytical test methods for modified binders are outside the scope of BS 598-102, because not all of some modified binders are recovered using the standard methods, any modifications to the test method and/or corrections to the results need to be established before work commences with a modified binder.

D.3 Job mixture approval

The producer may submit the results of any tests carried out on the mixture or its component materials as part of the design that he/she considers relevant for the purposes of mixture approval. This may include results from a previous contract or trial carried out up to 18 months previously.

For the job mixture approval trial of a mixture from a specific mixing plant, at least 20 t should be mixed, transported, laid, compacted, sampled and tested. Within the laid total area, a designated section of sufficient size to allow it to be compacted properly should be left unchipped. This may include results from a previous contract or trial carried out up to 18 months previously



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D.4 Job mixture approval sampling

Three samples of uncompacted material should be taken from the paver as near to where cores are to be taken as is practicable from the paver augers in accordance with BS 598-100:1987, 6.3.

At least six 200 mm diameter cores and six 150 mm diameter cores should be cut from the trial area with pre-coated chippings; at least six 150 mm diameter cores should be cut from the trial area without pre-coated chippings.

D.5 Job mixture approval tests

A compositional analysis should be carried out on each sample of uncompacted material in accordance with BS 594-2:2003, 9.2.3.

The wheel-tracking rate and the rut depth of each 200 mm diameter core should be determined in accordance with BS 594-2:2003, 9.2.4 at the test temperature specified by the purchaser.

If a density gauge is used, readings should be taken on an area where sand has been applied to fill surface depressions so as to give a smooth surface adjacent to each core hole in the trial area with pre-coated chippings. The temperature of the surface when the reading is taken should be recorded.

The density gauge should be calibrated for the mixture being laid. In addition, correlation analyses should be carried out between the air voids content, as measured from the cores in accordance with BS 594-2:2003, 9.2.6, and the density determined using the density meter.

The bulk density of each 150 mm diameter core with pre-coated chippings, and the maximum density of each pair of cores, should be determined in accordance with BS 594-2:2003, 9.2.5 and the air voids content determined in accordance with BS 594-2:2003, 9.2.6.

To calculate the binder content by volume as specified in 5.4.2.1, the bulk density of the 150 mm diameter cores taken from the unchipped area should be determined in accordance with the procedure in BS 598-104:1989, Clause 4. The density of the compacted hot rolled asphalt without pre-coated chippings should be calculated as the mean bulk density of the individual cores.

The material in a job mixture approval trial carried out on site may have too many core holes to be suitable for retention as part of the permanent surface course, however the material may be retained as part of the permanent binder course.

D.6 Testing

Although it is preferable to take cores prior to the surfacing being open to traffic, this may not be possible when the road has to be re-opened by a specific time. If the time during which the site is available is not sufficient to allow:

a) the preparation for and laying of the mat and its cooling sufficiently for coring;

b) the coring operation; and

c) the reinstatement of the core hole.

There is no requirement to cut cores before trafficking.

After cores have been cut, a diamond shape can be sawn around the core(s) and the material within the diamond shape removed to leave the core(s) proud and more accessible for removal to minimize damage, particularly during warm weather. Reinstatement of a larger area may also permit better compaction by roller to be achieved. Removing cores which have not cooled sufficiently can reduce their density.

For the reinstatement of core-holes the normal practice of using cold-lay 0/20 mm size dense bitumen macadam binder course for layers more than 50 mm below the surface and cold-lay 0/6 mm size dense bitumen macadam surface course for the surface course may not be suitable for high stress sites or diamond shape cut outs.

D.7 Density gauge

It is recommended that the density gauge is used as a monitoring tool to identify if and when the mixture or its compaction changes and to indicate possible non-conformity to the specification. This method of screening is intended to keep the use of coring to a minimum. It is a requirement that on motorway and trunk road sites a density gauge is used.



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D.8 Air voids content

The determination of air voids content employs the concept of maximum density of compacted mixtures. The test method for determining the maximum density of a compacted mixture is given in BS EN 12697-5. The method is based on ASTM D 2041.

D.9 Wheel-tracking rate

The test method for wheel-tracking is given in BS 598-110. The option of using paraffin wax in determining the bulk density of cores should not be used in order to avoid problems with subsequent testing for maximum density.

The limiting wheel-tracking rut depth after 45 min testing is used to avoid the possibility of materials deforming significantly in their early life and then densifying so as to achieve an acceptable wheel-tracking rate in the last 15 min of the test.

When selecting the specified limiting wheel-tracking rate, the limiting wheel-tracking rut depth and the temperature of the test, all of which are given to producers, the limits given in Table D.1 for site classifications defined in Table D.2 should be considered.

D.10 Combinations of factors which promote wheel-track rutting

The bulk of permanent deformation occurs during the summer months when hot rolled asphalt is at higher temperatures, particularly in areas where there are slow heavy-goods vehicle movements, such as climbing lanes, and when newly laid material is not yet fully stable and is less resistant to deformation under wheel loads. Permanent deformation can occur on road construction sites during summer months when partially completed pavements are re-opened to highway traffic under contraflow arrangements. The added factor of concentration of traffic can provide the worst combination of factors to cause permanent deformation. For this reason, Table D.2 has special categories IA, IIA, IIIA and IVA to cater for schemes in which such conditions can be anticipated in the early life of the surface course to be laid. Special categories IA, IIA, IIIA and IVA are also applicable to locations which can be regarded as “sun traps”, in particular south facing cuttings where vehicles are travelling uphill.

In assessing the appropriate category, other local factors may also be influential, including areas which have previously demonstrated high surface temperatures and the need to use aggregate with particular characteristics such as dark or light colouring. The problems of high surface temperatures can also be exacerbated on elevated structures which have less thermal capacity than where there is ground support of the pavement, and consequently experience higher temperatures.

Table D.1 — Limiting wheel-tracking requirements for site classifications

Classification Test temperature Maximum wheel-tracking

No. Description Rate Rut depth

°C mm/h mm

0 Lightly stressed sites not requiring specific design for deformation resistance. Not required Not required Not required

1 Moderate to heavily stressed sites requiring high rut resistance. 45 2.0 4.0

2 Very heavily stressed sites requiring very high rut resistance. 60 5.0 7.0

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Table D.2 — Classification of sites by traffic and stress condition

Special category

Site category

Site definition Traffic at design life (Commercial vehicles per lane per day)

2 501- 3 000

3 001- 4 000

4 001- 5 000

5 001- 6 000

Over 6 001

I an 1 1 2 2 2

IA 2 2 2 2 2

III 2 2 2 2 2

IIIA2 2 2 2 2

IV — — — — —

IVA— — — — —

V— — — — —

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Up to 250

251- 500

501- 1 000

1 001- 1 500

1 501- 2 000

2 001- 2 500

d II A Motorway (main line) 0 0 0 0 1 1B Dual carriageway (all purpose) non-event sectionsD Dual carriageway (all purpose) minor junctionsC Single carriageway non-event sectionsE Single carriageway minor junctions

and IIA As I and II but with contraflow anticipated during summer months

0 0 0 1 1 1

F Approaches to and across major junctions (all limbs) 0 0 0 1 1 1G1 Gradient 3 % to 10 %, longer than 50 m:

Dual (uphill and downhill)Single (uphill and downhill)

L RoundaboutAs III, above, but with contraflow anticipated during summer months or in a south-facing cutting uphill 0 0 1 1 2 2G2 Gradient steeper than 10%, longer than 50 m: 0 0 1 1 2 2

Dual (uphill and downhill)Single (uphill and downhill)

As IV but with contraflow anticipated during summer months or in a south-facing cutting uphill 0 1 1 2 2 2J/K Approach to roundabout, traffic signals, pedestrian

crossings, railway level crossings and similar 0 1 1 2 2 2

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Annex E (normative)Specifying performance specified hot rolled asphalt

E.1 Information to be provided by the purchaser with the enquiry or order

The following information shall be provided by the purchaser:

a) limiting wheel tracking performance (see Table D.1 and Table D.2);

b) any additional requirements, e.g. coated chippings (see Clause 7), polished stone value category of coarse aggregate or chippings;

c) whether a density gauge is to be used in monitoring the compaction of the as-laid asphalt.

E.2 Information to be provided by the supplier with the quotation

The following information shall be provided by the supplier with the quotation:

a) details of modified bitumens and bitumen modifiers not having BBA HAPAS Roads and Bridges certificates (see 5.4.2.1 and 5.4.2.2);

b) job mixture approval particulars (see 5.4.3.1);

c) details of alterations to the test method or necessary corrections, supporting data and mix design (see 5.4.3.2);

d) any additional relevant information, including recommendations for early trafficking (see BS 594-2).



BS 594-1:2003


Bibliography

Standards publications

BS EN 12697-5:2002, Bituminous mixtures — Test methods for hot mix asphalt — Determination of the maximum density.

PD 6682-2:2003, Aggregates — Part 2: Aggregates for bituminous mixtures and surface treatments for roads, airfields and other trafficked areas — Guidance on the use of BS EN 13043.

PD 6682-9:2003, Aggregates — Part 9: Guidance on the use of European test method standards.

ASTM D 2041:2000, Standard test method for theoretical maximum specific gravity and density of bituminous paving mixtures.

Other documents

[1] HIGHWAYS AGENCY. Design Manual for Road and Bridgework, Volume 7, (HD 37/99).London: The Highways Agency.

[2] HIGHWAYS AGENCY. Notes for Guidance to the Specification for Highway Works.London: The Stationery Office.

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