dmrb volume 7 section 5 part 1 - hd 36/06 - · pdf filenovember 2006 design manual for roads...

November 2006

DESIGN MANUAL FOR ROADS AND BRIDGES

VOLUME 7 PAVEMENT DESIGN ANDMAINTENANCE

SECTION 5 PAVEMENT MATERIALS

PART 1

HD 36/06

SURFACING MATERIALS FOR NEWAND MAINTENANCE CONSTRUCTION

SUMMARY

This revision primarily updates Chapter 3 of thisStandard. This Standard provides a summary ofsurfacing options available for use on both flexible andrigid pavements and advises on current requirements forsurfacing. It also details requirements for aggregatespreviously covered in HD 28 (DMRB 7.3.1) and givesadvice on surface texture.

INSTRUCTIONS FOR USE

1. Remove Contents pages from Volume 7 andinsert new Contents pages for Volume 7 datedNovember 2006.

2. Remove HD 36/99 from Volume 7, Section 5which is superseded by this Stadard and archiveas appropriate.

3. Insert HD 36/06 into Volume 7, Section 5.

4. Please archive this sheet as appropriate.

Note: A quarterly index with a full set of VolumeContents Pages is available separately from TheStationery Office Ltd.

HD 36/06

Surfacing Materials for New andMaintenance Construction

Summary: This revision primarily updates Chapter 3 of this Standard. This Standardprovides a summary of surfacing options available for use on both flexible andrigid pavements and advises on current requirements for surfacing. It alsodetails requirements for aggregates previously covered in HD 28 (DMRB 7.3.1)and gives advice on surface texture.


THE HIGHWAYS AGENCY

TRANSPORT SCOTLAND

WELSH ASSEMBLY GOVERNMENTLLYWODRAETH CYNULLIAD CYMRU

THE DEPARTMENT FOR REGIONAL DEVELOPMENTNORTHERN IRELAND

Volume 7 Section 5Part 1 HD 36/06

November 2006

REGISTRATION OF AMENDMENTS

Amend Page No Signature & Date of Amend Page No Signature & Date ofNo incorporation of No incorporation of

amendments amendments

Registration of Amendments

VOLUME 7 PAVEMENT DESIGN ANDMAINTENANCE

SECTION 5 PAVEMENT MATERIALS

PART 1

HD 36/06

SURFACING MATERIALS FOR NEWAND MAINTENANCE CONSTRUCTION

Contents

Chapter

1. Introduction

2. Surfacing Options

3. Texture and Aggregate Properties

4. Not currently used

5. Tyre/Road Surface Noise

6. References and Bibliography

7. Enquiries


November 2006


Chapter 1Introduction

1. INTRODUCTION

1.1 This Part provides a summary of surfacingoptions available for use on both flexible and rigidpavements and advises on current requirements forsurfacings. The Part also details the requirements foraggregates to ensure that satisfactory skiddingresistance is provided on roads and should be read inconjunction with HD 28 (DMRB 7.3.1). This Part alsoincludes details of surface texture and how this affectssurface noise at the tyre/road interface.

1.2 Supplementary information on bituminousmaterials is given in HD 26 (DMRB 7.2.3). Furtherinformation on the maintenance of bituminous roadscan be found in HD 31 (DMRB 7.4.1) and in HD 32(DMRB 7.4.2) for the maintenance of concrete roads.

1.3 Detailed information on bituminous materialtypes, and surfacing processes, together with advice ontheir use, is presented in HD 37 (DMRB 7.5.2). Detailsof concrete surfacing and materials are given in HD 38(DMRB 7.5.3). Reference should be made to theSpecification (MCHW1) Series 700, 900 and 1000,together with the Notes for Guidance (MCHW2). Forsome materials there are British Standards and otherpublished documentation and these are referenced inthe appropriate chapters.

Implementation

1.4 This Part shall be used forthwith on all schemesfor the construction, improvement and maintenance oftrunk roads including motorways, currently beingprepared provided that, in the opinion of the OverseeingOrganisation this would not result in significantadditional expense or delay. Design organisationsshould confirm its application to particular schemeswith the Overseeing Organisation.

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Mutual Recognition

1.5 The construction and maintenance of highwaypavements will normally be carried out under contractsincorporating the Overseeing Organisation’sSpecification for Highway Works (MCHW1). In suchcases products conforming to equivalent standards andspecifications of other States of the European EconomicArea and tests undertaken in the other States will beacceptable in accordance with the terms of the 104 and105 Series of Clauses of that Specification. Anycontract not containing these clauses must containsuitable clauses of mutual recognition having the sameeffect regarding which advice should be sought.

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Chapter 2Surfacing Options

2. SURFACING OPTIONS

2.1 The choice of surfacing materials/systems plays avital role in providing roads that meet the needs of theuser, are safe and give value for money. For many yearshot rolled asphalt with chippings rolled into the surfacewas the most widely used surfacing on trunk roads,including motorways, for both new construction andmajor maintenance. However, recent years have seenthe development of new materials and techniques, manyof which are proprietary, which offer significantadvantages not just to the road user but also to theenvironment. For example, noise generation may bereduced, delays at road works curtailed, ride qualityimproved and deformation resistance enhanced, allwhile maintaining existing safety levels. Furthermore,new products such as energy efficient ‘cold-lay’materials are in their development phase. This Chaptergives guidance on the range of surfacing options thatare now available for both new construction andmaintenance.

Performance Specifications

2.2 To remove the barriers to trade and to encourageinnovation, the Construction Products Directive (CPD)of the European Union requires the introduction ofperformance related specifications wherever possible.Specification clauses of this type have been included inthe Specification for Highway Works (MCHW1&2)covering surfacings such as surface dressings (Clause922), slurry and micro-surfacings (Clauses 918), highfriction surfacing (Clause 924), (Clause 938), thinsurface course systems (Clause 942) and hot rolledasphalt (Clause 943). Performance is assessed either bytesting samples from the laid material, testing the laidmaterial in-situ or, for proprietary systems, byassessment and approval under the British Board ofAgrément Highway Authorities Product ApprovalScheme (BBA HAPAS).

2.3 Where BBA HAPAS certification isspecified but certificates are not in place, or inEngland, HA type approval has not been given, theapproval of the Overseeing Organisation must besought and a Departure agreed.

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oice of Surfacings

Apart from the suitability of surfacing materialsterms of safety and robustness, the permittedement surfacing options for use on trunk roads, haven determined by the Overseeing Organisations, asicated in Tables 2.2 (E), (S), (NI) and (W), takingount of the variations across the UK of a number oftors:

the nature of the existing network;

population density;

traffic intensity;

climatic conditions;

availability of materials.

The decision on which permitted options are toincluded should be made on a site-specific basis butne should be ruled out without justification. Inations where speeds are limited and tyre/roaderated noise low, or where traffic intensity andrefore the overall noise level is not very great, then full range of suitable surfacings should besidered

Where noise levels are high due to the intensityhigh-speed traffic, surfacing materials are availablet can significantly reduce tyre/road generated noiseission compared to hot rolled asphalt. These includet, paver-laid thin surface course systems,ecification Clause 942 (MCHW 1).

Advice on the different types of surfacings isen in HD 37 and 38 (DMRB 7.5.2 & 3). Althoughormation on various surfacings and treatments isvided in HD 37 and HD 38, it should not beumed that their use is permitted on the trunk roadwork. Advice is provided for certain treatments forormation only. Reference should be made to Table to check permitted options.

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2.8 In England, no surface treatment should beconsidered without taking into account theHighways Agency’s requirements for low-noisesurfacing. Retexturing of existing surfaces is notpermissible without Departure approval. Thisapproval will not be unreasonably withheld forsmall lengths of pavement with a particularskidding or other safety concern.

2.9 The surfacing options permitted shall bethose shown in Tables 2.2E, 2.2NI and 2.2W, forEngland, Northern Ireland and Wales respectively.Where an option is permitted with “DepartureRequired”, a Departure from Standard will berequired from the Overseeing Organisation.

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England

For Table 2.2S, for use in Scotland, where anoption is permitted subject to “Approval toProceed”, such approval is required from theOverseeing Organisation.

.10 In Table 2.2, high-speed roads are defined ashose with an 85th percentile traffic speed exceeding 65m/hr. The various pavement construction types areefined in HD 26 (DMRB 7.2.3).

This table is for use

in England

only

All construction types

Use without restriction Departure required

New Yes Thin Surface Course System Porous AsphaltConstructionor No High Yes Thin Surface Course System Hot Rolled AsphaltMajor (minor) speed? Porous AsphaltMaintenance? (85%ile Surface Dressing

above 65 Exposed Aggregate Concretekm/hr) (note 1)

Brushed/Burlap Drag/TinedConcrete (note 1)

No Thin Surface Course System Hot Rolled AsphaltPorous AsphaltSurface DressingSlurry/MicrosurfacingExposed Aggregate Concrete(note 1)Brushed/Burlap Drag/TinedConcrete (note 1)

Note 1: Rigid construction only

Table 2.2E (England): Permitted Pavement Surfacing Materials forNew and Maintenance Construction

November 2006




in Wales

only

Wales



New Yes Thin Surface Course System Hot Rolled AsphaltConstruction Porous Asphaltor Exposed Aggregate ConcreteMajor (note 1)Maintenance?

No High Yes Thin Surface Course System Hot Rolled Asphalt(minor) speed? Porous Asphalt

(85%ile Surface Dressingabove 65 Exposed Aggregate Concretekm/hr) (note 1)

Brushed/Burlap Drag/TinedConcrete (note 1)

No Thin Surface Course System Hot Rolled AsphaltPorous AsphaltSurface DressingSlurry/MicrosurfacingExposed Aggregate Concrete(note 1)Brushed/Burlap Drag/TinedConcrete (note 1)

Note 1: Rigid construction only

Table 2.2W (Wales): Permitted Pavement Surfacing Materials forNew and Maintenance Construction

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in Scotland

only

Scotland


Use without restriction Approval to Proceedrequired

New Yes Hot Rolled Asphalt Thin Surface Course SystemConstruction (note 1) Porous Asphaltor Generic SMAMajor Exposed Aggregate ConcreteMaintenance? (note 3)

No High Yes Hot Rolled Asphalt Thin Surface Course System(minor) speed? (note 1) Porous Asphalt

(85%ile Surface Dressingabove 65 Generic SMAkm/hr) Exposed Aggregate Concrete

(note 3)Brushed/Burlap Drag/TinedConcrete (note 3)

No Hot Rolled Asphalt Thin Surface Course System(note 2) Porous AsphaltSurface Dressing Generic SMA

Slurry/MicrosurfacingExposed Aggregate Concrete(note 3)Brushed/Burlap Drag/TinedConcrete (note 3)

Note 1: Not permitted on rigid constructionNote 2: Refer to Overseeing Organisation on rigid constructionNote 3: Rigid construction only

Table 2.2S (Scotland): Permitted Pavement Surfacing Materials forNew and Maintenance Construction

November 20062/4




in Northern Ireland

only

Northern IrelandFlexible and flexible composite


New Yes High Yes Thin Surface Course System Porous Asphalt (note 1)Construction speed? Hot Rolled Asphaltor (85%ileMajor above 65 No Thin Surface Course System Porous Asphalt (note 1)Maintenance? km/hr) Hot Rolled Asphalt Generic SMA

Coated macadam

No High Yes Thin Surface Course System Porous Asphalt (note 1)(minor) speed? Hot Rolled Asphalt

(85%ile Surface Dressingabove 65km/hr) No Thin Surface Course System Porous Asphalt (note 1)

Hot Rolled Asphalt Generic SMACoated macadamSurface DressingSlurry Surfacing

Note 1: not permitted on flexible composite construction

Rigid


New Yes High Yes Exposed Aggregate Concrete Brushed ConcreteConstruction speed? Burlap Drag Concreteor (85%ile Tined ConcreteMajor above 65Maintenance? km/hr) No Exposed Aggregate Concrete Brushed Concrete

Burlap Drag ConcreteTined Concrete

No High Yes Exposed Aggregate Concrete Brushed Concrete(minor) speed? Hot Rolled Asphalt Burlap Drag Concrete

(85%ile Surface Dressing Tined Concreteabove 65 Porous Asphaltkm/hr) Thin Surface Course System

No Exposed Aggregate Concrete Brushed ConcreteHot Rolled Asphalt Burlap Drag ConcreteSurface Dressing Tined ConcreteSlurry Surfacing Porous Asphalt

Thin Surface Course SystemGeneric SMA

Rigid composite


New Yes High Yes Hot Rolled Asphalt Porous AsphaltConstruction speed? Thin Surface Course Systemor (85%ileMajor above 65 No Hot Rolled Asphalt Porous AsphaltMaintenance? km/hr) Thin Surface Course System

Surface Dressing

No High Yes Hot Rolled Asphalt Porous Asphalt(minor) speed? Thin Surface Course System Generic SMA

(85%ileabove 65 No Hot Rolled Asphalt Porous Asphaltkm/hr) Thin Surface Course System Generic SMA

Surface DressingSlurry Surfacing

Table 2.2NI (N Ireland): Permitted Pavement Surfacing Materials for New and Maintenance Construction

November 2006 2/5


Chapter 3Texture and Aggregate Properties

ATE PROPERTIES
3. TEXTURE AND AGGREG
3.1 Friction between the tyre and road surfaceconsists of two main components, both of which arerelated to speed.

a) Sliding resistance between tyre and road surfacewith its magnitude determined by the nature ofthe materials in contact.

b) Loss of energy caused by deformation(hysteresis) of the tyre.

Therefore, during a single braking operation the frictionavailable to the vehicle is not constant.

3.2 In dry conditions all clean, surfaced roads have ahigh skidding resistance. The fine scale Microtexture(see Figure 3.1) of the surface aggregate is the maincontributor to sliding resistance and is the dominantfactor in determining wet skidding resistance at lowerspeeds. Coarse Macrotexture, which provides rapiddrainage routes between the tyre and road surface, andtyre resilience are important factors in determining wetskidding resistance at high speeds. Annex 3 of HD 28(DMRB 7.3.1) contains further discussion of skidresistance and the influence of micro- and macro-texture. Megatexture relates to the roughness of theroad and has no effect on skidding resistance but affectsnoise, (see Chapter 5 of this Part for details).

Figure 3.1: Surface Texture

3.3 The skidding resistance of wet roads is reducedby the lubricating action of the film of water on the wetroad surface. Drainage channels provided by the largescale texture (macrotexture) and/or the pattern on thetyre, assist in getting rid of the bulk of the water and areof increasing importance the higher the speed.

November 2006

Penetration of the remaining water film can be achievedonly if there are sufficient fine scale sharp edges(microtexture) on the road surface on which the tyrecan build up high contact pressures to establish areas of‘dry’ contact between the road and the tyre.

3.4 Aquaplaning is the condition where the vehicletyres are completely supported by a layer of water andthere is no contact with the road surface. High speedand a thick film of water on the road surface encouragea vehicle to aquaplane, but a relatively thin layer ofwater could cause a problem if combined with lowtexture depth and ‘smooth’ tyres. Although aquaplaningitself is not regularly identified, conditions may oftenexist where a high proportion of tyre/road contact islost.

3.5 Because of the effects of weight transfer whenbraking and/or cornering some wheels are likely to skidearlier than the skidding resistance of the road surfacealone indicates. In addition, if brakes are out ofadjustment and hence the distribution of braking efforton the wheels is uneven, the minimum skiddingresistance required to avoid skidding will be increasedstill further, as more of the retarding force will have tobe taken by the wheels of the functioning brakes.

MICRO-TEXTURE

3.6 The micro-texture characteristics of a particularstone depend on its polishing susceptibility under theaction of tyre forces.

Measurement

3.7 The accelerated polishing machine (Figure3.2) is used on aggregates to simulate the polishingaction of traffic. The Polished Stone Value (PSV)test, must be carried out and is specified inBS EN 1097-8:2000. It requires six hours ofpolishing designed to produce a state similar tothat which the aggregate would be subjected tounder actual traffic when equilibrium conditionsare reached.

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Figure 3.2: Accelerated Polishing Machine

3.8 The portable skid-resistance tester (Figure3.3) must used to determine the skid resistancevalue of the aggregate after polishing. This istermed the PSV.

Figure 3.3: Portable Skid Resistance Tester

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3.9 Aggregate durability must be measured bythe Aggregate Abrasion Value (AAV) test asdefined in Annex A of BS EN 1097-8:2000. TheAAV is a measure of the durability or resistance toabrasion of an aggregate under the action of traffic.

gregate Selection

0 To determine the correct PSV and AAV for aticular site the designer should have regard to theent and scale of the work. When specifying a PSV itndesirable to have too frequent changes of aggregate the aim should be to specify and provide the mostnomical aggregate available over the longestsible lengths. The highest PSV aggregates should betricted to those locations where they are requiredh as on bends and gradients, and at intersections andctions.

3.11 The minimum PSVs to be applied todifferent categories of site and related to trafficflow are given in Table 3.1. The appropriate AAVsare given in Table 3.2. Tables 3.1 and 3.2 refer toboth new works and maintenance and values ofPSV and AAV must be inserted into theappropriate part of Appendix 7/1 of theSpecification (MCHW1). The minimum values ofPSV given in Table 3.1 are the values to be used ifno other information is available. On an existingsite, if the life that has been achieved by theaggregates, the skid resistance and the skiddingaccident rate have all been satisfactory, then thecontinued use of the same aggregate source, albeitwith a lower PSV than that given in Table 3.1 maybe considered. If, however, the measured skidresistance of the site when related to the lifeachieved and the skidding accident rate are belowexpectations for an aggregate from a particularsource, then a higher PSV than that given in Table3.1 may be specified.

2 Although some motorways carry in excess of0 commercial vehicles per lane per day, PSVs iness of those shown in Table 3.1 must not becified. Although minimum PSV values have beenluded for all types of site and traffic level, some

binations are unlikely to occur in practice.

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0.45 60 65 65 68+ 68+ 68+ 68+ 68+ 68+ HFS

0.5 65 65 65 68+ 68+ 68+ HFS HFS HFS HFS

0.55 68+ 68+ HFS HFS HFS HFS HFS HFS HFS HFS

0.45 50 55 60 60 65 65 68+ 68+ HFS HFS

0.5 68+ 68+ 68+ HFS HFS HFS HFS HFS HFS HFS

0.55 HFS HFS HFS HFS HFS HFS HFS HFS HFS HFS

Minimum PSV required for given IL, traffic level and type of siteSite Site

category description IL Traffic (cv/lane/day) at design life

0-250 251- 501- 751- 1001- 2001- 3001- 4001- 5001- Over500 750 1000 2000 3000 4000 5000 6000 6000

Motorways where traffic is generally 0.30 50 50 50 50 50 55 55 60 65 65A1 free-flowing on a relatively straight

line 0.35 50 50 50 50 50 60 60 60 65 65Motorways where some braking

A2 regularly occurs (eg. on 300m approach 0.35 50 50 50 55 55 60 60 65 65 65to an off-slip)Dual carriageways where traffic is 0.3 50 50 50 50 50 55 55 60 65 65

B1 generally free-flowing on a relatively 0.35 50 50 50 50 50 60 60 60 65 65straight line 0.4 50 50 50 55 60 65 65 65 65 68+Dual carriageways where some braking 0.35 50 50 50 55 55 60 60 65 65 65

B2 regularly occurs (eg. on 300m approachto an off-slip) 0.4 55 60 60 65 65 68+ 68+ 68+ 68+ 68+Single carriageways where traffic is 0.35 50 50 50 55 55 60 60 65 65 65

C generally free-flowing on a relatively 0.4 55 60 60 65 65 68+ 68+ 68+ 68+ 68+straight line 0.45 60 60 65 65 68+ 68+ 68+ 68+ 68+ 68+Gradients >5% longer than 50m as 0.45 55 60 60 65 65 68+ 68+ 68+ 68+ HFS

G1/G2 per HD 28 0.5 60 68+ 68+ HFS HFS HFS HFS HFS HFS HFS0.55 68+ HFS HFS HFS HFS HFS HFS HFS HFS HFS

K Approaches to pedestrian crossings 0.5 65 65 65 68+ 68+ 68+ HFS HFS HFS HFSand other high risk situations 0.55 68+ 68+ HFS HFS HFS HFS HFS HFS HFS HFSApproaches to major and minorjunctions on dual carriageways and

Q single carriageways where frequent orsudden braking occurs but in agenerally straight line.

R Roundabout circulation areas 0.45 50 55 60 60 65 65 68+ 68+ HFS HFS

0.5 68+ 68+ 68+ HFS HFS HFS HFS HFS HFS HFS

Bends (radius <500m) on all types ofS1/S2 road, including motorway link roads;

other hazards that require combinedbraking and cornering

Notes:1. Site categories are grouped according to their general character and traffic behaviour. The Investigatory Levels (IL) for

specific categories of site are defined in HD 28 (DMRB 7.3.1). The IL to be used here must be that which has beenallocated to the specific site on which the material is to be laid, as determined by following the procedures in HD 28.

2. Motorway or dual carriageway slip roads may fit in a number of groups depending on their layout. For example, a free-flowing section close to the main line would be in Group 1 whereas the end of an off-slip approaching a give way line orthe point at which a queue develops would be in Group 3. Some slip roads with gradients may be in Group 4. Use themost appropriate Group depending upon the Site Category from HD 28 that was used to determine the IL.

3. Where ’68+’ material is listed in this Table, none of the three most recent results from consecutive PSV tests relating tothe aggregate to be supplied must fall below 68. See paragraph 3.21.

4. Throughout this Table, HFS means specialised high friction surfacing, incorporating calcined bauxite aggregate andconforming to Clause 924 of the Specification (MCHW 1) will be required. Where HFS is required on the approachesto a hazard, the minimum treatment length must be 50m. This may be extended where queuing traffic or sightlinesindicate that 50m may not be sufficiently long.

5. For site categories G1/G2, S1/S2 and R any PSV in the range given for each traffic level may be used for any IL andshould be chosen on the basis of local experience of material performance. In the absence of this information, the valuesgiven for the appropriate IL and traffic level must be used.

6. Where designers are knowledgeable or have other experience of particular site conditions, an alternative psv value canbe specified.

Table 3.1: Minimum PSV of Chippings, or Coarse Aggregate in Unchipped Surfaces, for New Surface Courses

November 2006 3/3



1001- 1751- 2501- >32501750 2500 3250

12 10 10 10

14 14 12 12

Traffic (cv/lane/day) at <250 251-design life (see 3.15) 1000

Max AAV for chippings 14 12for hot rolled asphalt andsurface dressing, and foraggregate in slurry andmicrosurfacing systems

Max AAV for aggregate 16 16in thin surface coursesystems, exposedaggregate concretesurfacing and coatedmacadam surface course

Note 1: For roads carrying less than 1750 cv/lane/day, aggrehas shown that satisfactory performance is achieved

Note 2: The maximum AAV requirement for porous asphalt(MCHW 1).

Table 3.2: Maximum AAV of Chippings, or Cofor New Surface

3.13 The PSVs in Table 3.1 are related to the IL fordifferent traffic flows set out in Chapter 4 of HD 28(DMRB 7.3.1). A margin of safety has been added foreach of the following reasons:

a) to allow for variability of aggregates, theprecision of the PSV test and variations inestimating traffic flows;

b) to allow for turning movements and traction/braking forces at junctions, on bends and ongradients;

c) where possible, to ensure that the skiddingresistance achieved on trunk roads does not fallbelow the requirements within the lifetime of thesurfacing. This avoids frequent maintenance onhigh speed and other trunk roads with consequenttraffic delays.

3.14 Using the appropriate PSV for a particular siteand traffic loading should result in a surfacing givingsatisfactory performance before reaching theinvestigatory level of Characteristic SCRIMCoefficient. See Chapter 4 of HD 28 (DMRB 7.3.1).

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gate of higher AAV may be used where experience by an aggregate from a particular source.

is specified in Clause 938 of the Specification

arse Aggregates in Unchipped Surfaces, Courses

3.15 The traffic flow used to determine theappropriate PSV and AAV for a particularsurfacing must be the maximum volume of trafficmeasured as commercial vehicles per lane per day(cv/lane/day) based on the Average Annual DailyFlow (AADF) predicted to be using the lane at theend of the anticipated life of the surfacing – seeHD 24 (DMRB 7.2.1). Estimates of traffic growthrates and life of the surfacing may be based onlocal experience.

3.16 The same levels of PSV and AAV must beused on different traffic lanes across thecarriageway and in the hardshoulder except that,where aggregates are used for demarcation, amaximum difference of 5 PSV points may beallowed.

3.17 The PSVs given in Table 3.1 apply to roadsconstructed within current design standards, andwill provide satisfactory skid resistance on sites ofaverage difficulty requiring the given investigatorylevel within the general site group for the life ofthe surfacing.

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3.18 For site categories G1/G2, S1/S2 and R a rangeof ILs and corresponding PSVs for each traffic level isgiven in Table 3.1. For sites in these groups, the PSV tobe specified should be based upon local experience ofmaterial performance. For maintenance resurfacing, thecurrent skid resistance in relation to the life achieved,the investigatory level and the skidding accident rateshould be considered. If satisfactory, the PSV and AAVof the new surfacing should be the same as theaggregates used previously. If consideredunsatisfactory, the PSV must be increased to that for ahigher IL within the range given for the appropriatetraffic level. For new construction, existing sites withsimilar traffic flows, IL and site geometry should beused to assist in determining the initial values of PSVand AAV to be specified. In the absence of any suchsuitable information, the values given for theappropriate IL and traffic level must be used.

3.19 The actual PSVs, AAVs and texture depthsbuilt into schemes of new construction and theassumptions on which the minimum values wereselected must be recorded and maintained in areadily available form, (eg. the schememaintenance manual). Standards to be adopted insubsequent renewal work may then be determinedin the light of the skidding resistance performanceset against those initial recorded values.

3.20 The requirements of Tables 3.1 and 3.2cover:

a) chippings for surface dressing;

b) the coarse aggregate in thin surface coursesystems, porous asphalt, bitumen macadamsurface courses and surface courses of rolledasphalt without coated chippings applied tothe surface;

c) coated chippings applied to the surface ofrolled asphalt, to mastic asphalt and to finegraded macadam;

d) coarse aggregate in slurry surfacing andmicrosurfacing systems; and

e) the coarse aggregate in non-surface dressedbinder courses of bitumen macadam or stonemastic asphalt and bases of bitumenmacadam or rolled asphalt used astemporary surfaces by general traffic forprolonged periods and not subject to speedrestrictions or without warning signs.

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3.21 Samples of the aggregate representative ofthose to be incorporated into the Works must betested in accordance with BS EN 1097-8 forcompliance with the specified PSV and AAVproperties. Alternatively, except where a PSV of68+ is specified, the aggregate must be deemed tocomply if the mean of the three most recent resultsfrom consecutive tests, relating to the material tobe supplied, is greater than or equal to thespecified PSV and less than the specified AAV.Where a PSV of 68+ is specified, none of the threemost recent results from consecutive tests shall beless than 68. Tests must have been carried out inthe previous six months by a laboratory accreditedby UKAS or equivalent for these tests or by alaboratory in a Member State of the EuropeanEconomic Area or a State which is party to arelevant agreement with the European Union thatcan demonstrate suitable and satisfactory evidenceof technical and professional competence andindependence for such tests. The latter requirementmust be satisfied if the laboratory is accredited in aMember State of the European Economic Area or aState which is party to a relevant agreement withthe European Union in accordance with therelevant parts of EN45000 series of standards forthe tests carried out.

3.22 It is essential that the aggregate supplied tosite must be the same in all respects to the samplesubmitted for acceptance. If it is considered thatthere is a change in the material delivered to site,further tests must be ordered.

3.23 There are few quarries that can supply aggregatewhere PSV is consistently over 68, together with amaximum AAV of 10. In order to achieve values inexcess of this, it is necessary to specify a high frictionsurface treatment as described in Clause 924 of theSpecification (MCHW1). Although highly skidresistant, material complying with Clause 924 is unableto meet the requirement of a texture depth of 1.5mm(measured by the volumetric patch test). Therefore, onhigh speed roads, this type of material must only beused where strictly necessary, eg. for braking sectionsand tight curves. When such materials are to be used onhigh speed roads, attention must be given to the need todrain water off the surface by profiling or by othermeans.

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3.24 The PSV of 70+ is considered to be the highestpractical level that can be consistently achieved usingartificial aggregate such as calcined bauxite. Forheavily stressed sites the use of a small size, hardaggregate with a PSV of 70+ effectively increases theinitial skidding resistance provided and thereby extendsits ‘life’, ie. the period before the investigatory level isreached. This effective increase in skidding resistancealso increases the stress on the chippings, hence thenecessity to use a binder modified with an epoxy or asimilar resin. Advice is given in Chapter 9 of HD 37(DMRB 7.5.2) and also in Series NG 900 of the Notesfor Guidance to the Specification (MCHW2).

3.25 To decide whether a high PSV stone should beused for renewing a surface, consideration should begiven to the PSV and AAV of the existing aggregate inrelation to the life achieved, the current skid resistanceof the surface and the skidding accident rate of the site.If all are satisfactory, the use of stone from the samesource and of the same PSV may be appropriate. Whererecords of PSV and AAV are not available,identification of the source of an aggregate may enablevalues that are sufficiently accurate for assessmentpurposes to be estimated.

MACRO-TEXTURE

3.26 Adequate macro-texture is required for the rapiddrainage of surface water from the tyre and roadpavement interface thereby reducing the chance ofaquaplaning. The texture depth is a measure of themacro-texture and is an important factor influencingskidding in wet conditions on high speed (>65km/h)roads.

3.27 Surface texture takes two forms:

a) ‘positive’ texture: a cluster of angular peaks orseries of ridges above a datum level, typical ofsurface dressings, hot rolled asphalt with chips,slurry and microsurfacings and brushed concrete;

b) ‘negative’ texture: a network of depressions orseries of grooves below the general level, typicalof thin surface course systems, and porousasphalt.

3.28 Ideally, choice of an appropriate texture depthwould be made on the basis of values related toaccident occurrence that could then become part of amaintenance policy. However, further research isrequired into this area and until such results areavailable, the approach is to specify minimum levels of

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re depth for new higher-speed roads to apply attruction or major maintenance. This is given ins 900 of the Specification (MCHW1).

For speeds in excess of 65km/h, the texture depthe surface should be that required by theification (MCHW1). This will ensure that theease in skid resistance that occurs at higher speedsinimised and will facilitate the rapid drainage ofr from the road surface. At lower speeds, textureh is less important and compliance with the moreral specification requirements or with specified of spread of chippings should be sufficient. Withr speed roads, micro texture is the major factor intaining skid resistance, although texture depth is

important. In bituminous and exposed aggregaterete roads, micro texture is provided by the use of ace aggregate with a specified resistance tohing given by the PSV.

surement

For many years texture depth has been measurede volumetric patch method in which a knownme of solid glass spheres or sand is spread into alar patch. The diameter of the patch is measured

the average depth under the peaks in the surfacelated. The technique is described inN 13036-1:2002.

More recently, laser-based techniques haveme available which determine the texture depthit by a different methodology.

Measurement of Texture at High Speed

It is possible to measure texture indirectly usings and reflected light at speeds up to 100km/h. Thisod has been incorporated in a number of devicesding the SCRIMTEX, the Highways Agencyrch tool HARRIS (Highways Agency Roadarch Information System: Figure 3.5) and Trafficd Condition Surveys (TRACS).

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Figure 3.5: Highways Agency Road Research Information System (HARRIS)

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OISE

Chapter 5Tyre/Road Surface Noise

5. TYRE/ROAD SURFACE N

GENERAL

5.1 Noise from road traffic has become, over the lastfew years, a very contentious environmental issue.Where traffic speeds are lower than 50 km/hr, trafficnoise is mainly attributable to engine, transmission andexhaust noise, especially from lorries. Where speeds arehigher, the major component of traffic noise comesfrom the tyre/road interface. This noise comes from,amongst other things, vibration of the tyre wall,compression of air within the contact area of the tyre,and the snapping out of the tread blocks as they leavethe road surface. The quality of the road surface, tyredesign and vehicle speeds all have an effect on tyrenoise.

5.2 Details of the available low noise surfacings andwhere they may be used is given in Chapter 2 of thisPart.

5.3 For many years it has been the UK practice toensure that there are interconnecting drainage pathswithin the surface over which the tyre runs to helpdisperse water and improve skidding resistance,particularly at high speeds. It was also recognised thatthe coarseness of the surface contributes to traffic noise.This coarseness has traditionally been measured by thesand patch test, which gives the average depth oftexture over an area similar to the contact patch of atyre.

Definitions of Texture Depths

5.4 It is now recognised that there are a number offactors within the road surface texture that playsignificantly different roles in improving skiddingresistance and generating noise. It is helpful todistinguish different scales of texture by defining theroles of the texture ranges as follows:

i) The fine scale microtexture of the surfaceaggregate is the main contributor to skiddingresistance and is the dominant factor indetermining skidding resistance at lower speeds.

ii) Macrotexture provides rapid drainage routesbetween the tyre and the road surface andcontributes to the wet skidding resistance athigher speeds. It also allows air trapped beneaththe tyre to escape.

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iii) Megatexture at a scale comparable with the tyrecontact patch is mainly associated with tyrenoise. Surfaces with high mega-texture includeHRA with gaps between groups of chippings andthe old-style cobbled surfacings.

iv) Unevenness in the longer ranges cause large tyreand suspension movements that affect thehandling of vehicles.

5.4 Fig 5.1 shows the difference between micro-,macro-, and mega-texture lengths and depths.

5.5 The texture depth is the average deviation of aroad surface from a true planar surface within anycategory of texture. It is represented at the road surfaceas:

i) Microtexture

Describes the roughness of the surface aggregate, whichis associated with the crystalline structure of the coarseaggregate and the sand particles in the surface laitanceof a brushed concrete surface.

ii) Macrotexture

Represents the height above a road surface of theaggregate chipping (eg. for HRA, surface dressing andbrushed concrete), or the depth of texture below theroad surface (eg. for porous asphalt, thin surfacings,tined and exposed aggregate concrete surfaces,(EACS)).

iii) Megatexture

Represents the degree of smoothness of the surface.

iv) Unevenness

Describes amplitudes of longer wavelengths, whichaffect vehicle suspensions.

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Figure 5.1: Details of Textu

.6 The effect of texture on noise and skidding isiven in Table 5.1.

.7 With recently developed laser based equipmenthe depth of the texture can be measured separatelyithin each texture range. The objective of modern

urfacing techniques is to reduce the depth of texture inhe megatexture range as much as possible, whileetaining an adequate depth of macrotexture to provideigh speed skidding performance. Low speed skiddingerformance is mainly controlled by the microtexture.he interrelationship of the effects of different types of

exture on skidding resistance and noise generation arehown in Figure 5.2.

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re Length and Depths

ositive and Negative Texture Depths

.8 An important difference between surfaces, whichas a strong effect on noise generation, is the degree tohich the surface aggregate particles protrude abovee plane of the tyre contact patch. Surfaces that arermed by rolling aggregate chippings into the softrface of an underlying matrix during construction are

escribed as positive texture. Those in which theggregate chippings are embedded at the surface withine matrix, leaving voids that are generally below the

lane of the contact patch, are described as having aegative texture. For the same texture depth the latterenerate much less tyre noise. Brushing concrete roadrfaces also produces a positive texture but this

process may, unless care is taken, build up unwantedmegatexture depths (see paragraph 5.20 for furtherdetails).

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Texture depth/ Skidding resistancenoise properties

Little noise contribution Low speed

Deep texture = High speedlow noise

Low texture = High speedlow noise

Low texture = High speedlow noise

Suspension noise Ride quality/handling


Range Texture length (mm)

Micro texture <0.5

Macrotexture 0.5-10

10-50

Megatexture 50-500

Uneveness >500

Table 5.1: Contribution of Textur

5.9 Positive and negative texture types are shown inFig 5.3. Hot rolled asphalt, surface dressing andbrushed concrete surfaces are generally considered tobe positively textured whereas porous asphalt, thinsurfacing and exposed aggregate concrete surfaces aregenerally considered to be negatively textured.

Aggregate Shape

5.10 The shape of the aggregate particles that areprovided at the surface to provide for skiddingresistance also can have an effect on noise. Particles ofa more cubical nature with a lower flakiness index packbetter into the surface to provide a flatter area on whichthe tyre can run. At a detailed level it can be seen thatthe tyre contact is spread more evenly over the contactarea, which in itself reduces the apparent contact patch.Conversely a rougher surface increases the contactpatch, which exacerbates tyre/road noise as the noise isrelative to the length of the escape path for the trappedair.

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e Depth to Noise and Skidding

5.11 Road surfaces with negative textures, providedthere is sufficient interconnection between the voidsbelow the running surface, reduce the amount of noisegenerated by reducing the air pressures within thecontact area. At high speed the compression and releaseof air trapped under the tyre is a significant componentof tyre noise.

5.12 These observations can be translated intopractical advice for the design and construction of roadswith lower noise surfaces. Advice for controllingtexture ranges is given in paragraphs 5.13 to 5.21.

Microtexture

5.13 The amplitudes of microtexture for bituminoussurfaces and EACS come from the roughness of thesurface of the coarse surfaces, the microtexture comesfrom the fine aggregate (sand). High amplitudes ofmicrotexture have a minimal, if any, effect on the tyre/road noise, but provide low speed skidding resistance.

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Figure 5.2: Effects of Texture Depth on Skidding and Noise

Figure 5.3: Details of Surface with Positive or Negative Texture

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Macrotexture

5.14 Macrotexture amplitudes on surface dressed andHRA roads come from the space between individualstones. This is a factor of the size and the evenness ofthe stones on the surface of the road. With PA, thinsurfacings and EACS, the macrotexture depths aredependant on the shape of the aggregate at the surfaceand the voids between adjacent stones. The voidsbetween the stones allow the air and water beneath thetyre to dissipate rather than be trapped. The cubicnature of stone with a low flakiness index enables aflatter surface of stone to be presented at the roadsurface with the benefits outlined in paragraph 5.10.Water trapped between the tyre and the road causesaquaplaning at high speed and trapped air causes noisewhen the pressure is released. At larger lengths ofmacrotexture vibrations in a tyre wall, which are asignificant cause of tyre noise, are excited. The ideal isto produce a macrotexture with high depths in the 0.5 to10mm lengths and low depths in the 10 to 50mmlengths.

5.15 The texture of traditional concrete roads isformed by transverse brushing the surface of theconcrete while it is still plastic. The aim is to producean even texture without occasional transverse ridges.The bristles form the macrotexture during thetransverse brushing operation. Brushing when theconcrete surface is either too wet, the brush pressure isincorrect or the bristles are of an inappropriate stiffnesscan form too deep a texture depth. A mix that has lostits workability or brushes that are clogged with mortarcan produce a shallow texture.

5.16 With EACS, porous asphalt and thin surfacings,the macrotexture is a function of the packing and size ofthe surface aggregate. A low flakiness index is specifiedto obtain more cubic aggregate that packs closelytogether to produce small voids. In the UK, a 10 to6mm coarse aggregate with a 1.5mm texture depth hasbeen selected to provide adequate skidding resistance.In Austria, an 8mm maximum sized aggregate was usedto reduce the macrotexture in the texture range >10mm,and achieve good noise reducing properties. An 8 to4mm sized aggregate with a 1.0mm texture depth isrecommended for lower speed roads (90km/hr) wherethe risk of aquaplaning is less than for high speed roads.

5.17 Porous asphalt and some thin surfacings havevoids that interconnect with the surface. The voidspermit water to drain to below the running surface ofthe road thereby giving these surfaces their sprayreducing qualities. Noise entering these voids is tosome extent trapped within the voids. The untrapped

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November 2006

oise tends to be in the lower frequencies that givehese surfaces their more distinct lower tonal qualities.hese surfaces tend to reduce both tyre/surface noisend engine/transmission noise.

.18 With voided surfaces the sand patch test does notive a true indication of the surface texture, or itsotential lower noise properties, due to the sand partlyntering the voids. The texture is better assessed bysing close proximity laser based systems to determinehe profile at the tyre contact surface. It has been foundhat the noise increases as the hydraulic conductivityeduces, indicating that the less porous surfaces giveigher noise levels. The test for hydraulic conductivityives an indication of the noise reducing properties oforous surfaces.

egatexture

.19 It has been found that high megatexture depthsause a tyre wall to deflect and vibrate under load. Thiss a major cause of tyre/road noise. Megatexture onRA surfaces comes from gaps between the groups of

hippings. This can be caused by the way the chipperpreads the chippings. The chipper dispenses chippingss a series of transverse bands, with the possibility ofaps between those bands. These gaps are often in theigh macrotexture to megatexture ranges (> 10mm). IfRA surfaces are allowed to cool excessively, such that

he chippings are not properly embedded, high depthsf macrotexture and megatexture can result.

.20 Concrete surfaces laid with a slipform or fixedorm paver may have megatexture undulations causedy the paver. These arise from the natural irregularitiesf the paver method of working. There are slightertical movements in the surfacing whenever the pavertops and starts, or the machine compensates for levelhanges. The vertical movements of the transverseinishing screed combined with the forward movementf the paver can cause regular depressions in theegatexture range. These can be reduced by the

ongitudinal oscillating float (super smoother) whichives the surface a final smoothing.

onclusion

.21 When examining the causes of tyre/road noise it ismportant to be aware of the various interacting factors.he aggregate at the surface makes a significantontribution to both the skidding and noise performancef the road. The construction techniques, that are underhe control of the contractor, also provide a majorontribution to the safety and the tyre/noise generated

by the surface.

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Chapter 6References

IOGRAPHY
6. REFERENCES AND BIBL
References

Design Manual for Road and Bridges (DMRB): TheStationery Office (TSO)

(http://www.official documents.co.uk/document/deps/ha/dmrb/index.htm gives access to the HighwaysAgency’s DMRB documents)

HD 24 Traffic Assessment (DMRB 7.2.1)

HD 26 Pavement Design (DMRB 7.2.3)

HD 28 Skidding Resistance (DMRB 7.3.1)

HD 29 Structural Assessment Methods(DMRB 7.3.2).

HD 31 Maintenance of Bituminous Roads(DMRB 7.4.1)

HD 32 Maintenance of Concrete Roads(DMRB 7.4.2)

HD 37 Bituminous Surfacing Materials andTechniques (DMRB 7.5.2)

HD 38 Concrete Surfacing and Materials(DMRB 7.5.3)

Manual of Contract Documents for Highway Works(MCHW): The Stationery Office (TSO)

(http://www.archive2.official-documents.co.uk/document/deps/ha/mchw/index.htm gives access to theHighways Agency’s MCHW Volumes 1 and 2documents)

Volume 1: Specification for Highway Works (MCHW1)Volume 2: Notes for Guidance on the Specification forHighway Works (MCHW2)

2000

BS EN 1097-8: Tests for mechanical and physicalproperties of aggregates - Determination of the PolishedStone Value (PSV), BSI.

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2002

BS EN 13036-1: Road and airfield surfacecharacteristics - Test methods - Measurement ofpavement surface macrotexture using a volumetricpatch technique, BSI.

Bibliography

1970

Road Note 27; “Instructions for using the Portable SkidResistance Tester”, HMSO.

1972

Szatkowski W. S. and Hosking J. R., “The Effect ofTraffic and Aggregate on the Skidding Resistance ofBituminous Surfacings”, LR504, TRRL.

1976

Hosking J. R. and Woodford G. C., “Measurement ofSkidding Resistance: Part II, Factors Affecting theSlipperiness of a Road Surface”, LR739, TRRL.

1998

Roe, P.G. and Hartshorne, S.A., “The Polished StoneValue of Aggregates and In-service SkiddingResistance”, TRL Report 322.

Roe, P.G., Parry, A.R. and Viner, H.E., “High and LowSpeed Skidding Resistance: the Influence of TextureDepth”, TRL Report 367.

1991

Roe, P. G., Webster, D. C. and West, G., “The RelationBetween the Surface Texture of Roads and Accidents”,RR296, TRRL.

1992

Roe, P. G., “Measurement of the Macrotexture ofRoads: Part 3 Development of the Highspeed TextureMeter”, RR297, TRRL.

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November 2006 7/1

7. ENQUIRIES

All technical enquiries or comments on this Standard should be sent in writing as appropriate to:

Chief Highway EngineerThe Highways Agency123 Buckingham Palace RoadLondon G CLARKESW1W 9HA Chief Highway Engineer

Chief Road EngineerTransport ScotlandVictoria QuayEdinburgh J HOWISONEH6 6QQ Chief Road Engineer

Chief Highway EngineerTransport WalesWelsh Assembly GovernmentCathays Parks M J A PARKERCardiff Chief Highway EngineerCF10 3NQ Transport Wales

Director of EngineeringThe Department for Regional DevelopmentRoads ServiceClarence Court10-18 Adelaide Street G W ALLISTERBelfast BT2 8GB Director of Engineering

Chapter 7Enquiries