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DEFENCE WORKS FUNCTIONAL STANDARDDESIGN AND MAINTENANCE GUIDE 01

Roads for Tracked Vehicles

COMPILED BY AIRFIELDS & BULK FUELS GROUP (ABFG)DEFENCE ESTATE ORGANISATION (WORKS)

Ministry of Defence

LONDON: HMSO

© Crown Copyright 1996Applications for reproduction should be made to HMSO, The Copyright Unit,St Clements House, 2-16 Colegate, Norwich NR3 1BQ

ISBN 0 11 7724858

Front cover: A tank on the unbound test track at Catterick.Back cover: The concrete block test track at Bovington.

Acknowledgements

This document has been produced by Major R P Sheldon RE during his posting toDefence Estate Organisation (Works), Airfields and Bulk Fuels Group. Notableassistance has been received from White Young Consulting Engineers and ScottWilson Kirkpatrick and Partners. The publication has in part evolved fromdocuments produced previously by the Property Services Agency, the RoyalEngineers, United States Federal Agencies and the Australian Department ofRoads.

Foreword

Technical advice on general highway works for wheeled vehicles is welldocumented and published by the Department of Transport and HMSO.

Guidance on roads trafficked by tracked vehicles is poorly documented andexperience within the civilian world is generally limited to slow movingconstruction plant. The military requirement is for roads able to sustain heavytracked vehicle use at speeds of 30 mph or greater.

This document is for the use of Top Level Budget Holders for application by theirProject Sponsors, Project Managers, Property Managers, Establishment WorksConsultants, Works Services Managers and other parties involved in theprovision of roads and hardstandings for tracked vehicles on the MOD estate.

This Defence Works Functional Standard was prepared under the patronage ofHeadquarters Land Command. It supersedes the DOE/PSA document TechnicalInstruction Civil Engineering (TICE) 48.

The application and limitations of this Functional Standard are outlined inChapter 1. Further technical assistance regarding the contents of this documentcan be obtained from Defence Estate Organisation (Works). Approaches may bemade through local DEO (Wks) offices or directly to Airfields and Bulk FuelsGroup:

SO2 (W)Airfields and Bulk Fuels GroupDefence Estate Organisation (Works)St George's BarracksBlakemore DriveSUTTON COLDFIELDWest Midlands (0121) 311 3623B75 7QB (0121) 311 2140

This Standard has been devised for the use of the Crown and its contractors inthe execution of contracts for the Crown. The Crown hereby excludes all liability(other than liability for death and personal injury) whatsoever and howsoeverarising (including but without limitation, negligence on the part of the Crown, itsservants or agents) for loss or damage however caused where the Standard isused for any other purpose.

Compliance with the contents of this document will not in itself confer immunityfrom legal obligations.

iv

References

1. ME Vol II Pam 8A—Roads (1983).

2. ME Vol III Part 1—Basic Bridging (1981).

3. ME Vol IV—Soil Mechanics and Foundations (1981).

4. ME Vol V Part 1—Roads (1984).

5. DWS Functional Standard Hot Rolled Asphalt and Coated Macadam forAirfield Pavement Works (1995).

6. DWS Functional Standard Specification 033 Pavement Quality Concretefor Airfields (1996).

7. DWS Functional Standard Specification 035 Concrete Block Paving forAirfields (1996).

8. DoT Manual of Contract Documents for Highway Works published in 6volumes. Volume 1 Specification for Highway Works is particularlyrelevant.

9. TICE 48—Pavements Subjected to Tracked Vehicles—DOE/PSA TechnicalInstruction (1984) incorporating Amdt 1 (Sep 90).

10. TICE 50—Road Design and Layout Criteria—DOE/PSA TechnicalInstruction (1989).

11. Design of paved areas for industrial usage - Concrete Society TechnicalReport No 24 (1983).

12. TM-822-12—Design of Aggregate Surfaced Roads and Airfields—US ArmyTechnical Manual (1990).

13. Design and Construction of Interlocking Block Pavements—B Shackel(1990).

14. Road Aggregates and Skidding - Roger Hosking—TRL State of the ArtReview /4 (1992).

15. Road Building in the Tropics—Dr R S Millard—TRL State of the ArtReview 79(1993).

16. Unsealed Roads Manual Guidelines to Good Practice—Australian RoadsResearch Board (May 1993).

Abbreviations

AAV Aggregate Abrasive ValueABFG Airfields and Bulk Fuels GroupAFV Armoured Fighting VehicleASC Alternate Start CornerBBA British Board of AgrémentBS British StandardCBM Cement Bound MaterialCBR California Bearing RatioCRCP Continuously Reinforced Concrete PavementCVR(T) Combat Vehicle Reconnaissance (Tracked)DEO (Wks) Defence Estate Organisation (Works)DOE Department of the EnvironmentDoT Department of TransportDIA DiameterEXG Existingggbs Ground granulated blastfurnace slagHRA Hot Rolled AsphaltMax MaximumMET Main Battle TankME Military Engineeringmicron MicrometreMin Minimummm MillimetreMOD Ministry of Defencemph Miles per hourOPC Ordinary Portland CementPBC Portland Blastfurnace Cementpen Penetrationpfa Pulverised fuel ashPSA Property Services AgencyPQC Pavement Quality ConcreteRC Reinforced ConcreteSC Start CornerTICE Technical Instruction Civil EngineeringTRL Transport Research LaboratoryVC Vitrified Clay430 Series Armoured personnel carrier

Diameter

Contents

1

2

3

4

Foreword

References

Abbreviations

Contents

Introduction

1.1 Background1.2 Aim1.3 Scope1.4 Functional Requirements1.5 Special Requirements of Tracked Vehicles

Principles of Design2.1 General2.2 Route Selection2.3 Site Investigation2.4 Geometric Layout2.5 Choice of Construction Type2.6 Reinforced Concrete2.7 Unreinforced Concrete2.8 Concrete Block Paving2.9 Mastic Asphalt2.10 Hot Rolled Asphalt2.11 Grouted Macadam2.12 Unbound Roads

Reinforced Concrete3.1 General3.2 Design3.3 Materials3.4 Laying3.5 Joints3.6 Surface Finish

Unreinforced Concrete4.1 General4.2 Design4.3 Materials4.4 Laying

Page

iv

vi

vii

1

11122

4444555666677

999

10111212

1515151515

4.5 Joints4.6 Bay Layouts4.7 Surface Finish

5 Concrete Block Paving5.1 General5.2 Design5.3 Materials5.4 Edge Restraints5.5 Laying5.6 Expansion Joints5.7 Surface Finish

6 Hot Rolled Asphalt6.1 General6.2 Design6.3 Materials6.4 Laying6.5 Surface Finish

7 Mastic Asphalt7.1 General7.2 Design7.3 Materials7.4 Laying7.5 Joints7.6 Surface Finish

8 Grouted Macadams8.1 General8.2 Design8.3 Materials8.4 Laying8.5 Surface Finish8.6 Trafficking

9 Unbound Roads9.1 General9.2 Design9.3 Materials9.4 Laying9.5 Surface Finish9.6 Construction Sequence9.7 Maintenance Regime

10 Special Surface Treatments10.1 Concrete Surface Hardeners10.2 Concrete Fibres10.3 Concrete Admixtures10.4 Concrete Block Sealants10.5 Grouted Macadams10.6 Modified Binders

151617

1919191920212121

232323232525

26262626272728

29292929303030

3232323333333335

37373737383838

Appendix A — Magnesium Sulfate Soundness Test

A.1

A.2

A.3

A.4

A.5

A.6

A. 7

A.8

A.9

AppendixB.1

B.2

B.3

B.4

Scope

Apparatus and Reagents

Preparation of Test PortionsA. 3.1 Bulk SamplesA.3.2 Test Portions

Preparation of Sand Test Specimens for Each FractionA.4.1 Particle Size DistributionA.4.2 Fraction Passing 300 um SieveA.4.3 Test Specimen

Preparation of Coarse Aggregate Test Specimens for EachFractionA.5.1 Particle Size DistributionA. 5. 2 Minor FractionsA. 5. 3 Test Specimen

Procedure

Calculation and Expression of Test ResultsA. 7.1 Minor FractionsA.7.2 Fine Aggregate SamplesA. 7. 3 Soundness ValueA.7.4 Magnesium Sulfate Soundness Value (MSSV)

Precision

Test Report

B — Stripping TestScope

Apparatus

Samples

ProcedureB.4.1 Test ProcedureB.4.2 Test CriteriaB.4.3 Check Tests

39

39

39

393939

39394040

40404040

41

4141414141

43

43

4444

44

44

44444545

List of Figures1/13/13/23/33/43/53/64/14/24/35/15/26/1

Typical Kerb DetailsFoundations for Rigid PavementsPermissible Test Limits for Fine AggregateGradings 1 and 2 for SandPermissible Test Limits for Coarse AggregatesExpansion Joints Reinforced and Unreinforced Concrete SlabsContraction JointsWarping JointsTypical Bay Layout at Road JunctionJoint Layout at Turning BaysEdge Restraint for Precast Concrete BlocksConcrete Block Laying PatternsFoundations for Flexible Pavements

3101011111314161718202223

6/2 Coarse Aggregate Properties6/3 Fine Aggregate Properties6/4 HRA Filler6/5 Asphalt Temperatures7/1 Mastic Asphalt Coarse Aggregate Grading7/2 Mastic Asphalt Fine Aggregate Grading7/3 Mastic Asphalt Bitumen Properties7/4 Mastic Asphalt Composition8/1 Grouted Macadams9/1 Unbound Pavement Thickness9/2 Typical Cross Section9/3 Intervention Levels for Unbound RoadsA.4/1 Mass of Each Test Specimen for SandA.5/1 Mass of Each Test Specimen for Coarse AggregateB.4/1 Mixing Temperatures

242425252627272731323436404145

1 Introduction

1.1 BACKGROUND

This Defence Estate Organisation (Works) [DEO (Wks)] Functional Standard is adesign guide for pavements subjected to the passage of tracked vehicles. Theinformation contained within the guide is largely based on an update of the oldPSA Technical Instruction Civil Engineering Number 48 (Reference 9) which itsupersedes.

The Ministry of Defence (MOD) is expanding its use of tracked vehicles in the UKas a result of the reduction of forces in Germany. At the same time, most types oftracked armoured fighting vehicles (AFVs) are becoming bigger and heavier withmore powerful engines. The consequence of these changes is a growingrequirement to provide adequate roads and hardstandings resistant to thedamaging effects of tracked vehicles.

It is intended that this functional standard will be of assistance to projectsponsors, project managers, design consultants and anyone else involved indesigning or building new facilities for tracked vehicles.

This design guide does not cover short term or temporary requirements fortracked vehicle crossings or roads, for which a variety of expedients includingClass 60 trackway, timber baulks or hardcore ramps would be appropriate. Thereis ample guidance available for these situations in the Military Engineeringpublications (References 1-4).

1.2 AIM

The aim of this functional standard is to provide guidance on the design andconstruction of pavements to be used by tracked vehicles.

1.3 SCOPE

The design guide covers a wide range of subjects associated with the provision ofa new road or hardstanding. Thus, guidance is given on the essentials of roaddesign as well as the factors to be considered when siting a road or whenselecting a suitable type of construction. Further guidance is available from thereferences quoted at the beginning of the guide or from DEO (Wks) ABFG.

No publication of this type can claim to be comprehensive in its treatment andthis guide introduces only the major elements of the subject. Chapter 2 describesthe principles of design, with detailed guidance being given about the differentconstruction materials in chapters 3-10.

May 1996

Roads for Tracked Vehicles 1 Introduction

1.4 FUNCTIONAL REQUIREMENTS

To serve the purpose for which it has been designed a pavement, whether a road,apron, car park or workshop floor, must fulfil certain criteria satisfactorily. Thecriteria are dealt with in more detail below.

The paved surface must protect the subgrade from damage caused by traffic. Toachieve this, the pavement must provide a suitable running surface andsufficient additional strength to protect the underlying soil.

The pavement must protect the vehicles from damage caused by sharp edges orlarge pieces of loose material and excessive bumpiness. This requirement isclosely related to the need to provide reasonable rideability both for the comfortof vehicle occupants and to reduce wear and tear to the vehicles themselves.

The paved surface must provide a suitable texture and skidding resistanceparticularly in wet conditions. It must be shaped either in camber or crossfall toachieve good drainage to reduce the risk of skidding and to prevent spray whichcan reduce visibility.

Among a number of other criteria that a pavement must meet, a key requirementis the ability to resist damage in use.

1.5 SPECIAL REQUIREMENTS OF TRACKED VEHICLES

In addition to the general criteria listed above which apply to all paved surfaces,roads for tracked vehicles need to be able to withstand the particularly damagingcharacteristics of heavy AFVs.

AFVs operate with relatively low ground bearing pressures compared to thepressures under a modern commercial vehicle tyre. This is based on therequirement for AFVs to operate off road in a variety of soil and weatherconditions. However, the overall load imposed by a main battle tank (MET) suchas Challenger 2 is high.

In order to achieve the protection and mobility demanded by modern battlefieldconditions, the manufacturers have increased vehicle weights, sizes and power-to-weight ratios substantially. The consequence of high weight and high power isa considerable increase in damaging power to the pavement.

The method by which a tracked vehicle is driven and turned is completelydifferent to other vehicles. The action of a steel linked track on a straight road atconstant speed, even when fitted with rubber track pads, is much moreaggressive than the effect of a pneumatic tyre. On turns, gradients and whenaccelerating or decelerating, the difference in effect is much more dramatic. Putsimply, a rubber tyre slips and leaves a small rubber deposit when there is achange in motion; a track tends to scrape causing a grinding action. Whenslewing at speed the scraping action is especially onerous.

Tracked vehicles roads should be provided with kerbs or other visible edgerestraints to assist vehicle drivers and to prevent damage to adjoining areas.Current experience suggests that no kerb can withstand frequent contact withtracks without sustaining damage. Consequently, any kerb should be consideredas a form of sacrificial barrier. There are essentially two possibilities—a precastconcrete kerb or a cast in situ kerb. If it is essential to prevent a tracked vehiclefrom leaving the carriageway, then a large cast in situ kerb with a substantialupstand will be required. It is generally cheaper to use standard precast kerbs toBS 340 than to cast in situ. Figure 1/1 shows typical kerb details.

May 1996

Roads for Tracked Vehicles 1 Introduction

Figure 1/1 Typical Kerb Details.

May 1996

FLUSH KERBSFLUSH KERBS MAYBE USED WHERE THERE IS NO FOOTWAY AND NO REQUIREMENTS ORSURFACE WATER TO BE TAKEN TO GULLIES BUT LATERAL SUPPORT IS REQUIRED TO THECARRIAGEWAY.

[NOTE: FLUSH KERBS TEND TO ENCOURAGE DRIVERS TO LEAVE THE CARRIAGEWAY CAUSINGDAMAGE TO THE VERGES]

FLEXIBLE CONSTRUCTIONSTANDARD CROSS-SECTIONS

RAISED KERBS AND EDGINGS TO BS 340 (PRECAST CONCRETE)

2 Principles of Design

2.1 GENERAL

All roads are designed to spread vehicle loading sufficiently so that the pressureat foundation level is less than the maximum allowable bearing capacity of thesoil.

2.2 ROUTE SELECTION

The factors governing route selection for highways are well known to practisingengineers and do not need to be reviewed here. However, there are one or twospecialist points that should be borne in mind when selecting tracked vehicleroutes.

It is vital for the statement of requirement to clarify whether only trackedvehicles, or mixed wheeled and tracked traffic, is to use the route. It is frequentlya requirement to separate tracked vehicles from other traffic and this placesconsiderable restraints on the routes available to the designer. This isparticularly important when near public roads.

Where tracked vehicles routes have to cross other roads, the designer mustensure that the tracked route is clearly and immediately obvious even topersonnel unfamiliar with the area. This may conflict with a military trainingdesire to make the tracked vehicle routes blend in with the landscape as much aspossible.

Where unbound construction is concerned, the importance of adequate drainagecannot be overemphasised. Clearly, routes that make the best use of naturaldrainage are to be preferred as the costs of providing positive drainage will bereduced and the maintenance bills are likely to be lower.

2.3 SITE INVESTIGATION

The site investigation should not only include the routine gathering ofinformation on soil types, topography and existing usage but should also assessthe impact of heavy tracked vehicles on the local ecology. One of the advantagesof building even an unbound road for tracked vehicles is that damage to thenatural ground is significantly reduced.

It is recommended that at least one trial pit should be dug per kilometre, withaugered holes at more frequent intervals. There should be further investigationswhere changes in the ground are detected and where any structures such asculverts are to be built.

May 1996

Roads for Tracked Vehicles 2 Principles of Design

Overall costs will be minimised if construction plant can be operated efficiently.This can be achieved only by ensuring that the site investigation is in sufficientdetail for the engineer to design an economic pavement for each section of theroad.

2.4 GEOMETRIC LAYOUT

In general, a tracked vehicle route will have a low design speed, typically amaximum of 30 mph. However, where wheeled traffic shares the road, a higherdesign speed may be selected. Guidance on wheeled vehicle design speed isavailable from Department of Transport (DoT) publications.

The ability of tracked vehicles to negotiate very steep slopes means thatgradients steeper than 10% can be used, particularly for short sections. Indeed,training needs may require special climbing sections with gradients of up to 35%.Clearly, such slopes would be dangerous for two way traffic so they should notform part of a major through route and they must be sited with great care.

It should be noted that a heavy commercial vehicle can negotiate a maximumgradient of approximately 15%. Due to insufficient traction, this reduces to notgreater than 8% for an unbound road.

For low speed roads it is normal practice to use circular curves and to dispensewith transition curves. However, it remains important that superelevation isintroduced on curves for design speeds of 30 mph or greater. Superelevationassists tracked vehicles when cornering at speed so it is particularly importantwhen wheeled traffic shares the road. Roads should be widened for sharp bendsto allow tracked vehicles plenty of room to slew round.

2.5 CHOICE OF CONSTRUCTION TYPE

Considerable experience has been gained over the years with the use by trackedvehicles of roads built using a variety of construction materials. Many of theseroads were designed to take wheeled traffic but have since been used extensivelyby tracked AFVs. For purpose built roads and hardstandings the choice betweenthe various types of flexible and rigid pavements is largely determined bylocation, cost, availability of construction materials, expected rate of use andestimated design life.

A workshop floor requires a high quality material capable of withstanding highpoint loading with the absolute minimum of maintenance. In addition, it shouldbe resistant to abrasion and oil spills whilst still providing an easily cleaned nonslip surface.

A road across a training area can often be constructed satisfactorily from locallysupplied stone despite the fact that it requires significantly more maintenanceand does not provide a very smooth ride.

The advantages and disadvantages of the different pavement types areconsidered in more detail below.

2.6 REINFORCED CONCRETE

Reinforced concrete (RC) has been used extensively for tank roads all round theworld. It has proved to be a reliable surface when properly constructed withcarefully detailed joints. It provides a high quality surface with good abrasion

May 1996


resistance, even in the more onerous situations, and it provides a smooth ride forvehicles. It has proved to be a long lasting material when well built with a life ofup to 40 years.

RC suffers from a number of disadvantages. It is relatively expensive comparedto some alternatives; joint defects are difficult to rectify; it requires a skilledworkforce to produce a good quality product and, perhaps of more significanceunder modern environmental constraints, it is intrusive upon an open landscape.

RC roads can be built without any joints using extra reinforcement to form acontinuously reinforced concrete pavement (CRCP). Although it is moreexpensive, CRCP construction should produce a high quality finish and shouldproduce a virtually maintenance-free road.

2.7 UNREINFORCED CONCRETE

Unreinforced concrete has also provided a satisfactory pavement historically. Themajority of unreinforced slabs used for tracked vehicles have employed steeldowels to provide shear connections between adjacent slabs.

Where the underlying soil conditions are good, an unreinforced slab can beconsidered and it is likely to be cheaper, though thicker, than a reinforcedalternative. It suffers from the same disadvantages as RC apart from being lessexpensive.

2.8 CONCRETE BLOCK PAVING

Concrete block paving has been used increasingly as a cost effective surfacing forheavy duty pavement uses in industrial applications, including container storageareas, ports and airports. Concrete blocks have been used for tracked vehicles inEurope and to a lesser extent in the UK.

Concrete blocks have a number of advantages over other surfacing materials, notleast being a lower overall cost. They require a firm level base, normally ofdrylean concrete, for heavy duty use. They provide good rideability and excellentskid resistance. Concrete blocks have proved to be resistant to thermalmovements, settlement and heavy wear.

2.9 MASTIC ASPHALT

Mastic asphalt has been used successfully for tracked vehicle roads and otherheavy duty applications. It is resistant to abrasion and is highly resilient so thatlocal deformations do not lead to long term distress in the pavement layers.

The material suffers from several disadvantages. It is susceptible to deformationin periods of hot weather, it is expensive (due in part to being hand laid) and it issusceptible to damage by oil and fuel spillage.

The material is particularly useful in small, awkward shaped areas wheremachine laying is difficult or impracticable. It cannot normally be laid bymachine, making it unsuitable for large areas.

2.10 HOT ROLLED ASPHALT

Hot Rolled Asphalt (HRA) has been used on a few occasions for tracked vehicleroads. It is considered to be substantially less resistant to rutting anddeformation than mastic asphalt. It is the most common road surfacing used in

May 1996


the UK for all categories of traffic although tracked vehicles are not normallypermitted to use UK roads. Where HRA has been used for straight roads it hasperformed fairly well under tracked vehicle loading.

DEO (Wks) has recently published a new Functional Standard (FS) entitled HotRolled Asphalt and Coated Macadams for Airfield Pavement Works (Reference 5).Although not written for roads, this standard provides an excellent basis for thedesign of HRA for tracked vehicle roads. It should be appreciated that modernaircraft loading with its high tyre pressures causes scuffing and wear of a similarorder of magnitude to a rubber track pad.

HRA has a number of advantages over alternative materials for tracked vehicleroads. It is widely available in the UK, a large number of British contractors areexperienced in laying it and it can be obtained and laid at a competitive price. Itcan be laid in small, awkward areas by hand but major areas are machine laid.Repairs are comparatively simple and can be carried out by a large number of UKcontractors. It should be noted that HRA is rarely used outside the UK and so itwould not be recommended for overseas stations including Germany.

2.11 GROUTED MACADAM

Grouted macadams consist of pervious bituminous wearing courses which aregrouted with proprietary cementitious products to achieve a sealed surfaceresistant to fuel and oil spillages.

Although it would not be appropriate to use grouted macadams for long lengths ofroad, due to their cost, they are well suited to use in small heavily traffickedareas particularly workshops and garages where the possibility of fuel spills andoil leaks is high.

The major disadvantages of grouted macadams are their relatively high cost andirreparable failure of the pavement surface where the grouting is deficient. Theyhave been used successfully in the UK and abroad for areas subject toparticularly heavy use such as locked track turns on firing ranges.

2.12 UNBOUND ROADS

Unbound roads have been used extensively for tracked vehicles roads. All modernAFVs are designed to operate across country on unbound surfaces.

However, the ability of a tracked vehicle to cross rough ground easily does notmean that it does so without damage to the ground surface. In fact, even strongnatural subgrades suffer damage rapidly when trafficked by AFVs. This can beseen on any tracked vehicle training area.

Unbound roads can provide excellent, economic roads for tracked vehiclesprovided that they are properly designed and built and, most importantly, thatthey are properly maintained. By definition, an unbound road is one where thesurface is not held together by bitumen or cement so the road surface willdeteriorate with natural weathering and by the action of traffic. The only waythat such a road can continue to serve satisfactorily without disintegrating is bybeing maintained correctly. The maintenance regime following initialconstruction is an integral part of the design and funding of an unbound road.

Where the ground conditions are suitable and only military vehicles are involved,an unbound road should always be considered as an option for tracked vehicles.This is because unbound roads can be built at a considerably lower capital costthan a bound alternative.

May 1996


There are a number of disadvantages associated with unbound roads includingthe cost of maintenance, rideability, dust and susceptibility to weather conditions.

The ability to improve an unbound road progressively is particularly useful. Itcan be built relatively cheaply for temporary or short term use and then can beimproved using higher quality materials if a bound road is required ultimately.

This inherent flexibility can be most useful when planning new roads throughtraining areas. The client may not be certain beforehand which routes are goingto be most heavily used. A simple track layout can be built, monitored and alteredat comparatively low cost. If maintenance costs become too high, it is easy toupgrade parts of the track network.

May 1996

3 Reinforced Concrete

3.1 GENERAL

A properly designed and constructed reinforced concrete road has a design life of40 years. The ability of a road to survive for that length of time is criticallydependent on the quality of the materials used, good substructure includingdrainage, good concrete detailing and carefully controlled placing, compactingand finishing.

3.2 DESIGN

Reinforced concrete slabs for use by heavy tracked vehicles are recommended tobe not less than 200 mm thick and reinforced with long mesh reinforcement ofnot less than 4.34 kg/m2. (C503 mesh to BS 4483).

Reinforced concrete slabs are recommended to be not more than 30 metres longand 6 metres maximum width.

Reinforced concrete slabs trafficked only by smaller AFVs (ie. CVR(T) and 430Series or similar) may have the slab thickness reduced to 175 mm.

In areas designed for particularly heavy use such as turnouts, the slab depthsshould be increased by 25 mm.

For strength and durability under exposure to UK weather, the specified designstrength of the concrete is recommended to be 40 N/mm2 with a minimum cementcontent of 320 kg/m3 and 5% ± 1% air entrainment for the full depth of the slab orat least for the layer above the reinforcement. A maximum water/cement ratio of0.45 is also recommended.

The precise mix design remains the responsibility of the supplier andalternatives to the recommended cement content are permissible. Volume 1 of theDoT Specification for Highway Works (Reference 8) gives rules for the use ofcement replacements and blends which would be appropriate for tracked vehiclepavements. The use of pfa or microsilica may well produce a more dense anddurable concrete.

A minimum thickness of 150 mm Cement Bound Material 2 (CBM2) orexceptionally Wet Lean Concrete (C10) is recommended beneath reinforcedconcrete slabs. On weak subgrades (CBR < 5%) the thickness of CBM2 may beincreased to a minimum thickness of 175 mm laid in two layers. Alternatively, thesubgrade may be improved using a capping layer. Actual thicknesses of sub-basemust be sufficient to provide the required pavement strength.

May 1996

Roads for Tracked Vehicles 3 Reinforced Concrete

Figure 3/1 gives guidance on foundations below rigid pavements. The thicknessesshould be treated with some caution. On frost susceptible subgrades, a minimumthickness of 450 mm of non frost-susceptible material is recommended.

Figure 3/1 Foundations for Rigid Pavements.

Formation

Subgrade

[Optional Capping thickness]

150 mm CBM2 or Wet Lean Concrete (C10) Sub-base

CBR < 2%

[600 mm]

2% < CBR < 5%

[350 mm]

5% < CBR <15%

[150mm]

CBR > 15%

[No capping]

3.3 MATERIALS

Capping material should be a granular material with a CBR of 15% or greater asdefined in the DoT Specification (Reference 8).

Cement Bound Material (CBM) is a mixture of aggregate and cement at amoisture content compatible with compaction by rolling. (The American term isRoller Compacted Concrete). Reference 8 gives details of acceptable grading.

CBM 1 has a characteristic strength of 4.5 N/mm2 at 7 days.



Wet Lean Concrete (C10) is a weak concrete which has to be mixed, placed andcompacted in the same way as a high strength concrete. It should have amaximum water/cement ratio of 0.6 and a minimum cement content of 130 kg/m3.C10 has a characteristic strength of 10.0 N/mm2 at 28 days.

Cement should be ordinary portland cement (OPC) complying with BS 12.Portland blastfurnace cement (PBC) complying with BS 146 or Portlandpulverised-fuel ash cement (Portland pfa cement) complying with BS 6588 mayalso be used separately or in combination with OPC.

Other cementitious materials which may be used include ground granulatedblastfurnace slag (ggbs) complying with BS 6699, pfa complying with BS 3892and microsilica which should have a current British Board of Agrément (BBA)certificate.

Fine aggregate should be natural sand, crushed rock or gravel or a blend of these.The properties of the fine aggregate should fall within the limits of Figure 3/2.

Figure 3/2 Permissible Test Limits for Fine Aggregate.

10 May 1996

Permissible Limits

As Gradings 1 or 2 in Figure 3/3

82 (each source)70 (each fraction)

4 (natural sand or crushed gravel)9 (crushed rock)

Test Property Test Reference

Particle size distribution BS 812: Section 103.1

Minimum magnesium sulfate Appendix Asoundness value

Maximum fines content BS 812: Section 103.1


Figure 3/3 Gradings 1 and 2 for Sand.

BS 410 Sieve Size Percentage by Mass Passing

10.0mm

5.0 mm

2.36 mm

1.18mm

600 microns

300 microns

150 microns

Grading 1

100

90-100

60-[95]

30-[70]

15-34

5-[20]

0-[10]

Grading 2

100

90-100

[75]-100

[55]-90

35-59

8-[30]

0-[10]

Notes: (1) A total tolerance of up to 5% may be applied to the percentages in square brackets in the Figure. Thetolerance may be split up. For example, it could be 1% on each of three sieves and 2% on another.

(2) For crushed rock sand, the permissible limit on the 150 micron sieve may be increased to 20%.

To provide durability against wear and weather a coarse aggregate of a toughigneous or metamorphic rock with an aggregate abrasive value (AAV) of not morethan 12 when tested in accordance with BS 812 is recommended. Where the costof such a stone is considered excessive, the slab may be laid in two courseconstruction using a less expensive coarse aggregate for the lower course. Wheretwo courses are used in this way, the top course should be of sufficient thicknessto provide the specified cover to the reinforcement (see Fig 3/5 and Fig 3/6). Thetop course should be laid directly on the reinforcement without a constructionjoint. The maximum size of the aggregate is recommended to be 20 mm in the topcourse and 20 or 40 mm in the lower course.

The properties of the coarse aggregate should fall within the limits of Figure 3/4.

Figure 3/4 Permissible Test Limits for Coarse Aggregate.

Test Property

Particle size distribution

Minimum magnesium sulfatesoundness value

Maximum Flakiness Index (%)

Minimum 10% fines value

Maximum fines content

Maximum shrinkage(1)

Test Reference

BS 812: Section 103.1

Appendix A


BS 812: Part 111


BS 812: Part 120

Permissible Limits

40mm, 20 mm andas BS 882, Figure 3

82 (Each source)70 (Each fraction)

30

100kN

4

0.075

10 mm single sized

(1) Testing is required only if crushed rocks other than limestone are used. Reinforcement used in RCroads should comply with the DoT Specification (Reference 8) which lays down the materialstandards, sizes and spacing for reinforcing steel, tie bars and dowel bars.

3.4 LAYING

The concrete should normally be machine laid and compacted except on smalljobs where such a requirement would be uneconomic. The suitability of the plantwhich the Contractor proposes to use should be proved by laying a sample slabbefore the main concreting commences.

The trial slab should be checked by taking four 150 mm diameter cores andtesting them in accordance with BS 1881: Part 4. If any of the cores showhoneycombing as defined in the BS, or more than 10 voids having a dimensiongreater than 3 mm in the top 40 mm, the trial slab should be deemed to havefailed and a new trial slab should be laid by the Contractor and tested at hisexpense.

111996May


The trial is set to ensure that the Contractor is able to produce consistentlystrong, well compacted concrete, free from defects and capable of being finished tothe specified requirements. It should be noted that these requirements are nomore onerous than a Contractor would face when laying any concrete road to DoTstandards.

Concrete compliance should be tested in situ by taking a set of 2 cores from every1,000 m2 of finished pavement (or part thereof).

3.5 JOINTS

Transverse and longitudinal joints should be as for normal concrete roadconstruction with transverse joints at 90° to the longitudinal axis of thepavement. Dowel bars and tie bars should be incorporated. Where joints arehand-finished, the edges should have a 5 mm radius arris. Details of jointspacing can be found in Reference 8.

Typical joint details can be seen in Figures 3/5 and 3/6.

3.6 SURFACE FINISH

A simple brush finish is appropriate for a concrete road used by tracked andwheeled traffic. Even where a road is nominally only for tracked vehicles aminimal surface texture is desirable as there is no guarantee that there will notbe a change in use in the life of the pavement.

The finished surface of the reinforced concrete should be measured using aTransport Research Laboratory (TRL) rolling straightedge or a 3 m straightedgelaid parallel to the centreline of the road. Transverse regularity should bechecked with the 3 m straightedge set at right angles to the centreline of theroad. The procedure is laid down in the DoT Specification (Reference 8). Themaximum allowed surface depression under the straight edge is 3 mm.

12 May 1996


Figure 3/5 Expansion Joints Reinforced and Unreinforced Concrete Slabs.

May 1996 13


Figure 3/6 Contraction Joints.

14 May 1996

4 Unreinforced Concrete

4.1 GENERAL

The general comments on reinforced concrete apply equally to unreinforcedconcrete. There is no substitute for good design and good construction and if theyare done well, unreinforced concrete roads can also serve for 40 years.

4.2 DESIGN

Unreinforced slabs are normally constructed approximately 25 mm thicker thanequivalent reinforced slabs. Given the cost of buying and fixing reinforcing steel,it is nearly always less expensive to use an unreinforced slab.

In order to prevent premature failure of the slabs from cracking, it essential thatthey are cast in short, approximately square bays. For slabs less than 225 mmthick, the bays should be no longer than 4 m. For slabs 225 mm thick or greater,the bays should not exceed 5 m in length.

The concrete should be designed to have a characteristic strength of 40 N/mm2

with 5% ± 1% entrained air. The slab may be cast in two courses with the lowercourse having no air entrained. The top course is recommended to be a minimumof 75 mm thick with air entrainment. The two courses should be placed without aconstruction joint between them. DEO (Wks) FS 033 on PQC for Airfieldscontains useful design guidance (Reference 6).

4.3 MATERIALS

Advice on material specifications is provided in Chapter 3. The only difference forunreinforced slabs is the absence of reinforcing mesh. It is standard practice touse tie bars and dowel bars with unreinforced concrete slabs.

4.4 LAYING

The procedures for laying unreinforced concrete should be identical to those forreinforced concrete, including the production and testing of a trial slab and the insitu testing of the pavement.

4.5 JOINTS

Joint details are similar to those for reinforced concrete except for the absence ofthe reinforcement and the spacing of joints. Details can be seen in Figures 3/5and 3/6.

An unreinforced slab requires warping joints. A typical warping joint detail canbe seen in Figure 4/1.

151996May

Roads for Tracked Vehicles 4 Unreinforced Concrete

Figure 4/1 Warping Joints.

4.6 BAY LAYOUTS

Details of standard bay layouts can be obtained from the DoT Specification(Reference 8). In addition, standard details for bay layouts for road junctions andturning bays are shown in Figures 4/2 and 4/3.

16 May 1996


4.7 SURFACE FINISH

A brush finish is appropriate for an unreinforced concrete road.

The finished surface of the concrete should be measured using a straightedge asdescribed in Chapter 3.

Figure 4/2 Typical Bay Layout at Road Junction.

UNREINFORCED C O N C R E T E REINFORCED C O N C R E T E

N O T E S1. X = 6.0m, 6.75m OR

Y = 4.0m, 5.0m, 5.5m OR 6.0m

2. JOINT L A Y O U T S ARE T Y P I C A L O N L Y .

3. JOINT POSITIONS MAY BE VARIED IN ORDER TO POSITION THEM AT GULLIES, PROVIDEDT H A T THE MAXIMUM WIDTH AND LENGTH OF SLABS IS NOT GREATER THAN THE PRESCRIBED LIMITS.

RIGID C O N S T R U C T I O NJOINT L A Y O U T AT JUNCTION OF A C C E S S

AND DISTRIBUTOR R O A D S

May 1996 17


Figure 4/3 Joint Layout at Turning Bays.

NOTES1. W = 4.0m, 5.0m OR 5.5m2. JOINT L A Y O U T S ARE TYPICAL ONLY3. JOINT POSITIONS MAY BE VARIED IN ORDER TO POSITION THEM AT GULLIES, PROVIDED

THAT THE MAXIMUM WIDTH AND LENGTH OF SLABS IS NOT THAN THE PRESCRIBED LIMITS.

RIGID CONSTRUCTIONJOINT L A Y O U T AT TURNING B A Y S

18 May 1996

5 Concrete Block Paving

5.1 GENERAL

Concrete block pavements can be expected to have a design life of 20 yearsproviding that they are correctly designed and built and are properly maintainedwhen there are any signs of distress such as excessive deflection, loss of jointsand etc.

Although UK experience with tracked vehicles on concrete blocks is limited, theuse of blocks for heavy duty pavements in the UK and worldwide is increasingrapidly.

DEO (Wks) FS 035 on Concrete Block Paving for Airfields contains useful designguidance (Reference 7).

5.2 DESIGN

The general design process for concrete blocks follows the procedures for thedesign of flexible pavements. It is generally agreed that a properly built layer of80 mm thick blocks on a 35 mm bed of compacted sand is at least equivalent tothe structural strength of 50 mm of bituminous surfacing.

Concrete blocks for tracked vehicle use should be plain rectangular blocks 200 x100 x 80 mm thick. The blocks should be laid on a sand bed of 35 mm nominaldepth. Research has shown that concrete block paving performs best with a sandbed of 20- 40 mm.

The sand bed should be supported by a bound sub-base selected from thefollowing list:

a. DoT CBM 3.

b. DoT CBM 2.

c. Drylean concrete.

d. Bituminous basecourse.

5.3 MATERIALS

The concrete blocks should be to BS 6717: Part 1.

The sand bedding should be a sharp sand, or crushed rock fines, evenly gradedand with not more than 10% retained on a 5 mm BS sieve. Clay, silt and fine dustcontent should not be more than 3% by mass.

191996May

Roads for Tracked Vehicles 5 Concrete Block Paving

The jointing sand should be a clean, dry sand with 100% passing a 1.18 mm BSsieve and up to 10% passing the 75 microns sieve.

5.4 EDGE RESTRAINTS

Concrete blocks impose a significant horizontal load on their surrounding whensubjected to traffic. This lateral thrust has to be resisted by substantial edgerestraints.

The most common type of edge restraint uses in situ concrete of sufficient widthand depth to prevent outward movement of the blocks.

Special arrangements have to be made to provide adequate edge restraint whenconcrete block paving abuts flexible construction or natural ground. See Figure5/1 for recommended designs.

An adjoining PQC slab is usually adequate as an edge restraint. It is normalpractice to insert a flexible filler board between the slab and the concrete blocksto allow for expansion.

Figure 5/1 Edge Restraint for Precast Concrete Blocks.

NOTE

A SIMILAR EDGE RESTRAINT ISRECOMMENDED EVEN WHERETHERE IS NO UPSTAND.

EDGE RESTRAINTPRECAST CONCRETE BLOCKS

20 May 1996


5.5 LAYING

The sub-base should be laid accurately by a paving machine to a tolerance of± 10 mm. It is essential that the sub-base is fully compacted to leave a smooth,dense surface on which to lay the bedding sand.

The sand bed should be laid to a smooth finish to achieve an average depth of35 mm after final compaction.

The blocks should be either hand or machine laid in a regular herringbonepattern set at 45° to the axis of the road.

Blocks should be cut by sawing not by splitting. No cut blocks smaller than half ablock should be permitted. Manufactured half blocks should be used whereavailable. Mitre blocks are useful as starter blocks set against edge restraints.See Figure 5/2 for laying pattern details.

After the blocks have been laid hand tight with average joints of 2 mm, theyshould be compacted using a vibrating plate compactor to achieve a smooth evensurface.

After initial compaction, the joints should be sealed using a suitable sharp sandwhich should be brushed into place. It is normal practice to compact the surfaceagain and to leave excess jointing sand on the surface for the first few days toensure that a good mechanical interlock is established.

5.6 EXPANSION JOINTS

In normal use, concrete blocks do not require special provisions for expansion.However, problems have been known to occur where the blocks were laid withextremely tight joints.

In order to prevent problems with expansion in hot weather it is recommendedthat care is taken to ensure that the blocks used do have integral joint spacersand that they are only laid hand tight.

5.7 SURFACE FINISH

For satisfactory performance concrete block paving should be laid to a smoothsurface finish with no blocks protruding above their neighbours. The blocks willtolerate considerable deflections under loading provided that they are wellcompacted together using a vibrating plate compactor.

A surface tolerance of 5 mm in 3 m should be achieved with new or restoredpaving.

May 1996 21


Figure 5/2 Concrete Block Laying Patterns.

22 May 1996

6 Hot Rolled Asphalt

6.1 GENERAL

Hot rolled asphalt surfacing can be expected to have a design life of about 20years before it must be replaced.

6.2 DESIGN

The design mix should achieve a stability of not less than 7 kN, a flow of notmore than 4.00 mm and a void content in the total mixture of between 2% and4%.

The hot rolled asphalt wearing course should normally be 40 mm thick.Exceptionally, where particularly heavy wear is expected, the wearing coursemay be increased to 50 mm.

The hot rolled asphalt should be laid on a basecourse of hot rolled asphalt to athickness of 60 mm. The lower layers of the pavement should consist of a boundroadbase and a sub-base.

Where the roadbase is of bituminous construction it should be constructed ofdense bitumen macadam not less than 150 mm thick. A 100 pen binder should beused with a coarse aggregate of crushed rock.

Where a cement bound roadbase is chosen it should be laid as a composite baseconsisting of a minimum of 150 mm of CBM 3 overlaid by a 60 mm course ofHRA. To control reflective cracking through the HRA, the thickness of CBMshould not exceed twice the overall thickness of overlying asphalt.

The sub-base should consist of either DoT Type 1 granular material or CBM 1.Thicknesses will vary with the subgrade CBR as shown in Figure 6/1.

Figure 6/1 Foundations for Flexible Pavements.

6.3 MATERIALS

The hot rolled asphalt courses should be produced in accordance with BS 594:Parts 1 and 2 except where noted in a particular specification.

May 1996 23

Layer Material Thicknesses

Subgrade CBR 2% 2 % < C B R < 5 % 5% < CBR 15% CBR>15%

Sub-base 150mm 150mm 225mm 150mm

[Optional capping thickness] [600 mm] [350 mm] [No capping] [No capping]

Roads for Tracked Vehicles 6 Hot Rolled Asphalt

Aggregates should be clean, hard and durable and should not contain deleteriousmaterials in such a form or quantity to affect adversely the strength ordurability of the asphalt.

The coarse aggregate should be crushed rock. The coarse aggregate should be aminimum of 40% of the total aggregate. It should conform to the limits given inFigure 6/2.

Figure 6/2 Coarse Aggregate Properties.

Test

Property


Maximum flakiness index (%)

Maximum aggregate crushingvalue (%)

Maximum absorption (%)

Stripping

Reference

Appendix A

BS 812: Part 105.1

BS 812: Part 110

BS 81 2: Part 2

Appendix B

Aggregate type Material

HRA Macadam

Each source

Each fraction

Crushed rock

Gravel

Crushed rock

Gravel

All except slag

Slag

All

82

70

30

n/a

30

n/a

2

n/a

82

70

30

30

30

25

2

4

Not greater than 6particles from a 150particle test sample

should indicate evidenceof stripping

Minimum polished stone value

Maximum sulfur content (%)

Stability

Minimum bulk density (kg/m3)

BS 81 2: Part 114

BS1047

BS1047

BS 81 2: Part 2

Wearing course

Slag

Slag

Slag

45

n/a

n/a

n/a

n/a

2

Requirementsas Appendix A

1120

The fine aggregate should be either sand or crushed rock or a blend of these. Sea-dredged sand should not be used. The fine aggregate should conform to the limitsgiven in Figure 6/3.

Figure 6/3 Fine Aggregate Properties.

Test

Property


Maximum absorption (%)

Stripping

Reference

Appendix A

BS 81 2: Part 2

Appendix B

Aggregate type

Each source

Each fraction

All

Parent rock ifcrushed rock

fines

Material

HRA Macadam

82 82

70 70

2 2

Not greater than 6particles from a 150particle test sample

should indicate evidenceof stripping

The filler should be either OPC or crushed limestone or crushed rock. It shouldmeet the grading requirements set out in Figure 6/4.

24 May 1996

Roads for Tracked Vehicles 6 Hot Rolled Asphalt

Figure 6/4 HRA Filler.

Percentage by Mass Passing

Minimum Maximum

300 10075 85 100

The binder should be penetration grade bitumen meeting the requirements ofFigure 1 of BS 3690: Part 1. Wearing course binders should be either 50 or 70pen. Regulating course binder may be either 50, 70 or 100 pen.

6.4 LAYING

Apart from small, irregular shaped areas the hot rolled asphalt should bemachine laid. The surface to receive the hot rolled asphalt should be swept cleanof debris and standing water.

The material should be mixed, delivered, laid and compacted within the materialtemperature limits given in Figure 6/5.

Figure 6/5 Asphalt Temperatures.

Course

Wearing course

Wearing course

Regulating

BitumenGrade

50 pen

70 pen

100 pen

Temperature (°C)

Mixing(Max)

185

180

170

Delivery(Min)

140

135

130

RecommendedPaver-out (Min)

130

125

120

Compaction(Min)

100

95

85

6.5 SURFACE FINISH

Unless otherwise specified, the hot rolled asphalt should be covered with a layerof coated chippings while still warm and in a plastic state.

The chippings should be evenly distributed at the rate of 7.5 kg/m to 10.0 kg/mfor 14 mm chippings or 10.0 kg/m to 13.0 kg/m for 20 mm chippings.

The chippings should then be rolled into the surface of the asphalt with asuitable hand or mechanical roller.

The finished surface of the hot rolled asphalt should be measured using a 3 mstraightedge laid parallel to the centreline of the road. The maximum allowedsurface depression under the straight edge is 7 mm.

May 1996 25

BS 410 Sieves

7 Mastic Asphalt

7.1 GENERAL

Mastic asphalt surfacing can be expected to have a design life of about 20 yearsbefore it must be replaced.

7.2 DESIGN

The mastic asphalt should normally be 40 mm thick. Exceptionally, whereparticularly heavy wear is expected, the wearing course may be increased to50 mm.

The mastic asphalt should be laid on a basecourse of hot rolled asphalt to athickness of 60 mm. The lower layers of the pavement should consist of a boundroadbase and a sub-base.

Where the roadbase is of bituminous construction it should be constructed ofdense bitumen macadam not less than 150 mm thick. A 100 pen binder should beused with coarse aggregate of either crushed rock or slag aggregate.

Where a cement bound roadbase is chosen it should be laid as a composite baseconsisting of a minimum of 150 mm of CBM 3 overlaid by a 60 mm course ofHRA. To control reflective cracking through the HRA, the thickness of CBMshould not exceed twice the overall thickness of overlying blacktop.


7.3 MATERIALS

The mastic asphalt wearing course should have coarse aggregate made withcrushed aggregate conforming to the grading shown in Figure 7/1. The aggregateshould be from a clean, hard igneous or siliceous rock with an aggregate abrasionvalue (AAV) of not more than 12 when tested in accordance with BS 812.

Figure 7/1 Mastic Asphalt Coarse Aggregate Grading.

Percentage by Mass

Passing BS Sieve Min

26 May 1996

14 mm 95

0

100

53.35 mm

Max

10020mm

Roads for Tracked Vehicles 7 Mastic Asphalt

The fine aggregate used in the mix is recommended to be limestone or siliceousrock containing not less than 70% calcium carbonate and ground to give thegrading shown in Figure 7/2.

Figure 7/2 Mastic Asphalt Fine Aggregate Grading.

The bitumen should have the properties shown in Figure 7/3.

Figure 7/3 Mastic Asphalt Bitumen Properties.

Properties

Specific gravity at 15.5°C

Penetration at 25°C

Flash point (open)

Ductility at 25°C

Solubility in carbon disulfide

Softening point (Ring and Ball)

Mineral matter (ash)

Loss on heating for 5 hours at 163°C

Penetration of residue after heating as apercentage of original penetration

Min

1.0

30

175°C

400mm

99.5%

50°C

-

-

60%

Max

1.06

40

-

-

-

-

0.5%

2.0%

-

The overall composition of the mastic asphalt should fall within the limits ofFigure 7/4.

Figure 7/4 Mastic Asphalt Composition.

Percentage by Mass

Material__________________Min__________________Max

Coarse aggregate 45 50

Limestone powder 41.7 48.5

(45-60% passing 75 urn sieve)

Soluble bitumen 6.5 8.3

7.4 LAYING

The surface to receive the mastic asphalt wearing course should be swept clean ofdebris and standing water.

The mastic asphalt should be laid as a single course at a temperature between175°C and 230°C. The material should be spread uniformly by hand usingwooden floats.

7.5 JOINTS

Care should be taken to ensure that all joints are properly and truly made.

May 1996 27

Passing BS Sieve Min Max

600

212

75

75 100

55 85

45 60

2.36mm 100

Percentage by Mass

Roads for Tracked Vehicles 7 Mastic Asphalt

The joints between sections of work should be made by warming the existingmastic asphalt by the application of an excess of hot mastic asphalt which issubsequently trimmed off to form an accurately level joint.

All projections into the road surface should be prepared before laying masticasphalt. Vertical surfaces of manholes, gully frames, boxes etc against which themastic asphalt is to abut should be cleaned and painted with a thin coat of hotbitumen.

The finished surface of mastic asphalt should be kept flush with or not exceeding3 mm above any projections. Where surfacing is to abut kerbs, these should alsobe treated with hot bitumen.

7.6 SURFACE FINISH

The mastic asphalt should normally be covered with a layer of coated chippingswhile still warm and in a plastic state.

The chippings should be evenly distributed at the rate of 7.5 kg/m to 10.0 kg/mfor 14 mm chippings or 10.0 kg/m to 13.0 kg/m for 20 mm chippings.

The chippings should then be rolled into the surface of the asphalt with asuitable hand or mechanical roller.

The finished surface of the mastic asphalt should be measured using a 3 mstraightedge laid parallel to the centreline of the road. The maximum allowedsurface depression under the straight edge is 7 mm.

28 May 1996

8 Grouted Macadams

8.1 GENERALResin or grouted macadam surfacing can be expected to have a design life ofabout 20 years before it must be replaced.

The grouted macadam should be one which is the subject of a current certificateissued by the British Board of Agrement as being suitable for use by trackedvehicles.

8.2 DESIGN

The grouted macadam should be laid 40 mm thick.

The grouted macadam should be laid on a basecourse of hot rolled asphalt ordense bitumen macadam to a thickness of 60 mm. The lower layers of thepavement should consist of a bound roadbase and a sub-base.

Where the roadbase is of bituminous construction it should be constructed ofdense bitumen macadam not less than 150 mm thick. A 100 pen binder should beused with coarse aggregate of either crushed rock or slag aggregate.

Where a cement bound roadbase is chosen it should be laid as a composite baseconsisting of a minimum of 150 mm of CBM 3 overlaid by a 60 mm course ofHRA. To control reflective cracking through the HRA, the thickness of CBMshould not exceed twice the overall thickness of overlying blacktop.


8.3 MATERIALS

The grouted macadam consists of a coated macadam of 14 mm or 20 mm sizeopen graded wearing course to BS 4987: Part 1 with 20-25% void content filledwith a high penetration proprietary grout.

Aggregates should be clean, hard and durable and should not contain deleteriousmaterials in such a form or quantity to affect adversely the strength or durabilityof the macadam.

The coarse aggregate should be crushed rock. The coarse aggregate should be aminimum of 40% of the total aggregate. It should conform to the limits given inFigure 6/2.

The fine aggregate should be either sand or crushed rock or a blend of these. Sea-dredged sand should not be used. The fine aggregate should conform to the limitsgiven in Figure 6/3.

May 1996 29

Roads for Tracked Vehicles 8 Grouted Macadams

8.4 LAYING

The Contractor should prepare and lay the grouted macadam in accordance withthe Agrement certificate.

The material is laid using conventional machinery except for the groutingprocess. Once the coated macadam has been laid and compacted, the grout ispoured onto the open textured macadam and a vibrating roller, or platecompactor, is used to achieve maximum penetration. The laying process is shownin diagrammatic form in Figure 8/1.

After rolling, the surplus grout is removed from the surface.

The success of the grouting process should be confirmed using cores taken fromthe completed pavement.

8.5 SURFACE FINISH

Grouted macadams provide good surface friction and so it is not normallynecessary to roll in chippings.

The finished surface of the grouted macadam should be measured using a 3 mstraightedge laid parallel to the centreline of the road. The maximum allowedsurface depression under the straight edge is 7 mm. The transverse measurementshould be done using the 3 m straightedge laid at right angles to the centreline ofthe road. The maximum transverse irregularity is 3 mm.

8.6 TRAFFICKING

Grouted macadams should not be subjected to traffic until the grout has fullycured.

The manufacturer's instructions for curing should be followed exactly. Somegrouts require up to 14 days to cure. No trafficking should be allowed during thistime.

30 May 1996

Roads for Tracked Vehicles 8 Grouted Macadams

Figure 8/1 Grouted Macadams.

PLATE VIBRATOR BRUSH POWER F L O A T

SUPPORT C O A T

BASE COURSE.

GROUTED M A C A D A M S

May 1996 31

9 Unbound Roads

9.1 GENERAL

An unbound or unsealed road can have an almost unlimited design life providedit is properly maintained.

In many situations, the provision of an unbound road may be a highly costeffective first stage in providing a new tracked vehicle route. This is because therequirements of an unbound road are very similar to the sub-bases required forbituminous construction. Thus, for a relatively low initial capital cost, a road canbe constructed and used quickly and can be incorporated into a subsequent boundpavement if one is found to be necessary.

9.2 DESIGN

The design thickness of unbound roads for use by heavy AFVs is governed by thesubgrade CBR and frost resistance criteria. Design pavement thicknesses fordifferent CBRs are shown in Figure 9/1.

Thicknesses less than 450 mm are based on the subgrade being non frostsusceptible or that frost damage is acceptable to the user.

Figure 9/1 Unbound Pavement Thicknesses.

CBR

10

9

8

7

6

5

4

3

2

1

Pavement Thickness (mm)

255

280

305

335

375

425

500

585

740

1050

Remarks

All figures are based on US Corpsof Engineers testing.

Capping recommended

Capping recommended

Capping recommended

Capping recommended

The pavement design of an unbound road should be checked for all user trafficnot just for tracked vehicles. However, the thicknesses given in Figure 9/1 exceedthe requirements for heavy commercial vehicles so there should be no problemwith mixed traffic.

Haul roads have to be designed with care since they are trafficked by heavilyladen vehicles. It is particularly important to ensure that construction traffic on apartly built road is minimised as such loading can easily damage the subgrade.

32 May 1996

Roads for Tracked Vehicles 9 Unbound Roads

The total pavement thicknesses can be made up using different materials. It isessential that at least the top 200 mm of material meets the requirements of DoTType 1 sub-base.

9.3 MATERIALS

The preferred material for the surfacing is a well graded crushed rock DoT Type 1sub-base.

Thicknesses below the top 200 mm can be made up using DoT Type 2 material.Where particularly poor ground is encountered, a capping layer may be used.Material specifications are contained in the DoT Specification (Reference 8). Atypical design is shown at Figure 9/2.

9.4 LAYING

Materials should be spread evenly, without damaging the formation andcompacted to 100% of Optimum Dry Density.

Placing should achieve the minimum of drying out or segregation. Compactionequipment should be chosen to achieve the desired compactive effort withoutdisturbing the subgrade.

Material should be compacted at a moisture content between 1% above and 2%below the optimum percentage as determined in accordance with BS 1377.

9.5 SURFACE FINISH

The final wearing course should achieve a surface tolerance of ± 20 mm from thedesign level at any point with no significant depressions or bumps.

The shaped and compacted surface should be free from roller marks, excess finesor loose stone.

9.6 CONSTRUCTION SEQUENCE

A typical construction sequence would be:

Clearance and site preparation which includes stripping and stacking of topsoilfor reuse. It is normal to remove tree roots to 300 mm below ground level.Unsuitable fill material should be removed and stored separately for use inlandscaping.

Drainage which is often done in stages. It is essential to keep water away fromexcavations so drainage is usually done in conjunction with earthworks. Sidedrains and culverts should be completed early in the construction period toimprove land drainage and to prevent damage to the unfinished road.

May'1996 33


Figure 9/2 Typical Cross Section.

34 May 1996


After stripping, the formation should be checked for soft spots which should bedug out and backfilled with suitable material. Where a substantial length of poormaterial is encountered, it may well be more efficient for the earthworkscontractor to take another cut ie increase the depth of the pavement over thesection, than to dig out individual soft spots.

Where an embankment is required, the Contractor should compact the formationfor a depth of 150 mm to at least the same standard as the overlyingembankment. Any material too wet to compact, or any soft spots, should be driedso that they can be properly compacted or they should be replaced with suitablefill.

The sub-base should be placed and compacted in layers as soon as possible oncethe formation has been checked. It is important that the subgrade is coveredearly to prevent deterioration from exposure to the weather. Although speed isimportant at this stage, it is essential to maintain the design shape of the crosssection at every level from formation upwards. A grader is recommended for useafter initial compaction to trim the bottom layer to shape.

Succeeding layers of sub-base and roadbase material should be placed andcompacted in layers until the full pavement depth is finished. It is important forcompaction to be carefully controlled to ensure that each layer achieves thedesign thickness and density. Rollers should always begin by compacting from thelowest point of the cross section to prevent material from migrating down thecamber or crossfall.

Finishing the construction includes landscaping, topsoiling and disposal of anysurplus material. It may also involve extensive planting since vegetationstabilises the disturbed ground, helps to prevent soil erosion and reduces thevisual impact of the road. Hydoseeding with a suitably selected native seed blendcan be particularly effective in re-establishing vegetation.

The Contractor may choose to construct a road from one end or both or indeed hemay work on several sections concurrently. Without unnecessarily restricting theContractor's freedom of action, it is essential that activities are confined to asnarrow a strip as possible to build the road. The plan for haul roads should bechecked to see that unnecessary land take is minimised and that heavyearthmoving plant and laden dump trucks do not run on incomplete sections ofroad.

9.7 MAINTENANCE REGIME

The importance of proper maintenance cannot be over emphasised. A wellmaintained unbound road will give good service for low cost over many years; apoorly maintained one will fail rapidly. The cost of maintenance will be directlyrelated to the amount of trafficking, the weather and how quickly repairs aredone when they are required.

One of the key factors in a successful maintenance regime is establishing at whattime repairs must be effected. Figure 9/3 gives some guidance on suitableintervention levels.

May 1996 35


Figure 9/3 Intervention Levels for Unbound Roads.

Defect

Windrows, channels,corrugations, soft spots,loose materialWheel ruts and potholesInsufficient crossfall

Excessive crossfallInsufficient height abovesurrounding ground

Level to Intervene

Safe travelling speed less than85% of design speed

Depth of 80 mm

Water ponds or 2% less thandesign crossfallCrossfall of 6% or steeperAt natural ground level in rollingcountry or 100mm in flat terrain(measured at the point of theshoulder)

Extent

>20% of anysection of road

Any

>20% of anysection of road>20% of any

>20% of anysection of road

Urgent MaintenanceRequired

Safe travelling speed lessthan 70% of design speed

Defect depth of 150 mm

Crossfall of 1% or less,water ponds

Crossfall of 8% or steeperWater ponds and surface islower than natural groundlevel (measured at the pointof the shoulder)

Typical Action

Grade orresurface

Resurface

Grade

GradeHeavy gradeand import fill

36 May 1996

10 Special Surface Treatments

10.1 CONCRETE SURFACE HARDENERS

There are numerous proprietary cementitious products for improving the surfacefinish, chemical resistance, abrasion resistance and surface hardness of concrete.

These materials may be appropriate in particularly demanding situations such astank garages or workshops where locked track turns or channelised movementsoccur.

The materials can be considered in 2 main groups; those which involve the use ofa resin and those which use a shake-on product to the wet concrete. Typical of theresin based products are materials like Addagrip and Flowshield which can beused to rehabilitate old concrete slabs using a hot, thixotropic resin and sprinkledaggregate. Shake-on products include MasterTop which involves the use ofspecial malleable iron aggregate to produce a surface capable of resisting metal-on-metal scraping contact.

Guidance is available from DEO (Wks) ABFG on the use of these proprietaryproducts.

10.2 CONCRETE FIBRES

Trials have been conducted using both polypropylene and steel fibres to assesstheir effectiveness in reducing damage to concrete surfaces subjected to heavywear.

Fibre reinforcement is effective in reducing surface cracking and can giveincreased resistance to abrasion. From the limited information available, it is notpossible to confirm whether the benefit of using fibres is cost-effective.

DEO (Wks) would welcome the opportunity to be involved in some trial areas,using the latest fibres, which can be trafficked by tracked vehicles.

10.3 CONCRETE ADMIXTURES

Air entraining agents are now specified routinely for use in concrete roads,whether for tracked vehicles or not. This is due to the improved resistance tofreeze/thaw action provided by the millions of microscopic bubbles in theconcrete. External concrete subject to tracked vehicles should be specified with aDoT approved air entraining agent.

May 1996 37

Roads for Tracked Vehicles 10 Special Surface Treatments

For certain applications such as slipformed concrete roads, there may be arequirement to add a superplasticiser to the mix. It is DEO (Wks) policy to avoidthe use of superplasticisers in concrete roads whenever possible. Thus, their useis not proscribed but advice should be sought from DEO (Wks) ABFG whenever acontractor wishes to use a superplasticiser.

To reduce the visual impact of concrete roads, particularly in sensitive areas, itmay be necessary to consider the use of tone down chemicals. These weredeveloped principally for use on airfields for camouflage purposes. All requests touse these admixtures should be referred to DEO (Wks) ABFG for advice.

10.4 CONCRETE BLOCK SEALANTS

Under most conditions, concrete block surfaces are effectively self-sealing after afew months when traffic deposits, dust etc. completely fill the joints between theblocks. In certain circumstances, there is a risk of water penetrating the blocksand washing out the bedding sand. This is easily dealt with by including a drainmasked by a suitable geotextile to prevent washout.

Where there is a threat of significant fuel or oil spills onto a concrete blocksurface it may be necessary to seal the surface with a proprietary sealant. MODhas some experience of using ACM PAVSEAL to seal concrete block pavements onairfields.

It should be noted that commercial filling stations have used untreated blockssuccessfully for many years. It is recommended that sealants are not normallyused on concrete block pavements.

10.5 GROUTED MACADAMS

Grouted macadams have produced distinctly mixed results when used by MOD.There have been cases where the receiving course or the grout have not beenbuilt properly leading to premature failure.

Salviacim and Hardicrete have been used in the past under PSA supervision.Both materials performed satisfactorily when carefully constructed. They aremore expensive than other materials and should be used only when oil andchemical resistance is a particular requirement.

10.6 MODIFIED BINDERS

To improve the resistance to deformation and abrasion, a variety of modifiedbinders have been prepared by the asphalt industry. Some of these products haveproved most successful under heavy tracked vehicle loading.

MOD has some experience of using ASHOPOL 2000 and Cariphalte DM.Modified binders cost considerably more than standard penetration binders. Theyshould only be considered for areas of exceptional wear.

Advice is available from DEO (Wks) ABFG on the appropriate use of thesespecialist products. While some materials have performed well, manufacturer'sclaims should always be treated with caution.

38 May 1996

Appendix A Magnesium SulfateSoundness Test

A.1 SCOPE

This method shall be followed to determine the soundness of aggregate bysubjecting the aggregate to cycles of immersion in a saturated solution ofmagnesium sulfate followed by oven drying.

A.2 APPARATUS AND REAGENTS

Apparatus and reagents are as detailed in BS 812: Part 121, clauses 5 and 6,(except that the balance for coarse aggregate, sub-clause 5.2, is to be accurate to 1gram). In addition, the following equipment is required:

a. 37.5 mm, 20 mm and 5.0 mm sized square-hole perforated-plate testsieves and 2.36 mm, 1.18 mm, 600 and 300 sized woven-wire testsieves (the additional test sieves shall comply with BS 410).

b. At least two brass or stainless steel mesh baskets for immersing aggregatespecimens, for fractions other than 10 to 14 mm. The baskets are to havemaximum dimensions of apertures not more than half the maximum aperture ofthe sieve on which the specimen is retained, but not less than 150

A.3 PREPARATION OF TEST PORTIONS

A.3.1 Bulk SamplesBulk samples from each nominal size of aggregate being used from each source ofsupply shall be tested separately. The procedure described here shall be appliedto each separate sample.

A.3.2 Test PortionsPrepare two test portions from the bulk samples of each aggregate supplied as in BS812: Part 121, clauses 7.1 and 7.2, replacing 'minimum mass of 500 g of the 10.0 mmto 14.0 clause 7.1 by the relevant masses from the tables in clauses A.4and A. 5.

A.4 PREPARATION OF SAND TEST SPECIMENS FOR EACH FRACTION

A.4.1 Particle Size DistributionThe particle size distribution of the test portion shall be determined by thewashing and sieving method described in clause 7 of BS 812: Part 103 using the10 mm, 5 mm, 2.36 mm, 1.18 mm, 600 and 300 sieves. The particle size

May 1996 39

Roads for Tracked Vehicles Appendix A

distribution shall be recorded giving the percentage of the mass of the testportion retained between each pair of sieves, together with that passing the 300urn sieve, to the nearest whole number.

A.4.2 Fraction Passing 300 SieveThe fraction passing the 300 sieve, together with those fractions retainedwhose proportions are less than 5% by mass of the test portion, shall bediscarded; nevertheless, the proportions which they represent shall be taken intoaccount in the calculation of the test result.

A.4.3 Test SpecimenOne test specimen, of mass in accordance with Figure A.4/1, shall be taken out ofeach fraction retained after completion of sub-clause A.4.2. If there is insufficientmaterial in any of these fractions to provide a test specimen of the required size,the procedure shall be repeated from sub-clause A.3.2; the particle sizedistribution recorded shall be that obtained from all the material sieved out.

Figure A.4/1 Mass of Each Test Specimen for Sand.

Passing (mm)

10.0

5.0

2.36

1.18

600

BS Sieves

Retained (mm)

5.0

2.36

1.18

600

300

Mass of Specimen Before Test (g)

300 +10 /-O

100 + 10/-0

100 + 10/-0

100 + 10/ -0

100 + 10/-0

A.5 PREPARATION OF COARSE AGGREGATE TEST SPECIMENS FOR EACH FRACTION

A.5.1 Particle Size DistributionThe particle size distribution of the test portion shall be determined by the drysieving method described in clause 7.3 of BS 812: Part 103 using the 37.5 mm,20mm, 10 mm, 5 mm, 2.36 mm and 1.18 mm sieves. The fractions retained on the37,5 mm sieve and passing the 1.18 mm sieve shall be discarded and not takeninto account in calculating the test result. The remainder of the reduced sampleshall be considered as the test portion. The particle size distribution shall berecorded giving the percentage of the mass of the test portion retained betweeneach pair of sieves to the nearest whole number.

A.5.2 Minor FractionsThose fractions retained whose proportions are less than 5% by mass of the testportion shall be discarded; nevertheless, the proportions which they representshall be taken into account in the calculation of the test result.

A.5.3 Test SpecimenOne test specimen, of mass in accordance with FigureA.5/1, shall be taken out of eachfraction retained after completion of sub-clauseA.5.2. If there is insufficient materialin any of these fractions to provide a test specimen of the required size, the procedureshall be repeated from sub-clause A.3.2; the particle size distribution recorded shall bethat obtained from all the material sieved out.

40 May 1996

Roads for Tracked Vehicles Appendix A

Figure A.5/1 Mass of Each Test Specimen for Coarse Aggregate.

BS Sieves Mass of Specimen Before Test

Passing (mm)

37.5

20.0

10.0

5.0

2.36

Retained (mm)

20.0

10.0

5.0

2.36

1.18

1500 ±50

1000 ±10

300 + 10/-0

100 + 10/-0

100 + 10/-0

A.6 PROCEDURE

The procedure for each test specimen is as in BS 812: Part 121, clause 8,replacing '10.0 mm sieve' in clause 8.6 by the sieve relevant to the lower size ofthe aggregate fraction.

A.7 CALCULATION AND EXPRESSION OF TEST RESULTS

Calculate the soundness value of each test specimen as in BS 812: Part 121,clause 9.1, replacing '10.0 mm sieve' by the sieve relevant to the lower size of theaggregate fraction.

A.7.1 Minor FractionsFractions not tested because they represent less than 5% by mass of the testportion shall be assumed to have a soundness value equivalent to:

a. The mean of the soundness values found by the tests on specimens of thetwo fractions immediately adjacent to it in size; or

b. The soundness value found by a test on a specimen of the fraction, eitherlarger or smaller, immediately adjacent to it if only one of these fractions wastested; or

c. The mean soundness value found by the tests on specimens of the two fractionsnext but one adjacent to it if both these fractions were tested and the adjacentfractions were not; or

d. The soundness value found by the test on a specimen of the fraction, eitherlarger or smaller, in this order of priority, most nearly adjacent to it.

A.7.2 Fine Aggregate SamplesFor samples of fine aggregate, the material passing the 300 sieve shall not betested but shall be taken as having a soundness value equivalent to that of thespecimen passing the 600 sieve but retained on the 300 sieve.

A.7.3 Soundness ValueThe soundness value of each test portion of aggregate shall be the sum of thesoundness values found for each aggregate fraction times the proportion by massof that fraction in the test portion.

A.7.4 Magnesium Sulfate Soundness Value (MSSV)The MSSV for the aggregate shall be the mean of the two results for the test portionsto one decimal place.

Note: A suitable worksheet (with two examples, one fine aggregate and onecoarse aggregate) is shown below:

May 1996 41

Appendix B Stripping Test

B.1 SCOPE

This method details the procedure to be followed to determine the resistance ofaggregates to stripping.

B.2 APPARATUS

Shallow tray(s).

Mixing bowl of 1.5 litres capacity.

Means of separately heating the aggregate and the binder to a temperaturewithin the ranges given in clause B.4.

Distilled water.

B.3 SAMPLES

The binder shall comply with BS 3690: Part 1 and shall be a representativesample of the binder to be used in the plant mixtures.

The test shall be carried out on a separate sample of aggregate from each sourceof supply. The sample shall be taken from the bin or stockpile at the quarry inwhich the 10 - 6.3 mm size predominates. It shall be a representative sample ofthe rock that is to be used in the plant mixtures.

B.4 PROCEDURE

B.4.1 Test ProcedureThe test procedure is as follows:

a. Each sample of aggregate shall be quartered and sieved out to provide aspecimen of 150 particles each passing the 10.0 mm sieve and beingretained on the 6.3 mm sieve. The specimen and the binder shall beheated separately. Under no circumstances shall the binder be heated to atemperature greater than that shown below. The specimen shall be placedin a heated mixing bowl and a quantity of binder equivalent to 4% bymass of the specimen shall be added to it when both specimen and binderare at the temperatures specified in Figure B.4/1.

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Roads for Tracked Vehicles Appendix B

Figure B.4/1 Mixing Temperatures.

Material Mixing Temperature

Hot rolled asphalt 175°C ±5 ° C

Dense bitumen macadam 160 °C ± 5 °C

b. The aggregate and binder shall be hand mixed until coating of theaggregate is complete. If coating is incomplete after 5 minutes of mixing,this procedure shall be repeated with a fresh specimen and an increasedproportion of binder. The binder shall be increased by steps of 0.5% bymass of the specimen until a mix giving complete coating of the aggregateis obtained.

c. The coated specimen shall be placed in one or more trays which have beenpreviously treated with a mixture of equal parts of glycerol and dextrin orsimilar agent to prevent adhesion of the binder to the tray. Each particleshall be completely separated from adjacent particles.

d. After standing for one hour, the coated specimen shall be covered withdistilled water at 18°C to 20°C and maintained at that temperature. Afterimmersion for 48 hours the water shall be decanted and the coatedspecimen allowed to dry at air temperature.

e. The dried sample(s) shall then be examined, particle by particle while stillin the tray(s).

B.4.2 Test CriteriaIf the binder has stripped exposing any part of the aggregate from more than sixof the total particles tested, the sample shall have failed the test.

B.4.3 Check TestsTo ensure that a fault during the test has not contributed to the failure, the testshall be repeated separately on each of a further 3 samples.

If any one of the further 3 tests fails, by indicating stripping in excess of thelimits described in sub-clause B.4.2, the aggregate will not be acceptable for theparticular mixture, and supplies from its source shall be rejected.

Printed in the United Kingdom for HMSODd302209 7/96 C7 G559 10170

451996May