design guide and specification for structural maintenance ... · design guide and specification for...

Design guide and specification for structuralmaintenance of highway pavements by coldin-situ recycling

Prepared for CSS, Colas Limited and the Pavement Engineering

Group, Highways Agency

L J Milton and M Earland

TRL REPORT 386

TRANSPORT RESEARCH LABORATORY

First Published 1999ISSN 0968-4107Copyright Transport Research Laboratory 1999.

Transport Research Foundation Group of Companies

Transport Research Foundation (a company limited by guarantee) trading as TransportResearch Laboratory. Registered in England, Number 3011746.

TRL Limited. Registered in England, Number 3142272.Registered Offices: Old Wokingham Road, Crowthorne, Berkshire, RG45 6AU.

This report has been produced by the Transport ResearchLaboratory, under/as part of a Contract placed by CSS, ColasLimited and the Highways Agency. Any views expressed arenot necessarily those of CSS, Colas Limited or the Agency.

TRL is committed to optimising energy efficiency, reducingwaste and promoting recycling and re-use. In support of theseenvironmental goals, this report has been printed on recycledpaper, comprising 100% post-consumer waste, manufacturedusing a TCF (totally chlorine free) process.

CONTENTS

Page

Executive Summary 1

General Introduction 3

Part1: Design guide 5

1 Introduction 5

2 Environmental considerations 5

2.1 Sustainable development 5

2.1.1 UK strategy for sustainable development 5

2.1.2 Minerals planning guidance 5

2.2 Waste management 5

2.2.1 Environmental Protection Act 1990 5

2.2.2 Regulations 5

3 Cold in-situ recycling 6

3.1 Applications 6

3.2 Current specifications 6

3.2.1 Sub-base materials 6

3.2.2 Roadbase materials 6

3.3 Implementation procedure 6

4 Site evaluation 7

4.1 Identification of sites for structural maintenance 7

4.2 Investigation of existing pavement construction 7

4.2.1 General considerations 7

4.2.2 Job size 7

4.2.3 Depth of existing pavement 7

4.2.4 Investigation framework 9

4.2.5 Suitability and consistency of existing materials 9

4.2.6 Preparation of representative test specimens 9

4.2.7 Underground services 9

4.3 Risk assessment 10

4.3.1 Design risks 11

4.3.2 Construction risks 11

5 Design of cold in-situ recycled material 11

5.1 Pulverised aggregate 11

5.1.1 Grading 11

5.1.2 Moisture content 12

5.2 Primary binder agent 12

iii

iv

Page

5.2.1 Portland cement 12

5.2.2 Foamed bitumen 14

5.3 Prelimary mix appraisal and design process 14

5.3.1 Cement bound recycled materials 15

5.3.2 Bitumen bound recycled materials 15

6 Pavement design 16

6.1 Definitions 16

6.2 Road categories 16

6.3 Design for Type 1 and Type 2 roads 16

6.4 Design for Type 3 and Type 4 roads 20

7 Specification for cold in-situ recycled material 22

7.1 General 22

7.2 Material composition and process control clauses 22

7.2.1 Cement bound material 22

7.2.2 Foamed bitumen bound material 23

7.3 End-product performance clauses 23

8 Construction 23

8.1 Pulverisation and stabilisation 23

8.2 Added water and moisture control 23

8.3 Application of cement or lime 24

8.4 Application of foamed bitumen 24

8.5 Compaction 24

9 References 24

Part 2: Specification and notes for guidance on thespecification 26

Clause C1 In-situ recycled cement bound material 26

Scope 26

Component materials 26

Pulverisation and stabilisation 26

Process control 28

End product performance of in-situ recycled cementBound material 28

Clause C2 In-situ recycled cement bound material - mixturedesign and characterisation 29

v

Page

Clause B1 Cold in-situ recycled bitumen bound material 34

Scope 34



Process control 36

End product performance of cold in-situ recycledBitumen bound material 37

Clause B2 Cold in-situ recycled bitumen boundmaterial - mixture design and characterisation 39

Notes for guidance on the specification for cold in-siturecycled materials 43

Site evaluation 43



Process control 46

End-product performance specification 48

Mixture design and characterisation 49

Acknowledgements 51

Appendix A: Research methodology 52

Appendix B: Examples to demonstrate the design process 57

Abstract 59

Related publications 59

1

Executive Summary

The Design Guide contains information and advicerelating to environmental considerations and siteevaluation, which are necessary for the design for cold in-situ recycled materials and their use in structuralmaintenance of highway pavements. The design processincludes flow charts, decision trees and methodologies forlayer thickness determination on a graphical basis for useby designers. The many variables associated withrecycling existing roads inevitably mean that there are anumber of aspects to be carefully considered by thedesigner. The Guide provides a refined structural solutionfor those who give due consideration to all of the optionsbut, at the same time, it has been kept relativelystraightforward to use.

Appendix A, outlines the research carried out andpresents the summarised findings of the monitoring of theperformance of recently recycled materials on medium toheavily trafficked roads and of the road trials in Somerset.Appendix B contains worked examples which demonstratehow the proposed design processes may be applied.

The Specification and Notes for Guidance on theSpecification for cold in-situ recycled material arepresented as free standing sections; the separatespecification clauses may be used unchanged or adaptedfor inclusion within the standard contract documentationfor structural maintenance works. Furthermore, thepossibility exists within the Specification to adopt non-destructive test methods to establish end-productperformance of the in-situ recycled layer. By reference tothe associated Notes for Guidance, the designer is able tomake reasoned decisions relating to the site specific itemsof the specification contained in the respectiveSpecification Appendices.

The information contained in this report offer the latestbest practice advice on the design, supervision andconstruction of cold in-situ recycling works, used forstructural maintenance of highway pavements. Whilst thepreviously used recipe and method specification wasadequate for lower trafficked roads, end-productperformance specification is seen as an appropriate meansof specifying recycled materials in their own right, usingperformance criteria stated in terms of engineeringproperties, thereby allowing the recycled material to beconsidered for more heavily trafficked sites on anequitable basis to conventional materials.

As the process becomes more accepted and greatervolumes of material are recycled, the design guidancegiven in this report may be subject to development in thelight of the increased data available.

Recycling of existing pavement materials has become anincreasingly important feature of the maintenance ofhighways in the UK. As a result of this, and in conjunctionwith efforts to rationalise standards for reinstatement,patching and of haunching (edge of carriagewaystrengthening), each of which promote the re-use ofmaterials and cold in-situ recycling techniques, it wasconsidered that nationally consistent guidelines forHighway Engineers for the wider use of recyclingtechniques in structural maintenance of highwaypavements would be beneficial. In particular, guidance onthe appropriate use of recycling, including binder selectionand structural design of cold in-situ recycling, for thereconstruction of the structural course and/or thefoundation platform of the pavement was required. Thiswould promote the concept of the existing highway beinga ‘linear quarry’ from which aggregates can be reclaimed.

Consequential environmental benefits are a reduction inthe extraction of primary aggregates, a reduction in the useof energy, a reduction in the amount of construction trafficservicing maintenance sites, a reduction in trafficcongestion from shorter duration roadworks and thesustainable development and improvement of the roadnetwork. The general public, central and local governmentand the transport industry are all beneficiaries.

This report describes research carried out under theLinear Quarry Project. The work was jointly sponsored bythe Highways Agency, County Surveyors Society andColas Limited. Guided by a Steering Group whosemembers were drawn from the Highways Agency, LocalHighway Authorities, Colas Limited and TRL, the aimswere to promote the use of cold in-situ recycling byproviding evidence of acceptable in-service performanceand to provide guidance on structural design and a draftspecification. Pathfinder methods for the measurement ofend-product performance are also included.

The report addresses three specific aspects of the research:

l measurement of the condition of medium to heavytrafficked roads recently recycled using cold in-situtechniques and the determination of their life expectancycompared with design traffic;

l construction of a road trial on the A3088 in Somerset toinvestigate the performance of both cement bound andfoamed bitumen bound cold in-situ recycled materials;and

l the production of a structural design method for cold in-situ recycling, a specification and a method ofperformance assessment.

The report is divided into two parts. Part 1 comprises theDesign Guide, which is supported by appendices thatdescribe the research methodology and worked examples.Part 2 contains the Specification and Notes for Guidanceon the Specification; the specification clauses arepresented separately for cement bound material andbitumen bound material, so that they may be included instandard contract documentation.

3

General introduction

Recycling of existing pavement materials has become anincreasingly important feature in the UK for themaintenance of highways. The concept of using theexisting highway as a ‘linear quarry’ from which roadstoneaggregates can be reclaimed has been gaining favour forboth environmental and economic reasons. Although plantand procedures for such techniques have been used in theUK for some time, there have been no nationallyconsistent guidelines on their use. This report gives adviceon the appropriate use, binder selection and structuraldesign of in-situ recycling, to reconstruct the foundationand/or structural course of road pavements.

In the context of structural maintenance of highwaypavements, the term ‘cold in-situ recycling’ refers to theprocedures using specialist plant to pulverise and stabiliseexisting road materials, in-place, at ambient temperature,with the addition of hydraulic cement and/or bitumenbinders. For the purposes of this report and in line withcommon practice within the United Kingdom the bitumenbinder referred to is foamed bitumen; in a world contexthowever, bitumen emulsions are also frequently used. Thehydraulic binders referred to are Portland cement orPortland blast furnace cement or Portland pulverised fuelash cement.

Foamed bitumen is a bituminous binder produced byinjecting cold water under controlled conditions,sometimes with certain additives, into hot penetrationgrade bitumen before application through speciallydesigned nozzles on a spray bar. The foamed bitumenexpands to 10 - 15 times the original volume of thepenetration grade bitumen.

The cold, in-situ recycling technique is currentlyaccepted and encouraged for lightly trafficked roads as avaluable alternative reconstruction method and is currentlypermitted for Highways Agency’s roads up to a designtraffic level of 5 million 8 tonne standard axles (msa).When used by a Local Highway Authority the design isusually based on advice from the specialist contractor andis often governed by the practical restraints of the site.

By setting out nationally consistent guide lines on theappropriate use of the recycling technique, binder selectionand the structural design of the layer produced, thisdocument seeks to encourage and extend the scope of coldin-situ recycling. Particular attention is paid to upgradingroads containing unbound granular and bitumen or cementbound roadbases by cold, in-situ recycling to produceflexible or flexible composite pavements for heavier trafficconditions than have previously been permitted.

In Part 1 of the report structural designs are given forpavements carrying cumulative traffic levels up to 20 msa.Guidance is also given on the design of the recycled mixtureand the pavement assessment and construction operationsnecessary to build a satisfactory recycled pavement.

Part 2 of this report sets out Specification Clauses andassociated Notes for Guidance for the construction of thepavement structural layer using cold in-situ recycling withcement and cold in-situ recycling with foamed bitumen.The specifications have been written with the aim of

moving away from recipe/method requirements towardsthose of end-product performance, measured by in-situnon-destructive tests or by laboratory tests on corespecimens extracted from the finished pavement.However, to ensure durability from the cold in-siturecycling techniques it has been found necessary tomaintain some detailed method specification clauses.

The guidance given is based on the results of a three yearresearch programme in which a review and detailed study ofselected recycled in-service roads carrying medium to heavytraffic was complemented by a full scale, monitored trial onthe A3088 Cartgate Link in Somerset. Both foamed bitumenand cement binders were considered.

A complementary report by Milton (1999) (the contentsof which are summarised in Appendix A to this report)describes in more detail the investigative studies used toprovide the data on which the guidance in this report isbased; this and the other unpublished TRL reports cited areavailable, at cost, on direct personal application only, fromthe Transport Research Laboratory.

5

Part 1: Design guide

1 Introduction

The guidance and advice contained herein are based on athree year research programme reviewing the performanceof in-service roads which had been maintained using coldin-situ recycling techniques and the construction andmonitoring of two full-scale trials.

Particular attention has been paid to upgrading roadscontaining unbound granular and open textured roadbasesby cold in-situ recycling, to produce flexible or flexiblecomposite pavements for heavier traffic conditions thanhave previously been permitted. Design traffic levelsroutinely up to 10 million standard 8 tonne axles (msa) andwhere good quality aggregates exist in the road, to 20 msaor possibly more, have been addressed.

2 Environmental considerations

The use of cold, in-situ recycling can often be a practical,cost effective and environmentally beneficial alternative tousing conventional materials. However, before using arecycled material it is necessary to assess the risk of earlydeterioration in relation to the potential benefits,particularly when viewed in terms of the currentenvironmental and waste management issues that affectHighway Authorities.

2.1 Sustainable development

The 1992 Earth Summit in Rio De Janiero placed anobligation on the 150 governments attending to promotesustainable development to secure a viable future for ourplanet.

The objective and conclusion papers of the conference,issued as Agenda 21, set out how countries should worktowards sustainability. This involves reducing the use offinite resources, increasing energy efficiency, minimisingwaste and protecting the natural world. Agenda 21 ishaving considerable effect on the way HighwayAuthorities now have to plan and implement their newconstruction and maintenance works. Details are given inthe document Agenda for Change (1993).

2.1.1 UK strategy for sustainable development

‘It is Government policy to encourage conservationand facilitate the use of reclaimed and marginalmaterials, wherever possible, to obtainenvironmental benefits and reduce the pressures onsources of natural aggregates’. (Williams, 1995).

Related to highways, the suggested way forward isthrough broadening the specifications and increasing thetechnical scope for using by-product and recycledmaterials in road pavements. However, these changesshould follow research into the technical feasibility and

relative performance of these alternative materials. Theintroduction of the Landfill Levy for demolition and wasteconstruction materials should encourage more recycling ofthese materials.

2.1.2 Minerals planning guidanceThe Department of the Environment publicationMPG6 (1994), Minerals Planning Guidance for AggregateProvision sets out four objectives for sustainable developmentin relation to minerals planning. The first two are:

l to conserve minerals as far as possible, whilst ensuringan adequate supply to meet the needs of society;

l to minimise production of waste and to encourageefficient use of materials including appropriate use ofhigh quality materials and recycling of wastes.

Therefore, in the likelihood that ‘traditional’ aggregatesources will become increasingly constrained, alternativesources must be considered and developed, including thegreater use of secondary aggregates. Recent researchindicates that secondary aggregates account for about 10per cent of aggregate consumption in the UK at present.MPG6 envisages this rising to 12 per cent by 2006,comprising a total of some 5.2 million tonnes per annum.

MPG6 stresses the need to use all aggregate efficientlyby minimising wastage and avoiding the use of highergrade material if lower grade will suffice. Whilstspecifications for construction materials must have anadequate margin of safety, over-specification tends tooccur and materials are used, often with performancecharacteristics higher than required for the purpose. Thereasons for this stem from the relatively low cost ofprimary aggregate and the perceived lower risk elementusing virgin materials.

2.2 Waste management

2.2.1 Environmental Protection Act 1990The Environment Protection Act (1990) introduces strictcontrols over waste management activities for theprotection of health and the environment. It alsoencourages the minimisation, reuse and recycling of wasteand exempts from licensing control a significant range ofwastes and activities where genuine recycling takes place.

2.2.2 RegulationsThe Waste Management Licensing Regulations (1994)extend and amend the provisions of Part 2 of theEnvironmental Protection Act 1990, taking account ofEuropean directives.

Deciding whether a substance is waste or not under theseterms is not a simple matter. In order to be a waste substanceor object, it must fall under one of the categories set out inPart 2 of schedule 4 of the Regulations and be discarded, beintended to be discarded or be required to be discarded(being incapable of further use in their present form).

Therefore, there are substances generated by HighwayAuthorities and/or their contractors, which are a waste andothers that are not. For what constitutes a waste reference

6

should be made to the regulations and to the associatedcircular for guidance on this matter. Next, if it is a waste,then a range of exemptions may apply. Such exemptionsinclude:

l manufacture of roadstone or aggregate from wastewhich arises from demolition and construction worksand the storage of these wastes at the place where theactivity is to be carried out provided that the totalamount treated at that place does not exceed 100 tonnesand the total quantity of waste stored does not exceed50,000 tonnes in the case of roadstone from roadplanings and in any other case 20,000 tonnes(exemption number 13);

l the storage in a secure place on any premises of wastearticles (eg. aggregate, kerb stones) which are to be usedfor construction work which are capable of being usedin their existing state - maximum quantity 100 tonnesfor a maximum 12 months (exemption number 17);

l the storage on a site of waste which arises fromdemolition and construction provided it is suitable forrelevant work which will be carried on at that site, or ifit is not produced on the site, it must be used withinthree months of deposit (exemption number 19).

In the case of asphalt planings, up to 50,000 tonnes canbe stored for up to three months.

There is an over-riding requirement that any activityshould be carried out in such a manner as not to causepollution of the environment or harm to human health andthe operator must comply with the Waste ManagementDuty of Care (1991).

3 Cold in-situ recycling

3.1 Applications

The decision to use cold in-situ recycling will dependmainly on the nature and consistency of the existingmaterials and the availability of appropriate specialisedplant and skilled contractors.

The technique is applicable to all classes of road, at thisstage with designs routinely applicable to traffic levels upto 10msa and in circumstances where thick layers of goodquality aggregates are known to exist in the road, to 20msaor possibly more.

Cold in-situ recycling can involve the following types ofpavement, binder system and pavement layers:

Pavement types:- flexible- flexible composite

Binder systems: - portland cement- lime- emulsion bitumen (+ lime/cement)*- foamed bitumen (+ lime/cement)

Pavement layers:- sub-base (foundation course)- roadbase (structural course)- combination of the two

Subject to the nature of the existing road foundationmaterials and the ability to stabilise these materials, therepair of the structural layers of a road pavement byrecycling is an opportune time to improve the overallstructural life of the pavement by increasing its effectivethickness and structural life capability to avoid majormaintenance for the next 20 to 40 years. Whereverpossible, the recycling alternative should make maximumuse of the existing construction materials and thus,minimise imported material products.

3.2 Current specifications

In-situ recycling processes, typically, produce theStructural Course (also known as the roadbase) and thefoundation platform (also known as the sub-base) in oneoperation. Therefore the conventional specifications forthese two pavement layers are frequently not applicable tothe in-situ recycling technique. However, currentspecifications and design manuals do address the processin the terms of conventional terminology and their contentsare summarised as follows.

3.2.1 Sub-base materialsCold in-situ recycling is currently considered appropriatefor cemented sub-bases as CBM1 for flexible pavementsand CBM2 for flexible and flexible composite pavements(DMRB (HD 25/94); MCHW 1). For any design trafficlevel; any reclaimed surfacing, roadbase, sub-base orcapping material could provide 100 per cent of theaggregate for a new CBM1 or CBM2 sub-base producedby in-situ pulverisation and mixing.

3.2.2 Roadbase materialsCold in-situ recycling is currently considered appropriatefor foamed bitumen bound roadbases for flexiblepavements (DMRB (HD35/95) (HD31/94); MCHW1). Fortraffic levels up to 5 msa; any reclaimed surfacing,roadbase, sub-base or capping material could provide 100per cent of the aggregate.

For flexible composite reconstruction the minimumseven day compressive strength requirement for thecement bound roadbase is 10 N/mm2. The MCHW1specifies that such material be plant mixed and thereforethe technique of in-situ recycling is precluded for thesepavement types.

3.3 Implementation procedure

The life cycle and deterioration of the foundation platformand/or structural course of a highway pavement usuallyoccurs over an extended period, during which time thestructure of the overlying pavement may be reconstructedand/or overlaid using an assortment of techniques; leavingin place a variety and mixture of materials.

* For the purposes of this report and in line with common practice

within the United Kingdom the bitumen binder referred to is foamed

bitumen, however in a world context bitumen emulsions are also

frequently used.

7

Furthermore, the foundation platform and structurallayers are often composed of materials of outdatedspecification comprising unbound granular and opentextured bituminous materials. Therefore, prior to recyclingwork, it is vitally important that the site is evaluated toidentify the nature and consistency of the materials presentin the layers provisionally selected for recycling. Guidanceon the evaluation of the site, including assessment of thereclaimed materials, is given in Section 4.

Environmental issues referred to in Section 2 must alsobe addressed, and any wastes or potential wastes identifiedand classified for either storage or disposal. In appropriatecases, the presumption would be to obtain an exemptionfrom the regulations to store the reclaimed materials, if thematerials were likely to be suitable for recycling. Guidanceshould be sought from the local Waste RegulationAuthority to verify the ‘waste definition’ related toparticular materials.

The next stage is to evaluate the structural designoptions in relation to the nature of the reclaimed materialand different materials that may be manufactured fromthese reclaimed materials by recycling.

The structural design thicknesses for materials producedby cold in-situ recycling have been developed by buildingon recent experience gained by the UK recycling industryand by reference to design procedures used in othercountries. Ideally, the subgrade reaction to traffic loading,design traffic level, speed of traffic and the characteristicstrength properties of the recycled materials, should all betaken into account in the design procedure. However, theirparticular influence is not always clear.

It is recognised that the use of in-situ recycling techniqueswill necessitate additional site and material assessments tominimise risk and that greater effort for checkingspecification compliance is likely to be beneficial inmaintaining the standard of the end product. However, theextra investigational work and testing, must be balancedagainst the potential financial savings associated with re-using materials as well as the environmental benefits.

4 Site evaluation

4.1 Identification of sites for structural maintenance

The reasons for first assessing that a road pavement is inneed of structural maintenance may be various, fromsimple visual inspection to advanced deflectionmeasurement surveys. Although a great deal of usefulinformation may already be provided by these surveys,irrespective of the remedial strategy ultimately decided,sites should be identified for maintenance in terms of:

l Location;

l Length of deterioration;

l Width of deterioration;

l Type and severity of deterioration;

l Condition of drainage; and

l Edge detail and verge condition.

In the event that the deterioration is identified as being afailure of the road haunch, the site assessment should becarried out in accordance with the advice contained in thefollowing documents:

Road Haunches: A Guide to Maintenance Practice[Published Article PA/SCR243, TRL, 1994].

Practical Guide to Haunching [County Surveyor’sSociety, Report ENG/1/9, 1991].

Road Haunches: A Guide to Re-useable Materials [TRLReport TRL216, 1996].

If the deterioration is identified as being a structuralfailure of the road in the running lane(s), then the issuesraised in Flow Chart A should all be addressed, to decidewhether the site is suitable for structural maintenance usingthe cold in-situ recycling process. To answer thesequestions, the site evaluation should be organised andimplemented as described below.

4.2 Investigation of existing pavement construction

4.2.1 General considerationsIn keeping with the environmental objectives, each siteshould be investigated with a view to determine thesuitability of the existing materials for re-use; either asreclaimed raw materials for re-use elsewhere or for in-siturecycling. Therefore a thorough assessment should bemade of the existing pavement materials, either separatelyor as a mixture, to determine whether or not, all or part ofthe reclaimed product is acceptable for re-use.

The investigation methods and techniques described inHD 30/97 (DMRB 7) may be used as the basis of thedetailed assessment. However, the site work and laboratorytesting will need to be adapted to suit the recycling processand related to the particular site conditions. Previousexperience has shown that a properly conducted siteevaluation for cold in-situ recycling, followed by thelaboratory design process and enhanced quality controltesting during the works, is essential if a well engineeredsolution is to be completed.

4.2.2 Job sizeThe recycling of a road pavement necessitates the use of asubstantial amount of plant and equipment unique to suchworks, which involves significant mobilisation costs.Therefore, in order to achieve the economies of scaleoffered by this process, it is desirable that each job size isabove a suitable minimum area or can be combined withsimilar works in the nearby district. A minimumprogramme of work in the order of 3,000m2 is offered as areasonable guide, but in particular circumstances, whereconventional methods of reconstruction are onerous orprecluded, smaller scale recycling works may still offer analternative cost effective solution.

4.2.3 Depth of existing pavementThe use of the cold in-situ recycling process will alsonormally depend on whether there is sufficient thickness ofexisting pavement to accommodate the designed thickness

8

Flow Chart A: Site Evaluation

No

Structural maintenance byconventional reconstruction

Structural maintenance bycold in-situ recycling

Is the site of sufficient area towarrant the use of cold in-situ

recycled material ?[see 4.2.2]

No

Is the existingpavement of

sufficient depth?[see 4.2.3, Table 6and Figures 1 & 2]

Yes

No Is the subgradesuitable for inclusion

in the recycledmaterial and

the CBR >2% ?

No

YesYes

Does the pavement contain materialsuitable for pulverisation ?

[see 4.2.5]

No

Yes

Is the pulverised aggregateconsistent?[see 4.2.5]

Central plant recycling inwhich the pulverised

aggregate is processedNo

Yes

Is it possible to design a mixture ofsuitable strength/stiffness ?

[see section 5]

Recycled as an alternativematerial

No

Yes

Can underground services besafeguarded properly or moved

economically ?[see 4.2.7]

No

Yes

Can finished roadlevels be raised ?

No

Yes

Import secondary aggregate tosupplement existing pavementmaterial prior to pulverisation

No

No

No

No

No

No

No

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

9

of the reconstructed structural course, with remainingunderlying material to act as a suitable foundation.

Although, in situations where the depth of the existingpavement is insufficient to accommodate the newpavement design and the finished level cannot be raised, itmay be possible to include the existing subgrade into therecycled material, in which case, the pulverised mixturemay contain cohesive fines that require additionalmodification prior to stabilisation. Alternatively, if thefinished levels can be raised, the required pavementthickness may be achieved using imported secondaryaggregate material.

4.2.4 Investigation frameworkThe fieldwork needed to achieve a reasonable level ofconfidence will depend on the specific site conditions, butin general, trial pits excavated at a frequency of not lessthan 1 per 500 m2 should suffice. However, particularattention should be paid to unsupported edge conditionsand areas where previous reinstatements have been made,since these are likely to contain variable materials,possibly of poor quality, including contamination bysubgrade soils which may be cohesive in nature. In thesesituations, the location and frequency of trial pits should bedecided on site and/or intermediate cores extracted, ofsufficient size and number, to determine the full extent andnature of the various material conditions.

Trial pits must be of sufficient size and depth to providea clear view of the consistency and thickness of the variousconstruction materials. Also, to allow extraction ofadequate representative material for laboratory testing todetermine factors such as:

l Atterberg limits, natural moisture content and CBR ofthe subgrade;

l thickness and nature of the various pavement andfoundation layers;

l grading of the pulverised aggregates available as rawmaterials for the recycled mixture, and

l compressive strength of lean concrete bases if suspectedof being too strong for planing or pulverisation. (i.e.compressive strength greater than 15 N/mm2.)

Guidance for the site investigation requirements for coldrecycling projects on medium to heavily trafficked sitesare given in Table 1. Whereas a similar logic exists forinvestigation of lower trafficked sites, in practice the rateof sampling and testing for these roads may besubstantially less, to reflect the relative importance andvalue of the works involved.

4.2.5 Suitability and consistency of existing materialsWhere available, as-constructed records are always useful,but it is important to carry out sufficient cores or trial pits tocheck these data, since the actual as-constructed situationdoes not always reflect in detail, what was recorded or anysubsequent changes that may have taken place since.

Modern designed pavements are normally consistentand contain only a small number of standard materials. Forolder pavements, however, that have been built up and

altered over many years, construction details are mostlyunknown and often exhibit significant changes withinshort distances. In these cases the site assessment andrecycling design process is particularly difficult, since aseparate mixture design is required for these areas definedboth by plan areas and depth. However, dependent oftraffic loading, a judgement needs to be made of theimportance of such detailed design, particularly for trafficloading below 2.5msa (Type 3 and 4 roads).

Non-destructive testing of the existing pavement bysuch techniques as deflection testing, visual assessmentand the use of ground penetrating radar are recommended,in conjunction with the cores and trial pits, to determinethe consistency of the pavement layers throughout the site.Ground radar, may be particularly useful in indicatingchanges in construction layer thicknesses and the locationof density and moisture content anomalies.

In the event that the existing pavement materials arerecognised in general to be re-usable as a pulverisedaggregate but too inconsistent to allow any reasonabledesign, section by section, consideration may be given tothe alternative recycling process using plant mixedmaterial. In this process the opportunity is available toclean and process the existing variable materials in to areconstituted well graded aggregate (Table 1).

4.2.6 Preparation of representative test specimensFor any assessment related to the design of recycling works, itis particularly important that any sample obtained is fullyrepresentative of the pavement to be recycled. The sample canbe obtained as a mixed sample or in separate components, forrecombining later in appropriate proportions.

Furthermore, test specimens should ideally berepresentative of the aggregate obtained by pulverisationor planing, for both grading and particle shape. However,since actual

pulverised aggregate is not generally available duringthe pre-contract investigation, the design process must relyon test specimens derived from samples crushed in thelaboratory. A variety of laboratory crushing methods arecurrently available, however, none are believed to bespecifically designed to recreate the pulverised aggregateproduced by a recycler or planer.

Modern pulverisers and planers, however, tend toproduce aggregates of finer grading

when compared with pulverised material from oldermachines, related to the power and effectiveness of themilling process. Therefore, separate guidance from theplant manufacturer may be necessary.

4.2.7 Underground servicesBecause of their disruptive potential within in-situ recyclingworks, particularly if disturbed or damaged, it is vital toaccurately locate and record the depth of all undergroundservices. If a pipe or cable lies within 150mm of formationlevel, it should be deemed at risk, particularly if the servicesare old. It is prudent, therefore, to consult with theStatutory Undertakers at an early stage of the designprocess. Although, additional enquiries and investigation

10

will probably be needed to establish the location and depthof service connections to adjacent properties, since theseconnections are often unrecorded and are at a shallowdepth in relation to the depth of the mains supply.

If premature deterioration of the existing road has beencaused by damaged or defective services, any suchproblem should be remedied before or as part of thepavement renovation contract.

4.3 Risk assessment

The use of recycling techniques uniquely involves a numberof risks which should be assessed prior to implementing anywork. These risks are often difficult to quantify in terms ofany standard measure, but their consideration and equitableallocation may provide the best chance for improved designand supervision techniques.

In all types of construction work, even wherecomprehensive site evaluation has been carried out, there

Table 1 Guidance on site investigation requirements for cold in-situ recycling projects on medium to heavilytrafficked sites

Pavement type/condition Fieldwork proposals Sampling and testing

Designed pavement structure comprising Excavate trial pits at a target frequency of 1 per Collect sufficient representative material from eachstandard materials of known thickness and 200m in each of the lanes to be recycled, with a construction layer to produce a 100 kg bulk sampleconsistency. minimum of three pits for any scheme. comprising proportionally recombinedmixture of

materials from all trial pits.

Record details of each construction layer, Use bulk sample for design and trial mix tests.including any unbound foundation. Obtainseparate representative samples of eachdistinct material.

Determine the nature and condition of thesubgrade and obtain a measure of bearingstrength.

Designed pavement structure comprising As above. As above, with additional representative bulkstandard materials of known thickness samples from each distinct area of reinstatement/and consistency - but with reinstatement Plus one trial pit or full-depth 200mm diameter repair, used to produce additional recombined bulkof openings or pavement repairs that could core from each distinct reinstatement/repair samples to assess any mixture design changes thatlocally affect the consistency of the that has an area greater than 25m2 or extends may be needed in these areas.pulverised aggregate. full width for more than 5m in any lane.

Plus minimum of one full-depth 200mmdiameter core from smaller, closely spaced andrecurrent areas of reinstatements, where theircombined area locally, accounts for more than20 per cent of the paved area in any lane.

Undesigned pavement structure comprising Carry out an initial evaluation by extracting Visually assess the material retrieved from thea variety of standard and/or non-standard full-depth 200mm diameter cores at target initial cores to decide on the consistency ofmaterials built over time by maintenance frequency of 1 per 100m in each lane to be materials.processes, in layers/zones of unknown recycled.thickness or continuity. For a consistent material profile use the materials

If materials are consistent proceed with design from the cores to produce a proportionallyusing the material from the cores as the test representative 100 kg bulk sample for overallsamples. design and trial mix tests.

If pavement structure is inconsistent, carry out For inconsistent material profiles, collect sufficientfurther investigations to try to determine the representative material from each construction layerfurther investigations to try to determine the in each of the defined sections to produce 100 kgextent and/or thickness changes of the different bulk samples comprising proportionallymaterials. As an alternative to widespread recombined mixtures of materials from eachcoverage of further cores, traverses of ground section.penetrating radar may be found useful to revealthickness and profile changes, to help divide Use bulk sample from each section for separatethe site into reasonably consistent sections and design and trial mix tests.target the position of trial pits and/or furthercores.

Investigate each section using a minimum of threetrial pits or three sets of three full-depth 200mmdiameter cores, dispersing evenly throughoutthe section, with at least one trial pit or core ineach lane to be recycled. Obtain representativesamples from each layer from each section.

11

will always remain those sites where unsuspectedsituations arise.

However, for recycling works, such situations are morelikely to play a part in the final outcome, since thematerials present are intended to form part of the finishedworks. Furthermore, for cold in-situ recycling, thepotential for variability of materials to be included in theworks can be higher.

To offset this risk, greater understanding of shared riskshould be accepted, where both parties to the contract aregiven the opportunity to satisfy themselves and agree thatthe existing pavement materials in the sections of theworks defined by the contract, are capable of beingrecycled by pulverisation to form the primary aggregatecomponent of the new in-situ recycled mixture. Also, thatthe recycled mixture is capable of being designed andproduced to meet the specified end-product performancerequirements.

However, for the purposes of competitive tenderarrangements, the Client is normally expected to organiseand implement the site investigation works separately, aspart of the general design process. In these circumstances, ifrisk is to be shared, the investigation must becomprehensive, and offer all potential contractors suitabledata for designing and programming their individual methodof working, appropriate to the particular site conditions.

The risks associated with any particular pavementrecycling scheme also need to be assessed in the light oflikely life cycle costs. In which case, experience to datehas indicated that even where quite pessimistic projectionsfor the service life of cold in-situ recycled pavements areused, significant whole life cost savings are possible.

Risks can be broadly classified into design andconstruction risks.

4.3.1 Design risksA comprehensive site investigation needs to be carried outto minimise the risks in the calculation of the design of thepavement structure, including a detailed subgrade studylooking at such aspects of moisture, density and strength ofthe subgrade where these properties need to be takenaccount in the design process.

The fatigue life of cemented pavements is very sensitiveto thickness and stiffness. It is imperative that thepavement thickness design and material parameters areachieved in construction otherwise substantial reductionsin performance may occur. Also, the type of binder willaffect the workability and setting time which is importantin being able to achieve the required layer density.

The foamed bitumen or cement content will alsoinfluence the stiffness and strength of the recycled mixture.An inadequate quantity may lead to the material beingsusceptible to moisture, whereas too much bitumen couldlead to premature deformation problems or too muchcement to increased likelihood of thermal cracking.

4.3.2 Construction risksBecause the recycling process is generally much quickerthan conventional reconstruction techniques, there is a

corresponding reduced risk as a result of exposure of thelower pavement layers to inclement weather and trafficduring construction.

One of the most critical parts of the constructionprocedure is the compaction of the recycled material. Anydelay after mixing or poor selection or use of compactionequipment may lead to a substantial loss of serviceabilityof the finished pavement due to reduced levels ofcompaction and consequential loss of stiffness.

In urban situations, the risk of causing nuisance andpossible risk to health by dust must be assessed whenrecycling by pulverisation. In addition, the effects from theuse of the pulveriser and large compaction plant need to beconsidered and monitored if works are adjacent tounderground services and buildings or other structureslikely to be damaged by high amplitude vibrations.

5 Design of cold in-situ recycled material

5.1 Pulverised aggregate

The nature and grading of the aggregate produced bypulverisation using any of the recycling machinescurrently available, will depend largely on the nature,thickness and proportions of the existing road material tobe recycled. Although, in situations where the depth of theexisting pavement is insufficient to accommodate the newpavement design and the finished level cannot be raised, itmay be necessary to include subgrade material into therecycled structural layer, in which case, the pulverisedmixture may contain a cohesive soil component thatrequires modification using lime or cement prior tostabilisation. Alternatively, if the finished levels can beraised, the required pavement thickness may be achievedusing imported aggregate, which could also be derivedfrom other recycling works in the locality.

5.1.1 GradingIdeally, the particle size distribution of the pulverisedaggregate, immediately prior to stabilisation, including anysupplementary aggregate and/or filler, should be equivalentto a uniformly graded aggregate of 50mm nominal size,complying with the Zone A grading envelope described inTable 2. However, in a recycled aggregate there is thelikelihood that a significant proportion of particles arebroken pieces of the original material, comprising aconglomerate of aggregate and old binder.

In certain circumstances, pulverised aggregate fallingwithin Zone B grading envelope may be acceptable,provided the results of mixture design tests demonstratethat an acceptable recycled material can be producedconsistently using this aggregate.

For cement bound recycled material, the aggregatecomponent may consist of reclaimed aggregate made from100 per cent of bituminous surfacing, roadbase, sub-base,capping or subgrade material. Normally, the cement boundrecycling option is relatively insensitive to the aggregategrading, nevertheless there is a recommended upper limitof 35 per cent passing the 75 micron BS sieve.

12

In comparison, bitumen bound recycled material is oftenhighly sensitive to the pulverised aggregate grading,particularly the fines component. In recycled mixtures thebitumen has a tendency to mix and conglomerate with thefines while only partially coating the coarse aggregatecomponent. As a result, it has been found that the amountpassing the 75 micron BS sieve should ideally, berestricted to the range of not less than 5 per cent and notmore than 20 per cent, none of which should be clay.

Finer material may be tolerated, provided any clayfraction is modified by treatment with lime or cement toform a non-cohesive component. This pre-treatment wouldnormally be required if the percentage of pulverisedaggregate passing the 75 micron BS sieve was greater than20 per cent and the Plasticity Index of the material passingthe 425 micron BS sieve was greater than 6. Conversely,any material that is too coarse may be modified to meet thedesired grading, by augmenting the finer material usingeither pit sand or PFA as a filler.

5.1.2 Moisture contentThe moisture content of the pulverised aggregate prior tostabilisation is equally important as grading, since it is ofprimary importance in controlling the workability of themixture and therefore, governs the degree of compactionthat may be achieved. The optimum moisture content wouldnormally be considered as the target moisture content, but inpractice for recycled mixtures, the specified moisturecontent depends to a certain extent, on the binder used andwhether a filler has been added in any great quantity.

For cement bound mixtures, experience has shown thatthe best results are obtained by targeting a moisture contentin the range 0% to +4% of optimum moisture contentdetermined in accordance with BS 1924: Part 2: 1990. Asexpected, this achieves a workability higher than wouldnormally expected for conventional CBM, but is required ifthick-lift, full-depth compaction is to be achieved. However,

enhancement of the density may be countered by a lowercompressive strength resulting from the changed water/cement ratio. In those cases where only small proportions offiller are mixed with the pulverised aggregate, the optimummoisture content of the pulverised aggregate will normallysuffice as the control datum, since the moisture absorbed byfiller is mostly balanced by the suppression of the optimumvalue. Where the addition of filler accounts for more than 4per cent by mass, the moisture control datum should bebased on the optimum moisture content of the pulverisedaggregate including the filler.

For the pulverised aggregate stabilised using foamedbitumen binder, the ‘fluid’ component of the binder willenhance the workability of the mixture and aid the thicklift compaction of the material. Therefore, a targetmoisture content in the range ±2% of optimum moisturecontent, determined in accordance with BS 1924: Part 2:1990, is considered appropriate to achieve adequate thick-lift, full-depth compaction. Also, where more than 4 percent by mass of adhesion agent and/or filler are added tothe pulverised aggregate, the optimum moisture contentshould be determined using the modified aggregate.

Where the moisture content prior to stabilisation fails tomeet the target range, the moisture content should beadjusted either by aeration to reduce the moisture contentor by controlled addition of water, if the moisture contentis lower than required. For the cement bound material, anycontrolled addition of water may be carried out at the sametime as the stabilisation pass of the recycling machine, butin these circumstances a greater degree of care and controlare needed to ensure that the single pass operation iscompleted without mistake.

5.2 Primary binder agent

The majority of the cold in-situ recycling works completednationally have used hydrated lime or Portland cement asthe primary binder agent. More recently, because of theparticular health and safety issues assigned to the use oflime and the problem of thermal cracking in the strongercement bound structural layers, a variety of alternativebinder agents have been used, including bitumen emulsion,foamed bitumen and slow curing hydraulic binders.

However, for the purpose of this guidance documentrelated to UK conditions, only foamed bitumen or Portlandcement are recommended for use as the primary binderagent. The process of selection between these binders isoutlined in Flow Chart B.

5.2.1 Portland cementPortland cement as a binder for in-situ recycling works toproduce a flexible composite pavement structure, isadaptable to most conditions and apart from the thermalcracking of stronger mixes, it has the following advantages:

l readily available at reasonable cost;

l current accepted methods of working to satisfy H&Srequirements;

l is generally suitable for mixing with a wide range ofpulverised aggregates comprising existing pavementmaterials;

Table 2 Particle size distribution of granular materialfor cold in-situ recycling

Percentage by mass passing

Sieve size (mm) Zone A Zone B

50 100 –37.5 94 - 100 –20 66 - 100 10010 48 - 75 75 - 1005 35 - 57 57 - 952.36 25 - 42 42 - 770.6 13 - 28 28 - 520.3 10 - 24 24 - 450.075 5 - 20 20 - 35

i Zone A material - ideal material.ii Zone B material - suitability of material from this zone is subject to

the results of material performance tests on trial mixtures.

iii Granular material to be stabilised should contain not more than 2%of organic matter determined in accordance with BS 1377: Part 3:Clause 3.

iv Aggregate grading should have a coefficient of uniformity [Cu]exceeding 10.

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Flow Chart B: Primary Binder Agent Selection

Design using Portland cementas the primary binder agent inaccordance with SpecificationClause C2.

Structural maintenanceby cold in-situ recycling

Does the pulverised aggregate containover 20% passing the 75 micron BS

sieve and do fines passing 425 micronBS sieve have PI >6 ?

YesPre-treat with hydrated lime orcement to produce non-plastic

aggregate

No

Is there any doubt about the binderto use ?

Yes

No

Design using foamed bitumenas the primary binder agent inaccordance with SpecificationClause B2

Is the subgrade free from movementcaused by seasonal moisture

content changes ?

Is groundwater likely to rise withinthe pavement structure ?

No

Yes

No

Yes

Overriding engineering preference or decision basedon providing a cost effective and practical solution.

Yes

Yes

Yes

Yes

No

No

No

No

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l tolerant of adverse wet weather (often the case in the UK);

l tolerant of contamination by plastic fines and organicmaterial; and

l may be used, based on the Highways AgencySpecification for Highway Works (MCHW1) clauses foreither cement stabilised or cement bound materials andthe standard design criteria for these materials.

5.2.2 Foamed bitumenFoamed bitumen as a binder for in-situ recycling works toproduce a flexible pavement structure, is adaptable to awide range of situations, although if there are any doubtsthat foamed bitumen may not perform satisfactorily,cement is likely to offer a safer option where adverseconditions exist. However, foamed bitumen binder offersthe following advantages:

l significant energy savings compared with conventionalhot-mix materials;

l is generally suitable for mixing with a wide range ofpulverised aggregates comprising existing pavementmaterials;

l same day construction cycle to completion, with noextended curing period;

l less susceptible to moisture content than bitumenemulsion; and

l can be stockpiled, relocated and reworked if necessaryin their early life.

The original method of producing foamed bitumeninvolved the expansion of a paving grade bitumen into afoam by the injection of saturated steam. But to provide amore controlled expansion and increased bubble life, apatented system was developed involving the injection ofbetween 1 and 2 percent cold water under controlledconditions and with air and foaming agents into a hotpenetration grade bitumen stream, through speciallydesigned nozzles and spraybar (Lee, 1980).

An increase in the bitumen foaming temperature or thewater content has the effect of increasing the expansionratio but decreasing the life of the foam bubbles. Toprovide the best combination for useful application, acompromise between expansion ratio and life of the foambubbles is required.

It is possible to use penetration grade bitumen fromgrade 40 to over 200 as the base bitumen for foaming.Higher penetration grades tend to foam better, but thelower grades produce material of higher stiffness. Onbalance, the foamed bitumen recommended for cold in-siturecycling is based on penetration grade 100, as the binderthat achieves the highest stiffness, consistent with areasonable coating ability.

The significant properties of the foamed bitumen are:

l low apparent viscosity;

l ten fold increase in volume over volume of hot liquidbitumen; and

l lower surface or interfacial tension.

It is these properties that enable the bitumen to coat moist,cold aggregate surfaces, particularly the fine aggregate

portion. The resultant mixture is easily worked cold and canbe readily compacted with conventional roller compactionplant. The process does not require the evaporation of asolvent or excess water prior to compaction and the materialcan be reworked if necessary up to about 48 hours afterprocessing.

The curing regime of foamed bitumen mixtures iscritical for long term success since these materials relymuch upon early life strength for ongoing development ofstiffness properties. However, provided that the densityachieved is at least 95 per cent refusal density, opening totraffic can be achieved in a one day construction cycle.

5.3 Prelimary mix appraisal and design process

The design procedures adopted to date, have beendeveloped by various organisations for their own localneeds, although in general, most design processes for in-situ recycled material are based on the determination ofcompressive strength for cement bound material or thestiffness modulus for bitumen bound material, for arecycled layer of specified thickness, to carry a requiredtraffic loading over a period of time.

In practice, since the material to be stabilised does notexist until after the pulverisation process, the initial mixappraisal or design process often becomes a matter ofexperience by the specialist contractors using theirparticular pulverisation/stabilisation plant, to gain anunderstanding of the near optimum component design.

Also, since the results of strength, stiffness and othertests performed on laboratory prepared specimens arehighly dependent on the curing regime of the specimens,which is unlikely to be recreated on site, these tests arevalid only for comparison and assessment of the optimummixture condition. The values obtained do not necessarilyrelate to the in-situ condition of the material.

Furthermore, where the site evaluation has identifiedsignificant and discrete variation of existing pavementmaterials between different sections of the site, eachsection should be subject to a separate mixture design.

Details of the procedures to carry out a preliminary mixappraisal and design, for both cement bound and foamedbitumen bound materials are given in the relevantspecifications in Part 2 of this report. At this stage, theserequirements are based on the current industry practices,but are open to development if more representativespecimens and test results can be verified.

For the preliminary mix appraisal, the source material isobtained from bulk representative samples extracted fromthe road during the site evaluation. Each appraisal willrequire at least 100kg of proportionally representativesource material.

Each aggregate sample is crushed and processed in thelaboratory to produce a ‘pulverised aggregate’ test specimenhaving a particle size distribution curve meeting the Zone Aor Zone B grading as described in Table 2. There arecurrently a variety of laboratory crushing methods used,including the simple mechanical vibratory hammer approach.However, no crushing system has been specifically designedto recreate the pulverised aggregate produced by the recyclingmachine or planer. Therefore, where it is found difficult to

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achieve sufficient crushing of the recycled aggregate samplein the laboratory, to obtain sufficient fine material, (which isoften the case where the existing road materials containHRA), a suitable quantity of fine material, either crushed rockfines, pit sand or PFA, may be added and thoroughly mixedwith the crushed material, to obtain the required grading. Thefiner grading should not be achieved by excessive laboratorycrushing, since this would not reflect pulverisation in thefield, which tends not to cause breakage of the existingaggregate component.

Ideally, the optimum moisture content of the pulverised andmixed aggregate is determined in accordance with BS 1924:Part 2: 1990. In the laboratory trial mixtures, sufficient watershould be added to target the optimum moisture content, withappropriate allowance made for any change to the optimumcondition caused by additives to the mixture. If lime isrequired for stabilisation and/or modification of any plasticsoil component within the mix, the correct proportions of soiland lime should be included in the trial mixture.

5.3.1 Cement bound recycled materialsFor lower traffic situations, cold in-situ cement boundrecycling is often used to provide a new foundation and/orstructural course which would be designed to have anaverage 7 day cube compressive strength of 4.5 N/mm2 or7 N/mm2 (i.e either CBM1 or CBM2 equivalent). Innormal circumstances, this recycled layer would then beoverlain by surface dressing or plant mixed bitumen boundmaterials to form a new pavement at a higher level.

For higher traffic loading, used as the main structuralcourse, the recycled layer would normally be designed tohave an average 7 day cube compressive strength of 10 N/mm2 (i.e CBM3 equivalent). In theory, this could beconsidered structurally equivalent to plant mixed CBM ofequal compressive strength. In practice, however, the in-situ recycling process is subject to potential problems andincreased risks that are less applicable to the plant mixedoption, including:

l variability of aggregate grading;

l non-uniformity of distribution and mixing of bindingagent;

l variability of moisture content, often dependent onweather;

l variability of recycled thickness; and

l difficult compaction at bottom of thick lift construction.

In consequence, the design thickness used for earlierrecycling works in the UK was based on a factor of safetyof 25 per cent applied to the design thickness forequivalent plant mixed material (Walsh 1988). Later workstended to use a factor of 20 per cent, including the designof phase 2 of the A3088 Cartgate Link road trial.

For the stronger recycled structural course mixtures, thepotential for thermal cracking and reflective cracking ofthe bituminous surfacing, is the same as that forconventional plant mixed CBM. To restrict or overcomethis problem, consideration could be given to the processof inducing transverse cracks in the structural course priorto laying the surfacing materials.

The cement contents used to manufacture the sets of testspecimens should normally be similar to the plant mixedequivalent, except in the case of in-situ recycled mixtureswhere a minimum cement content of 3 per cent by weightis recommended. This absolute minimum value is appliedto ensure there is adequate cement available fordistribution throughout the mixture during the relativelyshort period of in-situ mixing. Subject to this minimumvalue, the designed cement content will normally be theminimum cement content that achieves the requiredaverage compressive strength.

To ensure durability of the material in the presence ofadverse groundwater conditions, the average compressivestrength determined after 7 days immersion in water of fivetest specimens of the target composition mixture, should notbe less than 80 per cent of the average compressive strengthof five control specimens when subjected to the testprocedure described in BS 1924: Part 2: 1990, clause 4.3.Furthermore, after the 7 days immersion the test specimensshould show no signs of cracking of swelling.

5.3.2 Bitumen bound recycled materialsIrrespective of how well the in-situ recycling of foamedbitumen bound material is carried out, the nature andvariability of the materials which are the feedstock of therecycling process, will result in the recycled mixturehaving a stiffness equivalence factor of less than unity,when compared to conventional plant produced materials.Performance assessment of some of the earlier recycledpavements, using either the Deflectograph or FallingWeight Deflectometer, have indicated that the typicalstiffness equivalence factor for recycled foamed bitumenbound roadbase is in the order of 0.7 to 0.75, whencompared with dense bitumen macadam (DBM)containing penetration grade 100 bitumen.

A mixture design based on binder film thickness wouldbe inappropriate for a recycled material, since thedistribution and coating characteristic of the foamedbitumen is significantly different to that of the plant hot-mix. In general, the larger particles remain substantiallyuncoated with the bitumen adhering mostly to the finerparticles, forming a fines/bitumen mortar matrix. Thedesign principle for such material is to waterproof the finesand provide enough adhesion within the matrix to hold thematerial together and at the same time, to achieve efficientaggregate packing for low air voids content.

The optimum added foamed bitumen content ofrecycled mixtures is often not very well defined, andadequate stiffness may be obtained over a wide range ofbitumen contents. Hence the specification of addedbitumen content is not so critical and for earlier recyclingworks in the UK, a typical binder content range for eitherpenetration grade 100 or 200 bitumen was 3.5% ± 0.75%.

This target range appeared to achieve near optimumstiffness conditions for the pulverised aggregate from arange of typical UK roads in need of rehabilitation.However, in response to concerns about durability of therecycled material, related mainly to the partially coatednature of the course aggregate, an absolute minimumadded bitumen content of 3.5% is recommended.

16

Existing bitumen in pulverised aggregate would notnormally be activated in the stabilisation process in thesense of mixing with the new binder, although the effect ofthe residual bitumen in the finished mixture may influencethe stiffness achieved.

In the mix appraisal and design process, the laboratoryprepared aggregate is thoroughly mixed with measuredproportions of the appropriate foamed bitumen binder andany adhesion agent, to produce trial mixtures of differentbitumen content. The type and grade of the bitumen usedin the trial mixture should be the same as that intended forthe finished works.

To date there are no specified means for producinglaboratory manufactured foamed bitumen, particularlysince there are a variety of methods that may be used in thefield. Therefore, it is recommended that the anticipatedbitumen supplier is consulted, in conjunction with themanufacturer of any foaming agent used, in an attempt toreplicate as closely as possible, the characteristics of thefoamed bitumen to be used, particularly in terms of thesize and sustainability of the air bubbles during mixing.

At least four 150mm diameter x 75mm to 100mm high,cylinder test specimens (briquette specimens) should beproduced for each of the trial mixtures, compacted torefusal by vibratory compaction in a cylindrical metalmould, using the compaction mould assembly andvibrating hammer described in BS598: Part 104.

Also, because of the relatively small size of the cylindertest specimens, great care is required in ensuring a uniformdistribution of the courser aggregate particles within thetest sample, with particular concern that the perimeter ofthe cylinder does not contain segregated aggregate, leadingto a voided load contact area in the test rig.

Regarding the specified curing programme for thespecimens prior to testing, including baking of thespecimens for 72 hours at 600C, this is not an attempt torepresent the curing conditions in the field, but is astandardised attempt to model the longer term ageingprocess of the recycled material. The drawback of usingthe baking technique is that it can disguise the true earlylife stiffness of the recycled material, in favour of a higherset of values that may be appropriate in the longer term.

6 Pavement design

6.1 Definitions

In the context of structural maintenance of highwaypavements using cold in-situ recycling, whilst carrying outthe same function, a standard pavement layer may beconstructed significantly differently to that of a same layerin a new pavement. Therefore, the broader definitionsapplicable to this report are:

Subgrade: Underlying natural soil or rock.

But in the situations where the subgrade is weak orthere is insufficient depth to the existing pavement,the upper layer of the subgrade may be stabilisedusing the in-situ recycling technique andincorporated as part the foundation platform.

Foundation platform: A layer which protects the subgradeand provides a consistent stable platform upon which thestructural course can be adequately compacted.

This layer will normally comprise the undisturbedlower sections of the existing pavement. But insituations where there is insufficient depth ofexisting pavement to satisfy the current design, thisplatform may be constructed in part or whole, usingcold in-situ recycling.

Structural course: The main stress distribution layerwithin the pavement whose thickness is dependent onstiffness of the material itself, stiffness of the underlyingstructure and the traffic loading.

This layer will normally comprise cold in-situ recycledmaterial, but where there is insufficient depth ofexisting pavement and the in-situ recycled material isused to form the foundation platform, it may comprisein part or whole, new plant mixed material.

Surfacing: The upper layer or layers of the road, designedto provide an even surface with a high resistance todeformation and an adequate resistance to skidding.

6.2 Road categories

As a starting point in any design, it is necessary todetermine the category of the road to be recycled. Thisdepends on the amount of commercial traffic to be carriedin one lane, or one direction, over a 20 year design life.The categories are given in Table 3 and are the same asthose specified for the HAUC specification forreinstatement of openings in highways (1992).

Table 3 Road type categories

Road type category Traffic design standard (msa)

1 More than 10 up to 30*2 More than 2.5 up to 103 More than 0.5 up to 2.54 Up to 0.5

* The research to date for in-situ recycling has been for traffic levels upto 20 msa; engineering judgement must be used to increase designtraffic loading.

Guidance on how to assess the traffic levels is given inTRL Report TRL216 (Potter, 1996)

In addition the design criteria and specification complianceprogrammes for the different traffic loadings are as describedin Flow Chart C for cement bound recycled material andFlow Chart D, for foamed bitumen bound materials.

6.3 Design for Type 1 and Type 2 roads

For Type 1 and Type 2 roads, the design of the structuralcourse using cold in-situ recycled material, assumes thatthe existing pavement contains a foundation platformequivalent to those given in Table 4.

Where the thickness of the existing foundation is foundto be below the requirements of Table 4 it may be possible

17

Flow Chart C: Design criteria and specificationcompliance programme for in-situ cement boundrecycled material

Design criteria andspecificationcompliance for in-situcement boundrecycled material

0.5msa to2.5msa

Type 3 road

2.5msa to5msa

Type 2 road

10msa to20msa

Type 1 road

Traffic loading and road type

5msa to10msa

Type 2 road

Mean minimum7 daycompressivestrength of4.5 N/mm2

Mean minimum 7 day compressivestrength of 10 N/mm2

Thickness as described in Figure 1

Mean minimum7 daycompressivestrength of10 N/mm2

Thickness asdescribed inFig 1

Is thepulverisedaggregate

uniform and ofgood quality ?

NoYes

Specification complianceachieved by process controltests in accordance withsub-clauses 30 to 32 ofClause C1.

Specification compliance achieved byprocess control tests in accordance withsub-clauses 30 to 32 of Clause C1 ( butwith compressive strength test ing optional)and by end-product performance tests inaccordance with sub-clauses 33 to 42 ofClause C1.

Less than0.5msa

Type 4 road

20msa to30msa

Type 1 road

Thickness may be governed by existingpavement thickness and subgrade condition,but subject to a minimum recycled thickness of150mm.

Thickness of surfacing may be offset againstrecycled thickness as described in Table 9.

Mean minimum7 daycompressivestrength of7 N/mm2

Mean mimimum7 dayscompressivestrength of10 N/mm2

Thickness asdescribed byprovisional designline shown dottedin Figure 1

NoYes

18

Flow Chart D: Design criteria and specificationcompliance programme for in-situ bitumen boundrecycled material

Design criteria andspecificationcompliance for in-situbitumen boundrecycled material

0.5msa to2.5msa

Type 3 road

2.5msa to5msa

Type 2 road

10msa to20msa

Type 1 road

Traffic loading and road type

5msa to10msa

Type 2 road

Mean minimumITSM of2000MPa

Mean minimum ITSM of 2500MPa

Thickness as described in Figure 2

MeanminimumITSM of2500MPa

Thickness asdescribed inFigure 2

Is thepulverisedaggregate

uniform and ofgood quality ?

NoYes

Specification complianceachieved by process controltests in accordance withsub-clauses 33 to 47 ofClause B1. Specification compliance achieved by

process control tests in accordance withsub-clauses 33 to 47 of Clause B1 ( butwith sub-clauses 44 and 45 optional) andby end-product performance tests inaccordance with sub-clauses 48 to 51 ofClause B1.

Less than0.5msa

Type 4 road

20msa to30msa

Type 1 road

Thickness may be governed by existingpavement thickness and subgrade condition,but subject to a minimum recycled thicknessof 150mm.

Thickness of surfacing may be offset againstrecycled thickness as described in Table 9.



Thickness asdescribed byprovisionaldesign lineshown dotted inFigure 2

NoYes

19

to upgrade its effectiveness by incorporating an extra depthof the stabilised layer as the foundation. However, cautionshould be exercised if the attempt to upgrade the thicknessof the foundation results in the disturbance of existingmaterials that have been in place for many years; are overconsolidated and are currently performing satisfactorily asthe foundation. Furthermore, for the Type 1 and 2 roads, itis strongly recommended to avoid mixing subgradematerial into the recycled mix.

If there is any doubt as to the bearing capacity of thefoundation platform this should be determined as part of theinvestigation phase, using a Dynamic Cone Penetrometer(DCP) or similar. If found to be less than 100MPa then thethickness of the stabilised layer should be increased inaccordance with the equivalence factors given in Table 5,which relate the thickness of granular foundation to theequivalent thickness of in-situ recycled materials.

equivalent to a foundation platform comprising granularmaterial, but are deficient in thickness by 100mm, theincrease in thickness of the stabilised layer can bespecified as:

For cement stabilised recycledmaterial (10 N/mm2): = 0.45 x 100mm = 45mm

For cement stabilised recycledmaterial (4.5 N/mm2): = 1.0 x 100mm = 100mm

For foamed bitumen boundrecycled material: = 0.65 x 100mm = 65mm

The recommended depth of cold in-situ recycling for thestructural course for road category types 1 and 2 are givenin Figure 1 and Figure 2 for cement bound and foamedbitumen bound constructions respectively. These figuresrelate the design traffic loading to the thickness of thestructural course and the associated thickness of surfacing.

Where the design thickness of the recycled layer is inexcess of 225mm, which is the maximum thicknessnormally considered acceptable for the compaction of asingle lift for standard unbound and bound materials,consideration should be given to the use of heavier thanusual compactors, to avoid the situation where a densityprofile is developed, such that the lower part of the layerdoes not achieve the same density as the upper part.

This effect may be minimised when applyingcompaction at the earliest possible time using either heavyvibratory compaction or using a compactor capable of‘kneading’ the material at depth, as is the case using atamping roller. To date in the UK, heavy compaction forcold in-situ recycling works has been carried out almostexclusively using the heavy vibratory roller option,although more recently, a heavy combined pneumatic tyreroller (PTR) and vibratory drum roller has been trialed, buttheir field performance has yet to be verified.

From past monitored works, it is evident that thevibratory compaction did not always achieve full depthcompaction of thicker layers. Therefore, where thestabilised material is assessed as having a poorworkability, it is recommended that consideration be givento the use of heavy tamping rollers for the initial deep-seated compaction, particularly for layers having acompacted thickness in excess of 225mm, followed bygrading of the surface and final compaction using theconventional heavy vibratory compaction. This is similarto the compaction methodology commonly used inAustralia for thick-lift construction.

Table 4 Assumed foundation platform thickness of existing pavement of Type 1 and 2 roads

Foundation platform thickness (mm)

Subgrade CBR Subgrade CBR Subgrade CBR Subgrade CBR2-4 5-7 8-14 >15

Remaining Remaining Remaining Remainingbound bound bound bound

Granular construction Granular construction Granular construction Granular construction

300 85 250 70 200 60 150 40

However, this is an iterative process, since the increasein thickness of recycled material will cause the thicknessof foundation platform to be deminished still further,which in turn should be offset. Therefore, for designpurposes, any required increase in thickness of thestabilised layer will be determined in accordance with therespective thickness deficit factors given in Table 5.

For example, if a recycled pavement has been designedassuming that the remaining pavement materials are

Table 5 Thickness conversion factors relative togranular foundation material

In-situ recycled Equivalence Thickness deficitend product factor factor

Cement stabilised materialwith 7 day compressivestrength of 10 N/mm2 0.3* 0.45

Cement stabilised materialwith 7 day compressivestrength of 7 N/mm2 0.4* 0.65

Cement stabilised materialwith 7 day compressivestrength of 4.5 N/mm2 0.5* 1.0

Foam bitumen stabilisedmaterial with ITSM of2500MPa 0.4** 0.65

* Source BS 7533: Table 4 (1992)

** Derived from Ullidtz and Peattie (1980)

20

Use of the in-situ recycling process for traffic levels above20 msa would require extrapolation beyond reasonableexpectation. However, there is a practical thickness limit ofabout 300mm, above which, adequate compaction of a single,thick lift of recycled material would be too difficult toachieve, even using the heavy compaction process describedabove. Recycling using a two layer process is feasible, but thecompromised in-situ working, caused by the need totemporarily stockpile the top layer whilst recycling the bottomlayer, would reduce the energy saving and advantage gainedby the in-situ recycling process.

Where the subgrade CBR is less than 2 per cent the useof the cold in-situ recycling technique is not recommendedfor any level of traffic loading.

Design examples for Type 1 and 2 roads related totypical site conditions are included in Appendix B.

6.4 Design for Type 3 and Type 4 roads

This section is included for the completeness of the designguide, although the sites examined in the current studywere designed for heavier traffic loading conditions.

Therefore, the design proposals are based primarily onthe earlier findings of performance reviews reported byKennedy on behalf of the Department of the Environment,Energy Efficiency Office (ETSU 1994). The design alsotakes into account the criteria published in TRL Report216 (Potter 1996), which refers to the cold in-siturecycling of road haunches.

0

5 0

1 00

1 50

2 00

2 50

0 .1 1 1 0 1 00

Thi

ckne

ss (

mm

)

0

50

100

150

200

250

300

350

400

0.1 1 10 100

Traffic loading (msa)

Thi

ckne

ss (

mm

)

Design thickness of the structural course related to a mean minimum 7 day compressive strength for the recycled material of 10 N/mm2

Traffic loading below 2.5msa [Type 3 and 4 roads]:

Where suf ficient thickness of existing road construction is present, the pavement design thickness options are contained in Table 9, related to the combined thickness of foundation and structural course and a mean minimum 7 day compressive strength for the recycled material of 4.5 N/mm2 for Type 4 roads and 7 N/mm2 for Type 3 roads.

Where insufficient thickness of existing road construction is present to meet the requirements of Table 9, the deficit thickness may be off set by increasing the thickness of surfacing by an equivalent amount - but for practical purposes the recommended minimum thickness of recycling is 150mm

Minimum recycled layer thickness

Provisional design thickness of the structural course related to a mean minimum 7 day compressive strength f or the recycled material of 10 N/mm2

Thickness of structural course using in-situ cement bound recycled material

Thickness of surfacing

Traffic loading (msa)0.1 10 1001

Traffic loading below 2.5msa (Type 3 and 4 roads):

Surface thickness options are contained in Table 9

Any deficit in the thickness of the recycled layer(ie combined foundation and structural course)may be offset by increasing the thickness of thesurfacing by an equivalent amount

Figure 1 Pavement layer thicknesses using in-situ cement bound recycling

21

The ETSU performance review of roads reconstructedby cold in-situ recycling from 1985 to 1987, showedclearly that the performance of Type 3 and 4 roads,recycled to a depth of between 150 to 250mm, was rated assatisfactory or better in more than 97 per cent of cases.Furthermore, the very few defects reported after anaverage six years life, were all associated with poor edgedetail and no fault related to the performance of the coldin-situ recycled layer.

Therefore, since the design thicknesses recommendedfor road haunch design refer to the same order of recycledthicknesses used for reconstruction of the monitored sites,ranging between 150 and 300mm, the design thicknessesfor wider areas of recycled reconstruction are considered

to be satisfied by the same criteria, although slightlymodified in detail to account for the different constructionprocesses and scale of the works. The design thicknessesare detailed in Table 6, listed against three surfacingthickness options.

In comparison with the design for Type 1 and 2 roads,these design thicknesses relate to the thickness of thecombined structural course and foundation layer.Furthermore, the validity of the design process iscontingent on the process control testing being carried outas specified, to ensure that the in-situ recycled material isstabilised and compacted to the specified standard.

Design examples for Type 3 and 4 roads related totypical site conditions are contained in Appendix B.

0

50

100

150

200

250

0 .1 1 10 100

T ra ff ic load ing (m sa )

Thi

ckne

ss (

mm

)

Traffic loading below 2.5msa (Type 3 and 4 roads):

Surface thickness options are contained in Table 9

Any deficit in the thickness of the recycled layer(ie. combined foundation and structural course)may be offset by increasing the thickness of thesurfacing by an equivalent amount

Optional 50mm thick surfacing usedwith increased thickness of recycledmaterial

Thickness of surfacing

0

50

100

150

200

250

300

350

400

0.1 1 10 100


Thi

ckne

ss (

mm

)

Traffic loading below 2.5msa [Type 3 and 4 roads]:

Where sufficient thickness of existing road construction is present, the pavement design thickness options are contained in Table 9, related to the combined foundation and structural course thickness and a mean minimum ITSM value for the recycled material of 2500Mpa.

Where insufficient thickness of existing road construction is present to meet the requirements of Table 9, the deficit thickness may be offset by increasing the thickness of surfacing by an equivalent amount - but for practical purposes the recommended minimum thickness of recycling is 150mm.

Design thickness of the structural course related to a mean minimum ITSM value for the recycled material of 2500Mpa and a surfacing thickness of 100mm.

Minimum recycled layer thickness

Optional increased thickness of recycled material related to surfacing thickness of 50mm.

Provisional design thickness of the structural course related to a mean minimum ITSM value for the recycled material of 2500MPa and surfacing thickness of 100mm.

Thickness of structural course using cold in-situ foamed bitumen bound recycled material

Figure 2 Pavement layer thicknesses using cold in-situ foamed bitumen bound recycling

22

7 Specification for cold in-situ recycledmaterial

7.1 General

The process of cold in-situ recycling for the structuralmaintenance of highway pavements has been developedand used in a variety of countries, each with their ownlocal requirements, often related to climate and geology.Consequently, the types of road available for recycling arediverse. As a result, the specification for recycling workshas been derived from a variety of component materialdesigns and construction methods, aimed mostly atproducing materials of quasi standard form and expectingthat their performance would be similar to the equivalentplant mixed option.

These recipe and method specifications have served theindustry reasonably well, particularly in the UK, becausethere is more likely to be a quickly changing geology profilelinked with a wide array of historic road pavements.However, the recycled materials produced from thispotentially varied feedstock, often referred to as secondary,reclaimed or waste aggregate, has attracted the suggestion ofbeing inferior in some way. This suggestion is not deserved.

Therefore, as a means of encouraging the use ofrecycled material, a move towards end productperformance specifications is seen as a positive step. Thespecification of recycled materials in their own right, usingperformance targets stated in terms of engineeringproperties, allows the recycled material to be consideredfor more heavily trafficked sites, on an equitable basis tostandard plant produced materials.

Specified and closely monitored performance targetsshould offer the engineer a greater degree of confidence inthe prediction of life for the recycled treatment. Inconsequence, the cost effectiveness of the recycled option,in comparison with normal reconstruction methods, maybe more readily demonstrated.

7.2 Material composition and process control clauses

7.2.1 Cement bound materialBecause of the similarities between the materials,significant sections of the specification clauses for CBMgiven in the Specification for Highway Works applyequally well for the recycled option. In fact, theSpecification for Highway Works refers directly to theoption of using a mix-in-place method of construction forCBM1 and CBM2 mixtures. In consequence, many of theassociated NG clauses, as given in the accompanyingNotes for Guidance on the Specification for HighwayWorks, are equally applicable.

One exception to the guidance relates to the curingperiod and use by traffic, since in the structuralmaintenance situation, there is often a requirement tomaintain immediate access through and within the site, forresidents and service traffic. In addition, for most recyclingcontracts, any access restriction will inevitably delay theworks programme.

However, any damage to the recycled layer by earlytrafficking may be mitigated by ensuring that adequatecompactive effort has been applied and high densityachieved. In addition, the use of a higher cement contentfor early strength gain could be employed. Conversely, itcould be argued that early life trafficking is beneficial tothe structural course by establishing a closer spacedpattern of crack, thus making the finished road less proneto reflective cracking problems. In addition, provided theas-installed performance measured by dynamic plateloading or penetrometer technique, to determine elasticmodulus, meets the targets set by the specification, noproblem is foreseen.

A further aspect for consideration, relates to thecompaction of thick lifts of recycled material up to 300mmthick. Although the process control for compaction of suchthick layers is the same as for thinner layers, requiring thesame level of compaction for the full depth, thecompactive effort needs to be considerably greater, usingeither heavy vibratory compaction or possibly, a tampingroller. In some situations, the use of a heavy pneumatictyre roller (PTR) may also be considered worthwhile as afinishing roller. The compaction options are discussedfurther in Section 8.

Table 6 Thickness of pavement layers using cold in-siturecycled materials as the combined structuralcourse and foundation platform in Type 3 andType 4 roads

Thickness of cold in-situ recycled material

Type 3 road Type 4 road

Binder type Cement bound in-situ recycled material

Surfacingthickness Surface Surface(mm) dressing 40 100 dressing 40 100

SubgradeCBR (%)

<2 n/r n/r n/r n/r n/r n/r2-4 280 240 180 240 200 1505-7 260 220 160 220 180 1508-14 240 200 150 200 160 150>15 220 180 150 190 150 150

Binder type foamed bitumen bound in-situ recycled material

Surfacingthickness Surface Surface(mm) dressing 40 100 dressing 40 100

SubgradeCBR (%)

<2 n/r n/r n/r n/r n/r n/r2-4 n/r 310(n/r) 250 320(n/r) 280 1955-7 330(n/r) 290 230 300 260 1858-14 315(n/r) 275 215 285 245 160>15 285 245 185 255 215 150

n/r not recommended

For intermediate thicknesses of surfacing, the thickness of recycledmaterial may be interpolated from the above data.

23

7.2.2 Foamed bitumen bound materialAlthough this material is generally labelled as a bitumenbound material, it is unlike any standard hot plant mixedbitumen bound material. The foamed bitumen tends tocombine more readily with the fines component of thepulverised aggregate, forming a ‘mortar’ matrix, whichfills the voids between the partially coated coarseaggregate. In addition, cement is commonly used as anadhesion agent, in which case a component of the stiffnessis likely to derive from the hydration of the cement.Therefore, unlike the cement bound option, thespecification or notes for guidance for standard bitumenbound plant mixes are not readily applicable to the cold in-situ recycled product.

Experience has found that a base bitumen withpenetration grade 100 most often offers the bestcompromise between workability during the laying processand the compacted stiffness of the material. But subject tothe results of the mixture design, base bitumen with ahigher penetration grade may be used.

To ensure adequate mixing of the foamed bitumen withthe aggregate, the minimum expansion rate of the foamshould be 10, linked with a minimum half-life of 10seconds. Also, in the interests of durability, irrespective ofthe results of the design tests, the absolute minimum addedbitumen content should be 3.5 percent. The uniformity ofmixing should be continuously inspected visually by thecontractor and work should stop if bitumen streaks orblotches are observed.

Compaction control is essentially the same as for thecement bound option, and provided adequate stability of thelayer is achieved, early life trafficking is seen as no problem.The collapse of the foam will take place shortly after mixingto allow development of stiffness by a curing process, whichinvolves hardening of the bitumen and cement boundmortar. As an additional safeguard, the as-installedperformance measured by either the dynamic plate loadingor penetrometer technique, should be able to demonstratethat the layer has achieved a required stiffness, beforeproceeding with the construction of the overlying pavement.

7.3 End-product performance clauses

Throughout the current research project, the development ofthe end-product performance specification for the cold in-situ recycled materials has passed through different stages.The initial intention was to define performance in terms ofeither the compressive strength of cored cement boundmaterial or by the Indirect Tensile Stiffness Modulus(ITSM), obtained for the bitumen bound material.

The above option was set aside, however, when it wasdecided that the destructive coring should only beperformed as a last resort. This decision was reinforced bythe difficulties experienced on the Cartgate trial andseveral of the other monitored sites, where the coring itselfwas sometimes found difficult and insufficient testspecimens were obtained, to the extent that there was nocertainty of consistently extracting whole cores from theroad. The current specification now retains the core testingoption only as the last resort rejection method.

The choice of non-destructive testing as a means ofacceptance, but not rejection, now relies on the pavementstiffness reaching a value pre-stated in the contract, obtainedusing the analysis of the FWD survey data. Where the FWDstiffness values do not reach the required level, then thecoring and testing of core samples option may be invoked.

Prior to either of the above assessments, thespecification also requires that the as-installed performanceof the stabilised layer is evaluated using a dynamic plateloading or penetrometer technique to determine values ofelastic modulus at points on a closely spaced grid pattern.The average elastic modulus for the assessment areas mustcomply with a stated minimum standard and furthermore,before proceeding with the surfacing construction,repeated values shall be expected to demonstrate that therespective elastic modulus values have increased by astated minimum percentage.

8 Construction

8.1 Pulverisation and stabilisation

Road pulverisation and stabilisation involves the use ofspecialised plant that operates to the specified depth plusconstruction tolerances. To ensure adequate pulverisationand mixing of materials it is recommended that the driveperformance of the machine is at least 260kW, whichshould be capable of carrying out an initial pulverisation toa depth of about 450mm.

Most stabilisers are manufactured with the mixing boxlocated centrally, which incorporate special rotorsdesigned to pulverise or mix the material within the mixinghood. The use of smaller agricultural equipment is nosubstitute, since they are predominantly designed to workon cohesive soils and therefore, are not designed toproduce pulverised granular aggregate of the requiredgrading for construction purposes.

Since the powerful equipment can easily damageservices, the Overseeing Organisation should identify ifany services or obstructions are present. The time requiredto lower any services should be taken into account withinthe works programme.

The specialist manufactured plant will almost certainlyincorporate all the features and facilities necessary tocomplete the works in accordance with the currentrecycling specification. Some will be larger and morepowerful than others, whereas others may incorporatemore refined control systems.

The systems normally employed to control the depth ofpulverisation relate the depth of rotor to the verticalposition of the wheels. Therefore, to ensure that theappropriate depth of pulverisation or stabilisation is carriedout consistently, it is particularly important that a workingplatform is prepared prior to the stabilisation process,having a known uniform level profile.

8.2 Added water and moisture control

Although the control of moisture content is of primeimportance for optimum compaction conditions, there is

24

currently no automated process available that can ensurethe provision of moisture at a uniform and optimum levelduring the recycling process. It is vital therefore, that theprocess is controlled by an experienced operator who hasaccess to controls for added water, particularly when thewater is sprayed directly in the mixing box at the time ofstabilisation.

The stabiliser should ideally, be fitted with a separatewater pumping and injection system for metering theadded water, regulated to the ground speed of the machine.An experienced operator will normally assess the moisturecontent of the mix relative to the target optimum bysqueezing samples of the material regularly by hand andbe guided by test results at the commencement or duringany job so as to ‘calibrate’ personal judgement. Theoperator must assess the moisture content immediatelybehind the stabiliser and be prepared to make quickadjustments as the machine may be progressing forward ata rate of 4-6 metres per minute.

8.3 Application of cement or lime

Cement may be required either as the primary binder or as asupplementary binder to act as an adhesion agent or helpimprove the short term properties of the compacted material.Currently, hydrated lime is only used as a plasticity modifierfor cohesive fines within the pulverised aggregate, althoughas in the past, it was used as a primary binder agent.

Specialist spreaders are vital for the application of thesematerials, which should incorporate control systems toensure that the rate of spread is achievable to a targetaccuracy of ±0.5 percent of the specified spread rate. Theassociated construction tolerance for the rate of spreadwould normally be ±10 percent of the specified value.

The particle size of the different cements and lime mayvary and such behaviour should be noted as it may affectthe accuracy of application. The use of consistent sourcesand standard routines for storage and loading of thespreader is recommended to minimise any variation.

8.4 Application of foamed bitumen

Because of the short life span of the foamed bitumen,usually defined in terms of its ‘half-life’ (i.e. time taken inseconds for the foamed bitumen to settle to one half of themaximum expanded volume) it is necessary for thefoaming process to be incorporated into the spraybar of therecycling machine, for immediate distribution and mixingwith the pulverised aggregate in the mixing hood. Thereduced viscosity and greater volume of the foamedbitumen enables it to be distributed and mixed with thedamp cold aggregate.

A typical stabiliser has computer-controlled devices onboard that calculate the application rate of the binder as thestabiliser moves along the pavement. The pumping andinjection equipment for the foamed bitumen should ideallybe a separate spraybar system, and one that allows variablewidths of binder to be applied.

An inspection or test jet must be fitted to ensure that theflow of bitumen and the required expansion and half-lifequalities of the foamed bitumen are achieved. The bitumen

jets must be of a self cleansing design and bitumen linesshould be heated for reasons of safety.

The spraybar control systems incorporated into thestabiliser should ensure that the rate of spread is achievableto a target accuracy of ±0.5 per cent of the specified spreadrate, in order to achieve a constructed tolerance for addedbitumen of ±0.6 per cent of the target binder content. As ameans of verification, dipping in the tanker before and aftera run can be used to verify the computer collected data.

8.5 Compaction

Compaction is a critical part of the stabilisation processand demands particular care. This is especially the case forthicker layers of construction, where there is the possibilityfor a density profile to develop during compaction, suchthat the lower part of the layer does not achieve the samedensity as the upper part.

This effect may be minimised when applyingcompaction at the earliest possible time using either heavyvibratory compaction or using a compactor capable of‘kneading’ the material at depth, as is the case using atamping roller. To date in the UK, heavy compaction forcold in-situ recycling works has been carried outexclusively using the vibratory roller option.

However, from the results of the monitoring reported inPart 1 of TRL Project Report PR/CE/193/98 (Milton, 1999),it is evident that the vibratory compaction was not alwaysable to achieve full depth compaction of thick layers.Therefore, where the stabilised material is assessed to havea poor workability, it is recommended that heavy tampingrollers should be considered, particularly for layers havinga compacted thickness in excess of 250mm.

When using heavy vibratory compactors, caution shouldbe exercised where there is any danger of vibratorydamage to shallow culverts, underground services oradjacent buildings due to the transmission of vibrations.

The use of a pneumatic tyre roller (PTR), is sometimesadvocated as a finishing roller, particularly for the cementbound material. However, whereas the PTR may tend toassist in the compaction of the lower level material, greatcare is required to ensure that the near surface materialdoes not dry out or stiffen too quickly, which may result indisruption and shear displacement of the near surfacematerial caused by the narrow loading under the individualtyres. Thus resulting in an unstable surface finish and thenecessity to remove unacceptable material.

9 References

Agenda for Change (1993). A plain language version ofAgenda 21 and other Rio agreements. Earth Summit Agendafor Change. Centre for Our Common Future, London.

British Standards Institution (1990). Sampling andexamination of bituminous mixtures for roads and otherpaved areas. British Standard BS 598. Part 2: Method of testfor the determination of the composition of design wearingcourse rolled asphalt. British Standards Institution, London.

25

British Standards Institution (1990). Stabilised materialsfor civil engineering purposes. British Standard BS 1924.Part 2: Methods of test for cement-stabilised and lime-stabilised materials. British Standards Institution, London.

British Standards Institution (1990). Soils for civilengineering purposes. British Standard BS 1377. Part 3:Chemical and electro-chemical tests. British StandardsInstitution, London.

British Standards Institution (1992). Guide for structuraldesign of pavements constructed with clay or concreteblock pavers. British Standard BS 7533. British StandardsInstitution, London.

County Surveyors Society (1991). Practical Guide toHaunching. CSS Report ENG/1/91. County SurveyorsSociety, Wiltshire County Council.

Department of the Environment (1994). Guidelines foraggregate provision in England (MPG6). Mineralsplanning guidance. Stationery Office.

Department of the Environment, Energy EfficiencyOffice (1994). Performance of roads reconstructed by coldin-situ recycling 1985 - 1987. Best Practice programme,General Information Report 17, Energy EfficiencyEnquiries Bureau, ETSU, Harwell.

Department of the Environment, the Welsh Office andScottish Office Environment Department (1991). WasteManagement. The duty of care code of practice. StationeryOffice.

Department of the Environment, the Welsh Office andScottish Office Environment Department (1994).Environmental Protection Act 1990: Part II,. Wastemanagement licensing. The Framework Directive onWaste. Circular 11/94 (Department of the Environment),Circular 26/94 (Welsh Office), Circular 10/94 ScottishOffice Environment Department). Stationery Office.

Department of the Environment, the Welsh Office andScottish Office Industry Department (1992). The Codeof Practice, Specification for the reinstatement of openingsin highways. Stationery Office.

Department of the Environment, the Welsh Office andScottish Office Industry Department (1994). Wastemanagement licensing regulations. Stationery Office.

Department of Transport, Scottish Office IndustryDepartment, Welsh Office and Department of theEnvironment for Northern Ireland (1994). DesignManual for Roads and Bridges, Volume 7, Pavementdesign and maintenance. DMRB Section 3 Pavementmaintenance assessment. Part 3, HD 30/97 Structuralassessment procedure. Stationery Office.

Department of Transport, Scottish Office IndustryDepartment, Welsh Office and Department of theEnvironment for Northern Ireland (1995). DesignManual for Roads and Bridges, Volume 7, Pavementdesign and maintenance. DMRB Section 4 Pavementmaintenance methods Part 1, HD 31/94 Maintenance ofbituminous roads. Stationery Office.

Department of Transport, Scottish Office IndustryDepartment, Welsh Office and Department of theEnvironment for Northern Ireland (1995). DesignManual for Roads and Bridges, Volume 7, Pavementdesign and maintenance. DMRB Section 1 Preamble Part 2,HD 35/95 Technical Information. Stationery Office.

Highways Agency, Scottish Office DevelopmentDepartment, the Welsh Office and the Department ofthe Environment for Northern Ireland (1998). Manualof Contract Documents for Highway Works. Volume 1(MCDHW1) Specification for highway works. StationeryOffice.

Lee D Y (1980). Treating Iowa’s marginal aggregates andsoils by foamix process. Final Report. Iowa StateUniversity, Iowa, USA.

Milton L J (1999). Design guide and specification forstructural maintenance of highway pavements by cold in-situ recycling. Part 1: Investigation Reports. Part 2:Development of design guide and specification. ProjectReport PR/CE/193/98. Transport Research Laboratory,Crowthorne. (Unpublished report available on directpersonal application only)

Potter J F (1996). Road haunches: A guide to re-useablematerials. TRL Report TRL216. Transport ResearchLaboratory, Crowthorne.

Transport Research Laboratory (1994). RoadHaunches: A guide to maintenance practice. Report of aWorking Group chaired by R A Luck (GloucestershireCounty Council). Published Article PA/SCR243. TransportResearch Laboratory, Crowthorne.

Ullidtz P and Peattie K R (1980). Pavement analysis byprogrammable computer. Transportation and EngineeringJournal. American Society of Civil Engineering, 106 (5)pp581-597, September.

Walsh I D (1988). Cold mix recycling - the client’s view.Asphalt ’88. A review of technical developments in theconstruction of flexible pavements. Reprinted fromHighways, January 1988. Mobil, High Wycombe.

Williams J (1996). Highways and Conservation. Paperpresented at the 1995 BACMI ACMA Seminar,Reproduced in Quarry Management, 1996 23 (1) 37-40.

26

Part 2: Specification andnotes for guidance onthe specification

Clause C1 In-situ recycled cement boundmaterial

Scope

1 In-situ recycled cement bound material shall bedesigned and produced to form the foundation or mainstructural layer of a road pavement. The primaryaggregate source shall be obtained by cold in-situpulverisation of all or part of the existing road structure.The stabilising agent shall be hydraulic cement withPortland cement as the main component. The aggregategrading may be adjusted by the addition of a filler. Limemay also be used to modify any cohesive subgrade soilincorporated in the pulverised layer.

2 Prior to commencing the pulverisation andstabilisation works, the Contractor shall demonstrateto the satisfaction of the Overseeing Organisation,using the results of the mix design proceduresdescribed in Clause C2, that the existing pavementmaterials in the sections of the works defined inSpecification Appendix (Item 1), are capable of beingrecycled by pulverisation to form the primaryaggregate component of a in-situ recycled cementbound material which can meet the specified end-product performance requirements.

Component materials

Aggregates and fillers

3 The pulverised road material and anysupplementary aggregate and/or filler shall normallybe granular material with not less than 5% and notmore than 20% passing the BS 75 micron sieve [ZoneA graded material]. Approval for use of pulverisedgranular material containing up to 35% passing theBS 75 micron sieve [Zone B graded material] shallrequire confirmation by the Overseeing Organisationsubject to the results of the mixture designprocedures described in Clause C2.

4 The pulverised granular material shall containnot more than 2% of organic matter determined inaccordance with BS 1377: Part 3: Clause 3.

Cement, filler and lime

5 The constituents and required quality standardsof hydraulic cement, filler and lime delivered to siteshall be certified by the supplier, whosemanufacturing and delivery processes shall beimplemented using quality management systems inaccordance with the ISO 9000 series of standards andcertified by an accredited body.

6 The primary binder shall be Portland cement orPortland blast furnace slag cement or Portland pfacement in accordance with sub-Clause 3 of Clause1001 in the Specification for Highway Works.

7 PFA used as a filler shall be in accordance withBS 3892: Part 1.

8 Lime for lime stabilisation (or as a modifier forplastic fines) shall be either quicklime or hydratedlime, as stated in Specification Appendix (Item 2),complying with sub-Clause 3 of Clause 615 in theSpecification for Highway Works.

Water

9 Water for moisture content control of thepulverised granular material shall normally beobtained from a water company supply and usedwithout testing. Water from an alternative sourceshall comply with BS 3148 and be approved by theOverseeing Organisation.

Pulverisation and stabilisation

10 The Contractor shall satisfy the OverseeingOrganisation that the plant used for pulverisation iscapable of uniformly pulverising the existing road ina single pass, to a depth required by the contract. Theplant used for stabilisation shall be capable ofuniformly mixing controlled amounts of water andcementing agent(s) into the full depth of thepulverised layer. For either operation, the plant shallbe equipped with a means for controlling the depth ofprocessing to ±15mm of the required depth.

11 The plant used for stabilisation shall be equippedwith a spraybar system within the mixing chambercapable of uniformly distributing water at a monitoredand controlled rate. Evidence confirming thecapabilities of the plant and calibration of flow meters,shall be submitted to the Overseeing Organisationprior to the stabilisation works commencing.

12 The material shall be pulverised and stabilised ina single layer if the compacted thickness is 300mm orless. If the compacted thickness is greater than300mm, the material shall be pulverised and stabilisedin a minimum number of layers between 100mm and300mm thick. Where more than one layer is required,the Contractor shall satisfy the OverseeingOrganisation that the lower layer has achievedadequate stability in accordance with sub-Clause 27 ofthis Clause before proceeding with the overlying layer.

Pulverisation process

13 Pulverisation of the existing road structure shallbe carried out in a systematic pattern, to the requireddepth, to ensure that all parts of the existing road

27

designated in Specification Appendix (Item 1) areincluded in the works. An overlap of at least 150mmshall be made between adjacent passes of themachine. Any material missed along hard edges oraround obstructions shall be excavated and placed inthe path of subsequent passes of the machine until auniform fully pulverised aggregate is obtained. Thesurface of the pulverised layer shall be graded to therequired level profile and nominally compacted.

14 All longitudinal and transverse joints shall beclean cut and vertical. Where work continuesadjacent to previously recycled material transversejoints shall be reformed a minimum 0.5m into thepreviously treated construction. Where a layer ofmaterial for stabilisation is placed over a layerpreviously stabilised, the depth of pulverisation/stabilisation of this layer shall be set to cut into theunderlying stabilised layer by at least 20mm.

15 Excess pulverised material shall be removed bygrader and/or excavator for use elsewhere on the siteor transported to stockpile at locations given inSpecification Appendix (Item 3). The surface of thelayer shall be graded to the required level profile andnominally compacted.

16 Moisture content of the pulverised aggregateimmediately prior to stabilisation shall be measuredin accordance with BS 812: Part 109 using the hightemperature method. The moisture content shall beuniform throughout the layer within the range 0% to+4% of optimum moisture content for theunstabilised aggregate, including any designedproportion of filler, determined in accordance withBS 1924: Part 2: 1990.

17 If the moisture content of the unstabilisedpulverised aggregate fails to meet the specifiedmoisture content range, corrective action shall betaken either by aeration to reduce the moisturecontent or controlled addition of water to increase themoisture content.

18 Aeration of the affected area shall be achievedby full depth passes of the recycling machine todisturb and loosen the material and assist theevaporation of excess moisture. The material shall bekept in a loose condition until subsequent moisturecontent tests show that the treated material hasreached the required moisture content range. Thelayer shall be re-graded nominally to level andcompacted in preparation for stabilisation.

19 Increase in moisture content of the affected areashall be carried out by the controlled addition ofwater through an adjustable spraybar system inconjunction with full depth passes of the recyclingmachine to achieve a uniform distribution of thewater throughout the layer. Increments of water shallbe added and mixed in until subsequent moisturecontent tests show that the material has reached the

required moisture content range. The layer shall bere-graded nominally to level and compacted inpreparation for stabilisation.

Stabilisation process

20 Stabilisation shall not be carried out during or afterperiods of rainfall where the duration and intensity arelikely to cause the stabilised mixture to exceed thespecified moisture content criteria and compromise thestability of the layer under compaction (as described inSub-Clause 27 of this Clause). Stabilisation of frozenmaterials shall not be permitted.

21 Prior to stabilisation, pulverised materials within100mm of restricted hard edges such as kerbs andchannels, or around obstructions such as gullies, shallbe removed and spread uniformly over the remainingfull width of the pulverised material.

22 Cement binder, filler, hydrated lime or quicklimeshall be spread full-width on the surface of the layerusing a mechanical spreader capable of distributingthe material(s) in a uniform controlled manner. Therate of spread of these materials shall be calculated toachieve mixture composition determined inaccordance with Clause C2 and monitored as thespreading operation proceeds in accordance with sub-Clause 31 of this Clause.

23 The stabilisation shall be carried out to the requireddepth in a systematic pattern similar to that used for thepulverisation process, with an overlap of at least 150mmbetween adjacent passes of the machine. Wherenecessary, additional water shall be introduced anddistributed through the spraybar system, directly into therotor and mixing box of the stabiliser.

24 The layer of stabilised material shall be graded tolevel and compacted within two hours of the final passof the stabilising plant, unless a curing or ‘maturing’period of aeration is required. Any furrow formed byprior excavation of edge material shall be re-filled bygrading the adjacent stabilised material into the spaceusing a minimum amount of re-working.

25 The compaction of each layer shall be carried outusing compaction plant approved by the OverseeingOrganisation, until such time as the in-situ densitycomplies with the minimum compaction fieldrequirements in Table 10/8 of the Specification forHighway Works and the stabilised layer provides astable and dense tight surface. Any open orsegregated surface area shall be blinded using a drycrushed rock fines.

26 Sub-clause for induced cracking deleted.

27 The stability of the layer under compaction shallbe deemed adequate if the finished surface does notmove, rut or exhibit transverse cracking under theload of subsequent construction traffic.

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28 Where required by the Overseeing Organisation,the stability of a layer in any area shall be assessedafter a curing period of at least 24 hours by channelledtrafficking using a rigid three-axle tipper truck loadedto a gross mass of 24 tonnes (assumed equivalent tothree standard axles). The vertical deformation shall bemeasured in all wheeltracks at monitoring points oneach of 5 transverse sections set 1m apart after 5, 15,30 and 40 passes of the truck. The mean verticaldeformations at the above trafficking increments shallbe plotted against the respective number of truckpasses and the mean vertical deformationcorresponding to 100 standard axles shall beinterpolated. The layer shall be deemed acceptable ifthe mean vertical deformation corresponding to 100standard axles is less than 10mm.

29 On completion of compaction the surface shallbe sealed using a sprayed membrane of Class K1 - 70bitumen emulsion complying with Clause 920 in theSpecification for Highway Works. The bitumenemulsion shall be sprayed at the rate stated in theSpecification Appendix (Item 4). Where the surfaceis opened to traffic, the sealing membrane shall beblinded with fine aggregate or sand applied at a rateof 5.5 to 7.0 kg/m2.

Process control

30 The sampling and testing of the in-situ recycledcement stabilised roadbase shall be carried out asrequired for cement bound materials [CBM] inaccordance with Clauses 1040 and 1041 in theSpecification for Highway Works.

31 The rate of spread of cement, filler, hydratedlime or quicklime shall be measured by weighing theamount of material retained on each of five trays ormats of known area laid in the path of the spreadingmachine. The trays shall be positioned approximatelyat points equally spaced along a diagonal bisectingthe area of coverage. The mean rate of spread andpercentage addition of the material shall bedetermined and recorded for each assessment area.

32 As directed by the Overseeing Organisation,where lime has been used to modify a cohesive soilcomponent of the pulverised aggregate, theacceptability of the modified materials shall be testedin accordance with sub-Clause 13 of Clause 615 inthe Specification for Highway Works.

End product performance of in-situ recycledcement bound material

33 The end-product performance of the in-siturecycled cement bound material shall be assessed onthe basis of measurements and tests carried out inareas of 800m2 or part thereof completed each

working day, which shall match the areas defined insub-Clause 1 of Clause 1040 in the Specification forHighway Works.

34 Within 24 hours of completion, the as-installedperformance of the stabilised layer shall be evaluatedusing a dynamic plate loading or penetrometertechnique to determine values of elastic modulus atpoints on a nominal 2m grid pattern. The elasticmodulus at each point and the mean elastic modulusfor the assessment area shall comply with theminimum standards stated in the SpecificationAppendix (Item 5). Additionally, before proceedingwith construction of the overlying pavement, theevaluation process shall be repeated to demonstratethat the elastic modulus value at all points and that ofthe mean value have increased over the respective as-installed values by not less than the percentage valuesstated in the Specification Appendix (Item 5). Wherethese criteria are not met, the full extent of non-compliant material shall be determined andappropriate remedial measures implemented.Remedial action shall comprise either a delay inconstruction to allow further curing and stiffening ofthe layer or a repeat of all or part of the recyclingprocess, followed by re-evaluation, until a compliantmaterial is achieved.

35 Within 270 days of completion of the surfacingworks a Falling Weight Deflectometer survey shallbe carried out and analysed in general accordancewith HD 29/94 (DMRB 7.3.2, 1994). In particular,the measurements shall be taken on the finished roadsurface in the nearside wheelpath, at a uniform andmaximum spacing of 10m. The survey shall becarried out during a period when the pavementtemperature at a depth of 50mm is within the range15 to 250C. The FWD results shall be analysed usinga linear elastic FWD back-analysis computerprogram, with the pavement modelled as a two layersystem. Layer 1 shall represent the combined designthickness of the bound materials (i.e. the combinedrecycled material and overlying surfacing materials)and layer 2 shall represent the unbound foundationlayer of infinite depth. End-product performanceshall be defined in terms of the calculated stiffness oflayer 1, uncorrected for temperature. Complianceshall be achieved when not more than 15% of thecalculated values within each assessment area fallbelow the stiffness value specified in theSpecification Appendix (Item 6).

36 In the event that the layer 1 stiffness requirementof sub-Clause 35 of this Clause are not met, the fullextent of the non-compliant material shall bedetermined by further investigation involving coringand laboratory testing. For each area of non-compliance, cores shall be extracted through the fulldepth of the stabilised layer at locations directed bythe Overseeing Organisation, at a minimum rate ofone x 150 mm diameter core per 75m2.

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37 The Contractor shall be responsible forextraction of the cores with the minimum of force ordisruption. Air flush coring shall be allowed formaterials that are disturbed by water flush coring.After extraction, each core shall be labelled andphotographed and prior to testing, shall be stored insealed polythene bags, in a uniformly supportedposition, at a temperature of 200C ± 50C. Thethickness of the recycled layer shall be measured andrecorded.

38 Reinstatement of all core holes shall becompleted before opening the area to traffic. Allbackfill materials shall comply with the‘Specification for the Reinstatement of Openings inHighways’ issued by the Highway Authorities andUtilities Committee.

39 If, at any of the prescribed core locations, it isnot possible to extract an intact core of suitable sizeor condition for the end-product performance testing,using a maximum of three attempts in an area of1.5m radius, the material in the vicinity shall bedeemed not to comply with the end-productperformance specification.

40 In the laboratory, each core extractedsuccessfully shall be trimmed to remove surfacingmaterials and any underlying material prior to themeasurement of core density and air voidscontent in accordance with the standards listed inTable C1/1.

41 Following the measurement of density and airvoids content, each core shall be prepared and testedto determine the compressive strength of the core, inaccordance with the procedures and standards givenin Table C1/2

42 The results obtained shall be used to judge theexpected performance of the recycled stabilisedmaterial in the works, in relation to the performanceof standard CBM roadbase materials. The recycledstabilised material in the assessment area shall bedeemed acceptable if the compliance criteriadescribed in Table C1/3 are met.

Clause C2 In-situ recycled cement boundmaterial - mixture design and characterisation

1 Mixture design characterisation of in-siturecycled cement bound material for each site, orsection of site, including details of the cementingagent and/or stabilising agent(s) and theirquantities, shall be submitted to the OverseeingOrganisation at least one week prior tocommencement of the recycling works. Wherethe site investigation has identified significantvariation of existing pavement materials betweendifferent sections of the site, a mix design shallbe submitted for each section of the site. Theproposed plan area and depth of the differentsections, covered by each mixture design, shallbe approved by the Overseeing Organisation.

2 The mixture design for in-situ recycled cementbound material shall use the same method ofmixture design as that used for plant mixed CBMspecified in Clauses 1035 to 1039 in theSpecification for Highway Works, except that theaggregate shall be crushed and processed in thelaboratory, using a method approved by theOverseeing Organisation, to replicate as closely aspossible the aggregate expected frompulverisation in the works. The permitted CBMalternatives and equivalent recycled mixturedesigns for each part of the Works shall be asdescribed in the Specification Appendix (Item 1).

Table C1/1 Procedures and standards to be used to determine the density of core samples of in-siturecycled cement bound material

Procedure Procedure Stage Standard to be Used

Core preparation Measurement of core dimensions and BS Draft prEN 12504.for density testing. accuracy of measurement.

Methods of trimming core to length.

Test specimen type, shape and moisture ISO 6275.condition.

Core testing for Apparatus specification. ISO 6275.density. Measurement of volume dimensions.

Volume by water displacement.Measurement of mass.Equations for density.Accuracy and units of density.

Core density as a proportion of theoretical SHW Clause 1003.density.

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Table C1/2 Procedures and standards to be used to determine the compressive strength of core samplesof In-situ recycled cement bound material

Procedure Procedure stage Standard to be used

Core preparation Measurement of core dimensions and accuracy BS Draft prEN 12504.for strength testing. of measurement.

Assessment of voids.Maximum and minimum dimensions forstrength testing.

Methods of capping core. ISO 4012.

Suitability of core for strength testing. BS 1881: Part 120.Storage of cores before capping.

Core testing for strength. Type of strength test. BS Draft prEN 12504.Minimum period of testing after end-preparation.Method of curing core prior to testing.Measurement of core test specimen dimensionsand accuracy.Equation for calculating core strength.

Testing machine specifications ISO 4012.Rate of loading.

Correction for length/diameter ratio and BS 1881: Part 120.orientation of coring.Equations for derivingequivalent in-situ cube strength.

Correction for excess voidage. BS 1881: Part 120.

Table C1/3 Compliance criteria for in-situ recycled cement bound material based on results of tests oncores extracted from the works

Mean from cores inProperty Individual cores each surveyed area

Core density relative to refusal density 93% minimum 95% minimumExcess voidage * 3.0% maximum 2.0% maximumLayer thickness [from core measurement] ± 25mm of specified ± 15mm of specifiedEquivalent cube compressive strength **CBM equivalence **CBM equivalence

* Excess voidage of a core is defined as the amount by which the actual air voids content exceeds theair voids content of the fully compacted moulded cube of the same cement bound material.

** Compliance criteria is quoted in relation to the design 7 day cube compressive strength appropriateto the equivalent CBM classification of the recycled material.

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3 The laboratory crushed and processed aggregatewith a particle [or ‘lump’] sized distributioncomplying with sub-Clause 3 of Clause C1, shallbe thoroughly mixed with measured proportionsof the cement to produce trial mixtures withdifferent cement contents. The type and grade ofthe cement used in the trial mixtures shall be thesame as that used in the finished works.

4 If lime is required for stabilisation and/ormodification of clay included from pulverisationof the upper subgrade layer, the same proportionof lime shall be added into the trial mixture.

5 The cement content of the in-situ recycledcement bound mixture shall be determined in thesame manner as the cement content for plantmixed CBM, to achieve the requirements inTable 10/8 in the Specification for HighwayWorks. The minimum cement content shall be3% by weight.

6 The mixture design process shall be repeateduntil an acceptable mixture design is achieved.To achieve this the target composition of themixture shall be systematically adjusted and themixture design tests repeated.

7 In addition to the requirements of Table 10/8 inthe Specification for Highway Works the averagecompressive strength determined after 7 daysimmersion in water of five test specimens of thetarget composition mixture, prepared inaccordance with sub-Clause 3 of this Clause, shallbe not less than 80% of the average compressivestrength of five control specimens when subjectedto the test procedure described in BS 1924: Part 2:clause 4.3. After 7 days immersion the specimensshall not show any signs of cracking or swelling.

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Specification appendix

Site specific details and requirements to be stated in the Contract for in-situ recycled cement bound material:

Item 1 Site description, location details and depth of recycling:

Overall location - reference to plans

Section details - reference to plans & sections

Location of services - reference to plans & sections

Depth of recycled layer ......mm.

Item 2 Type of lime required for modification of cohesive soils ......

Item 3 Location of places to stockpile excess pulverised materials awaiting re-use elsewhere

Item 4 Rate of application of bitumen emulsion sealant spray ......l/m2

Item 5 Minimum elastic modulus within 24 hours obtained using a dynamic plate or penetration test:

Single point value ......MPa

Mean value ......MPa

Minimum percentage increase of single point elastic modulus values ...... %

Minimum percentage increase of mean elastic modulus value ...... %

Item 6 Stiffness value below which not more than 15% of FWD derived stiffnessvalues shall fall for combined surfacing and recycled material ......MPa

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Publication appendix

British Standards Institution (1984). BitumenRoad Emulsions (Anionic and Cationic). BS 434. Part 1:Specification for bitumen road emulsions. London,British Standards Institution.

British Standards Institution (1984). Bitumen RoadEmulsions (Anionic and Cationic). BS 434. Part 2: Codeof practice for use of bitumen road emulsions. London,British Standards Institution.

British Standards Institution (1989). Sampling andexamination of bituminous mixtures for roads andother paved areas. BS 598. Part 102: Analytical testmethods. London, British Standards Institution.

British Standards Institution (1989). Sampling andexamination of bituminous mixtures for roads andother paved areas. BS 598. Part 104: Method of testfor the determination of density and compaction.London, British Standards Institution.

British Standards Institution (1990). Testingaggregates. BS 812. Part 109: Methods fordetermination of moisture content. London, BritishStandards Institution.

British Standards Institution (1990). Methods oftest for soils for civil engineering purposes. BS 1377.Part 2: Classification tests. London, British StandardsInstitution.

British Standards Institution (1990). Methods oftest for soils for civil engineering purposes. BS 1377.Part 3: Chemical and electro-chemical tests. London,British Standards Institution.

British Standards Institution (1990). Methods oftest for soils for civil engineering purposes. BS 1377.Part 9: In-situ tests. London, British StandardsInstitution.

British Standards Institution (1983). Methods oftesting concrete. BS 1881. Part 120: Method fordetermination of the compressive strength of concretecores. London, British Standards Institution.

British Standards Institution (1980). Water formaking concrete (including the suitability of thewater). British Standard BS 3148. London, BritishStandards Institution.

British Standards Institution (1997). Pulverized-fuel ash. BS 3892. Part 1: Specification forpulverized-fuel ash for use with Portland cement.London, British Standards Institution.

British Standards Institution (1980).Recommendations for testing of aggregates. BS 5835.Part 1: Compactability test for graded aggregates.London, British Standards Institution.

British Standards Institution (1996). Testingconcrete - core specimens- taking examining andtesting in compression. BS Draft prEN 12504.London, British Standards Institution.

Highways Agency, Scottish Office DevelopmentDepartment, The Welsh Office and TheDepartment of the Environment for NorthernIreland (1998). Manual of Contract Documents forHighway Works. Volume 1 (MCDHW1) Specificationfor highway works. London, Stationery Office.

International Organisation for Standardisation(1978). Concrete - determination of compressivestrength of test specimens. ISO 4012. Geneva,Switzerland, International Organisation forStandardisation.

International Organisation for Standardisation(1982). Concrete, Hardened - determination ofdensity. ISO 6275. Geneva, Switzerland,International Organisation for Standardisation.

International Organisation for Standardisation(1994). Quality Management and Quality AssuranceStandards. ISO 9000. Parts 1 to 4. Geneva,Switzerland, International Organisation forStandardisation.

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Clause B1 Cold in-situ recycled bitumenbound material

Scope

1 Cold in-situ recycled bitumen bound materialshall be designed and produced to form the foundationor main structural layer of the road pavement. Theprimary aggregate source shall be obtained by cold in-situ pulverisation of all, or part, of the existing roadstructure. The primary binder (stabilising agent) shallbe a foamed penetration grade bitumen, with cementor lime as an adhesion agent. The aggregate gradingmay be adjusted by the addition of a filler. Lime mayalso be used to modify any cohesive subgrade soilincorporated in the pulverised layer.

2 Prior to commencing the pulverisation andstabilisation works, the Contractor shall demonstrate tothe satisfaction of the Overseeing Organisation, usingthe results of mix design procedures described in ClauseB2, that the existing pavement materials in the sectionsof the works defined in the Specification Appendix(Item 1), are capable of being recycled by pulverisationto form the primary aggregate component of a cold in-situ recycled bitumen bound material which can meetthe specified end-product performance requirements.

Component materials

Aggregates and fillers

3 The pulverised pavement material and anysupplementary aggregate and/or filler shall normallybe granular material with not less than 5% and notmore than 20% passing the BS 75 micron sieve [ZoneA graded material]. Approval for use of pulverisedgranular material containing up to 35% passing theBS 75 micron sieve [Zone B graded material] shallrequire confirmation by the Overseeing Organisation,subject to the results of the mixture designprocedures described in Clause B2.

4 The pulverised granular material shall containnot more than 2% of organic matter determined inaccordance with BS 1377: Part 3: Clause 3.

Bitumen binder

5 The primary binder shall be foamed bitumen.The base bitumen shall comply with BS 3690: Part 1and shall normally have a penetration grade 100.Subject to the results of the mixture designprocedures described in Clause B2 and approval ofthe Overseeing Organisation, the base bitumen mayhave a penetration grade up to 200.

6 Other than foaming agent(s), bitumen modifiersshall not be used unless approved by the OverseeingOrganisation for special purposes or conditions.

7 The binder shall be transported to the site intankers capable of maintaining the requiredtemperature and a homogeneous binder consistencyand transferred to the stabilising plant in a controlledand uniform manner.

8 The foaming of the bitumen shall be carried outwithin the spraybar system of the recycling machineand immediately mixed with the pulverisedaggregate, at which point the foamed bitumen shallhave a volume of not less than 10 times the volumeof the base penetration grade bitumen.

Cement, filler and lime

9 The constituents and required quality standardsof hydraulic cement, filler and lime delivered to siteshall be certified by the supplier, whosemanufacturing and delivery processes shall beimplemented using quality management systems inaccordance with the ISO 9000 series of standards andcertified by an accredited body.

10 Hydraulic cement as a filler or adhesion agentshall be Portland cement, Portland blast furnacecement or Portland pfa cement, in accordance withsub-Clause 3 of Clause 1001 in the Specification forHighway Works.

11 PFA, used as a filler, shall be in accordance withBS 3892: Part 1.

12 Lime for lime stabilisation (or as a modifier forplastic fines) shall, as required in the SpecificationAppendix (Item 2), be either quicklime or hydratedlime, complying with sub-Clause 3 of Clause 615 inthe Specification for Highway Works.

Water

13 Water for moisture content control of thepulverised granular material, shall normally beobtained from a water company supply and usedwithout testing. Water from an alternative sourceshall comply with BS 3148 and be approved by theOverseeing Organisation.


14 The Contractor shall satisfy the OverseeingOrganisation that the plant used for pulverisation iscapable of uniformly pulverising the existing roadstructure in a single pass, to the depth stated in theSpecification Appendix (Item 1). The plant used forstabilisation shall be capable of uniformly mixingcontrolled amounts of water and binder agent(s) intothe full depth of pulverised layer. For eitheroperation, the plant shall be equipped with a meansfor controlling the depth of processing to ±15mm ofthe required depth.

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15 The plant used for stabilisation shall be equippedwith a spraybar system within the mixing chambercapable of producing and uniformly distributingfoamed bitumen binder at a monitored and controlledrate. An accessible sampling jet shall also be fitted thatproduces foamed bitumen having the samecharacteristics as that produced by the main spraybar.Flow rate meters for measuring the supply rate of hotbitumen and other liquid additives to the mixture shallbe capable of recording the correct rate of flow duringall states of pipeline flow (i.e. fully or partiallycharged). Evidence confirming the capabilities of theplant and calibration of flow meters, shall be submittedto and approved by the Overseeing Organisation priorto the stabilisation works commencing.

16 The material shall be pulverised and stabilised ina single layer if its compacted thickness is 300mm orless. If the compacted thickness is greater than300mm, the material shall be pulverised and stabilisedin the minimum number of layers between 100mm and300mm thick. Where more than one layer is required,the Contractor shall satisfy the OverseeingOrganisation that the lower layer has achievedadequate stability in accordance with sub-clause 31 ofthis Clause before proceeding with the overlying layer.

Pulverisation process

17 Pulverisation of the existing road structure shallbe carried out in a systematic pattern, to the requireddepth, to ensure that all parts of the existing roaddesignated in the Specification Appendix (Item 1) areincluded in the works. An overlap of at least 150mmshall be made between adjacent passes of themachine. Any material missed along hard edges oraround obstructions shall be excavated and placed inthe path of subsequent passes of the machine until auniform fully pulverised aggregate is obtained. Thesurface of the pulverised layer shall be graded to therequired level profile and nominally compacted.

18 All longitudinal and transverse joints shall beclean cut and vertical. Where work continuesadjacent to previously recycled material transversejoints shall be reformed a minimum 0.5m into thepreviously treated construction. Where a layer ofmaterial for stabilisation is placed over a layerpreviously stabilised, the depth of pulverisation/stabilisation of the upper layer shall be set to cut intothe underlying stabilised layer by at least 20mm.

19 Excess pulverised material shall be removed bygrader and/or excavator for use elsewhere on site ortransported to stockpile at locations given in theSpecification Appendix (Item 3). The surface of thelayer shall be graded to the required level profile andnominally compacted.

20 Moisture content of the pulverised aggregateimmediately prior to stabilisation shall be measuredin accordance with BS 812: Part 109 using the high

temperature method. The moisture content shall beuniform throughout the layer within the range ±2% ofoptimum moisture content for the unstabilisedaggregate including any designed proportion of filler,determined in accordance with BS 1924: Part 2.

21 If the moisture content of the unstabilisedpulverised aggregate fails to meet the specifiedmoisture content range, corrective action shall betaken either by aeration to reduce the moisturecontent or controlled addition of water to increase themoisture content.

22 Aeration of the affected area shall be achievedby full depth passes of the recycling machine todisturb and loosen the material and assist theevaporation of excess moisture. The material shall bekept in a loose condition until subsequent moisturecontent tests show that the treated material hasreached the required moisture content range. Thelayer shall be re-graded nominally to level andcompacted in preparation for stabilisation.

23 Increase in moisture content of the affected areashall be achieved by the addition of water through anadjustable spraybar system in conjunction with fulldepth passes of the recycling machine to achieve auniform distribution of the water throughout the layer.Increments of water shall be added and mixed in untilsubsequent moisture content tests show that thematerial has reached the required moisture contentrange. The layer shall be re-graded nominally to leveland compacted in preparation for stabilisation.

Stabilisation process

24 Stabilisation shall not be carried out during or afterperiods of rainfall where the duration and intensity arelikely to cause the stabilised mixture to exceed thespecified moisture content criteria and compromise thestability of the layer under compaction (as defined insub-Clause 31 of this Clause). Stabilisation of frozenmaterials shall not be permitted.

25 Prior to stabilisation, pulverised materials within100mm of restricted hard edges such as kerbs andchannels, or around obstructions such as gullies, shallbe removed and spread uniformly over the remainingfull width of the pulverised material.

26 Immediately prior to stabilisation, any filler and/or adhesion agent shall be spread uniformly over thefull-width of the layer using a mechanical spreadercapable of distributing the material(s) in a uniformcontrolled manner. The rate of spread of thesematerials shall be calculated to achieve the mixturecomposition determined in accordance with Clause B2and monitored as the spreading operation proceeds inaccordance with sub-Clause 35 of this Clause.

27 The stabilisation shall be carried out to the requireddepth in a systematic pattern similar to that used for the

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pulverisation process, with an overlap of at least 150mmbetween adjacent passes of the machine. The bitumenbinder shall be introduced as a foamed bitumen anddistributed through the spraybar system, directly into therotor and mixing box of the stabiliser. The penetrationgrade bitumen shall be supplied to the spraybar of therecycling machine by pumped pipeline from on-boardtanks or from a tanker moving in tandem with therecycling machine. The rate of supply of the bitumenand any foaming agent, calculated to achieve the targetbinder content determined in accordance with ClauseB2, shall be controlled and monitored as described insub-Clause 36 of this Clause.

28 The layer of stabilised material shall be graded tolevel and compacted within two hours of the final passof the stabilising plant, unless a curing or ‘maturing’period of aeration is required. Any furrow formed byprior excavation of edge material shall be re-filled bygrading the adjacent stabilised material into the spaceusing a minimum amount of re-working.

29 The compaction of each layer shall be carried outusing compaction plant approved by the OverseeingOrganisation, until such time as the in-situ densitycomplies with sub-Clauses 40 and 41 of this Clauseand the stabilised layer provides a stable and densetight surface. Any open or segregated surface areashall be blinded using a dry crushed rock fines.

30 The stability of the layer under compaction shallbe deemed adequate if the finished surface does notshove, rut or exhibit transverse cracking under theload of subsequent construction traffic.

31 Where required by the Overseeing Organisationthe stability of a layer in any area shall be assessedafter a curing period of at least 24 hours by channelledtrafficking using a rigid three-axle tipper truck loadedto a gross mass of 24 tonnes (assumed equivalent tothree standard axles). The vertical deformation shall bemeasured in all wheeltracks at monitoring points oneach of 5 transverse sections set 1m apart after 5, 15,30 and 40 passes of the truck. The mean verticaldeformations at the above trafficking increments shallbe plotted against the respective number of truckpasses and the mean vertical deformationcorresponding to 100 standard axles shall beinterpolated. The layer shall be deemed acceptable ifthe mean vertical deformation corresponding to 100standard axles is less than 10mm.

32 On completion of compaction the surface shallbe sealed using a sprayed membrane of Class K1 - 70bitumen emulsion complying with Clause 920 in theSpecification for Highway Works. The bitumenemulsion shall be sprayed at the rate stated in theSpecification Appendix (Item 4). Where the surfaceis opened to traffic, the sealing membrane shall beblinded with fine aggregate or sand applied at a rateof 5.5 to 7.0 kg/m2. A curing period of not less than36 hours shall be allowed before the surfacing is laid.

Process control

33 The condition or quality of the pulverisedmaterial or stabilised mixture shall be assessed forspecification compliance on the basis of each 800 m2

area of the works or part thereof, completed in thesame working day.

34 The moisture content specified in sub-Clause 20of this Clause shall be monitored using testspecimens extracted from three bulk samples ofpulverised aggregate taken from points evenly spacedalong a diagonal bisecting the assessment area. Thebulk samples shall comprise material taken from thefull depth of the pulverised layer. The depth ofpulverisation relative to the designed road level shallbe measured and recorded at each point. The samplesshall also be tested to determine the particle (or‘lump’) size distribution in accordance with BS 812:Part 103 (or by an amended method to obtain an earlyassessment of grading, provided correlation with thestandard test method can be demonstrated). Whereappropriate, the residue of the three samples shall becombined to form one bulk sample and the bitumencontent of the pulverised aggregate determined inaccordance with BS 598: Part 102. If any adjustmentof moisture content is carried out prior tostabilisation, subsequent samples shall be taken andfurther moisture content tests completed.

35 The rate of spread of cement, filler, hydratedlime or quicklime shall be measured by weighing theamount of material retained on each of five trays ormats of known area laid in the path of the spreadingmachine. The trays shall be positioned approximatelyat points equally spaced along a diagonal bisectingthe area of coverage. The mean rate of spread andpercentage addition of the material shall bedetermined and recorded for each assessment area.

36 The rate of supply of bitumen binder and anyother fluids to the stabilising plant shall be set andcontinuously monitored using the appropriate flowrate meters on the stabilising plant. As a check at thestart of each work period, the rate of supply ofbitumen shall be determined from before and afterdip measurements of the storage/delivery tanks,related to an area of stabilisation of not more than250m2. The calculated supply rate of bitumen foreach test area shall be recorded.

37 As directed by the Overseeing Organisation,where lime has been used to modify a cohesive soilcomponent of the pulverised aggregate, theacceptability of the modified materials shall be testedin accordance with sub-Clause 13 of Clause 615 inthe Specification for Highway Works.

38 After stabilisation, prior to final compaction ofthe stabilised mixture, five samples of the stabilisedmaterial shall be obtained. Each sample shall be taken

37

from a point equally spaced along a diagonal bisectingthe area under consideration. The location of eachsampling point shall be recorded. Each sample shallcomprise at least 40kg of material taken from the fulldepth of the layer. The depth of stabilisation relative tothe designed road level shall be measured and recordedat each point. Where appropriate and as directed by theOverseeing Organisation, the depth measurementsshall be made using a stringline stretched betweenpoints of known level.

39 In the field, each sample of the stabilised materialshall be mixed in a tray and sufficient representativematerial taken to produce a 150mm cube specimen,made in accordance with Clause 1040 of theSpecification for Highway Works. The refusal densityfor each cube sample shall be determined to thenearest 10kg/m3. The remainder of each sample shallbe retained in a sealed condition for subsequent testingon site or in the laboratory, as described in sub-Clauses42, 43 and 46 of this Clause.

40 After trimming and final compaction of thestabilised layer, the in-situ bulk density shall bemeasured close to the material sampling points, usinga nuclear density gauge in direct transmission mode,to a depth within 25mm of the layer thickness. Themeter readings shall be verified periodically inaccordance with Clause 1041 of the Specification forHighway Works, with the gauge calibrated inaccordance with BS 1377: Part 9.

41 The in-situ bulk density values obtained shall becompared with the refusal density value obtainedfrom the cube specimens at the respective samplingpoints. The average in-situ bulk density of each set offive values shall be at least 95% of the cube refusaldensity, with no individual in-situ density value lessthan 93% of the respective refusal density.

42 Either on site or immediately on arrival at thelaboratory, each of the five samples shall be testedfor moisture content in accordance with BS 1377:Part 2.

43 Either on site or within 24 hours of arrival at thelaboratory, one 150mm diameter x 75mm to 100mmhigh cylinder test specimen [briquette specimen]shall be manufactured from each of the five samples,compacted in a PRD mould to a target density of theaverage in-situ bulk density measured in the field.The final density of each briquette specimen shall bemeasured and using the respective moisture contentvalues, the dry density values shall be determined.

44 The curing history of the five briquettespecimens prior to testing shall be recorded, whichshall, as soon as possible after manufacture, include aperiod of 72 hours at a nominal temperature of 600C.Immediately before testing each briquette specimenshall be conditioned in air for a minimum period of12 hours at 200C and then tested in accordance with

BS DD 213 to determine the Indirect TensileStiffness Modulus (ITSM) of the material. Afterremoval from the test apparatus, each briquette shallbe immersed in water at 200C for a minimum periodof 24 hours, then retested to determine the ITSM ofthe material in a saturated state.

45 The air voids content of each briquette shall bedetermined in accordance with BS 598: Part 104except that the maximum density for the partiallycoated product, used in the air void contentcalculation, shall be standardised using the maximumdensity determined for a fully coated laboratoryprepared specimen. A sample of loose pulverisedaggregate obtained prior to the addition of foamedbitumen shall be dried to constant mass at 500C.Sufficient hot penetration bitumen shall then beadded in increments to the dried aggregate in amechanical mixer until the mixture is visually fullycoated (using in the order 4% of added bitumen). Thecoated specimen shall be tested to determinemaximum density as specified in DD 228 Issue 2.

46 The residue of the five samples of stabilisedmaterial shall be combined to form one bulk sample.From this bulk sample, four sub-samples shall beobtained. Three sub-samples shall be tested todetermine the particle size distribution and one sub-sample to determine bitumen content in accordancewith BS 598: Part 102. The added bitumen contentshall be the measured bitumen content of thestabilised mixture, less the bitumen content of thepulverised aggregate prior to stabilisation.

47 The specification compliance criteria for theprocess control tests shall be as described in Table B1/1

End product performance of cold in-siturecycled bitumen bound material

48 The end-product performance of the cold in-siturecycled bitumen bound material shall be assessed onthe basis of measurements carried out in areas of800m2 or part thereof completed each working daywhich match the areas defined in sub-Clause 33 ofthis Clause.

49 Within 24 hours of completion, the as-installedperformance of the stabilised layer shall be evaluatedusing a dynamic plate loading or penetrometertechnique to determine values of elastic modulus atpoints on a nominal 2m grid pattern. The elasticmodulus at each point and the mean elastic modulusfor the assessment area shall comply with theminimum standards stated in the SpecificationAppendix (Item 5). Additionally, before proceedingwith construction of the overlying pavement, theevaluation process shall be repeated to demonstrate thatthe elastic modulus value at all points and that ofthe mean value have increased over the respective

38

as-installed values by not less than the percentagevalues stated in the Specification Appendix (Item 5).Where these criteria are not met, the full extent of non-compliant material shall be determined and appropriateremedial measures implemented. Remedial action shallcomprise either a delay in construction to allow furthercuring and stiffening of the layer or a repeat of all orpart of the recycling process, followed by re-evaluation,until a compliant material is achieved.

50 Within 270 days of completion of the surfacingworks a Falling Weight Deflectometer survey shallbe carried out and analysed in general accordancewith HD 29/94 (DMRB 7.3.2, 1994). In particular,the measurements shall be taken on the finished roadsurface in the nearside wheelpath, at a uniform andmaximum spacing of 10m. The survey shall becarried out during a period when the pavementtemperature at a depth of 50mm is within the range15 to 250C. The FWD results shall be analysed usinga linear elastic FWD back-analysis computerprogram, with the pavement modelled as a two layersystem. Layer 1 shall represent the combined designthickness of the bound materials (i.e. the combinedrecycled material and overlying surfacing materials)and layer 2 shall represent the unbound foundationlayer of infinite depth. End-product performanceshall be defined in terms of the calculated stiffness oflayer 1, uncorrected for temperature. Complianceshall be achieved when not more than 15% of thecalculated values within each assessment area fallbelow the stiffness value specified in theSpecification Appendix (Item 6).

51 In the event that the layer 1 stiffness requirementof sub-Clause 50 of this Clause is not met, the fullextent of the non-compliant material shall bedetermined by further investigation involving coringand laboratory testing. For each area of non-compliance, cores shall be extracted through the fulldepth of the stabilised layer at locations directed bythe Overseeing Organisation, at a minimum rate of1 x 150 mm diameter core per 75m2.

52 The Contractor shall be responsible for extractionof the cores with the minimum of force or disruption.Air flush coring shall be allowed for materials that aredisturbed by water flush coring. After extraction, eachcore shall be labelled and photographed and prior totesting, shall be stored in sealed polythene bags, in auniformly supported position, at a temperature of 200C± 50C. The thickness of recycled layer shall bemeasured and recorded.

53 Reinstatement of all core holes shall be completedbefore opening the area to traffic. All backfillmaterials shall comply with the ‘Specification for theReinstatement of Openings in Highways’ issued by theHighway Authorities and Utilities Committee.

54 If, at any of the prescribed core locations, it is notpossible to extract an intact core of suitable size orcondition for the end-product performance testing, usinga maximum of three attempts in an area of 1.5m radius,the material in the vicinity shall be deemed not tocomply with the end-product performance specification.

55 In the laboratory, each of the cores extractedsuccessfully shall be trimmed to remove surfacingmaterials and any underlying material prior to cuttinginto core test specimens between 75mm and 100mmhigh. Where possible, three test specimens shall beobtained from each core, one from the upper surface,one from the centre and the other from the lower half.

56 All core test specimens thus obtained shall betested in accordance with the standards described inTable B1/2.

57 The results obtained shall be used for assessingthe expected performance of the stabilised material inthe works, in relation to the known performance of BSspecified roadbase materials. The stabilised material inthe trial area shall be deemed acceptable if thecompliance criteria described in Table B1/3 are met.

Table B1/1 Compliance criteria for process control tests on recycled bitumen bound material

Material property or characteristic Individual results Mean from test set

Relative in-situ density 93% minimum 95% minimumAggregate grading [BS 598: Part 102] In accordance with sub-Clause 3 of this ClauseAdded bitumen content [BS 598: Part 102] Target ± 0.6% ## N/AMoisture content [BS 1377: Part 2] Optimum ± 3% Optimum ± 2%Layer thickness [site measurement] ± 25mm of specified ± 15mm of specifiedCement content [site rate of spread measurements] Target ± 2% Target ± 1%Indirect Tensile Stiffness Modulus (ITSM) 2000MPa minimum 2500MPa minimum- dry specimensITSM - water saturated specimens 1500MPa minimum 2000MPa minimumPercentage air voids content 12% maximum 9% maximum

## Subject to the absolute minimum added bitumen content stated in the Specification Appendix (Item 7)

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Table B1/2 Testing standards for core specimens of recycled bitumen bound material

Test Standard

Bulk density BS 598: Part 104 & sub-Clause 39 of this ClauseAir voids content BS 598: Part 104 & sub-clause 45 of this ClauseIndirect Tensile Stiffness Modulus BS DD 213: 1996

Table B1/3 Compliance criteria for recycled bitumen bound material - core specimens from the works

Material property or characteristic Individual cores Mean from core set

Core density relative to refusal density 93% minimum 95% minimumAir voids content 9% maximum 7% maximumLayer thickness [from core measurement] ± 25mm of specified ± 15mm of specifiedIndirect Tensile Stiffness Modulus 2000 MPa minimum 2500 MPa minimum- dry [BS DD 213]

Clause B2 Cold in-situ recycled bitumenbound material - mixture design andcharacterisation

1 Mixture design and characterisation of cold in-situ recycled bitumen bound material for each site,or section of site, including details of filler, binder,adhesion and/or stabilising agent(s) and theirquantities, shall be submitted to the OverseeingOrganisation at least one week prior tocommencement of the recycling works. Where thesite investigation has identified significantvariation of existing pavement materials betweendifferent sections of the site, a mix design shall besubmitted for each section of the site. Theproposed plan area and depth of the differentsections, covered by each mixture design, shall beapproved by the Overseeing Organisation.

2 The testing standards used for the mixture designof the recycled bitumen bound mixture shall be thoselisted in Table B2/1.

3 The aggregate used in the design andcharacterisation process shall be obtained from theappropriate section of the works and shall berepresentative in terms of component materialproportions, to the in-situ pavement layers to bepulverised. The laboratory manufactured aggregate shallbe pulverised or crushed such that it closely replicates thenature and grading of the in-situ pulverised aggregate andthat the aggregate particle size distribution shall complywith sub-Clause 3 of Clause B1.

4 The laboratory prepared aggregate shall bethoroughly mixed with measured proportions of thebitumen binder and adhesion agent(s), to produce atleast three trial mixtures with different addedbitumen contents. The type and grade of the bitumenand adhesion agent(s) used in the trial mixtures shallbe the same as those used in the finished works.

5 The different added bitumen contents of the trialmixtures shall be set at increments of between 0.5%and 1.0% in the range 3.0% to 6.0%, with appropriateallowance made for residual binder in any crushedasphalt component. From each trial mixture, four150mm diameter x 75mm to 100mm high, cylindertest specimens (briquette specimens) shall bemanufactured, compacted to refusal by vibratorycompaction in a cylindrical metal mould, using thecompaction mould assembly and vibrating hammerdescribed in BS598: Part 104. The bulk density ofeach cylinder shall be determined.

6 The briquette specimens shall be cured for aperiod of 72 hours at a nominal temperature of 600C.Following this, the briquette specimens shall beconditioned in air for a minimum period 12 hours at200C and then immediately tested in accordance withBS DD 213 to determine the ITSM. After furtherconditioning of the briquettes, immersed in water at240C for a minimum period of 24 hours, the ITSMtests shall be repeated on each specimen.

7 The characteristics of the mixture to be used inthe works, including any added water, shall bedetermined using the optimum ITSM (dry) values. Ifpeak conditions are not clearly displayed then plateaucharacteristics shall be accepted and the lowest addedbitumen content for which all the criteria defined inTable B2/2 are met, shall be used in the workssubject to a minimum of 4.0% for mixturescontaining only pulverised unbound or cement boundaggregate and 3.0% for mixtures containing onlypulverised bitumen bound materials.

8 On the basis of the foregoing test results, thecontractor shall declare details of the Job StandardMixture(s) for the works setting out target aggregategrading and type, tolerance on the target gradation,added water content, adhesion agents, binder contentand tolerances. The method of compaction shall bedescribed such that the material to be utilised in theworks meets the mixture characterisation parameters.

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Table B2/1 Testing standards for the design and characterisation of recycled bitumen bound material

Test Standard

Moisture content BS 1377: Part 2Bulk Density BS 598: Part 104Air Voids Content BS 598: Part 104 & sub-Clause 45 of Clause 970ARGrading and Binder Content BS 598: Part 102Indirect Tensile Stiffness Modulus [ITSM] BS DD 213: 1996

Table B2/2 Acceptable design and characteristic requirements for recycled bitumen bound material

Property or characteristic Individual specimens Mean from test set

Moisture content N/A Optimum ±2%Indirect Tensile Stiffness Modulus [dry] 2000MPa 2500MPaIndirect Tensile Stiffness Modulus [wet] 1500MPa 2000MpaBitumen content N/A Target ±0.5%Particle size distribution N/A Zone A or Zone BAir voids content Maximum 9% Maximum 7%

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Specification appendix

Site specific details and requirements to be stated in the Contract for in-situ recycled foamed bitumenbound material:

Item 1 Site description, location details and depth of recycling:

Overall location - reference to plans

Section location details- reference to plans & sections

Location of services- reference to plans & sections

Depth of recycled layer ......mm

Item 2 Type of lime required for modification of cohesive soils ......

Item 3 Location of places to stockpile excess pulverised materials awaiting re-use elsewhere

Item 4 Rate of application of bitumen emulsion sealant spray ......l/m2

Item 5 Minimum elastic modulus within 24 hours obtained using a dynamic plate or penetration test:

Single point value ......MPa

Mean value ......MPa

Minimum percentage increase of single point elastic modulus values ...... %

Minimum percentage increase of mean elastic modulus value ...... %

Item 6 Stiffness value below which not more than 15% of FWD derived stiffnessvalues shall fall for combined surfacing and recycled material. ......MPa

Item 7 Absolute minimum added bitumen content ......%

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Publication appendix

British Standards Institution (1984). Bitumen RoadEmulsions (Anionic and Cationic). BS 434. Part 1:Specification for bitumen road emulsions. London,British Standards Institution.

British Standards Institution (1984). Bitumen RoadEmulsions (Anionic and Cationic). BS 434. Part 2: Codeof practice for use of bitumen road emulsions. London,British Standards Institution.

British Standards Institution (1989). Sampling andexamination of bituminous mixtures for roads andother paved areas. BS 598. Part 102: Analytical testmethods. London, British Standards Institution.

British Standards Institution (1989). Sampling andexamination of bituminous mixtures for roads andother paved areas. BS 598. Part 104: Method of testfor the determination of density and compaction.London, British Standards Institution.

British Standards Institution (1990). Testingaggregates. BS 812. Part 109: Methods fordetermination of moisture content. London, BritishStandards Institution.

British Standards Institution (1990). Methods oftest for soils for civil engineering purposes. BS 1377.Part 2: Classification tests. London, British StandardsInstitution.

British Standards Institution (1990). Methods oftest for soils for civil engineering purposes. BS 1377.Part 3: Chemical and electro-chemical tests. London,British Standards Institution.

British Standards Institution (1990). Methods oftest for soils for civil engineering purposes. BS 1377.Part 9: In-situ tests. London, British StandardsInstitution.

British Standards Institution (1989). Bitumens forbuilding and civil engineering. BS 3690. Part 1:Bitumens for roads and other paved areas. London,British Standards Institution.

British Standards Institution (1997). Pulverized-fuel ash. BS 3892. Part 1: Specification forpulverized-fuel ash for use with Portland cement.London, British Standards Institution.

British Standards Institution (1980).Recommendations for testing of aggregates. BS 5835.Part 1: Compactability test for graded aggregates.London, British Standards Institution.

British Standards Institution (1993). Method ofdetermination of the indirect tensile stiffness modulusof bituminous mixtures. BS DD 213. London, BritishStandards Institution.

British Standards Institution (1996). Methods ofdetermination of maximum density for bituminousmixtures. British Standard DD 228. London, BritishStandards Institution.

International Organisation for Standardisatin(1994). Quality Management and Quality AssuranceStandards. ISO 9000. Parts 1 to 4. Geneva,Switzerland, International Organisation forStandardisation.

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Notes for guidance on the specification forcold in-situ recycled materials

General advice for design and construction of coldin-situ recycled materials is published in Volume 7 ofThe Design Manual for Roads and Bridges (DMRB).

These notes, related directly to the associatedSpecification for Cold In-situ Recycled Materials,offer the Design Consultant, Overseeing Organisationand Contractor the latest best practice advice on therespective design, supervision and execution of coldin-situ recycling works, used for structuralmaintenance of highway pavements.

Dependent on the type of pavement and specific siteconditions, the cold in-situ recycling process may beused to form the structural course for a reconstructedpavement or the structural course and foundationplatform as a combined layer. Alternatively, it maybe used to provide a foundation course for a newoverlying pavement construction.

Site evaluation

Identification of sites for structural maintenanceby cold in-situ recycling.

Structural maintenance of a road pavement may berequired for a variety of reasons, when the runningsurface of the pavement becomes unserviceable andthe cost of local repairs too expensive to sustain, dueto the underlying pavement structure being incapableof offering the support required.

In the event that the deterioration is identified asbeing a failure of the road haunch, any remedialmeasures should be investigated and implemented inaccordance with TRL Report 216, Road Haunches: AGuide to Re-usable Materials (Potter, 1996).

If the deterioration is identified as being a generalstructural failure of the running lanes then anyremedial measures should be investigated andimplemented in accordance with TRL Report 386,Design Guide and Specification for structuralmaintenance of highway pavements by cold in-siturecycling (Milton and Earland, 1999).

In keeping with the objectives of sustainabledevelopment, each site should be investigated withthe prime aim to determine the suitability of theexisting materials for re-use. Irrespective of theremedial strategy ultimately to be implemented, thelimits and condition of the site should be identified,including the following details for completion of theSpecification Appendix (Item 1):

l location, length and width of the site;l construction of existing pavement;l type and severity of deterioration;

l subgrade bearing capacity and condition;

l location and condition of drainage;l location and condition of services;l edge detail and verge condition, and

l future traffic loading.

To achieve the economies of scale and energysavings offered by the in-situ recycling process, aminimum programme of works in the order of3,000m2 is suggested as a general guide, which couldbe a combination of a number of locally close smallerschemes. However, in particular circumstances,where conventional methods of reconstruction areonerous or precluded, smaller scale recycling worksmay still offer a cost effective solution.

The use of the cold in-situ recycling process may alsodepend on whether there is sufficient thickness ofexisting pavement available for recycling. Although,in certain circumstances, it may be possible toinclude subgrade material into the recycled structuralcourse, provided a non-plastic pulverised aggregate isproduced naturally or by modification using lime orcement. Alternatively, it might be possible to importadditional material suitable for recycling.

Investigation framework

Any pre-contract site evaluation forming the firststage of the design process, should be planned andimplemented to ensure that sufficient information isobtained, to demonstrate to the OverseeingOrganisation whether or not, the recycling option isfeasible. In addition, this evaluation should offer anyprospective contractor all information necessary toplan their own working practices and to tender on anequitable basis to achieve the targets set by an end-product performance specification.

The sampling and testing proposals for cold in-siturecycling projects on medium to heavily traffickedsites are summarised in Table 4 of TRL Report 386.However, the actual scope of investigation carriedout should reflect the nature and variation of theexisting pavement materials.

Sites known to contain a variety of materials ofuncertain origin should be evaluated more fully thanthose that are known to contain consistent layers ofstandard materials. The limits of each section of worksshould be identified and listed separately in theSpecification Appendix (Item 1). Also, sufficientrepresentative information should be collected to satisfythe design process within each of these sections.

Alternative recycling strategies

The situation may arise where, for the purposes ofdesigning and implementing in-situ recycling, the

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variation of thickness and/or materials is beyond asection by section definition. Although, as a mixedstockpile of materials from various parts of the site, itprovides suitable feedstock for a recycled aggregate.

In such cases, despite being less environmentallysustainable compared with the in-situ process, in termsof transport movements and energy used, alternativerecycling strategies could be considered using centralor mobile crushing, screening and mixing plants.

To encourage and advance the cause of sustainabledevelopment still further, attention should be paid tothe removal from site of excess pulverised aggregate,which could be used to strengthen other roads andlanes in the area. Local co-operation betweendifferent highway authorities should be sought andprogrammes of maintenance works on different partsof the local road network co-ordinated. Locations forstockpiles of excess materials should be included inthe Specification Appendix (Item 3).

Representative test specimens

For any assessment related to the design of recyclingworks, it is particularly important that any sample ofaggregate obtained for testing is typical of thepavement to be recycled. Either as a mixed sample inrepresentative proportions or alternatively, inseparate components for recombining later.

Ideally, the test specimens should also represent thegrading and particle shape of the pulverisedaggregate. Development and use of mini-planersdesigned for trenching works, used as an in-situsampling tool, may offer a means of obtaining suchsamples. However, to date, pulverised aggregate isnot generally available during the pre-contractinvestigation and the design process relies on testspecimens derived from samples crushed in thelaboratory. A variety of laboratory crushing methodsand devices are currently employed, but none isspecifically designed to recreate the pulverisedaggregate produced by a recycling machine.

Where it is recognised that the laboratory crushingprocess is not achieving sufficient fine material -which is often the case where the feedstock materialcontains a significant proportion of hot rolled asphalt- the finer grading should not be obtained by furtherexcessive crushing, since this would not reflect thepulverisation in the field, which tends not to causebreakage of the existing aggregate component.Although not ideal, the grading of the test specimencould be contrived to satisfy the specified gradingenvelop by the transfer of fine material from othersub-samples of the laboratory crushed material.

Alternatively, the grading of the test specimens couldbe made to meet the specified grading envelop by theaddition of crushed rock fines, pit sand or PFA,

particularly if their addition is considered beneficialto the performance of the recycled material in thefield. Therefore, if the design using these testspecimens is accepted, the proportion of fine materialadded to the material pulverised in the field shouldideally, equal the proportion of the same fine materialused in the design process.

Underground services, ducts and culverts

Because of their potential for disrupting the recyclingworks, all known services, ducts and culverts within150mm of underside of the recycled layer should beaccurately located and included with the site detailsgiven in the Specification Appendix (Item 1).

Risk assessment

Before making a Contract involving the use of coldin-situ recycled materials, which are inherently morevariable than plant produced new materials, theadditional risks should be identified, apportioned andtheir management pre-planned to the satisfaction ofall parties concerned. For this reason, the Client,Overseeing Organisation and Contractor should besatisfied and be agreed that the existing pavementmaterials in all sections of the works, as defined inSpecification Appendix (Item 1), are capable of beingrecycled by pulverisation, to form the primaryaggregate component of a new cold in-situ recycledmixture. Also, that the mixture designed inaccordance with either Clause C2 for cement boundmaterial or B2 for foamed bitumen bound material, iscapable of being produced to meet the end-productperformance requirements.

Component materials

Pulverised aggregate

The nature and grading of the aggregate produced bypulverisation will depend largely on the nature,thickness and proportions of the existing roadmaterials. In situations where the depth of the existingpavement is insufficient to accommodate the newpavement design, it may be necessary to includesubgrade material into the recycled structural layer ortreat the subgrade as the only foundation, compensatedby an equivalent increase in thickness of the recycledlayer. Alternatively suitable additional aggregate couldbe imported provided site level changes are acceptable.

Normally the cement bound recycling option isreasonably insensitive to the aggregate grading,nevertheless an upper limit of 35 per cent by masspassing the 75 micron BS sieve is specified.

In comparison, the foamed bitumen bound option isoften highly sensitive to the fines component, since the

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foamed bitumen has a tendency to mix andconglomerate with the fines. As a result, the amountpassing the 75 micron BS sieve should ideally, berestricted to the range of not less than 5 per cent and notmore than 20 per cent, none of which should be clay.

Finer material may be tolerated, provided any clayfraction is modified using either hydrated lime orPortland cement. This pre-treatment is normallyrequired if the percentage of aggregate passing the75micron BS sieve is greater than 20 per cent and thePlasticity Index of material passing the 425 micronBS sieve is greater than 6.

Conversely, any material that is too coarse may bemodified by the addition of fine material to meet thespecified grading. Crushed rock fines, pit sand, PFAor lime filler are examples of materials mostcommonly used.

Moisture

The moisture content of the pulverised aggregateduring stabilisation and compaction is as important asthe grading, since it is a prime feature controlling theworkability and therefore, the degree of compactionthat is achievable.

For compaction of granular material used inconstruction, the moisture content is usuallytargeted on the optimum moisture contentdetermined in accordance with BS 5835. However,for in-situ recycled mixtures, the specifiedmoisture content is dependent on the bindercontent, targeted slightly on the wet side ofoptimum moisture content determined inaccordance with BS 1924: Part 2. Furthermore, theconstituents of the mixture to determine optimummoisture content are dependent on the proportionof filler added in the field.

For cement bound mixtures, experience has shownthat best compaction results are achieved using aspecified moisture content range of optimummoisture content to +4% of optimum moisturecontent. But for foamed bitumen bound material,since the foam contributes to the fluid content of themixture, a specified moisture content range ±2% ofoptimum moisture content is recommended.

In those cases where only a small amount of filler isadded in the field, the optimum moisture content ofthe unmodified pulverised aggregate will normallysuffice for moisture content control purpose, sincethe moisture absorbed by the filler is mostly balancedby the suppression of the optimum value. However,where the addition of filler in the field accounts formore than 4 per cent by mass, the moisture contentcontrol should be based on the optimum moisturecontent determined for the modified aggregate.

Binder agents

Primary binder agents:

The selection of the primary binder agent for aparticular recycling contract will depend to a greatextent on the site conditions, cost factors, and thedesign requirements in terms of either a flexible orflexible composite pavement. But for UK conditionsthe current recommended choice is restricted toPortland cement or foamed bitumen.

Portland cement is readily available at reasonablecost and apart from the potential for thermal crackingof stronger mixes, it has the advantage of beingadaptable to a wide range of site conditions. Methodsfor safe working are well established and it iscurrently an accepted binder for mix-in-place CBM1and CBM2, as described in Table 10/8 of theSpecification for Highway Works.

In practice it is possible to use penetration gradebitumen from grade 40 to over 200 as the basebitumen for foaming. However, higher penetrationgrades which tend to foam better, are likely toproduce mixtures of significantly lower stiffness.Experience in the UK has shown that on balance, abase bitumen of penetration grade 100 achieves thehighest possible mix stiffness consistent with anacceptable foaming and coating ability.

The stiffness gain of foamed bitumen bound mixturesis slower than that achieved by the cooling of hot-mix bitumen mixtures and is influenced by theambient conditions which dictate curing rate.

In winter conditions and particularly in colderdistricts, the use of higher penetration grade bitumenmay more easily achieve the specified degree ofcompaction. However, this is likely to produce alower stiffness material, which should be checked aspart of the design process, bearing in mind that a mixof lesser stiffness will require a thicker constructionto achieve equal performance.

Foamed bitumen has a low apparent viscosity, highvolume and low surface tension characteristics whichenable moist, cold aggregate surfaces to be coated,particularly the fine aggregate portion. The processdoes not require the evaporation of a solvent or excesswater prior to compaction and the material can bereworked if necessary, up to 48 hours after processing.

The success of foamed bitumen mixtures rely uponearly life stability derived from aggregate interlockfor pre-trafficking and ongoing development ofstiffness. However, provided the density achieved isat least 95% refusal density, experience has shownthat opening to traffic in a one day construction cycleis feasible within the contract. Although, a curingperiod of at least 36 hours should be allowed beforecommencing with the surfacing, to avoid a situation

46

where the bitumen from the recycled layer couldimigrate into the hot applied surfacing.

Supplementary binder agents:

Portland cement is commonly used as a supplementarybinder in foamed bitumen bound mixtures, added inthe proportion of about 2 per cent by mass, to act as anadhesion agent between the bitumen and dampaggregate. By using this amount of cement, it is likelyto contribute significantly to the development ofstrength and in consequence, a partially cementedbitumen bound hybrid material is formed.

Lime may be added as filler or as the modifier forplastic fines within the pulverised aggregate. Despitethe practical advantages of using quicklime related towater absorbtion and control of spreading, thestringent safety measures lead to the conclusion thathydrated lime is the preferred option for inclusion inthe Specification Appendix (Item 2).


Road pulverisation and stabilisation involves the useof specialised stabiliser plant that operates to thespecified depth plus construction tolerances. To ensureadequate pulverisation and mixing of materials to fulldepth, it is recommended that the drive performance ofthe recycling machine is at least 260kW.

Stabilisers are manufactured with a height adjustablemixing box situated close to road level, incorporatinga special toothed rotor designed to pulverise or mixthe material within the mixing hood. The use ofsmaller agricultural equipment is no substitute, sincethey are usually designed to work on cohesive soilsand therefore, are not designed to produce pulverisedgranular aggregate of the required grading or shapefor construction purposes.

Since the powerful stabiliser plant can readily damageservices, the Overseeing Organisation should identifyif any services or obstructions are present and includetheir details in the Specification Appendix (Item 1).The time required to lower any services should also betaken into account within the works programme.

A specialist manufactured stabiliser plant will almostcertainly incorporate all the features and facilitiesnecessary to complete the works in accordance withthe current recycling specification. Some will belarger and more powerful than others, whereas othersmay incorporate more refined control systems.

The systems normally employed to control the depth ofpulverisation relate the position of the rotor relative tothe vertical position of the wheels. Therefore, to ensurethat the appropriate depth of pulverisation orstabilisation is carried out consistently, it is particularlyimportant that a working platform of known levelprofile is prepared prior to the operation of the stabiliser.

Process control

This section provides guidance for the OverseeingOrganisation to help supervise the works, but in addition,describes the best practice for the Contractor to follow, tocontrol the pulverisation and stabilisation processes.

Cement bound material

Because of the similar nature of the cement boundrecycled material to that of plant mixed CBM,significant sections of the specification clauses forCBM related to process control given in theSpecification for Highway Works apply equally wellfor the recycled option. In fact, the Specification forHighway Works refers directly to the option of usinga mix-in-place method of construction for CBM1 andCBM2 mixtures. In consequence, most of the NGclauses given in the Notes for Guidance on theSpecification for Highway Works, are also applicableto in-situ recycling.

One exception to the above guidance, relates to thecuring period and use by traffic. In a structuralmaintenance situation using in-situ recycling, there isoften a requirement to maintain immediate accessthrough and within the site, for residents and servicestraffic. Also, for most recycling contracts, any accessrestriction will inevitably delay the worksprogramme. Therefore, early life or same daytrafficking is sometimes unavoidable.

However, any impairment to the recycled layer byearly trafficking may be mitigated by the use of highercement content for early strength gain or by ensuringthat adequate compactive effort has been applied andhigh density achieved. Provided the as-installed elasticmodulus measured by dynamic plate loading orpenetrometer technique, meets the targets set by thespecification, there should be no problem proceedingwith construction of the overlying pavement.

Conversely, without additional cement to enhancestrength development, it is possible to argue thatearly life trafficking could be beneficial to the longerterm performance of the pavement, by establishing acloser spaced pattern of crack in the structural course,thus making the surfacing less prone to reflectivecracking problems.

Foamed bitumen bound material

Although this material is generally labelled as a bitumenbound material, it is unlike any standard hot plant mixedbitumen bound material. The foamed bitumen tends tocombine more readily with the fines component of thepulverised aggregate, forming a ‘mortar’ matrix, whichfills the voids between the partially coated coarseaggregate. In addition, cement is commonly used as anadhesion agent, in which case a component of thestiffness is likely to derive from the hydration of the

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cement. Therefore, unlike the cement bound option, thespecification and notes for guidance for standardbitumen bound plant mixes are not readily applicable tothis cold in-situ recycled product.

Compaction control using the Nuclear Density Meteris essentially the same as for the cement boundoption, and provided adequate stability of the layer isachieved, early life trafficking is seen as no problem.The collapse of the foam will take place shortly aftermixing to allow development of stiffness by a curingprocess, which involves stiffening of the bitumen andcement bound mortar. As an additional safeguard, theas-installed performance measured by either thedynamic plate loading or penetrometer technique,should be able to demonstrate that the layer hasachieved a required stiffness, before proceeding withthe construction of the overlying pavement.

Added water and moisture control

Although the control of moisture content is of primeimportance for optimum compaction conditions,there is currently no automated process available thatcan ensure the provision of moisture at a uniform andoptimum level during the recycling process. It is vitaltherefore, that the process is controlled by anexperienced operator who has access to controls foradding water, particularly when the water is sprayeddirectly in the mixing box at the time of stabilisation.

The stabiliser should ideally, be fitted with a separatepump and spraybar system for metering the addedwater, regulated to the ground speed of the machine.An experienced operator will normally assess themoisture content of the mix relative to the targetoptimum by squeezing samples of the materialregularly by hand and be guided by test results at thecommencement or during any job so as to ‘calibrate’personal judgement. The operator must assess themoisture content immediately behind the stabiliserand be prepared to make quick adjustments as themachine may be progressing forward at a rate of 4-6metres per minute.

Application of cement or hydrated lime

Cement may be required either as the primary binderor as a supplementary binder to act as an adhesionagent or to help improve the short term properties ofthe compacted material. In comparison, hydratedlime is only used occasionally, most often as aplasticity modifier for cohesive fines within thepulverised aggregate.

Specialist spreaders are vital for the application ofthese materials, which should incorporate controlsystems to ensure that the rate of spread is achievableto a target accuracy of ±0.5 per cent of the specifiedspread rate.

The particle size of cement and lime as supplied mayvary and such behaviour should be noted as it mayaffect the accuracy of application. The use ofconsistent sources and standard routines for storageand loading of the spreader is recommended tominimise any variation.

Application of foamed bitumen

Because of the short life span of the fully foamedbitumen during the mixing process, usually definedin terms of its ‘half-life’ (i.e. time taken in secondsfor the foamed bitumen to settle to one half of theinitial expanded volume), it is necessary for thefoaming process to be incorporated into the spraybarof the recycling machine, for immediate distributionand mixing with the pulverised aggregate in themixing hood. The reduced viscosity and greatervolume of the foamed bitumen enables it to bedistributed and mixed with the damp cold aggregate.

To ensure adequate mixing of the foamed bitumen withthe aggregate, the minimum expansion ratio of the foamshould be 10, linked with a minimum half-life of 10seconds. Also, in the interests of durability, irrespectiveof the results of the design tests, the absolute minimumadded bitumen content should be 3.5 per cent. Theuniformity of mixing should be continuously inspectedvisually by the contractor and work should stop ifbitumen streaks or blotches are observed.

A typical stabiliser has computer-controlled deviceson board that calculate the application rate of thebinder as the stabiliser moves along the pavement.The stabiliser should ideally, be fitted with a separatepump and spraybar system for metering the addedbitumen and one that allows variable widths of binderto be applied. The bitumen jets should be of a selfcleansing design and for reasons of safety, bitumenlines should be heated.

The spraybar control systems incorporated into thestabiliser should ensure that the rate of spread isachievable to a target accuracy of ±0.5 per cent of thespecified spread rate, in order to achieve a constructiontolerance for added bitumen of ±0.6 per cent of thetarget binder content. As a means of verification,dipping in the tanker before and after a stabilisationrun can be used to verify the computer collected data.

An inspection or test jet should ideally be fitted toensure the flow of bitumen and that the requiredexpansion and half-life qualities of the foamedbitumen are achieved.

Compaction

Compaction is a critical part of the stabilisationprocess and demands particular care. This isespecially the case for thicker layers of construction,

48

where there is the possibility for a density profile todevelop during compaction, such that the lower partof the layer does not achieve the same density as theupper part.

This effect may be minimised when applyingcompaction at the earliest possible time using eitherheavy vibratory compaction or using a compactorcapable of ‘kneading’ the material at depth, as is thecase using a tamping roller. To date in the UK, heavycompaction for cold in-situ recycling works has beencarried out almost exclusively using the heavyvibratory roller option, although more recently, aheavy combined pneumatic tyre roller (PTR) andvibratory drum roller has been trialed, although theirfield performance has yet to be verified.

From past monitored works, it is evident that thevibratory compaction did not always achieve fulldepth compaction of thicker layers. Therefore, wherethe stabilised material is assessed as having a poorworkability, it is recommended that consideration begiven to the use of heavy tamping rollers for theinitial deep-seated compaction, particularly for layershaving a compacted thickness in excess of 225mm,followed by grading of the surface and finalcompaction using the conventional heavy vibratorycompaction. This is similar to the compactionmethodology commonly used in Australia for thick-lift construction.

When using heavy vibratory compactors, cautionshould be exercised where there is any danger ofvibratory damage to shallow culverts, undergroundservices or adjacent buildings due to the transmissionof vibrations.

The use of a pneumatic tyre roller (PTR), is oftenadvocated as a finishing roller, particularly for thecement bound material. However, whereas the PTRmay tend to assist in the compaction of the lower levelmaterial, care is required to ensure that the nearsurface material does not dry out or stiffen too quickly,which may result in disruption and shear displacementof the near surface material caused by the narrowloading under the individual tyres - thus resulting in anunstable surface finish and the necessity for removingloosened unacceptable material.

Surface sealant

The type and rate of spread of the bitumen sealant, asstated in the Specification Appendix (Item 4), shouldcomply with the recommendations given in BS434.

End-product performance specification

The process of cold in-situ recycling for the structuralmaintenance of highway pavements has been developedand used in a variety of countries, each with their own

local requirements, often related to climate and geology.Consequently, the types of road available for recyclinghave been diverse. As a result, previous recyclingspecifications have been derived from a variety ofcomponent material designs and construction methodsthat were generally aimed at producing materials ofquasi standard form with anticipated performancesimilar to the plant mixed option.

Whilst the recipe and method specification has served theindustry well for the lower trafficked roads, end-productperformance specification is seen as a means ofspecifying recycled materials in their own right, usingperformance targets stated in terms of engineeringproperties, allowing the recycled material to beconsidered for more heavily trafficked sites on anequitable basis to standard plant produced materials.

The end-product performance assessment isdesigned to follow a three stage procedure, to allowthe construction to proceed at the same time asgiving the Overseeing Organisation the opportunityto verify the acceptability of the product at theearliest possible time.

As-installed stiffness using a dynamic plate orpenetrometer test

The as-installed performance of the stabilised layer,within 24 hours of completion of compaction, isevaluated using a dynamic plate loading orpenetrometer technique to determine values of elasticmodulus at points on a closely spaced grid pattern.Furthermore, before proceeding with the surfacingconstruction, repeated values should be expected todemonstrate that the elastic modulus values haveincreased by a reasonable amount, as an indicationthat the curing/stengthening process has started. Thefirst repeat measurements should normally be madeafter 24 hours and thereafter, at intervals dependenton the measured rate of increase of elastic modulus.

The single point and mean value of elastic modulus forthe assessment areas, also their respective percentageincrease, must comply with the minimum standardsstated in the Specification Appendix (Item 5).

Experience to date using a dynamic (light) plateloading technique, has determined that fresh, wellcompacted cold in-situ recycled material typicallyachieves a single point elastic modulus value (E

vd) in

the range 40 to 70 MPa. Therefore, the as-installedperformance of a acceptable constructed layer, basedon at least 100 point evaluations, is expected todisplay an initial minimum mean value of elasticmodulus in excess of 50 MPa, with no single pointvalue less than 30 MPa. Prior to surfacing, anincrease of 20 per cent for single point values and 30per cent for the mean value, would be indicative thatthe curing process is underway. For the as-installedcondition and initial stage of curing, these values

49

should be applied to both the cement bound andbitumen bound materials.

For other plate loading or penetrometer test methodsan equivalent correlation shall be provided to thesatisfaction of the Overseeing Organisation.

Pavement stiffness from falling weightdeflectometer (FWD) survey

The current status of the FWD and associated elasticstiffness evaluation does not allow the procedure tobe used as a rejection method. However, ifacceptably high stiffness modulus values aredetermined consistently, as described in theSpecification Appendix (Item 6), the method shouldprovide the Overseeing Organisation with sufficientconfidence and a means of acceptance for either thecement bound or foamed bitumen bound materials.

Experience to date using the FWD survey andanalysis, as described in the Specification, suggeststhat a pavement stiffness value for the combinedbound layers of the pavement (i.e. recycled layer plussurfacing) in the order of 5000 MPa for the cementbound option and 2500 MPa for foamed bitumenbound option, below which not more than 15 per centof the derived values shall fall, offers an acceptableperformance standard.

Compressive strength/stiffness measurements ofcore specimens

The development of the end-product performancespecification for the cold in-situ recycled materialshas passed through various stages, in which the initialintention was to determine the performance of coredspecimens, in terms of either the compressivestrength of cement bound material or the IndirectTensile Stiffness Modulus (ITSM) of bitumen boundmaterial.

The above option was set aside, however, when itwas decided that the destructive coring should onlybe performed as a last resort. This decision wasreinforced by the experience gained on somemonitored sites, where the core extraction itself wasdifficult, such that a suitable number of testspecimens could not be obtained.

The rate of success for extraction of cores from coldin-situ recycled material is generally enhanced byusing air flush coring, in comparison with the successrate achieved using the more usual water flushmethod. Also, removal of the cored asphalt surfacinglayers, before proceeding with the coring into therecycled material, was found to improve the successrate of core extraction.

In the event that acceptance is not achieved using theFWD survey and analysis, the current specification

uses the core testing option as the last resortperformance assessment. Therefore, if carried outafter the FWD survey, as late as possible within theContract maintenance period, it should maximise thesuccess rate for the extraction of cores and offer thebest opportunity for obtaining suitable test specimensand achieving the required ITSM values.

Mixture design and characterisation

The design procedures adopted to date, have beendeveloped by various organisations for their ownlocal needs, although in general, most mixture designprocedures for cold in-situ recycled materials arebased on the determination of compressive strengthfor cement bound material or the stiffness modulusfor bitumen bound material, related to a recycledlayer of specified thickness, to carry a required trafficloading over a stated period of time.

In practice, since the feedstock material to bestabilised does not usually exist until afterpulverisation, the initial mix appraisal or designprocess is often a matter of experience by thespecialist contractors using their particular recyclingplant, to gain an understanding of the near optimumcomponent design.

Also, since the results of stiffness and other testsperformed on laboratory prepared specimens arehighly dependent on the curing regime of thespecimens, which is unlikely to be recreated on site,these tests are realistically only valid for comparisonand assessment of the optimum mixture condition.Therefore, the values obtained do not necessarilyrelate to the in-situ condition of the material.

The details of the procedures given in Clauses C2 andB2 of the Specification are based on the currentindustry practices, which are open to development ifmore representative specimens and test results can beverified.

Cement bound mixtures:

For lower traffic situations, cold in-situ cementbound recycling is often used to provide a newfoundation and/or structural course, designed to havean average 7 day cube compressive strength of 4.5N/mm2 or 7 N/mm2 (i.e either CBM1 or CBM2equivalent strength).

For higher traffic loading, the recycled layer is used asthe main structural course, designed to have anaverage 7 day cube compressive strength of 10 N/mm2

(i.e CBM3 equivalent). In ideal circumstances thismaterial might be considered structurally equivalent toplant mixed CBM of equal compressive strength. Inpractice, inherent variability of the feedstock materials,short mixing period and practical difficultiesassociated with thick-lift construction, will require afactor of safety applied to the design thickness.

50

For the stronger recycled mixtures, the potential forthermal cracking and reflective cracking of thebituminous surfacing is similar to that for conventionalplant mixed CBM. Therefore, the thickness ofsurfacing layers should normally be the same asspecified for a conventional flexible compositepavement carrying the same traffic loading.

The cement contents used in the design process forrecycled mixtures are similar to that required for theplant mixed equivalent, except that an absoluteminimum cement content of 3 per cent by weight isrecommended, to ensure there is adequate cementavailable for distribution throughout the mixtureduring the short period of in-situ mixing.

Bitumen bound mixtures:

The main objective of the design process for foamedbitumen bound recycled material is to check that anadequate level of stiffness is achieved using anoptimum added bitumen content, when mixed with apulverised aggregate derived from the existing roadconstruction also containing the correct proportionsof any adhesion agent and/or added filler.

The target stiffness for all levels of traffic isgenerally accepted as a NAT measured individualITSM value of 2000 MPa and an average value of2500 MPa.

Experience has shown that the stiffness for recycledmixtures is generally insensitive to variations ofadded bitumen content, with an adequate stiffnessachieved for an added bitumen content over a plateauoptimum range of 3 to 6 per cent, subject to therecommended absolute minimum added bitumencontent of 3.5 per cent to account for durability.

Any existing bitumen in pulverised aggregate is notnormally activated in the stabilisation process in thesense of mixing with the new binder, although theeffect of the residual bitumen in the finished mixturecould influence the stiffness achieved.

For the laboratory production of foamed bitumen, itis recommended that the anticipated bitumen supplieris consulted, in conjunction with the manufacturer ofany foaming agent used, in an attempt to replicate asclosely as possible, the characteristics of the foamedbitumen to be used, particularly in terms of the sizeand sustainability of the air bubbles during mixing.

The specified curing programme for the specimens priorto testing, including baking of the specimens for 72hours at 600C, is not an attempt to represent the curingconditions in the field, but is a standardised attempt toreplicate the longer term ageing process of the recycledmaterial. The drawback of using this technique is that itmay disguise the true early life stiffness of the recycledmaterial, in favour of a higher set of values that mayonly be appropriate in the longer term.

51

Acknowledgements

The work described in this report was carried out in the Civil Engineering Resource Centre on behalf of theCSS, Colas Limited and the Highways Agency. The Quality Audit Review Officer was Mr J F Potter.

The research was guided by a Steering Committee members were:

S Biczysko (Chairman) Northamptonshire County Council

J Mercer Quality Services, Pavement Engineering Group, Highways Agency

M Roy Somerset County Council **

S Childs Surrey County Council

T Lomas Hampshire County Council

D Laws W S Atkins East Anglia Limited

B Hicks Colas Limited

J Potter Transport Research Laboratory

M Earland Transport Research Laboratory

L Milton Transport Research Laboratory

Substitute and supplementary members were:

R Dudgeon Quality Services, Pavement Engineering Group, Highways Agency.

B McWilliams W S Atkins - South West (latterly of North Somerset EngineeringConsultancy)

G Mountjoy W S Atkins - South West

** withdrew on retirement from Somerset CC during 1996

52

Appendix A: Research methodology

A1 Introduction

The Linear Quarry Project spanned a three yearinvestigative period during which time data were collectedfrom a review and examination of nine in-service roadswhich had been maintained using cold in-situ recyclingtechniques, by Local Authorities, over the preceding decadeand from the construction and monitoring of full-scale trialson the A3088, Cartgate Link Road, in Somerset.

A complementary report by Milton (1999), summarisedbelow, gives the full details of the investigative studiescarried out.

A2 Sites investigated

The in-service sites had been constructed over a range ofsubgrades and were designed to carry, over a 20 yearperiod, traffic loadings ranging between 2.5 msa and 20

msa. However, despite the fact that much of the earliercold in-situ recycling work in the UK was undertakenusing cement or lime as the primary binding agent, thesearch for sites carrying revealed only two suitable cementbound sites worthy of further investigation. Details of thein-service sites are given in Table A1.

The site of the full-scale construction trials, on theA3088 was a 15-year-old, two lane single carriagewayroad that was built as a major access route from theindustrial estates and ferry ports to south to the A303 to thenorth. It was built over much of its length following thenear level alignment of an abandoned railtrack, passingthrough a rural landscape for the most part at grade or onshallow embankment but with short lengths of cutting. Theoriginal road had exceeded its design life and distress waspresent in the form of surface rutting and cracking.Interpretation of deflections from a series of deflectographsurveys showed that the residual life had been exceeded.

The original pavement construction comprised 100mmof asphalt surfacing over 140mm of wet-mix macadam

Table A1 Cold in-situ recycled roads selected for performance and condition measurement

SpecifiedDesign recycled Binder content (%)20 year layer

Site Date of traffic thicknessArea Bitumen Subgrade Site/trafficlocation works (msa) (mm) # (m2) (pen) Lime Cement type conditions

Lake Road, July 9 220 4950 4.0 (100) 1.0 Hardcore over Inner urban access/bus routePortsmouth, 1989 soft alluvium with significant commercialHampshire flow

Kingston Road March 4.5 210 2500 4.0 (100) 2.0 Thames Valley Main urban access routeTeddington, 1994 Tertiary deposits with modest commercial flowLondon

Kingsway, May 20 300 3256 4.0 (100) 2.0 Hardcore over Urban distributor road withBedford, 1994 alluvial deposits mixed traffic/heavy rush hourBedfordshire

A24 London Road, Oct. 11 250 5080 2.5 (100) 1.0 Hardcore over Urban principal route withEpsom, 1989 North Downs low commercial flowSurrey Tertiary beds

Park Road, Nov. 20 300 4500 4.0 (200) 1.0 Clay-with-flints Urban distributor road withDartford, 1987 significant commercial flowKent

Priory/Knight Road, July 7 300 4950 4.0 (200) 1.0 Hardcore/ash Industrial urban access andStrood, Rochester, 1987 over soft through route, parts alreadyKent alluvium carried 13msa over 10 years

Valley Drive, 1987 2.5 200 2200 ** (200) ** Coombe valley Access route to town centre,Gravesend, Kent deposits bus route but otherwise a low(Winchester/Hillside) commercial vehicle flow

Valley Drive, 1987 2.5 300 2400 ** Coombe valley As aboveGravesend,Kent deposits(St Hildas/Livingstone)

A1078 South Sept. 10 250 3500 4.0(100)## ** Glacial sands Access to docks, withWootton, Kings Lynn, 1995 2.0 ## and gravels significant commercial flowNorfolk

** Values not reported# Plus 100mm asphalt surfacing specified for all sites## 100m section of foamed bitumen bound material Ch 0 to 100m westbound

53

roadbase founded on a Type 1 sub-base of variablethickness between 150 and 470mm, built to reflect thechanges in the CBR of the subgrade.

The Cartgate Road trial was carried out in two phases inconsecutive years. Phase 1 of the trial occupied the full-widthof the north and south bound lanes over a length of 1.25km,divided into eight trial sections varying in length between100m and 150m; the monitored length of each bay wasstandardised at 100m. In addition, there were two controlsections constructed using conventional materials, one offlexible design and the other of flexible composite design.

Four of the trial sections were constructed using acement stabilised recycled roadbase and four with foamedbitumen bound recycled roadbase. The sections includednot only different binder agents and thickness of treatment,but also different combinations of source aggregate,dependent on how much of the existing pavement wasremoved prior to pulverisation. Details of the designs ofthe sections are given in Table A2.

For Phase 2 of the Cartgate Road trial two adjacent full-width, 600m long sections were constructed on a furtherstretch of the A3088 to test the viability of draftspecifications for both cement bound and foamed bitumenbound cold in-situ recycled material under normalcontractual conditions.

In both sections, the recycled materials comprisedaggregates reclaimed from the wet-mix roadbase and sub-base layers of the existing road, which were exclusivelyconstructed using crushed carboniferous limestone fromthe Mendips. The construction details of each section ofthe Phase 2 trial are given in Table A3.

A3 Measurement of performance and pavementcondition

The performance and condition of each of the nine in-service selected sites was assessed by:

l Extraction of representative cores.

l Visual survey to identify and log surface defects.

l Falling Weight Deflectometer (FWD) survey.

l Laboratory testing of selected core specimens:

– Bulk density by gamma-ray scanner.

– Bulk density by weighing in air and water.

– Indirect tensile stiffness modulus (ITSM) using theNottingham Asphalt Tester (NAT).

– Core compressive strength/ estimated cube strength ofcement bound material.

The data collected from the in-service road monitoringwas supplemented by data collected from the CartgateRoad trials. During construction of the trials the followingquality control and compliance testing of the material wascarried out:

l Particle (lump) size distribution.

l Monitoring of moisture content.

l Cube refusal density determination.

l As placed density determination by Nuclear DensityMeter.

l Thickness of recycled layer.

l Cube compressive strength of moulded samples.

l ITSM of moulded samples (foamed bitumen materialonly).

l Compositional analysis (foamed bitumen material only).

Following construction of the Cartgate Road trials theperformance and condition of the test sections wereassessed by:

l Visual inspections.

l Laboratory tests on cores.

– Bulk density by gamma-ray scanner.

– Bulk density by weighing in a air and water.

– Indirect tensile stiffness modulus (ITSM) using theNottingham Asphalt Tester (NAT).

– Core compressive strength/ estimated cube strength ofcement bound material.

l Falling Weight Deflectometer (FWD) surveys.

l Deflectograph surveys (carried out routinely by theHighway Authority).

A4 Performance compared with original design

Compilation and subsequent analysis of the data collectedas outlined above enabled comparisons to be madebetween the in-service performance of the sites and theiroriginal design.

The comparisons for the sites where foamed bitumenbinder was used are summarised in Figure A1. Thecorresponding comparisons for the cement bound materialsare summarised in Table A4.

A5 Discussion

The results of the research carried out for roads recycledwith foamed bitumen binder, showed that in all but onecase the predicted life of the recycled road was at least aslong as the design life. Therefore, the plotted dashed line,in Figure A1, was considered to offer a reasonable designcurve for traffic loading between 2.5 msa and 20 msa,associated with a standard foundation, dependant onsubgrade conditions and 100mm surfacing comprisingstandard asphalt materials.

Similarly, a consideration of the findings from roadsrecycled with cement enabled a design curve for thesematerials to be formulated. As was the case for thebitumen bound design, for traffic loadings between 2.5msa and 20 msa the cement bound design curve assumes astandard foundation dependant, on subgrade condition andhas associated with it a variable thickness of asphaltsurfacing.

For both the foam bitumen bound and cement bound in-situ recycled roads carrying less than 2.5 msa the thicknessof the recycled material is generally governed by the depthof the existing road construction and the subgradecondition. The design of these lower traffic category roadswere based on the findings reported by Kennedy on behalfof the Department of the Environment, Energy Efficiency

54

Table A2 Details of reconstruction of Cartgate Phase 1 trial sections

Existing BituminousSection number construction surfacing (and(chainage (m)) depth (mm) (Lower) roadbase and foundation construction upper r/b)

1 Control Section 1: (Composite construction - CBM3R). 50 mm HRA w/c100 mm DBM b/c or

(1200-1300) 450 200 mm plant mixed CBM3R lower roadbase. DBM upper r/b100mm Type 1 sub-base remains.

2 40 mm HRA wearing course removed. As above310 mm basecourse + granular rotovated.

(1300-1400) 450 Excess 110mm removed.200 mm recycled to produce CBM3R equivalentlower roadbase.

3 40 mm HRA wearing course removed. As above350 mm base course + granular rotovated.

(1400-1500) 450 Excess 100 mm removed.240 mm recycled to produce CBM3R equivalentlower roadbase.

4 100 mm bituminous surfacing removed. As above250 mm granular materials rotovated.

(1500-1600) 450 Excess 50 mm removed.200 mm recycled to produce CBM3R equivalentlower roadbase.

5 100 mm bituminous surfacing removed. As above290 mm granular material rotovated.

(1600-1675) 450 Excess 50 mm removed.

(1675-1700) 660 240 mm recycled to produce CBM3R equivalentlower roadbase.

6 40 mm HRA wearing course removed. 50 mm HRA w/c280 mm basecourse + granular rotovated. 50 mm DBM b/c

(1700-1850) 660 Excess 60 mm removed.220 mm recycled to produce foamed bitumenDBM (100 pen) equivalent roadbase.

7 40 mm HRA wearing course removed. As above325 mm basecourse + granular rotovated.

(1850-1975) 660 Excess 60 mm removed.265 mm recycled to produce foamed bitumenDBM (100 pen) equivalent roadbase.

8 Control Section 2: (Flexible construction - DBM) As above[NB. excluding existing areas of reconstruction].

(1975-2000) 660(2000-2200) 450 220 mm plant mixed DBM (100 pen) roadbase.

Where necessary and subject to proof rolling,excavate to incorporate a minimum 150 mm Type 1sub-base.


(2200-2325) 710 No excess removed.220 mm recycled to produce foamed bitumenDBM (100 pen) equivalent roadbase.


(2325-2450) 710 No excess removed.265 mm recycled to produce foamed bitumenDBM (100 pen) equivalent roadbase.

55

Table A3 Details of construction of Cartgate Phase 2trial sections

Recycled road AsphaltSection base construction surfacing details

1 Cement 100mm asphalt surfacing removed; 50mm HRA w/cbound 290mm granular materials rotovated; 100mm DBM b/c

Excess 50mm removed; and240mm stabilised with 4% cement toproduce lower roadbase.

2 Foamed 100mm asphalt surfacing removed; 50mm HRA w/cbitumen 265mm granular materials rotovated; 50mm DBM b/cbound No excess removed; and

265mm stabilised with 4% foamedbitumen produce roadbase.

Table A4 Summary of design life and predictedperformance of cement bound recycledpavements

. Original 20 Predicted overallyear design life of the recycled

Site No life (msa) pavement (msa)

Valley Drive, Gravesend 2.5 10St Hildas/Livingston

A1078 10 10South Wooton, Kings Lynn

A3008 22 22Cartgate Road, Yeovil

0

50

100

150

200

250

300

350

400

0.1 1 10 100


Str

uctu

ral c

ours

e th

ickn

ess

(mm

)

Design traffic loading (msa)

Traffic carried to 1997 (msa)

Predicted life (msa)

85

2

3

6

41

7 Site key:

1. Lake Road, Portsmouth 2. Kingston Road, Teddington 3. Kingsway, Bedford 4. London Road, Epsom 5. Park Road, Dartford 6. Priory/Knight Road, Strood 7. Valley Drive, Gravesend

8. Cartgate

Figure A1 Predicted life in relation to design traffic loading with structural course thickness design line using cold in-situfoamed bitumen bound recycled material

56

Office (ETSU, 1994) and also takes into account thecriteria published in TRL Report TRL216 (Potter, 1996),for the in-situ recycling of road haunches.

The draft specification for in-situ recycling that wasprepared for construction of Phase 2 of the Cartgate Roadtrial was written with the aim of moving away from recipe/method requirements towards those of end-productperformance, measured by laboratory tests on corespecimens extracted from the finished pavement or bynon-destructive in-situ tests. However, to ensure durabilityfrom the recycled material some method specificationsclauses were retained.

In general terms the draft specification was found to beworkable and robust under normal contractual conditions.Following completion of the monitoring of the sites,compilation and analysis of the data gathered enabled thespecification to be refined into that which is presented inPart 2 of this Report.

A7 References

Department of the Environment, Energy EfficiencyOffice (1994). Performance of roads reconstructed by coldin-situ recycling 1985 - 1987. Best Practice programme,General Information Report 17, Energy EfficiencyEnquiries Bureau, ETSU, Harwell.

Milton L J (1999). Design guide and specification forstructural maintenance of highway pavements by cold in-situ recycling. Part 1: Investigation Reports. Part 2:Development of design guide and specification. ProjectReport PR/CE/193/98. Transport Research Laboratory,Crowthorne. (Unpublished report available on directpersonal application only)

Potter J F (1996). Road haunches: A guide to re-useablematerials. TRL Report TRL216. Transport ResearchLaboratory, Crowthorne.

Williams J (1995). Highways and Conservation. Paperpresented at the 1995 BACMI ACMA Seminar.

57

Appendix B: Examples to demonstratethe design process

Example 1

Design requirements:Type 1 road with cumulative traffic loading of 15msaExisting surface level to be retained

Existing road construction:Bound layers (mm) = 250Granular material (mm) = 2205% CBR subgrade

Cement bound design option:

From Figure 1:Thickness of surfacing (mm) = 140Thickness of structural course (mm) = 240Total (mm) = 380

Referring to Table 4, the thickness of remaining granularfoundation is 160mm deficient. Therefore, in accordancewith Table 5, the thickness of recycled layer should beincreased by 0.45 x 160 = 72mm

Revised design:Thickness of surfacing (mm) = 140Thickness of recycled layer (mm) = 312Total (mm) = 452

But the thickness of recycled material is marginally inexcess of the specified maximum of 300mm, which maybe offset by an equivalent increase in the thickness ofsurfacing. (i.e. 10mm thickness of surfacing isapproximately equivalent to 12mm thickness of recycledmaterial).

Working design:Thickness of surfacing (mm) = 150Thickness of recycled layer (mm) = 300Total (mm) = 450

Foamed bitumen bound option:


Referring to Table 4, the thickness of remaining granularfoundation is deficient by 115mm. Therefore, inaccordance with Table 5, the thickness of recycled layershould be increased by 0.65 x 115 = 75mm

Revised design:Thickness of surfacing (mm) = 100Thickness of recycled layer (mm) = 310Total (mm) = 410

But the thickness of recycled material is marginally inexcess of the specified maximum of 300mm, which maybe offset by an equivalent increase in the thickness ofsurfacing.


Example 2

Design requirements:Type 2 road with cumulative traffic loading of 7msaExisting surface level to be retained

Existing road construction:Bound layers (mm) = 250Granular material (mm) = 3003% CBR subgrade

Cement bound design option:


Referring to Table 4, the thickness of remaining granularfoundation is deficient by 90mm. Therefore, in accordancewith Table 5, the recycled layer should be increased inthickness by 0.45 x 90 = 40mm

Working design:Thickness of surfacing (mm) = 120 Thickness of recycled layer (mm) = 260Total (mm) = 380

Foamed bitumen bound option (i):


Referring to Table 4, the thickness of remaining granularfoundation is deficient by 50mm. Therefore, in accordancewith Table 5, the recycled layer should be increased inthickness by 0.65 x 50 = 32mm.


Foamed bitumen bound option (ii):


58

Referring to Table 4, the thickness of remaining granularfoundation is deficient by 60mm. Therefore, in accordancewith Table 5, the recycled layer should be increased inthickness by 0.65 x 60 = 40mm


Example 3

Design requirements:Type 3 roadExisting surface level to be raised by 50mm.

Existing road construction:Bound layers (mm) = 100Hardcore = 250Ash (mm) = 506% CBR subgrade

Cement bound design options:

From Table 6:Thickness of surfacing (mm) SD 40 100Thickness of recycled layer (mm) 260 220 160Total (mm) 260 260 260

But since the surface level is to be raised by 50mm, theobvious approach would be use an overlay of 50mm as thesurfacing. Therefore, from interpolation of the above data:


However, the surface level could be raised by theimportation of aggregate from a quarry or recycledpulverised material from another site.

Alternative design:Thickness of surfacing = SDThickness of imported aggregate for recycling (mm) = 50Thickness of in-situ pavement for recycling (mm) = 210Total (mm) = 260

Foamed bitumen bound option:

From Table 6:Thickness of surfacing (mm) SD 40 100Thickness of recycled layer (mm)330(N/R) 290 230Total (mm) N/R 330 330

Again, the practical approach would be use an overlay of50mm as the surfacing. Therefore, from interpolation ofthe above data:


In this case an alternative design using a surface dressingand imported aggregate is not appropriate because themaximum recommended depth of recycling would beexceeded.

59

Abstract

This Report describes research carried out with the aim of promoting the use of cold in-situ recycling for thestructural maintenance of highways.

A description of the research methodology is given. Data collected from two full-scale road trials and from ninein-service roads which had been recycled within the previous decade were collated. Using this data a Design Guidefor cold in-situ recycling with foamed bitumen and cement binders was produced. A series of flow charts anddecision trees guide the reader through the many variables that come to the fore when recycling, in-situ, an existingroad. Environmental factors and site evaluation are also given due consideration.

A Specification and Notes for Guidance on the Specification for cold in-situ recycling are presented in a stand-alone format so that the specification clauses are available for inclusion in standard contract documentation forstructural maintenance works.

Related publications

TRL216 Road haunches: A guide to re-usable materials by J Potter. 1996 (price £35, code J)

SR675 In-situ recycling of asphalt wearing courses in the UK by G D Goodsall. 1981 (price £20)

CT20.1 Road building and the environment update (1993-1997). Current Topics in Transport: selected abstractsfrom TRL Library's database (price £20)

CT36.1 Recycling of road materials update (1993-1996). Current Topics in Transport: selected abstractsfrom TRL Library's database (price £20)

CT89.1 Aggregates in road construction update (1996-1998). Current Topics in Transport: selected abstractsfrom TRL Library's database (price £20)

Prices current at August 1999

For further details of these and all other TRL publications, telephone Publication Sales on 01344 770783 or 770784,or visit TRL on the internet at http://www.trl.co.uk.