DMRB VOLUME 7 SECTION 2 PART 4 - HD 27/04 - PAVEMENT ...

February 2004

DESIGN MANUAL FOR ROADS AND BRIDGES

VOLUME 7 PAVEMENT DESIGN ANDMAINTENANCE

SECTION 2 PAVEMENT DESIGN ANDCONSTRUCTION

PART 4

HD 27/04

PAVEMENT CONSTRUCTIONMETHODS

SUMMARY

Chapter 2 of this Part has been revised to reflect currentpavement design issues. It offers broad guidance of theissues to be considered when widening existing roads.Chapter 3 that deals with rapid concrete constructionhas not been revised with this update of the Standardand although the advice continues to be valid,references may need to be checked.

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1. Remove existing Contents pages for Volume 7.

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3. Remove HD 27/94 [Incorporating AmendmentNo. 1 dated March 1995 and Amendment No. 2dated February 1999] from Volume 7, Section 2,Part 4 and archive as necessary.

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HD 27/04

Pavement Construction Methods


Summary: Chapter 2 of this Part has been revised to reflect current pavement designissues. It offers broad guidance of the issues to be considered when wideningexisting roads. Chapter 3 that deals with rapid concrete construction has notbeen revised with this update of the Standard and although the advicecontinues to be valid, references may need to be checked.

THE HIGHWAYS AGENCY

SCOTTISH EXECUTIVE

WELSH ASSEMBLY GOVERNMENTLLYWODRAETH CYNULLIAD CYMRU

THE DEPARTMENT FOR REGIONAL DEVELOPMENTNORTHERN IRELAND

Volume 7 Section 2Part 4 HD 27/04

February 2004

Registration of Amendments

REGISTRATION OF AMENDMENTS

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

amendments amendments

VOLUME 7 PAVEMENT DESIGN ANDMAINTENANCE

SECTION 2 PAVEMENT DESIGN ANDCONSTRUCTION

PART 4

HD 27/04

PAVEMENT CONSTRUCTIONMETHODS

Contents

Chapter

1. Introduction

2. Widening of Pavements

3. Rapid Construction and Repair of ConcretePavements

4. References and Bibliography

5. Enquiries


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February 2004

General

1.1 This Part contains details of various constructionmethods and techniques which are particularly relevantto Volume 7. General requirements for pavementconstruction methods can be found in the Specification(MCHW1) and in the Highway Construction Details(MCHW3). This Part includes details for the wideningof existing pavements and covers the area of design,materials and construction. These techniques will beused more frequently as a high proportion of the trunkroad network needs to be widened or improved tohandle increased traffic capacity. Rapid constructionand repair of concrete pavements is also covered anddraws on experience gained from contracts both in theUK and in the United States.

Implementation

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

Mutual Recognition

1.3 The construction and maintenance of highwaypavements will normally be carried out under contractsincorporating the Overseeing Organisation’sSpecification for Highway Works (MCHW1). In suchcases, products conforming to equivalent standards andspecifications of other member states of the EuropeanCommunity and tests undertaken in other member stateswill be acceptable in accordance with the terms of the104 and 105 Series of Clauses of that Specification.Any contract not containing these Clauses must containsuitable clauses of mutual recognition, having the sameeffect regarding which advice should be sought.

1. INTRODUCTION

Chapter 1Introduction

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NTS

Chapter 2Widening of Pavements

2. WIDENING OF PAVEME

General

2.1 With the projected increases in traffic, elementsof the trunk road network, ranging from singlecarriageways to Dual 4-lane motorways, will continueto need to be widened and/or improved.

2.2 Each individual scheme will vary in scope sinceother improvements including changes in geometry,levels and superelevation and improvements to sightlines will often be included in addition to the provisionof extra lanes. Widening may be symmetrical on-line,asymmetrical on-line (see Figure 2.1) or off-line on newground, depending on the site and, in the case ofwidening from single to dual carriageway, will usuallybe a combination of all three in order to improve theline and gradients. Such changes will generally affectlevels and crossfalls and, therefore, also impact onpavement design.

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2.3 Widening, and associated improvement works,presents a valuable opportunity to upgrade the whole ofthe existing pavement, in line with current standards.All options for carrying out the works must be assessedon the basis of minimising whole life costs over a40-year analysis period. Consideration should also begiven to the principles of sustainable development,which will generally favour maximum use, or re-use, ofthe existing construction.

2.4 This chapter gives broad guidance on some of thepavement design and construction issues that should beconsidered where the widening of existing roads isproposed. It does not cover earthworks or generaldrainage issues associated with widening; advice onthese is given in HA 43 (DMRB 4.1.7).

EXTRA LANE EXTRA LANE

EXISTING CENTRAL RESERVE & DRAIN

SYMMETRICAL ON-LINE WIDENING

ASSYMMETRICAL ON-LINE WIDENING

Figure 2.1 Basic Approaches to Road Widening

EXISTING CENTRAL RESERVE AND CARRIAGEWAY RECONSTRUCTED NEW CONSTRUCTION

EXTRA LANES EXISTING CARRIAGEWAYS

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works.


Evaluation of Existing Pavement

2.5 For on-line widening, where the newconstruction will abut the existing carriageway, a fullassessment of the condition of the existing pavementshould be obtained through surveys and detailedinvestigations on site in accordance with the advicegiven in HD 29 (DMRB 7.3.2) and HD 30(DMRB 7.3.3). As-constructed records may alsoprovide a useful source of information but it isimportant that the accuracy of such records, inparticular the depths and extent of the pavementconstruction, is verified through exploratoryexcavation.

2.6 Guidance on the analysis of pavement surveys isgiven in HD 29 (DMRB 7.3.2) while advice on theinterpretation of results and design of appropriatestrengthening measures is given in HD 30(DMRB 7.3.3).

2.7 In the case of flexible, and certain flexiblecomposite, pavements the categorisation of the existingpavement as ‘Long Life’, ‘Upgradeable to Long Life’ or‘Determinate Life’ should be determined, if not alreadyknown, in accordance with HD 29 (DMRB 7.3.2).Where the pavement is determined to be ‘Upgradeableto Long Life’ appropriate works to achieve the upgradeto the ‘Long Life’ classification should be considered,provided this is justified on the basis of the whole lifecost assessment.

2.8 In conjunction with new construction and anymaintenance or strengthening works to the existingpavement, consideration should be given to assessingthe skidding resistance and riding quality of the existingpavement with a view to improvement where necessary.It is likely that the existing pavement will require aquiet surface course and to match the surface of thewidened sections. Further information on the factorsthat affect skidding resistance and appropriate levels forvarying site conditions is given HD 28 (DMRB 7.3.1)while advice on surfacing options is provided in HD 36,HD 37 and HD 38 (DMRB 7.5).

Design

2.9 The design of widened areas of pavement shouldbe in accordance with HD 26 (DMRB 7.2.3). Proposalsfor on-standard designs must be submitted to theOverseeing Organisation for approval.

2.10 The ground conditions beneath an existingpavement, as determined during the investigation and

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evaluation process, may be used as the basis forestimation of the long-term condition beneath anadjacent new pavement.

2.11 Where the carriageway is to be widened on-line itis essential that the greatest care is taken during designto ensure that the drainage paths under old and newpavements are maintained, particularly where falls andelevation are being altered. It is suggested thatlongitudinal and cross sections are produced at frequentintervals to check that the drainage is not hindered.Maintenance of drainage paths may result in a thickerbound construction than is required for the newpavement in accordance with HD 26 (DMRB 7.2.3),notably where an overlay is applied to strengthen orreprofile the existing pavement. Particular care must betaken in the use of bound sub-bases for widening toensure that this layer does not effectively form animpermeable barrier, trapping water in the foundationof the existing construction.

2.12 Where the proposed new design thickness for awidening strip is thicker than the adjacent, structurallysound, existing flexible pavement, special provisionmay have to be made for sub-base drainage or theexisting pavement may have to be overlaid to maintaindrainage paths.

2.13 As some surface water does percolate through thepavement surface it is essential not to impede the flowof water in the underlying pavement layers. Whenmatching new lanes against an existing carriageway thethickness of new bound layers will usually have to bethe same or less. The interfaces of the underlayersshould lead into each other or into positive drainagepaths.

2.14 However, where the new and existingconstruction cannot be adequately matched, due, forexample, to the use of different forms of construction ormaterials, the use of drainage layers may be required.Adjustment to the crossfall may also be required toensure water is not trapped under the pavement.

2.15 Advice on crossfalls and other surface drainageconsiderations for wide carriageways is given in TA 80(DMRB 4.2.2).

2.16 Where a new or modified drainage system isrequired for the widened pavement the detailing shouldtake into account the need to keep the existing systemoperative until the new system can be brought into use.

2.17 The construction sequence may need to beplanned to avoid the possibility of ponding during the

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2.18 The overall design should take account of theneed to keep disruption to a minimum. It is oftenbeneficial that sections of new carriageway are madeavailable to traffic as quickly as possible. Dueconsideration must also be given to the safety of thepublic and the Contractor’s workforce.

2.19 Consideration should be given to providing ahardened central reserve in conjunction with wideningworks, in order to reduce routine maintenance. Thesurface finish of a hardened central reserve shouldcontrast with that of the adjacent carriageway.

Pavement Materials

2.20 The only restriction on the type of material to belaid alongside the existing pavement, providing thematerials conform to the requirements of theSpecification (MCHW1), is that continuouslyreinforced concrete pavement construction should notbe laid alongside an existing jointed rigid pavement.This is because it is not possible to tie the twoconstructions to provide satisfactory edge and cornersupport while accommodating relative movement due tothermal effects. The choice of which constructionoptions to include in the tender documents is theresponsibility of the Overseeing Organisation at thecontract documentation stage and decisions should takeaccount of future maintenance costs so that the wholelife cost is kept to a minimum.

2.21 Consideration should be given to the use of highperformance bond coats to enhance adhesion and sealbetween adjoining constructions (see MCHW1,Clause 901).

2.22 In the assessment of whole life costs, on the basisof a 40-year analysis period, consideration should begiven to the future maintenance of both the existing andwidened elements of the pavement. This is likely tofavour options that ensure future maintenance can betimed to minimise interventions that cause disruptionand delay. However, where site constraints and/oroperational procedures indicate a preferred solutionother than that which would give the lowest whole lifecost, approval must be sought from the OverseeingOrganisation, supported by evidence to demonstratethat the proposed solution will provide acceptable valuefor money.

2.23 Where it is required to provide increased loadcarrying capacity for the additional lanes yet maintainthe same thickness as the existing pavement, the use ofHigh Modulus Base (HMB) asphalt, flexible composite

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nstruction or Continuously Reinforced Concretevement (CRCP) should be considered.

4 Similarly, where overlay thickness is restricted,th HMB and CRCP should be considered as optionsr strengthening the existing carriageway.

nstruction

5 In matching new pavements to existing, the level the existing surface or any proposed overlay willve to be taken as datum for levels of the newrfacing irrespective of minor settlements. Any areasth major settlements affecting the riding qualityould be identified for regulating or reconstructionior to adding the new lanes. Alternatively, in the case a rigid concrete pavement, local settlements may bectified by slab jacking and vacuum grouting; see

32 (DMRB 7.4.2).

6 Asymmetrical widening should be designed soat longitudinal joints between old and new are mid-e or near lane divisions so avoiding wheel tracks.ort lengths crossing a lane diagonally, which may be

ctated by realignment, may be acceptable.

7 Widening may result in existing drainage runsing beneath the carriageway. It is normallyacceptable for manholes, gullies or other ironwork to placed within vehicle running lanes. If this cannot beoided then the use of higher specification chamberd gully tops should be considered. Advice onamber and gully tops is given in HA 104MRB 4.2.5), while guidance on general safetypects of road edge drainage is given in HA 83MRB 4.2.4). The use of combined drainage and kerbstems may also provide a viable option in somecumstances, and advice on these systems is given in 39 (DMRB 4.2.1).

8 Where widening asphalt pavements in similarnstruction, layers should be cut back and benched toy into the old construction (see Figure 2.2 forinimum widths). Joints into sub base or capping layerould be made where there is clean material. Ifcessary the 150 mm minimum should be increasedtil clean material is encountered. Special care isquired during compaction of any granular layers tosure a sound joint between the two materials.

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Figure 2.2 Benching at Joint between Sections of Bituminous Paving

SURFACING

BASE

SUB-BASE

CAPPING

Existing

ConstructionProposed

Construction

150 mm(min)

150 mm(min)

150 mm(min)

2.29 Where the pavement construction is on theprogramme critical path rapid construction methodsmay need to be considered.

2.30 Where sufficient space is available asphaltmaterials can be laid quickly with pavers in echelon toavoid longitudinal joints which need cutting back whencold. In winter, successive layers can be placed in rapidsuccession, but both this and echelon work will dependon sufficient compaction plant being available to ensureadequate compaction can be achieved. Information onlaying of asphalt surface course is given in HD 37(DMRB 7.5.2).

2.31 When ambient temperatures are high, it may benecessary to delay the opening of the pavement totraffic to ensure that the surface course and lower layersare sufficiently stiff to resist deformation under vehicleloading.

2.32 Where asphalt material is to be laid against anexisting pavement, drainage channels, kerbs, bridgeparapets etc, suitable preformed sealing strips should beconsidered for application to the vertical surface of theexisting pavement, after cutting back. This could avoidthe need to overband the longitudinal joint or to cut asealing groove and apply a poured sealant.

2.33 Details of rapid methods of concrete pavementconstruction are given in Chapter 3 of this Part. Theroad may be opened to normal traffic when the strengthof the concrete has been demonstrated to have reached25 N/mm2.

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2.34 Where an extra jointed concrete lane is added toan existing jointed concrete carriageway, the transversejoints should be aligned and of the same type andwidth. At the longitudinal joint between the existingand new concrete, a groove should be sawn to anappropriate depth and filled with an approved sealingcompound.

2.35 To reduce the time and cost of drilling for tiebars, consideration may be given to the use of barswhich are deformed and so which may be shorter inlength and/or larger in diameter than the requirementsof the Specification (MCHW1).

2.36 Where existing concrete slabs have to bereplaced the slabs could be sawn into small sectionsduring one traffic closure and removed and replacedduring the next.

2.37 A technique for strengthening a concrete road inconjunction with the widening of the carriageway hasbeen developed in the USA. The strengthening consistsof an overlay, of minimum depth 50mm, which isbonded to the surface of the existing paving. Thewidening can be placed separately from the bondedoverlay or monolithically with the overlay in one pass(see Figure 2.3). Longitudinal joints are required in thenew concrete at positions which are dependent on thedimensions of the existing carriageway and thewidening strips. Tie bars are inserted into holes drilledin the sides of the existing slab.

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2.38 Prefabricated slabs have been used for newconcrete pavements in other countries. Construction isexpensive but fast and can significantly reduce trafficdelays. The slabs, which should be made to a highstandard of dimensional accuracy, can have self-levelling devices and special dowel fixings to connectwith neighbouring slabs. The voids between sub-baseand slabs are filled by pressure grouting. The processneeds special equipment.

Figure 2.3 Strengthening of Concrete Road in Conjunction with Widening

EXTRA WIDTH

EXISTING CONCRETE

EXISTING LONGITUDINAL JOINT

CONCRETE OVERLAY EXTRA WIDTH

LONGITUDINAL JOINTS WHERE REQUIRED

TIE BARS

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AND REPAIR OFS

Chapter 3Rapid Construction and Repair of Concrete Pavements

3. RAPID CONSTRUCTIONCONCRETE PAVEMENT

General

3.1 It has been traditional to wait long periods of 14to 21 days for concrete to cure before use by traffic.The degree of maturity was based on the requiredstrength at 28 days. This imposed restrictions on repairsand reconstruction in concrete when compared withbituminous surfaces. However, increases in traffic onmajor roads and the need to keep lane closures to aminimum has heightened the need for concrete tomature to sufficient strength in hours rather than days.

3.2 Extra rapid hardening cements were first used inthe UK in 1970 for repairs to the M4 motorway whichwere opened to traffic in 6 hours. However, longpossessions of carriageways for normal repairs orreconstruction gave no incentive for use of the moreexpensive rapid hardening cements. Other rapidconstruction methods have since been studied byBritish engineers and successful full scale trials havebeen carried out in the UK.

3.3 This Chapter gives the requirements for earlyopening of concrete pavements to traffic and includesadvice on materials and methods for rapid construction.It will be of particular importance in reconstruction,widening schemes, minor improvements and repairs forbenefits in traffic management.

Principles

3.4 Rapid construction in concrete depends on therate at which the concrete can develop sufficientstrength for opening the pavement to traffic.

3.5 Early strength development can be controlled bythe type of cement, cement content, the water-cementratio and by curing. Normal ingredients as forconventional pavement quality concrete should be usedtogether with admixtures or additives depending on thedegree of urgency. This may be under 6 hours or over 3days according to the type of construction or repairbeing considered.

3.6 Rates of gain in strength can be enhanced byusing rapid hardening types of cements, and increasingthe cement content to reduce the period before use bytraffic. Figure 3.1 illustrates this and the use of an early

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strength cement in preference to larger quantities ofOrdinary Portland Cement (OPC) will depend on theurgency and economics.

Figure 3.1 Increasing Cement Content toReduce Time before Traffic

3.7 Further increase in strength can be achieved byaccelerating curing methods.

Requirements

3.8 For designed mixes the concrete shall have toachieve the required 7 or 28 day strength forcompliance with the Specification (MCHW1) 1000Series.

3.9 Before use by any traffic, the following are thecharacteristic compressive strengths which eachpavement layer shall be expected to reach, subject tothe proviso given in paragraph 3.10.

Early strengthcement

OPC

Time toopeningroad totraffic

QUANTITY OF CEMENT INCREASING

6 hrs

12 hrs

18 hrs

24hrs

30hrs

3 days

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Pavement quality concrete surface slabs 25N/mm2

Pavement quality concrete roadbases 20N/mm2

Roller compacted concrete, cement bound material orwet-lean concrete of the following grades:

CBM 4 or C20 concrete 15N/mm2



CBM 1 or C 7 concrete 4.5N/mm2

3.10 In the case of roller compacted concrete or CBMthe next pavement layer may be laid within 4 hours ofplacing the cement bound layer. Once the next layer islaid the pavement shall not be trafficked until thecement bound layer is expected to reach the requiredstrength given above.

3.11 Mortars for bedding iron work such as manholecover frames during repairs may be trafficked when thestrength is expected to be 20 N/mm2. For rapidconstruction, this strength should be achieved within 2hours.

MATERIALSCements

3.12 High early strength cements are now permitted inthe Specification (MCHW1) 1000 Series and should beused for rapid construction and repairs. Concretes withstandard rapid hardening Portland cements conformingto BS 12 (1991) have achieved 25 N/mm2 strength inless than 18 hours, with cement contents of 400 kg/m3

or more.

3.13 Examples of special cements or concrete mixeswhich can give high early strength include:

a) A calcium sulpho-aluminate based cement usedextensively in the mining industry (40N/mm2 in3 hours).

b) A high strength proprietary cement and fibrereinforced, non-shrink concrete (25N/mm2 in3 hours).

c) A mixture of early strength Portland Cement,microsilica and superplasticiser.

d) Proprietary polymer modified concrete mixes.

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Pozzolanas

3.14 When Pulverized Fuel Ash (PFA) is added to themix it improves the workability and allows a lowerwater-cement ratio, which in turn increases the concretestrength. It can be as additional fine material or as apartial Portland cement replacement. With the latter,early strength will be reduced as the pozzolanic reactionis secondary but leads to higher ultimate strength anddenser concrete.

3.15 Microsilica can also be used to increase earlystrength and density, but it reduces the workability, soplasticisers or superplasticisers are necessary to keep alow water-cement ratio.

3.16 These materials tend to make cohesive mixeswhich require vibration for compaction and finishing.

Admixtures

3.17 As many of the high early strength cements havequick setting properties, the workability needs to bemaintained during transit to site. Plasticisers andsuperplasticisers should be used for this as well asreducing the water-cement ratio. Air entraining agentsshould be used for slab replacement wherever possiblebut need not be used for small batches of high strengthconcrete for thin bonded patches.

Aggregates

3.18 For high early strength concrete, angularaggregates from crushed rock or crushed gravel arepreferable. The addition of more fines in the form ofPFA and microsilica will produce a denser concretewith few voids.

3.19 As some cements may have high alkali contents,the requirements for prevention of Alkali SilicaReaction (ASR) will still apply, so non-reactiveaggregates may be needed.

MAIN CONSTRUCTION

3.20 Normal paving operations as specified in theSpecification (MCHW1) 1000 Series will apply.Concrete mixes should usually be designed mixes andtested for compliance with the Specification at theappropriate age, unless the use of prescribed mixes isapproved by the Engineer.

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3.21 Slip form pavers with their higher outputs havean advantage over fixed form plant for rapidconstruction, and setting out guide wire posts is quickerthan laying forms more common with the necessarybedding.

3.22 Auger pavers or truss type vibrating finishingbeams provide a good finish and are more versatile forsmall areas and are recommended for use with internalvibration using poker vibrators for compaction of thickslabs, as in the Specification (MCHW1) 1000 Series.

3.23 Where there is restricted access, eg. in single lanewidening, conveyors can help to spread the concretequickly.

3.24 Transverse joints other than in single bayreplacement, should be sawn but may be wet-formed inwinter. Cork seals can be used as formers and so avoidthe need for a separate sealing operation, for individualslabs or short lengths.

3.25 Higher slab temperatures may result from theheat of hydration of higher cement contents and causemore thermal stress on cool nights. It may beadvantageous to saw some joints early within 2 hours ofplacing the concrete, using a light saw which cuts agroove through a bearing plate which holds the concretein place and prevents coarse aggregate being pluckedout, instead of waiting about 4 hours or more beforebeing able to use a conventional saw. This may relieveearly stress and avoid random cracking before the jointscan be properly sawn. Any such joint grooves should bedeepened and widened for sealing using a conventionalsaw as required in the Specification (MCHW1) 1000Series if the joint is not already cracked.

3.26 Dowels can be inserted satisfactorily with slipform pavers, without creating surface irregularities andpoor riding quality, if the insertion mechanism does notstop the paver nor have a vertical reaction on anyconforming plate. Alternatively, dowels may be placedon cages. When dowels are inserted from the surface orif joints are to be wet-formed, additional compactionand regulation is necessary, by a longitudinal oscillatingand vibrating finisher.

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uring

.27 The concrete should be cured, as required in thepecification (MCHW1) 1000 Series using resinompound or bituminous spray for the relevantavement layer.

.28 In addition thermal insulation blankets aspecified in Specification (MCHW1) 700 Series shoulde used to accelerate the strength development to meethe specified strength in the required time. Insulationlankets will be necessary if the road is to be traffickedn any period between 5 hours and 3 days after theoncrete is placed. They may also help the strengthevelopment of the special cements which can berafficked in under 5 hours.

.29 The purposes of the insulation blankets are to:

) Assist in the prevention of loss of moisture fromthe concrete so increasing the rate of hydrationand reducing shrinkage.

) Promote a uniform temperature gradient throughthe slab so reducing the risk of thermal cracking.

) Induce a higher temperature within the slab byretention of the heat of hydration and acceleratethe chemical reaction, leading to strengthdevelopment.

ONCRETE PAVEMENT REPAIRS

.30 Concrete for repairs may be designed mixes orrescribed mixes. Before prescribed mixes can be used,vidence of the strength development of such a mixhould be obtained. Proprietary prepacked mixes comeithin the term of prescribed mixes. All such mixes

hould be able to develop 40N/mm2 at 28 days and5N/mm2 at the time required for use by traffic.

.31 Once a prescribed mix has been approved, theroportions and ingredients should not be changed.uality will depend on correct proportioning.

3.32 Non-shrink concretes are preferred for thinbonded patch repairs. Some high strength concretesused for patching can be affected by high temperaturessoon after placing. The patches can be subjected towarping and tend to de-bond around the perimeter.Under traffic these can then crack.

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3.33 Effective curing will reduce the risk oftemperature stress and warping. The traditional methodof curing patches is to spray with resin curingcompound and cover the patches with damp hessian andan impermeable sheet to retain moisture in the patch.Large variations of temperature in the patch can beavoided by using insulation blankets.

Sealing Joints

3.34 Most hot and cold poured sealants need to beplaced into dry mature concrete. They need to be placedinto grooves which have been grit blasted to ensure agood bond. Grit blasting may be carried out as soon asthe concrete is expected to reach 15N/mm2 and thejoints can be sealed as soon as possible after thatinstead of waiting 14 days as required in the BritishStandard. Otherwise the joints should be sealed inaccordance with the Specification (MCHW1) 1000Series.

3.35 As most joints will have to be sawn, the sealinggroove would be suitable for compression seals or pre-compressed neoprene impregnated expanding foamseal, or cork strips, which can be placed as soon as thegroove has been cut which would be earlier than sealingwith applied sealants. Pre-compressed neopreneimpregnated expanding foam sealant strips shouldcomply with The British Board of Agrément certificate88/2123C.

STRENGTH ASSESSMENT

3.36 Assessment of strength for trafficking willdepend on whether the mix is a designed mix or aprescribed mix. For designed mixes, cubes should betaken and tested at early ages commensurate with thetime required for opening to traffic, which should beallowed as soon as the concrete reaches 25N/mm2.

3.37 Cubes made, stored and tested in accordance withBS 1881 (1983) will not necessarily reflect the realstrength in the pavement. Without accelerated curing,the strength in the pavement will vary with temperatureand climatic conditions and is usually 5% less than thestrength of the cubes stored under laboratoryconditions. Temperature matched curing (TMC) ofspecimens for testing would give more realistic resultsif time allows.

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3.38 In the absence of TMC, approximate values ofthe pavement strength can be obtained from cubes madeand stored alongside the pavement, insulated in such away as to simulate the conditions in the pavement.

3.39 Strength development curves for a particular mixcan be obtained by testing cubes at different ages ontrial mixes before work starts. If such curves are used toassess the time for opening to traffic or for gaugingwhen to test cubes on site, ambient temperatures at timeof placing should be compared with the temperature atwhich the strength development curve was obtained.For any significant drop in temperature (more than 5oC)additional time should be allowed, as strengthdevelopment slows in cooler weather. Insulationblankets will help to maintain an even temperature.

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4. REFERENCES AND BIBLIOGRAPHY

References

1983

BS 1881; Part 108; “Making Cubes”, BSI.BS 1881; Part 111; “Storing Cubes”, BSI.BS 1881; Part 116; “Testing Cubes”, BSI.Note: BS 1881 now replaced by BS EN 12390

1991

BS 12; “Specification for Portland Cements”, BSI.Now replaced with BS EN 197-1.

Design Manual for Roads and Bridges

HD26 (DMRB 7.2.3) Pavement Design.HD28 (DMRB 7.3.1) Skidding Resistance.HD29 (DMRB 7.3.2) Structural Assessment Methods.HD30 (DMRB 7.3.3) Structural Assessment Procedure.HD32 (DMRB 7.4.2) Maintenance of Concrete Roads.HD36 (DMRB 7.5.1) Surfacing materials for new andmaintenance construction.HD37 (DMRB 7.5.2) Bituminous surfacing materialsand techniques.HD38 (DMRB 7.5.3) Concrete surfacing and materials.HA39 (DMRB 4.2.1) Edge of pavement details.HA43 (DMRB 4.1.7) Geotechnical considerations andtechniques for widening highway earthworks.HA83 (DMRB 4.2.4) Safety aspects of road edgedrainage features.HA104 (DMRB 4.2.5) Chamber tops and gully tops forroad drainage and services: Installation andmaintenance.

Manual of Contract Documents for Highway Works

Specification for Highway Works (MCHW1).

Notes for Guidance on the Specification for HighwayWorks (MCHW2).

Chapter 4References and Bibliography

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Chapter 5Enquiries

5. ENQUIRIES

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

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

Chief Road EngineerScottish ExecutiveVictoria QuayEdinburgh J HOWISONEH6 6QQ Chief Road Engineer

Chief Highway EngineerTransport DirectorateWelsh Assembly GovernmentLlywodraeth Cynulliad CymruCrown Buildings J R REESCardiff Chief Highway EngineerCF10 3NQ Transport Directorate

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

DMRB VOLUME 7 SECTION 2 PART 4 - HD 27/04 - PAVEMENT ...

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