CementTreatedRecycledCrushedConcrete
andMasonryAggregatesforPavements
Dongxing Xuan
CementTreatedRecycledCrushedConcrete
andMasonryAggregatesforPavements
Proefschrift terverkrijgingvandegraadvandoctor aandeTechnischeUniversiteitDelft, opgezagvandeRectorMagnificusprof.ir.K.C.A.M.Luyben, voorzittervanhetCollegevoorPromoties, inhetopenbaarteverdedigenopmaandag01oktober2012om10:00uur door DongxingXuan MasterofScienceinMaterialsScience&Engineering WuhanUniversityofTechnology,P.R.China geborenteQinggang,Helongjiang,P.R.ChinaCopromotor: Ir.L.J.M.Houben Samenstellingpromotiecommissie: RectorMagnificus TechnischeUniversiteitDelft,voorzitter Prof.dr.ir.A.A.A.Molenaar TechnischeUniversiteitDelft,promotor Prof.dr.Z.H.Shui WuhanUniversityofTechnology,promotor Ir.L.J.M.Houben TechnischeUniversiteitDelft,copromotor Prof.F.AgrelaSainz,PhD UniversityofCordoba Prof.dr.ir.H.E.J.G.Schlangen TechnischeUniversiteitDelft Prof.ir.A.Q.C.vanderHorst TechnischeUniversiteitDelft Dr.ir.C.A.P.M.vanGurp KOACͲNPC Prof.dr.ir.K.vanBreugel TechnischeUniversiteitDelft,reservelid Publishedanddistributedby: DongxingXuan SectionofRoadandRailwayEngineering FacultyofCivilEngineeringandGeosciences DelftUniversityofTechnology P.O.Box5048,2600GADelft,theNetherlands EͲmail:xuandx@whut.edu.cn;xuandx@gmail.com ISBN: 978Ͳ94Ͳ6203Ͳ150Ͳ0 Printing:WohrmannPrintService,Zutphen,theNetherlands ©2012byDongxingXuan
All rights reserved. No part of this publication protected by this copyright may be reproduced, stored in any retrieval system or transmitted in any form or by any means, electronic or mechanical, including photocopying or recording, without the priorwrittenpermissionfromthepublisher.
Tomywife,XuanXUAN(⦴⪷),whoalwayssupportsme, andmyson,HemingXUAN(⦴㦧䬝),whosesmilealways cheersmeup.
Acknowledgements
TheresearchpresentedinthisdissertationwasfundedbytheChinaScholarship Council and the Road and Railway Engineering section of the Faculty of Civil Engineering and Geosciences at the Delft University of Technology (TUD) in the Netherlands.TheworkofthisresearchwasfullycarriedoutatTUD.Theauthor wouldliketothankthesectionandstaffforalltheirassistanceandcooperation duringthelastfiveyears.
Inparticularmythanksandsinceregratitudegotomypromotor,Prof.dr.ir.A.A.A. Molenaar.Heproposedthisresearchpositiontome,andhasgivencarefulreview and invaluable comments on test results and reports during my PhD study. This dissertation could not be completed without his overall support. I also wish to extendmyappreciationtomypromotor,Prof.dr.Z.H.Shui.Heencouragedmeto study abroad and to broaden my academic horizon, which is important for my futurecareer.
The assistance I got from my coͲpromotor, Associate Prof.Ir. L.J.M. Houben, is greatlyappreciated.TheknowledgeIobtainedfromhisdailysupervision,careful concerns and precious detailed comments on my dissertation was extremely valuable.Iwasveryluckytoworkwithhim.
The help I got from Prof.dr.ir. H.E.J.G. Schlangen (Microlab, Faculty of Civil EngineeringandGeosciences,TUD)ishighlyappreciatedaswell.Iamgratefulfor hisguidanceandcommentsonmynumericalwork.Itmadeitfeasibletopredict the mechanical properties of my researched material by means of computer simulations.
Special thanks go to Dr.ir. C.A.P.M. van Gurp and Ir. F. Stas (KOACͲNPC in the Netherlands), who presented their experience of cement treated recycled materials and arranged an onͲsite visit in Belgium. It made me realize that the qualitycontrolofmyresearchedmaterialshouldbecomprehensivelytakeninto account.IappreciatedtheirhelpandIenjoyedthediscussionswithIr.F.Stas. AwordofthanksisalsoextendedtoProf.dr.F.AgrelaSainz(AreaofConstruction Engineering, University of Cordoba, Spain) for his information about the real applicationofcementtreatedmixgranulatewithrecycledmasonryandconcrete in practice. His results showed the applicability of my researched material in practice.
Marco, Jan Moraal, Dirk, Gang, Milliyon and Jian) as well as all present Ph.D. studentsattheRoadandRailwayEngineeringsectionofTUDfortheirsupport.It wasanicetimetoworkwithallofyou;thankyouallforthecontributiontomy work and help to me. Special thanks are given to my colleagues in my office, DiederikvanLentandNingLi,whomademylifeenjoyableduringthebusyand challengingyearsasaPhDstudent. ⦴ьޤ August,2012 Delft
Summary
This research is focusing on the characterization of the mechanical and deformation properties of cement treated mixtures made of recycled concrete and masonry aggregates (CTMiGr) in relation to their mixture variables. An extensive laboratory investigation was carried out, in which the mechanical properties of CTMiGr and the deformation characteristics relevant to shrinkage cracksusceptibilitywereevaluated.
The main aim of this research is to develop models which allow the structural
propertiesofCTMiGrtobeestimatedfromitsmixturecomposition.Thesemodels
are then used to develop a mixture optimization tool for CTMiGr taking into account the requirements that have to be set to the material in structural pavementdesigns.
To realize the research objective, firstly a series of tests were conducted on CTMiGr mixtures which varied in composition. The test program comprised of measuring compression, indirect tension and deformation properties of CTMiGr mixtures. The recycled construction and demolition materials used in this study were recycled masonry aggregate (RMA) and recycled concrete aggregate (RCA) whichareusedforunboundgranularbases/subͲbasesintheNetherlands.Fora goodunderstandingoftheinfluenceofthemixturevariablesonthepropertiesof
CTMiGr,fourimportantmixturevariables(ratioofamountofRMAtoRCAbymass,
cement content, degree of compaction and curing time) were selected to be takenintoaccountinanelaborateexperimentalprogram.
Theexperimentalresultsgaveinsightintotheinfluencesofthedifferentmixture
variables on the structural properties of CTMiGr. They showed that the
mechanical properties and deformation behavior of CTMiGr depend on the
mixture proportioning of CTMiGr. It was possible to develop accurate models to estimatethestructuralpropertiesofCTMiGrfromthemixturevariables.
It is noteworthy that the RMA content in CTMiGr strongly determines its
mechanicalanddeformationproperties.DuetothepresenceofthelowͲstrength RMA, failure of CTMiGr originates either through the RMA particles or in cracks and discontinuities in the internal structure (the matrix) or in the bonding layer between aggregates and matrix. This will depend on the mixture variables. Numerical work using a lattice model further demonstrated that if the tensile
strengthofRMAishigherthan1.0MPa,itscontributiontothestrengthofCTMiGr
designedpavementstructure.Ifinapavementtheverticalcompressivestresses atthetopoftheCTMiGrlayerarelow,crushingthatmightoccuratthetopofthe CTMiGr layer is not an issue. In that case it is preferred to design the CTMiGr mixture by lowering the cement content, enhancing the degree of compaction and increasing the RMA content. On the other hand, when the vertical
compressivestressesatthetopoftheCTMiGrlayerarehigh,itisrecommended
to decrease the RMA content as well as to adjust the cement content and the degree of compaction. In all cases increasing the degree of compaction is beneficial.
Samenvatting
Dit onderzoek betreft de karakterisering van de mechanische en vervormingseigenschappen van cementgebonden mengsels van gerecycled
betonͲenmetselwerkaggregaat(CTMiGr)inrelatietotmengselvariabelen.Ineen
uitgebreid laboratoriumonderzoek op CTMiGr mengsels zijn de mechanische
eigenschappenendevervormingskarakteristieken,relevantvoordegevoeligheid vanhetmateriaalvoorkrimpscheuren,geëvalueerd.
Het belangrijkste doel van dit onderzoek was om modellen te ontwikkelen
waarmeedestructureleeigenschappenvanCTMiGrvoorspeldkunnenwordenop
basis van de mengselsamenstelling. Deze modellen zijn vervolgens gebruikt om een procedure voor de optimalisatie van het ontwerp van CTMiGr mengsels te ontwikkelen, rekening houdend met de eisen waaraan het materiaal moet voldoenbijhetstructureelontwerpvanverhardingen.
Om het onderzoeksdoel te realiseren is allereerst een serie proeven uitgevoerd
op CTMiGr mengsels met verschillende samenstelling. Het proefprogramma
omvatte het meten van de drukͲ, indirecte trekͲ en vervormingseigenschappen
van CTMiGr mengsels. De in dit onderzoek gebruikte gerecyclede bouwͲ en
sloopafval materialen zijn gerecycled metselwerkaggregaat (RMA) en gerecycled betonaggregaat (RCA) waarvan mengsels in Nederland worden toegepast als ongebonden wegfundering. Voor een goed begrip van de invloed van de
mengselvariabelen op de eigenschappen van CTMiGr mengsels zijn vier
belangrijke variabelen (verhouding van de massapercentages RMA en RCA, cementgehalte,verdichtingsgraadencuringtijd)inbeschouwinggenomenineen uitgebreidexperimenteelonderzoek.
De proefresultaten geven inzicht in de invloed van de verschillende mengselvariabelen op de structurele eigenschappen van CTMiGr. De resultaten tonen aan dat de mechanische eigenschappen en het vervormingsgedrag van CTMiGr afhankelijk zijn van de samenstelling van het mengsel. Het is mogelijk gebleken om accurate modellen te ontwikkelen voor het voorspellen van de
structureleeigenschappenvanCTMiGropbasisvandemengselvariabelen.
Het RMA gehalte in CTMiGr bepaalt in sterke mate de mechanische en
vervormingseigenschappenvanhetmengsel.Alsgevolgvandeaanwezigheidvan zwak RMA aggregaat treedt bezwijken van CTMiGr op door het RMA aggregaat heenofinscheurenendiscontinuïteitenindeinternestructuur(dematrix)ofin de hechtlaag tussen het aggregaat en de matrix. De wijze van bezwijken is
Op basis van een uitgebreide analyse van de structurele eigenschappen van
CTMiGrwordentenslotteenkelerichtlijnengegevenvoordeoptimalisatievanhet
mengsel. Op deze wijze wordt het mengselontwerp van CTMiGr optimaal
gekoppeld aan de karakteristieken van de ontworpen verhardingsconstructie. Indienineenverhardingsconstructiedeverticaledrukspanningaandebovenzijde van de CTMiGr laag klein is, dan is verbrijzeling van die CTMiGr laag niet aan de orde. In dat geval heeft het de voorkeur om van het CTMiGr mengsel het cementgehalteteverlagenenzoweldeverdichtingsgraadalshetRMAgehaltete verhogen. Wanneer echter de verticale drukspanning aan de bovenzijde van de
CTMiGrlaaggrootis,danwordtaanbevolenomhetRMAgehaltetereducerenen
zowelhetcementgehaltealsdeverdichtingsgraadaantepassen.Inallegevallen heeftverhogingvandeverdichtingsgraadeengunstigeffect.
1 INTRODUCTION ... 1 1.1CEMENTTREATEDBASES/SUBͲBASES ... 2 1.1.1TypicalpavementdesignswithCTGrM... 2 1.1.2Granularmaterialsusedforcementtreatment ... 3 1.1.3TraditionalmixturedesignofCTGrM ... 4 1.2AIMANDSCOPEOFTHERESEARCH ... 5 1.3ORGANIZATIONOFTHEDISSERTATION... 6 REFERENCES ... 7 2 LITERATUREREVIEW ... 9 2.1STRUCTURALREQUIREMENTSOFCTGrMASAPAVEMENTLAYER ... 10 2.2MATERIALSANDTRADITIONALMIXTUREDESIGNOFCTGrM... 13 2.2.1Materialssuitablefortreatmentwithcement... 13 2.2.2Requirementsoftreatedgranularmaterials... 15 2.2.3Traditionalmixturedesign ... 18 2.3TYPICALSTRUCTURALPROPERTIESOFCTGrM ... 19 2.3.1Unconfinedcompressivestrength ... 20 2.3.2Tensilestrength... 26 2.3.3Modulusofelasticity... 29 2.3.4VolumetricdeformationofCTGrM... 35 2.3.5FatigueofCTGrM... 40 2.4CONCLUSIONS ... 43 REFERENCES ... 44 3 MATERIALS,MIXTUREDESIGNANDTESTPROGRAM... 49 3.1RECYCLEDMATERIALS ... 50 3.1.1Recycledmasonryaggregate ... 52 3.1.2Recycledconcreteaggregate ... 57 3.1.3Gradingcurveofmixgranulates ... 60 3.1.4Portlandcement ... 61 3.2MOISTURECONTENTͲDRYDENSITYRELATIONSHIPOFCTMiGr... 61 3.2.1VisualworkabilityoffreshCTMiGr... 61 3.2.2InfluenceofcementcontentonmoistureͲdrydensitycurve... 63 3.2.3InfluenceofRMAcontentonmoistureͲdrydensitycurve ... 63 3.2.4OptimummoisturecontentanddrydensityofCTMiGr... 64 3.3MIXTUREDESIGN... 65 3.3.1Investigatedmaterialvariables ... 65 3.3.2Centralcompositedesignintwofactors... 67 3.3.3Mixturepreparation... 68 3.4TESTPROGRAM ... 70
REFERENCES ... 73
4 MONOTONICANDCYCLICCOMPRESSIVETESTS ... 75
4.1APPLICATIONOFFRICTIONREDUCTIONSYSTEM ... 75
4.1.1Influenceoffrictionreductionsystem ... 76
4.1.2Failurebehavioranditscriteria ... 78
4.2EdynamicANDPOISSON’SRATIOOFCTMiGr... 79
4.2.1CycliccompressivetestsetͲupandtestconditions... 79
4.2.2Determinationofpropertiesfromrepeatedloadcompression ... 81
4.2.3Measurementofaxialandradialdeformation ... 82
4.2.4EdynamicandPoisson’sratio... 84
4.3EstaticANDUCSOFCTMiGr... 87
4.3.1MonotoniccompressivesetͲupandtestconditions ... 87
4.3.2Determinationofpropertiesfrommonotoniccompression ... 87
4.3.3DataofEstaticandUCS ... 88
4.3.4StressͲstraincurveinmonotoniccompressivetest ... 92
4.4ESTIMATIONOFUCS,Estatic,EdynamicANDPOISSON’SRATIO ... 96
4.4.1EstimationofUCSinrelationtomixturevariables... 96
4.4.2RelationbetweenEstaticandUCS ... 100
4.4.3EstimationofEstaticinrelationtomixturevariables... 100
4.4.4RelationbetweenEstaticandEdynamic... 103
4.4.5EstimationofEdynamicinrelationtomixturevariables... 104
4.4.6Poisson’sratio ... 106 4.4.7Estimationmodelsofmechanicalpropertiesincompression... 107 4.4.8Verificationoftheproposedmodels... 108 4.5CRITERIAFORUCSASAROADBASEMATERIAL ... 109 4.6RESPONSESURFACEANALYSISOFCOMPRESSIVEPROPERTIES... 110 4.6.1Responsevariablesofresponsesurface ... 110
4.6.2EstimationmodelsofUCSandEstaticfromexplanatoryvariables.. 111
4.6.3ContourplotofUCSofCTMiGr... 111
4.6.4ContourplotofEstaticofCTMiGr... 112
4.6.5ResponsesurfaceanalysisofratioofUCStoEstatic... 113 4.6.6ContourplotofUCSandratioofUCStoEstatic... 114 4.7DURABILITYOFCTMiGrSUBJECTEDTOFREESEͲTHAWCYCLES... 115 4.8CONCLUSIONS ... 117 REFERENCES ... 118 5 MONOTONICANDCYCLICINDIRECTTENSILETESTS ... 121 5.1INDIRECTTENSILETESTEQUIPMENTANDTESTCONDITIONS... 122 5.1.1Monotonicindirecttensiletest ... 122 5.1.2Cyclicindirecttensiletest ... 123
5.2.2EstimationofITSinrelationtomixturevariables ... 127
5.2.3EstimationofErinrelationtomixturevariables ... 131
5.2.4RelationbetweenITSandEr... 134
5.2.5RelationbetweenErinITTandEdynamicincompression ... 135
5.2.6StrengthcriteriaofITSforacementtreatedbasematerial... 136 5.2.7FailurepatternofCTMiGr... 137 5.3RESPONSESURFACEANALYSISOFINDIRECTTENSILEPROPERTIES ... 138 5.3.1Responsevariablesofresponsesurface ... 138 5.3.2EstimationmodelsofITSandErfromexplanatoryvariables... 139 5.3.3ContourplotofITSofCTMiGr... 139 5.3.4ContourplotofErofCTMiGr... 140 5.3.5ResponsesurfaceanalysisofratioofITStoEr... 140 5.3.6ContourplotsofITSandratioofITStoEr... 141 5.4RELATIONBETWEENITSANDUCSOFCTMiGr... 142 5.4.1DerivedrelationbetweenITSandUCS... 142 5.4.2SimplifiedrelationbetweenITSandUCS ... 143 5.5ESTIMATIONMODELSOFMECHANICALPROPERTIESOFCTMiGr... 144 5.6CONCLUSIONS ... 146 REFERENCES ... 147 6 DEFORMATIONANDCRACKINGBEHAVIOROFCTMiGr... 149 6.1SPECIMENPREPARATIONANDDEFORMATIONDETERMINATION ... 150 6.1.1Mixturedesign ... 150 6.1.2Specimenpreparation... 152 6.1.3Determinationofdeformationduringcuringtime ... 154 6.1.4Determinationofcoefficientofthermalexpansion(CTE)... 154 6.2DEFORMATIONBEHAVIOROFCTMiGr... 155 6.2.1ResultsobtainedduringoneͲyearcuring ... 155 6.2.2ModelingthedeformationofCTMiGrsealedfor7days... 159 6.2.3ShrinkagemodelingofCTMiGrwhenexposedto50%RH... 162 6.2.4EstimationmodelofthedeformationofCTMiGr... 168 6.3THERMALDEFORMATIONBEHAVIOR... 169 6.3.1Thermaldeformationdata ... 169 6.3.2IdentificationofvariableseffectingtheCTE ... 171 6.3.3AsimplifiedmodeltoestimatetheCTE ... 172 6.4ESTIMATIONOFCRACKSPACINGANDWIDTHINACTMiGrBASE ... 173 6.4.1MechanicalanalysisofshrinkagecrackingofCTB... 174 6.4.2InducedtensilestressinthebaselayerofCTMiGr... 177 6.4.3ModelsforclimateandstructuralpropertiesofCTMiGr... 179 6.4.4SpacingandwidthofcracksinacontinuousCTMiGrlayer... 184 6.5CONCLUSIONSANDRECOMMENDATIONS... 189 6.5.1Conclusions ... 189
7 NUMERICALANALYSISOFTHEFRACTUREOFCTMiGr... 195 7.1THEBEAMLATTICEMODEL ... 196 7.1.1ConstructionofthelatticemeshformonotonicITT ... 196 7.1.2Implementationofheterogeneity... 197 7.1.3Fracturecriterion ... 198 7.2CHARACTERIZATIONOFMECHANICALPROPERTIESOFEACHPHASE... 198 7.2.1Testedsamples ... 198 7.2.2Measuredandestimatedpropertiesofeachphase... 200 7.3NUMERICALANALYSISOFTHEFRACTUREOFCTMiGr... 204 7.3.1Fracturesimulation ... 204 7.3.2Simulationresults... 206 7.3.3Comparisonbetweensimulatedandexperimentalresult ... 207 7.3.4InfluenceofRMAcontentonthesimulation ... 209 7.3.5InfluenceofRMAstrengthonthefracture ... 210 7.4CONCLUSIONSANDRECOMMENDATIONS... 211 7.4.1Conclusions ... 211 7.4.2Recommendations ... 212 REFERENCES ... 212 8 PRACTICALIMPLICATIONSFORAPPLICATIONOFCTMiGr... 215 8.1OPTIMIZATIONOFMECHANICALPROPPERTIESOFCTMiGr... 215 8.1.1ContourcurvesoftheUCSandtheratioofUCStoEstatic... 215 8.1.2ContourcurvesoftheITSandtheratioofITStoEr... 217 8.2MITIGATIONOFSHRINKAGECRACKINGOFCTMiGr... 218 8.3CONSIDERATIONSFORMIXTUREDESIGNOFCTMiGr... 219 8.3.1TendencyofmixtureoptimizationofCTMiGr... 219 8.3.2QualitycontrolofrecycledCDW ... 221 8.4CONCLUSIONS ... 222 REFERENCES ... 223 9 CONCLUSIONSANDRECOMMENDATIONS... 225 9.1CONCLUSIONS ... 225 9.2RECOMMENDATIONS ... 228 AppendixA ... 229 AppendixB ... 233 AppendixC ... 237 AppendixD... 240 AppendixE ... 243 AppendixF ... 246
ACV AggregateCrushingValue CBR CaliforniaBearingRatio CDW ConstructionandDemolitionWaste CTGrM CementTreatedGranularMaterials CTMiGr CementTreatedMixGranulateswithRecycledMasonryandConcrete Aggregates CTB CementTreatedBase CTE CoefficientofThermalExpansion
CR2 CR2 implies that the specimen is a sealed specimen and is curing
during7Ͳdaysat20±2°Cduringwhichthereisnolossofwater.After these7daysthewrappedfoilisremovedandthespecimenisfurther exposedinairat50±5%RHand20±2°C. DTS DirectTensileStrength Edynamic Dynamicelasticmodulusincycliccompressivetest Er Resilientelasticmodulusincyclicindirecttensiletest
EsorEstatic Staticelasticmodulusinmonotoniccompressivetest
FTS FlexuralTensileStrength ITS IndirectTensileStrength ITT IndirectTensileTest PI PlasticityIndex RH RelativeHumidity RMA RecycledMasonryAggregates RCA RecycledConcreteAggregates SN Ratioofappliedtensilestresstotensilestrengthofthematerial UCS UnconfinedCompressiveStrength 2D TwoDimensional 3D ThreeDimensional
1
INTRODUCTION
he tremendous development of traffic both on roads and airfields in the last decades has resulted in a need of constructing pavements capable of bearingheavilyloadedvehiclestravellingathighspeedwhilstsubjectedto serious environmental and climatic conditions. New innovative concepts in the mixturedesignandevaluationofmaterials,inthestructuraldesignofpavements, in the construction techniques and in the maintenance of pavements, are thereforeencouragedtobepromotedandimplementedinpractice.
Base/subͲbase courses play a very vital role in pavement structures by carrying wheelͲloads as well as withstanding environmental impacts. In the late 20th centurymuchinteresthasgrowninthetreatmentofroadbases/subͲbaseswith cement to obtain a high load spreading capacity in preference to unbound materials;and,progressively,awiderangeofnaturalmaterialstreatedbycement havebeenusedinpavementnetworksinmanycountries(Williams,1986). The use of cement treated bases/subͲbases however can introduce some problems affecting the pavement’s serviceability, especially fatigue cracking and shrinkagecrackingstemmingfromtheirbrittlenature(Adaska&Luhr,2004).Asa result, overloading as well as severe climatic conditions can deteriorate the pavement performance during the service life, which can lead to high maintenance or reconstruction costs. In order to preserve the pavement with cement treated bases/subͲbases, pavement design and maintenance engineers need to know the performance of cement treated materials when used as base/subͲbase courses and the most appropriate methods for mitigating the disadvantages.
The challenge to pavement engineers is therefore to comprehensively evaluate thestructuralperformanceofcementtreatedbases/subͲbasesinordertoobtain pavements which will have a considerable period of service life. Doing so, an importantrequiredprerequisiteistooptimizethemixtureofthecementtreated materials applied in road bases/subͲbases. Relevant performance evaluation modelsshouldbedevelopedforobtainingtherequiredpropertiesorsuggesting
T
structures.
1.1CEMENTTREATEDBASES/SUBͲBASES
1.1.1TypicalpavementdesignswithCTGrM
Figure1.1,Figure1.2andFigure1.3illustratethreetypesofpavementstructures
withcementtreatedgranularmaterials(CTGrM)(Molenaar,2005;Williams,1986).
Traditionally, road and airfield pavements are classified as being either ‘rigid’ or ‘flexible’.Herein,CTGrMisregardedasasemiͲrigidbasecourseforeitherflexible orrigidpavements.Itisdescribedasamixtureinwhicharelativelysmallamount of cement is used as a binder of coarse granular particles, and which needs an optimal amount of water for both compaction and cement hydration. It is wellͲknownthattreatmentofthebasewithcementisagoodoptiontoobtaina pavementstructurewithahighloadspreadingcapacity.
Concrete carriageway, or slab with joints
Cemented Base
Subbase
Compacted Subgrade
Uncompacted Subsoil Concrete carriageway, or slab with joints
CTGrM Sub-base Compacted Subgrade Uncompacted Subsoil Figure1.1RigidpavementswithCTGrM Figure1.2FlexiblepavementswithCTGrM Cemented Base Subbase Compacted Subgrade Uncompacted Subsoil Intermediate Asphalt Surface Course F lex ib le P a v e m e n t St ru ct u re Asphalt Surface Intermediate Asphalt CTGrM Sub-base Uncompacted Subsoil Compacted Subgrade Fl e x ib le Pa ve m en t
Figure1.3PavementswithCTGrMinSouthAfrica
1.1.2Granularmaterialsusedforcementtreatment
Over the past fifty years, an extensive range of granular materials has been treatedbycement.InareaslackinghighͲqualitynaturalaggregates,treatingother lowͲquality aggregates with cement is an excellent option since it significantly reduces the need to procure expensive highͲquality crushed aggregates from elsewhere.
Because of environmental reasons, construction and demolition waste (CDW) is recycled in a number of countries and now promoted as sustainable road base/subͲbasematerial.Figure1.4showstheconcreteandmasonryrubbleata stockpileofaDutchrecyclingcompany.
Figure1.4Recycledconcreterubble(left)andmasonryrubble(right)
Each year billions of tons of CDW are produced in the world, which certainly causes environmental impacts due to the CDW dumping in landfills (Hansen,
Thin Surfacing layer
Granular/Cemented base
Cemented sub-base Equivalent granular
Granular selected layers
Granular sub-grade Thinsurfacinglayer Granular/CTGrM CTGrM Granularlayer Granularsubbase Equivalentgranular
successfully as unbound road base courses (Van Niekerk, 2002). Currently over 80% of the material used for road bases in the Netherlands are mix granulates withrecycledconcreteandmasonry(Molenaar,2005).
As mentioned above, treatment of other lowͲquality material with cement is a good choice to solve the shortage of goodͲquality aggregates. The feasibility to reuse demolition waste as cement treated material is however not enough investigatedyet(Xuan,Houben,Molenaar,&Shui,2010;Xuan,Houben,Molenaar, &Shui,2012).Thiscanberemarkablesincetreatmentwithcementwouldallow meaningfulandeconomicalreuseofCDWascementtreatedbaseorsubͲbasein heavilyloadedpavements.
1.1.3TraditionalmixturedesignofCTGrM
The traditional mixture design of CTGrM is a laboratory approach, which mainly evaluates its mechanical properties to meet the requirements for structural pavementdesign(Kennedy,1983;NITRR,1986;Terrel,Epps,Barenberg,Mitchell, & Thompson, 1979). Figure 1.5 shows several stages in the traditional design of CTGrM. Start Selectmaterialfor pavementlayer Iscementation suitable? Modificationby stabilizer No Or Determineoptimal moisturecontentand choosecementcontent Laboratorytests:
Unconfined compressive strength, indirect tensile strength and plasticity index(alsodurabilityifnecessary) Comparisonwithdesigncriteria.Are resultssatisfactory? Finish Yes No Yes Figure1.5Stagesinthetraditionaldesignofcementtreatedroadbasematerials
NotethatthetraditionalmixturedesignofCTGrMisstronglydeterminedbythe
required minimum strength. Other structural properties of CTGrM are not
considered such as deformation and cracking behavior. The traditional mixture
designofCTGrMdoesnottakeintoaccountallfactorsaffectingtheperformance
ofpavementswhichhaveacementtreatedlayer.
Furthermore, the problem with designing the CTGrM mixture and designing
pavementswithaCTGrMlayerforengineersisthelackofproceduresthatallow
its structural properties to be quickly estimated from mixture parameters like composition and characteristics of the granular particles to be stabilized. Such procedures do exist for asphalt and cement concrete and are very useful for designpurposes.
1.2AIMANDSCOPEOFTHERESEARCH
The general aim of this research is to develop estimation models which can predictthestrength,stiffnessanddeformationpropertiesofcementtreatedmix granulates with recycled concrete and masonry (CTMiGr) in relation to mixture variables. In particular, these models should allow to quickly design an optimal mixture for a real recycled material and consider all structural properties which areneededbyengineersforpavementdesign.
Toachievethisaimanextensiveresearchprogramwascarriedoutconsistingof thefollowingsteps:
1) characterization of recycled materials and design of CTMiG mixtureswith differentcompositions;
2) measurement of the structural properties of the designed mixtures and analysisoftheinfluenceofthemixturevariablesonthestructuralproperties;
3) development of models to estimate the structural properties of CTMiGr frommixturecompositionparameters;
4) determination of the mechanical properties of the individual components ofCTMiGrmixtures;
5) numerical simulation of the fracture process of CTMiGr mixtures when takingintoaccountthepropertiesoftheindividualconstituentsandthevariation thereͲin.
6)comprehensiveevaluationoftheinfluenceofthemixturevariablesonthe structural properties of CTMiGr and putting forward guidelines for mixture optimization.
experimental results will give an insight in the influence of different mixture
variablesonthestructuralpropertiesofCTMiGr.Aconceptualmixturedesignof
thismaterialisthenputforwardwhichisbasedontheexperimentaltestsandthe numerical analyses. A general overview of the research methodology is schematicallyshowninFigure1.6. Performance Models Model Verification Literature Review Figure1.6Generaloverviewoftheresearchmethodology 1.3ORGANIZATIONOFTHEDISSERTATION
This dissertation is composed of nine chapters. Chapter 1 gives a brief introductiononcementtreatedgranularmaterialsandtheresearchdoneinthis study. It describes the importance of reusing the construction and demolition waste as granular materials and the importance of treating this material with cement.Italsostatestheimportancetodevelopestimationmodelsforpredicting the structural properties of cement treated demolition waste as demanded by pavementdesignengineersinpractice.
Chapter2presentsaliteraturereview.Itdescribesthepresentknowledgeabout thebehaviorandcharacterizationofcementtreatedgranularmaterialsinrelation tomaterialvariables.
Inchapter3therecycledmaterialsused,themixturedesignmethodconsidered andtheplannedexperimentaltestprogramarepresentedindetail.Theresearch strategyisfurtheraddressed.
The properties of CTMiGr under compression as determined by monotonic and cyclic compressive tests are presented in chapter 4. This chapter also describes the modeling of the measured mechanical properties (unconfined compressive strength,staticanddynamicmodulusofelasticityandPoisson’sratio)inrelation tomixturevariables(cementcontent,degreeofcompaction,ratioofmasonryto concreteandcuringtime).
In chapter 5 details of the test program carried out to determine the indirect tensile properties of CTMiGr are presented. The test results (indirect tensile strength and resilient modulus of elasticity) are correlated to the mixture variables mentioned above. General estimation models for compressive and indirect tensile properties are summarized and their correlations are further discussed.
Inchapter6thedeformationbehaviorofCTMiGrispresented.Itsshrinkagecrack
pattern(initiationtimeofcracks,propagationofcrackspacinganddevelopment of crack width) when the material is used as a pavement layer is estimated by usingasimplifiedmechanisticmethod.
In chapter 7 a numerical simulation of the fracture behavior is done by using a lattice model which uses characteristics of the individual components of CTMiGr asinput.Itisshownthatbymeansofthismodeltheeffectsoftheconsiderable variation in the mechanical properties and in composition of these materials as theyoccurinpracticecanwellbeestimated.
Chapter8explainshowroadengineerscaninterpretandusethefindingsofthis
research for designing CTMiGr mixtures. Some guidelines relating material
propertiesandpavementdesignrequirementsaregiven.
Finally,chapter9presentstheconclusionsandrecommendations.
REFERENCES
Adaska,W.S.,&Luhr,D.R.(2004).ControlofReflectiveCrackinginCementStabilized Pavements. Paper presented at the 5th International RILEM Conference, Limoges,France.
Hansen, T.C. (1992). Recycling of Demolished Concrete and Masonry: Report of Technical Committee 37ͲDRC, Demolition and Reuse of Concrete. (1st ed.).
Kennedy, J. (1983). CementͲbound Materials for SubͲbases and Roadbases (No. Publication46.027).Slough(UK):CementandConcreteAssociation
Molenaar, A.A.A. (2005). Cohesive and NonͲcohesive Soils and Unbound Granular Materials for Bases and SubͲbases in Roads. The Netherlands, Delft: Delft UniversityofTechnology.
NITRR.(1986).CementitiousStabilizersinRoadConstruction(No.TRH13).Pretoria, South Africa: Committee of State Road Authorities, National Institute for TransportandRoadResearch.
Terrel,R.L.,Epps,J.A.,Barenberg,E.J.,Mitchell,J.K.,&Thompson,M.R.(1979).Soil Stabilization in Pavement Structures, a User’s ManualͲVolume 2: Mixture DesignConsiderations(No.FHWAͲIPͲ80Ͳ2).WashingtonD.C:FederalHighway Administration,DepartmentofTransportation.
Van Niekerk, A.A. (2002). Mechanical Behavior and Performance of Granular Bases andSubͲBasesinPavements.PhDThesis,DelftUniversityofTechnology,Delft, theNetherlands.
Williams, R.I.T. (1986). CementͲtreated Pavements: Materials, Design, and Construction.London:ElsevierAppliedSciencePublishers.
Xuan, D.X., Houben, L.J.M., Molenaar, A.A.A., & Shui, Z.H. (2010). Cement Treated Recycled Demolition Waste as a Road Base Material. Journal of Wuhan UniversityofTechnologyͲMaterialsScienceEdition,25(4),696Ͳ699.
Xuan, D.X., Houben, L.J.M., Molenaar, A.A.A., & Shui, Z.H. (2012). Mixture Optimization of Cement Treated Demolition Waste with Recycled Masonry andConcrete.MaterialsandStructures,45(1Ͳ2),143Ͳ151.
2
LITERATUREREVIEW
nmanycountriescementtreatedmaterialshavebeenwidelyappliedasroad baseand/orsubͲbase.Since1915,whenapavementinSarasota,Florida,was constructed and compacted by using a mixture of shells, sand and Portland cement,roadmaterialstreatedbycementvaryfromcoarseͲgrainedaggregates, recycled aggregates to fineͲgrained soils (Terrel, Epps, Barenberg, Mitchell, & Thompson, 1979a, 1979b). Figure 2.1 shows the ‘family’ of cement treated materials (Williams, 1986). In general coarse granular materials are the most appropriatematerialstobetreatedwithcement(Xuan,2009).Cement treated materials
Soil-cement Cement treated granular
Material
Lean concrete Concrete
Non-bound material
Mix-in-place Stationary plant Dry-lean Wet-lean
Technology of soils with cylinders or cubes at field density and emphasis on 7-day strength. Essentially sub-base materials.
Technology of concrete with cubes compacted to refusal and emphasis on 28-day strength. Dry-lean is
essentially a roadbase material.
Figure2.1 The‘family’ofcementtreatedmaterials(Williams,1986)
Cementtreatedgranularmaterials(CTGrM’s)aredefinedasmixturesinwhicha
relativelysmallamountofcementisusedasabinderofcoarsegranularparticles, and which need a proper water content for both compaction and cement hydration. Traditionally, CTGrM’s as road base materials are produced by using coarsenaturalorcrushedaggregates(Bell,1993).Duringthelastdecades,some recycling aggregates, such as recycled crushed concrete and recycled crushed masonry, have successfully been produced and used as construction materials (Hansen, 1992; Lim & Zollinger, 2003; Van Niekerk, 2002; Xuan, Houben,
I
ofcementismainlybecauseofthefollowingreasons(NITRR,1986): y improvingtheworkability,
y increasingthestrengthofthemixture, y enhancingthedurability,and
y increasingtheloadspreadingcapacity
Although CTGrM’s certainly have advantages to be used as base/subͲbase
materials, they still have some weaknesses stemming from material nature. Shrinkage and associated reflective cracking are well known problems of
pavementswithaCTGrMlayer.Furthermore,therepetitiveloadͲinducedfatigue
behavior and the degradation under environmental effects (wetͲdry and freezeͲthaw cycles) remain items of concern for pavement structures with a CTGrMlayer(ACI,1997;Adaska&Luhr,2004).
As a result, a lot of consideration has been given by road engineers to properly design CTGrM mixtures. It is recognized that if the mixture design of CTGrM is carefully done and a proper construction procedure is followed, some disadvantages, such as shrinkage cracking and environmental impacts, can be limited and controlled. Moreover, by optimizing the mixture design the fatigue
behaviorofCTGrM’smaybeimproved.Inaddition,whenpayingproperattention
tothestructuralpropertiesofCTGrM,aroadpavementwithaCTGrMlayerdoes
not need to be maintained within a short period of time. The objective of this chapter is to review material factors that influence the structural properties of CTGrM’s.
2.1STRUCTURALREQUIREMENTSOFCTGrM’SASAPAVEMENTLAYER
Typical pavement structures with a semiͲrigid CTGrM layer are shown in Figures 1.1,1.2and1.3.Figures2.2and2.3indicatehowtheloadspreadingcapacityina twolayersystemcanbeinfluencedbythepropertiesoftwolayers.Astiffbottom layer, resulting in a low E1/E2 ratio dramatically reduces the horizontal tensile stressesatthebottomofthetoplayer.Thiscanbehelpfultopreventthedamage ofthetoplayerduetobending.Meanwhile,whenastiffbottomlayerisapplied, the vertical stresses at its top greatly increase. The bottom layer then plays an importantroleincarryingheavywheelͲloads.
Figure2.2Distributionofthehorizontalstressesinatwolayersystemunderthe centreoftheload(Poisson’sratioequals0.25) Figure2.3Distributionoftheverticalstressesinatwolayersystemunderthe centreoftheload(Poisson’sratioequals0.25)
Table 2.1 gives a review of different pavement design methods as well as the
designcriteriaforpavementswithaCTGrMlayer(Molenaar,Houben,&Huurman,
2006). It shows that much attention is always paid to the elastic modulus, the occurringmaximumflexuraltensilestrain,thestrainatbreakandthefatigueat
thebottomoftheCTGrMlayer.
Method AnalyticalͲempiricalbynature;StressesandstrainscalculatedwithlinearͲelasticmultiͲlayer program. SAMDM (South African) Criteria 1)ModulusgivenasafunctionofpreͲcrackconditionand postͲcrackcondition; 2)MaximumflexuraltensilestrainatthebottomofCTGrM; 3)MaximumverticalcompressivestressatthetopofCTGrM; 4)Fatiguerelatedtotheratiooftheflexuraltensilestraintothe strainatbreak. Method MechanisticͲempiricaldesignmethod; StressesandstrainsfromstructuralanalysiswithlinearͲelastic multiͲlayerprogram; Developmentofdamagebasedonempiricaltransferfunctions. AASHTO (USA) Criteria 1)Uniaxialcompressionstrength>compressionstrength; 2)Uniaxialcompressionmodulus>Young’smodulusE; 3)4Ͳpointbendingstrength>flexuralstrength; 4)FatigueinCTGrMbase; 5)CrushingofCTGrMbase. Method StressesandstrainscalculatedwithlinearͲelasticmultiͲlayer program; Probabilisticapproachforthelayerthicknesses,theYoung’s modulusandthefatigueofCTGrM. French Design Manual (France)
Criteria 1)MaximumflexuraltensilestrainatthebottomofCTG2)FatiguerelationshipofCTG rM;
rM
Method LinearͲelasticmultiͲlayerprogram; ESSO
MOEBIUS
(Belgium) Criteria 1)FatigueIndexforexperimentalfatigueofCTGadjustmentfactor; rMwithafield 2)Stressesandstrainsduetothetrafficloadandtemperature. Method StressesandstrainscalculatedwithlinearͲelasticmultiͲlayerprogram; BOUNDBASE
(The
Netherlands) Criteria 1)Fatigueatthebottomofthebase; 2)Onecyclebrittleflexuralfailureatthebottomofthebase; 3)Flexuraltensilestrainatbreakandflexuraltensilestrength. Method StressesandstrainscalculatedwithlinearͲelasticmultiͲlayerprogram; CROW (The Netherlands) Criteria 1)MaximumflexuraltensilestrainatthebottomofCTGrM layer; 2)MaximumverticalcompressivestressatthetopofCTGrM layer. Method Stressesandstrainscalculated; ECOͲSERVE
(European) Criteria 1)MaximumflexuraltensilestrainatthebottomofCTGlayer; rM 2)MaximumverticalcompressivestressatthetopofCTGrM
2.2MATERIALSANDTRADITIONALMIXTUREDESIGNOFCTGrM
2.2.1Materialssuitablefortreatmentwithcement
Although it is possible to treat almost any material with cement to improve its properties, it is difficult to treat fine, clayey materials due to the high cement content required and the difficulty of pulverizing the soil and mixing it with cement homogeneously. For stabilization of fine clayed materials, lime is suggested to be a better stabilizing agent (NITRR, 1986). Thus, the question whetherornotamaterialissuitableforcementtreatmentisanimportantone. The answer to some extent is given in Table 2.2, Table 2.3 and Figure 2.4 (Molenaar, 1998). The effect of cement treatment depends on the particle size and the type of material. Stabilization of clays and silts with only cement is not verysuccessful.Thatisthereasonwhyinsomecasesadoubletreatmentisused, which implies first of all modification of the soil with lime and after that treatmentofthesoilͲlimemixturewithcement.Figure2.4showsdifferenttypes ofstabilizationwithlimeandcement.
Table2.2Stabilizingmodesofsoils
Designation claysFine Coarseclays Finesilts Coarsesilts sandsFine Coarsesand Aggregate Particlesize
(mm) <0.0006 0.0006Ͳ0.002 0.002Ͳ0.01 0.01Ͳ0.06 0.06Ͳ0.4 0.4Ͳ2.0 >2.0 Volume
stability VeryPoor Fair Fair Good Very Good
Lime Cement Stabilizing agent Bitumen
Rangeofmaximumefficiency Effective,butqualitycontrolisdifficult
Table2.3Effectsofcementonsoilcharacteristics
Changesoilproperties
Type Primary
mechanisms Bestsuited LL PL PI Limitations
Increase Strength Hydration, modificationof clayminerals Coarseand sandsoilsor leanclays Slight
reduction Increase Decrease
Organic soils Improve Plasticity Modificationof clay,change waterfilm Improve existingroad clays
Varies Increase Decrease
Low strength increase
Figure2.4Limeandcementstabilizations
As a result of cement treatment, the terms “modification” and “cementation” may be used to demonstrate the degree of treatment. When the addition of cementtoamaterialresultsinareductioninplasticity,butthereisnosignificant developmentofcompressiveandtensilestrength,thischangeinsoilpropertiesis referred to as “modification”. In such cases the degree of cementation is relativelypoor,buttheworkabilityofamaterialcanconsiderablybeimprovedin this way. When the tensile and compressive strength of the material is greatly improved,thisbehaviorcanberegardedasaresultof“cementation”.However, thereisnoclearlydefinedboundarybetweencementationandmodification.The onestatemergesintotheother(NITRR,1986).
On basis of experience and research extending over years, some general guidelineshavebeenprovidedregardingtheamountsofcementthatareneeded totreatamaterial.AnexampleisgiveninTable2.4wheretheamountofcement tobeusedisrelatedtotheclassificationofasoilfollowingtheAASHO(American Association of State Highway Officials) and USCS (Unified Soil Classification System)soilclassificationsystems(Molenaar,1998;Xuan,2009).
Table2.4Amountofcementfordifferentsoils
SoilType Cement(%)
AASHO USCS By
weight By volume Estimatedcement content,usedin moistureͲdensity test(%byweight) Cementcontents forwetͲdryand freezeͲthawtests (%byweight) AͲ1Ͳa GW,GP,GM, SW,SP,SM 3Ͳ5 5Ͳ7 5 3Ͳ5Ͳ7 AͲ1Ͳb GM,GP,SM,SP 5Ͳ8 7Ͳ9 6 4Ͳ6Ͳ8 AͲ2 GM,GC,SM,SC 5Ͳ9 7Ͳ10 7 5Ͳ7Ͳ9 AͲ3 SP 7Ͳ11 8Ͳ12 9 7Ͳ9Ͳ11 AͲ4 CL,ML 7Ͳ12 8Ͳ13 10 8Ͳ10Ͳ12 AͲ5 ML,MH,CH 8Ͳ13 8Ͳ13 10 8Ͳ10Ͳ12 AͲ6 CL,CH 9Ͳ15 10Ͳ14 12 10Ͳ12Ͳ14 AͲ7 OH,MH,CH 10Ͳ16 10Ͳ14 13 11Ͳ13Ͳ15 UCS=UnconfinedCompressiveStrength
Soil ModifiedSoil CementedSoil Leanmix Concrete
Lime
UCS<750kPa(approx.) UCS>750kPa(approx.)
A material is regarded to be suited for treatment with cement if its physical parametersmeetthevalueslistedinTable2.5(Molenaar,1998). Table2.5Materialssuitablefortreatmentwithcement Items Index %ч0.075mm <35% Maximumgrainsize(mm) <75 LL <50 PL <25 PI <6 2.2.2Requirementsoftreatedgranularmaterials
CTGrM as a road base material is traditionally produced by using natural or crushed aggregates as the main component. The amount of aggregates in the mixtureisnormallyover80percentbymass.Therefore,thephysicalpropertiesof thegranularaggregatesareveryimportantandwillaffectthemixturedesignof CTGrManditsproperties. 2.2.2.1Gradingcurvesofgranulates Differentnationalspecificationsforthegradationofgranularmaterialshavebeen developedinordertoachieveagoodmechanicalstabilization.WithwellͲgraded materials the void content can be reduced by compaction, and in this way the granulate arrangement and the stability of the material under loading improve. This can only happen to a limited extent with poorlyͲgraded materials; their stability can be improved by adding another material to fill the voids between particles.Allthesemeanthatthegradingofthegranularmaterialsisimportantto ensurethemechanicalstability.
Figure 2.5 illustrates the required gradations for road base materials as taken fromtheSpecificationforHighwayWorksintheUK(DT,1991).Cementtreated materials are traditionally categorized into three groups known as soilͲcement,
CTGrMandleanconcrete,respectively.Thegradingcurvesofroadbasematerials
from the Specification for Highway Works in the UK are thus referring to these threetypes.Thegradationofcementboundmaterial3(CBM3)likeleanconcrete isdesignedbyusinghighqualitycoarseaggregates.MaterialsmeetingCBM3also complywithCBM2andCBM1.Similarlymaterialswhichfulfilltherequirementsof CBM2 automatically fulfill the requirements of CBM1. In practice, the grading
Particl esize(mm) Su m m a ti o n pe rc e n ta g e (% ) P erc e n ta ge pa ss in g ( % ) Pe rc en ta ge pa ss in g (% ) Figure2.5GradingcurvesofcementtreatedmaterialsintheUK(DT,1991) Required gradations for CTGrM in South Africa, China and the Netherlands are showninFigure2.6(JTJ034,2000;Molenaar,1998,2005).InSouth Africathere are four classes of cemented materials for crushed stone, crushed gravel and natural gravel, namely C1, C2, C3 and C4. The grading curves of CTGrM in the Chinese specifications generally consider the maximum aggregate size and the materialtypefordifferentroadbasesandsubͲbases.IntheDutchSpecifications for base course materials, the gradation of recycled aggregates such as blast furnaceslag,crushedmasonryandcrushedconcreteisclearlydefined. 0 20 40 60 80 100 0.01 0.1 1 10 100 Sievesize(mm) Pe rc en ta ge p assi ng (% ) Fuller'sEquationn=0,45 ChineseUpperlimit(UL,31,5) ChineseLowerlimit(LL,31,5) SouthAfricaUL(37,5mm) SouthAfricaLL(37,5mm) Dutchbase(UL,45mm) Dutchbase(LL,45mm) ChineseUpperlimit(UL,37,5) ChineseUpperlimit(UL,37,5) Figure2.6SomegradingenvelopesforCTGrM’sinseveralcountries
Figure2.7showssomegradationsinrelationtothewaythematerialisusedin practice (Molenaar, 1998). Some remarks can be made with respect to those gradations:
z the grainͲsize distribution of CTGrM should be continuous for obtaining a goodmechanicalstability;
z a certain amount of fines is always needed for mixture stability.
Furthermore,thefinesshouldhavecertainplasticitycharacteristicsinorder toactasabinderthatkeepsthecoarseparticlestogether;
z by increasing the maximum grain size of particles, the load spreading
capacityofCTGrMcanincrease. Figure2.7Gradationsofgranularmaterialsinrelationtotheiruse 2.2.2.2Physicalpropertiesofgranularmaterials Withregardtothephysicalrequirementsforgranularmaterials,muchattention isalwayspaidtotheplasticityindex(PI)andtheaggregatecrushingvalue(ACV). The PI is considered to determine whether or not the material needs to be treatedwithlime.TheACVrequirementisincludedforobtainingamechanically stable mixture. Table 2.6 and Table 2.7 show the physical requirements for aggregates treated by cement in South Africa and China, respectively (JTJ034, 2000;Sherwood,1995)
Table2.6PhysicalrequirementsformaterialsinSouthAfrica
Items C1 C2 C3 C4
PI(%) <6 <6 <6 <6
ACV(%) <29 <29 n/a n/a
base/subͲbasesinChina
CementtreatedsubͲbase Cementtreatedbase Physical
properties Soils Crushed stone Natural gravel Soils Crushed stone Natural gravel PI(%) <12 <6(or9*) <6(or9*) <9 <6(or9*) <6(or9*) ACV(%) <30 <30 <30 <30 <26 <30
*ThevalueofPIis6inwetregionsand9inotherregions.
Basedontheinformationgivenabove,itcanbeconcludedthatthemostsuitable
granularmaterialstobeusedasCTGrMbases/subͲbasesshouldmeetsomebasic
requirements such as a continuous grading, a low PI and a proper aggregate crushingstrength. 2.2.3Traditionalmixturedesign Afterobtainingthesuitableaggregates,thetraditionalmixturedesignprocedure forCTGrMismoreorlessasfollows: 1) selecttherangeofthepreliminarycementcontentbymassorbyvolume; thisisgenerallydeterminedbythematerialtypeshowninTable2.4;
2) use the estimated cement content obtained in step 1 to conduct moistureͲdensitytesting;
3) prepare specimens by using the maximum dry density and optimum moisturecontentobtainedfromstep2;
4) determine the average compressive strength of specimens after the specified curing time. If the strength requirements are fulfilled, the cement content and the water content determined in step 2 are adequate for the constructionoftheCTGrMlayer.
Table2.8liststherequiredunconfinedcompressivestrength(UCS)forCTGrMin
different countries (JTJ034, 2000; Molenaar, 1998; NITRR, 1986). Note that the requiredUCSstronglydependsonthematerialtypeandtheroadclass.Inorder
toobtainagoodUCSinthefield,CTGrMshouldbecompactedto97%Modified
AASHTO Proctor density. Therefore, the designed UCS of CTGrM is normally
specified at 97% Modified AASHTO Proctor density in the laboratory. Since it is easy to compact samples to 100% Modified AASHTO Proctor density in the laboratory, some countries, like in South Africa, also specify the design UCS of
CTGrMat100%ModifiedAASHTOProctordensity.ThentheUCSat97%Modified
Table2.8RequirementsfortheUCSofCTGrM
Country Compaction Unconfinedcompressive
strengthat7days(MPa) C1 C2 100%modifiedAASHTO compaction 6Ͳ12 3Ͳ6 South Africa 97% modifiedAASHTO compaction 4Ͳ8 2Ͳ4 CBM1 CBM2 United Kingdom 97% modifiedAASHTO compaction 2.5Ͳ4.5 4.5Ͳ7.5 Base SubͲbase China 97% modifiedAASHTO compaction >4 >2 Note:1)C1andC2aredesignatedintheSouthAfricanspecification. 2)CBM1andCBM2areclassifiedonbasisofgradationintheBritishspecification
However, in practice optimum moisture content and maximum dry density can not always be found for some coarse materials. This might influence the preparation of CTGrM. Moreover, the traditional mixture design of CTGrM is strongly determined by the required minimum compressive strength. Other structural properties of CTGrM are not considered. Thus, the traditional mixture
designofCTGrMhasitslimitationswhenitcomestousetheresultsofthetests
donefordesigningtheCTGrMmixtureforpavementperformanceevaluation.The
problemwithdesigningaCTGrMmixtureanddesigningpavementswithaCTGrM
layer is the lack of procedures that allow its mechanical properties to be estimated from mixture parameters like component proportions and characteristics of the granular particles to be treated. Such procedures do exist for asphalt and cement concrete and are very useful for pavement design purposes.
2.3TYPICALSTRUCTURALPROPERTIESOFCTGrM
The mechanical strength of CTGrM comes from the coupled contribution of the compacted granular skeleton and cement hydration. The former strongly
determinesthemechanicalstabilityofCTGrMunderloading.Thelatterinfluences
thebondingstrengthbetweentheparticles.Byobservingthematerialstructure shown in Figure 2.8, it has been found that the aggregate structure is mainly governedbythetypeofaggregate,itsgradationandthedegreeofcompaction. The bonding phase or matrix is controlled by the cement content, the fines content,themoisturecontent,thecuringtime,curingconditionandsoon.Figure 2.8alsoshowstheinfluenceofdifferentfactorsonthemechanicalpropertiesof CTGrM.
Figure2.8InfluencefactorsonthemechanicalpropertiesofCTGrM
2.3.1Unconfinedcompressivestrength
It is generally accepted that the unconfined compressive strength (UCS) is an important indicator of the material quality of CTGrM. A number of material factors influence the UCS such as the cement content, the material type, the degreeofcompaction,thecuringtime,thecuringconditionandsoon.
2.3.1.1Influenceofcementcontent
ItiswellknownthatcementusedinCTGrMplaysanimportantroleinimproving
thecohesivenessofthetreatedmaterialanditsmechanicalproperties.Figure2.9 showstheinfluenceofthecementcontentontheUCSofacementtreatedgravel. A linear relationship is found between the UCS and the cement content. This phenomenonisobservedformostofthegranularmaterials(Bell,1993;BS6031, 1981;Kennedy,1983;NITRR,1986). Figure2.9InfluenceofcementcontentonUCS(Sherwood,1968) Material Type Gradation
Void or compaction degree
Structural factors Bonding factors
Cement content Cement type Moisture content Curing time Curing condition External conditions
Void content or degree of compaction
2.3.1.2Influenceofcementtype
Several types of cement have successfully been applied in cement treated materials. The influence of the cement type has been investigated by some researchers(Babic,1987;NITRR1986).Figure2.10illustratestheinfluenceoftwo types of cement, ordinary Portland cement (OPC) and Portland blast furnace cement (PBFC), on the strength development. The UCS of cement treated sand increaseslinearlywiththeincreaseoftheOPCcontent,whichisnotthecasefor thesandwithPBFC.After28curingdays,thesandtreatedwithahighcontentof PBFCshowsahigherstrengththanthesandtreatedwithOPC. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 2 4 6 8 10 12 14 Cementcontent(%) UC S (MP a ) 1day 2days 4days 7days 28days 56days 14days 112days 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 2 4 6 8 10 12 14 Cementcontent(%) UC S (M P a ) 1day 2days 4days 7days 14days 28days (a)OPC (b)PBFC Figure2.10InfluenceofthecementtypeontheUCSofcementtreatedsand (NITRR,1986) 2.3.1.3Influenceofmaterialtype
The linear relationship shown in Figure 2.9 is valid for one specific type of aggregate and a given grading. It means that other physical properties are not considered,suchasmineralogy,aggregatestrength,gradationand soon(Davis, Warr,Burns,&Hoppe,2007;Kolias&Williams,1984).Figure2.11andFigure2.12 showtheinfluenceoftheaggregatetypeandthefinescontent(particlessmaller than 0.075 mm) on the UCS. It is found that the aggregate size influences the linear relationship between the UCS and the cement content. There is a
significantdifferenceinstrengthforfourtypesofCTGrMaggregates,inorderof
increasing strength: mica, limestone, diabase/granite. The order of diabase/granitedependsonthefinesfractionorthegradingcurve.
Figure2.11InfluenceofmaterialtypeandcementcontentontheUCSat28days (Bell,1993) 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 Mi ca Di ab as e Limes to n e Gr an it e Mi ca Di ab as e Limes to n e Gr an it e Mi ca Di ab as e Limes to n e Gr an it e Mi ca Di ab as e Limes to n e Gr an it e
Fine 4% Fine 7% Fine 10% Fine 14%
f c (M P a )
cement 3% cement 4% cement 5% cement 6%
7-da y U C S ( M P a) Figure2.12Influenceofaggregatetypeonthe7ͲdayUCS(datafrom(Davis,etal., 2007)) 2.3.1.4Influenceofdegreeofcompaction TheeffectofthedrydensityaftercompactionontheUCShasbeenstudied,andit hasbeenfoundthattheUCSincreaseswithanincreaseofthedrydensityorthe degree of compaction (Kolias & Williams, 1984; Sherwood, 1995). Figure 2.13 showssomeresultsfortwomaterials.
Figure2.13Relationshipsbetweenthe7ͲdayUCSandthedrydensityfortwo
CTGrMs(Sherwood,1995)
It can be observed that if the relation between the UCS and the dry density is plottedonalogͲlogscale,therelationbetweenthemisbasicallylinearandmay thereforebeexpressedasapowerlaw:
log(UCS) logK nlogD (2.1)
or n
D k
UCS (2.2) Where,DisthedrydensityoftheCTGrMspecimen(kg/m3);Kisaconstant;nisa dimensionlessconstant
The value of n is a function of the moisture content and decreases with the increaseofthemoisturecontent.ThenͲvalueis7Ͳ15and11Ͳ22,respectively,for porphyry and asͲdug gravel. On average, a one percent increase in dry density yieldsa10percentincreaseinstrength.
InpracticethemixturedrydensityofCTGrMstronglydependsonthedegreeof
compaction. With the increase of the degree of compaction, the corresponding drydensityandstrengthwillincrease,regardlessofthematerialtype.Thatisone
ofthereasonsthatthestrengthrequirementsforCTGrMgenerallyassumethata
high degree of compaction is achieved. This is also based on the fact that although a low dry density may be compensated by increasing the cement content, it is generally more economical to achieve a high strength through a goodcompaction.
Thecuringtimeisanotherimportantfactoraffectingthestrengthdevelopmentof
CTGrM.AnumberofresearchershavereporteditsinfluenceontheUCS(DT,1991;
Moore, Kennedy, & Hudson, 1970; NITRR, 1986; Sherwood, 1995). The strength developmentwiththecuringtimeisshowninFigure2.14.Itcanbeobservedthat theUCSincreasesapproximatelylinearlywiththelogofthecuringtime. 0 2 4 6 8 10 12 Curingdays Co m pre ss iv e str en g th (M Pa ) 7%Sample1 5%Sample1 3%Sample1 5%Sample2 5%sample3 123728365 WellͲgradedsand 0 2 4 6 8 10 12 Curingdays Co m pre ss iv e st re ng th (M P a ) 7%Sample1 5%Sample1 3%Sample1 5%Sample2 5%sample3 123728365 Gravel Figure2.14Relationshipsbetweencompressivestrengthandcuringperiod(NITRR, 1986)
The relationship between the UCS and the curing time for a given material and cementcanthereforebegivenby: ) / log( ) ( ) (t UCS t0 k t t0 UCS (2.3)
Where, UCS(t)is the UCS at curing age of t days; UCS(t0)is the UCS at curing ageoft0days
Therealsoexistothermodelstopredicttheinfluenceofthecuringtime,andone of them was proposed by (Lim & Zollinger, 2003). The model from Lim resulted fromacalibrationoftheACICommitteemodelwhichisgivenbyEquation2.4and resultedinanewsetofcoefficientsofa=2.5andb=0.9: t b a t UCS t UCS t UCS c (28) ) 28 ( ) ( E˄˅ (2.4)
Where, ɴc(t) = the coefficient which depends on age t (days) and cement type; UCS(28)isthereference28ͲdayUCSanda,bareexperimentalcoefficients.
2.3.1.6Influenceofcuringconditions
ThepropertiesofCTGrMinthelaboratorydifferfromthosemeasuredinthefield,
which is particularly due to different curing conditions. For example, a high temperature may result in early strength formation. Figure 2.15 shows the influence of the curing temperature. The UCS increases as the temperature increases. This effect may be used to develop accelerated test methods, i.e. curingathightemperaturetogetanearlyindicationofthelongͲtermstrength. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 20 40 60 80 100 Curingtemperature(ć) UC S (M P a) Normalcuringtemperature Figure2.15RelationshipsbetweenUCSat7daysandcuringtemperature (NITRR,1986) 2.3.1.7EstimationmodelsofUCSforCTGrMandconcrete Fromtheinformationgivenaboveandusingknowledgeinconcretetechnology, Table 2.9 is derived in which existing models to predict the UCS of CTGrM and concrete from mixture parameters are listed. When comparing the models for
CTGrMandconcrete,somesimilaritiescanbefound.Tosomeextent,CTGrMcan beregardedasaleanconcreteͲtypeofmaterial.
Material PredictionmodelsofUCS Reference Remarks C A UCS u (Sherwood, 1968) C=cementby mass; n D K UCS u (Sherwood, 1995) D=density 32 . 3 28 . 0 4 ] ) ( [ 10 03 . 5 u V C UCS K (Consoli,Foppa, Festugato,& Heineck,2007) Cv=cementby volume ɻ=porosity ) / log( ) ( ) (t UCS t0 k t t0 UCS (Terrel,etal., 1979a) CTGrM t b a t UCS t UCS ) 28 ( ) ( (Lim& Zollinger,2003) t=curingtime ) 5 . 0 ( 6 . 24 W C UCS W C UCS 1470.0779 /
(Larrard,1999) W=waterbymass
n c UCS UCS ,0(1K) K k c e UCS UCS ,0 ) ln( 0 K K k UCS K k UCS UCS c 0, (Kearsley& Wainwright, 2002) UCSc,0isat0% porosity ¿ ¾ ½ ¯ ® »¼ º «¬ ª 1 ) 28 ( 1 exp ) 28 ( ) ( k t s UCS t UCS (EN199Ͳ1Ͳ1, 2005) Concrete t b a t UCS t UCS ) 28 ( ) ( (ACI,1998) Furthermore,thereisevidencethatitshouldbefeasibletoestablishaprediction
model for the UCS of CTGrM based on the material parameters mentioned in
Table2.9.Suchrelationshipsalreadyexistforcementconcrete.
2.3.2Tensilestrength
The tensile strength of CTGrM is always considered as a significant material propertyfordesigningpavementstructures.Thisisbecausethetensilestressat the bottom of the CTGrM layer is quite often taken as a design criterion. In general, flexural beam tests, direct tensile tests and indirect tensile tests have
beenemployedtoevaluatethetensilestrengthofCTGrM.Valuesdeducedfrom thesetestsdifferfromeachotherduetothedifferentstressdistribution.
2.3.2.1Directtensilestrength
Figure2.16showstheinfluenceofthematerialtypeontherelationbetweenthe direct tensile strength (DTS) and the UCS. One can observe that their strength ratioistosomeextentdependentonthematerialtype.However,atlowstrength levels, theDTS is typically aboutoneͲtenth of the UCS. Similar results were also reportedforcementtreatedcrushedstonebyBalboanditcanbe expressedas (Balbo,1997):
UCS
DTS 100. (2.5) Although the limited number of tests could not allow a firm conclusion to be drawn,theyimpliedthattheaggregatetypeisnotaprimaryfactorintherelation betweenDTSandUCS.
Figure2.16DTSplottedagainstUCS(Williams,1986) 2.3.2.2Flexuraltensilestrength
It has been shown by some researchers that the flexural tensile strength (ff) of CTGrM is about 1/10 to 1/6 of the UCS (Kolias & Williams, 1984; NITRR, 1986; Terrel,etal.,1979b).ForlowͲstrengthmixturestheratiooffftoUCSislarger(up to 1/6) than that of highͲstrength mixtures (down to less than 1/10). With
increasingparticlesizetheratiooffftoUCSdecreasesmoreorlessfrom1/6to
1/10.TestdataforsomeCTGrMsareshowninFigure2.17.Thefigureshowsthat
the aggregate type determines ff to some extent. A linear relationship between themisgenerallygivenby:
Where,aistheexperimentallydeterminedratiobetweenfftoUCS. Figure2.17FlexuraltensilestrengthplottedagainsttheUCS(Kolias&Williams, 1984) Regardlessofthematerialtype,however,agoodapproximationfortheflexural strengthonbasisofdataabovecouldbedeveloped(Equation2.7).Thisshows thatapowerrelationbetweenffandUCScanfitalldatawell. 75 . 0 25 . 0 UCS ff (R2=0.93) (2.7) 2.3.2.3Indirecttensilestrength
As reported before, relations between the UCS and the indirect tensile strength (ITS) are also established (Kolias & Williams, 1980; Molenaar, 2007; Williams, 1962).Twolinearmodelsaregiven: b UCS a ITS (2.8) ITS a'UCS (2.9) Where,a,a’andbarecoefficientsdependingonmaterialparameters.
Based on Babic’s results, the following conclusions can be drawn (Babic, 1987). ThetypeofcementdoesnotappeartoaffecttherelationbetweenUCSandITSto alargeextent.Thegradationofthegranularmaterialhaspracticallynoinfluence
