Influence of mix proportions on rheology of cement grouts co(5)

L.Svermovaetal./Cement&ConcreteComposites25(2003)737–749741

betterdescriptionofrheologicalbehaviourofthegroutsincludingastructuralbreakdownphenomenonofinnerforcesamongparticles[18,19].

Thevaluesofyieldstressandplasticviscosityareobtainedfrommodi edBinghammodel[20],whichisdescribedbytheequation:_þcc_2s¼s0þlpc

wheres0¼yieldstress(Pa),lp¼plasticviscosity(Pas),

_¼shearrate(sÀ1),c¼constant.c

Thevalueoftheconstantcismostlyabout10À3andless,whichismuchsmallerthanthevalueofplasticviscositylpandyieldstresss0,andforthisreasonthisconstantisconsideredtoequalzero.

Thecompressivestrengthwasdeterminedon55Â50-mmcylinders(diameterÂheight).Thespecimensweredemouldedonedayaftercastingandwerestoredinwateruntiltestingat7and28days.4.Testresultsanddiscussion4.1.Derivedstatisticalmodels

ThetestresultsformixesinvestigatedinthisstudyaregiveninTable3.Thevariousresponseswhichresultedfromthedesignedexperimentalprogrammewereanal-ysedandplottedusingastatisticalsoftwarepackage[14].Thederivedstatisticalmodelsforallthesetestsresultswithcorrelationcoe cient,Prob:>jtjvaluesandprospectivetransformationwereshowninTable4.Theestimatesforeachparameterrefertothecoe cientsofthemodelfoundbyaleast-squaresapproach.The

Prob:>jtjistheprobabilityofgettinganeventgreatertstatistic,inabsolutevalue,thattestswhetherthetrueparameteriszero.Probabilitieslessthan0.05areoftenconsideredassigni cantevidencethattheparameterisnotzero,i.e.thatthecontributionoftheproposedparameterhasahighlysigni cantin uenceonthemeasuredresponse.

ThepresentationinTable4enablesthecomparisonofvariousparametersaswellastheinteractionsofthemodelledresponses.Forthemajorityofparameters,theprobabilitiesthatthederivedcoe cientsofthevariousparametersin uenceeachresponsearelimitedto5%.Thissigni esthatthereislessthan5%chance,or95%con dencelimit,thatthecontributionofagivenpa-rametertothetestedresponseexceedsthevalueofthespeci edcoe cient.Anegativeestimatesigni esthatanincreaseofthegivenparameterresultsinareductionofthemeasuredresponse.

Transformationwasusedforstabilisingofthemodelintwocases.Forexample,thetransformationofnaturallogarithmwasusedforplatecohesionmeterandplasticviscosity.Inordertoillustratethemethod,assumethatresponsesY1andY2arefunctionsofW/B,dosagesofSPandVA,andtheproportionofLSP,thenLinearmodel:Y1¼a0þa1W=Bþa2SPþa3LSPþa4VAþa5W=BSPþa6W=BLSPþa7W=BVAþeNaturallogarithm:

lnY2¼a0þa1W=Bþa2SPþa3LSPþa4VA

þa5W=BSPþa6W=BLSPþa7W=BVAþe

Table3

ResultsoftestingmethodsusedforindividualmixesMix

Mini-slump(mm)77.061.577.0179.564.5118.0142.0172.5113.0126.0116.0111.5150.5104.5134.0142.0117.0

Flowtime(s)

Cohesionmeter(mm)1.3501.4091.0680.0821.7420.5700.0790.1640.4450.3620.3180.2710.1440.4300.2210.1530.296

ViscometerYieldvalue(Pa)11.188.4010.771.814.4311.262.555.4610.9810.189.819.096.1510.259.776.479.00

Plasticvis-cosity(Pas)0.520.401.170.110.790.170.170.130.350.330.270.290.190.240.200.160.31

Inducedbleeding(Lmin)1.091.220.930.510.921.291.291.401.241.301.251.251.281.521.011.321.35

fc07days(MPa)40.326.738.329.723.017.025.517.735.029.132.327.829.934.824.230.034.4

fc028days(MPa)47.534.739.233.531.423.726.820.037.939.234.133.540.045.328.933.842.5

1234567891011121314151617NMNMNM81.4NM184.3174.3197.5321.7295.9474.2566.961.0NM>20min242.4702.4

NM:notmeasurable.