Influence of mix proportions on rheology of cement grouts co(3)

L.Svermovaetal./Cement&ConcreteComposites25(2003)737–749739

consistedofeightfactorialspointswhereeachvariablewas xedattwodi erentlevels.

Fourreplicatecentralpointswerepreparedtoesti-matethedegreeofexperimentalerrorforthemodelledresponses.Thecentralpointsconsistedofmixeswithvariablescorrespondingto0.385,0.75%,0.045%,and28.5%forW/B,dosageofSP,VAandLSP,respectively.Finally, verandommixeswereproducedtoestablishtheaccuracyofthederivedmodels.Themixeswereproducedandtestedinrandomorder,whichisoneoftherequirementsoffactorialexperimentaldesign.

Thefreshcementgroutsweretestedwithmini-slumptest,Marshcone,Lombardiplatecohesionmeter,in-ducedbleedingtest,andcoaxialrotatingcylindervis-cometer.Thecompressivestrengthsweremeasuredat7and28days.

The17mixcombinations,expressedincodedandactualvalues,consideredintheexperimentaldesignofgroutsarelistedinTable1.Thecodedfactorsofvari-ablesarecalculatedasfollows:

CodedFactor¼ðActualvalueÀFactormeanÞ=

ðRangeofthefactorialsvalues=2Þ

CodedW=B¼ðActualW=BÀ0:385Þ=0:035CodedVA¼ðActualVAÀ0:045Þ=0:025CodedSP¼ðActualSPÀ0:75Þ=0:45CodedLSP¼ðActualLSPÀ28:5Þ=16:5

3.Materialproportionsandtestingprocedures

ThegroutsinvestigatedinthisstudywerepreparedusinganordinaryPortlandcementandlimestonepowder.Thechemicalandphysicalpropertiesofce-mentandlimestonepowderarepresentedinTable2.Thelimestonepowderwasproducedfromcarbonifer-ouslimestoneofaveryhighpurityandwas nerthancement.Thelimestonehadgradingof98%<45and25%<5lm.

Anewgenerationofsuperplasticiseronthebasisofmodi edpolycarboxylateswasusedwithasolidcontentof30%andspeci cgravityof1.11.TheviscosityagentwastheKelco–Cretewelangumthatisahighmolecularweight,microbialpolysaccharide.Thewelangumwassuppliedinapowdergum.

Allgroutmixeswerepreparedina5lplanar-actionhigh-shearmixer.Themixingtapwaterhadatemper-atureof16Æ1°C,whichwasmeasuredbeforemixingstarted.Theviscosityagentwasmixedwithcement.Thesuperplasticiserwasaddedtothewaterandmixedtogether.Mixingtimewasmeasuredfromwhenthelimestonepowder(the rstsolidcomponent)wasaddedintothemixofwaterandsuperplasticiser.Finally,themixofcementandviscosityagentwasaddedandallcomponentsweremixedfor7minfromthestartof

Table2

Chemicalandphysicalpropertiesofcementandlimestonepowder

Cement

LimestonepowderSiO220.8–Al2O35.0

–Fe2O3

3.2–CaO63.7–MgO2.6

0.2Na2Oeq.0.39–FreeCaO1.6–LOI0.65–CaCO3–99Relativedensity3.142.65Speci csurfacearea385

–

(m2/kg)

Standardcompressivestrength(MPa)Age(d)Cement741.528

57.8

measuringtime.Thegrouttemperaturefollowingtheendofmixingwasmaintainedat20Æ2°C.

Followingtheendofmixing,thepropertiesofthefreshcementgroutweremeasured.Thefollowingtestsofthefreshcementgroutwerecarriedout(the guresinbracketsshowtherangeoftimeswhentheindividualtestsstartafter nishingofmixing):mini-slumptest(1–2min),Marshcone(4–5min),Lombardiplatecohesionmeter(10–15min),coaxialcylinderrotationviscometer(10–20min),inducedbleedingtest(20–30min)andunitweight.Threecylinderswith50Â55-mmdiameterandheightwerecasttodetermine7and28dayscompressivestrength.

Themini-slumptestisbasedonthemeasurementofthespreadofgroutplacedintoacone-shapedmould.Themini-slumpconehasanupperdiameterof19mm,alowerdiameterof38.1mm,andaheightof52.7mm.Theconeisplacedinthecentreofasmoothplateandthespreaddiameterofthegroutafterliftingoftheconeismeasured.

TheMarshconetestisbasedonmeasuringthetimenecessaryforthe owofaparticularvolumeofgroutthrougha ow-cone.Nowadays,di erenttypesof ow-coneareused.Aplasticfunnelwithacapacityof1200mlwasusedinthiscase.Onehalfoftheupperpartofthefunnelwascoveredwithasieve.Thegroutwasplacedinthefunnelthroughthissieve,whichpreventedlargeparticlesblockingtheoutlet.Thefunnelwaswet-tedbeforeeachtest.Avolumeof1100mlofthegroutwasplacedintheconewiththeoutletsealedandthenthetimeforthe owofeach100mlofgroutwasre-corded.The owtimeofMarshconeat700mlwasevaluated.