Influence of mix proportions on rheology of cement grouts co(4)

740L.Svermovaetal./Cement&ConcreteComposites25(2003)737–749

ThecohesivenessofthegroutwasmeasuredwithaLombardiplatecohesionmeter[15].Theapparatusconsistsofathinsteelplate(100mmÂ100mmÂ1mm),onwhichthegroutcanstick,andanelectronicscale.Thecleandryplatewasweighedandthensub-mergedonceintothegrout.Theplatewasthenwith-drawnandweighedagainafteranydroppingofgroutstopped(Fig.1).

Thespeci cweightofthegroutwasmeasuredbyamudbalance.Thismudbalanceconsistsofaconstant-volumesamplecupwithlidconnectedtoabalancearm.Areaderismovedalongthebalancearmtoindicatethescalereading.Thereisaknifeedgeattachedtothearmnearthebalancecupandabubblelevelbuiltintothisknifeedgeforlevellingthearm.Itwaspossibletocal-culatethethicknessofgroutoneachsideoftheplatefromtheunitweightandtheamountofgroutstickingtothesteelplate.

Theresistanceofthefreshgrouttoinducedbleedingwasevaluatedusingapressure lter.Theequipmentconsistsofapressurevessel, lterpaper,whichisplacedonasieve,andagraduatedcylinder.A200mlgroutsampleisplacedinthepressurevessel.Afterclosingthecell,thegraduatedcylinderisplacedundertheoutletofthecell.Thecellispressuredbycompressedairto0.55MPa.Thevolumeofwatergoingoutthroughtheoutletonthebottomofthecellisrecordedat15and30s,thenateveryminuteupto10min,andthenatevery5minupto30min[16].Theresultsofthistestarepresentedasareaundercurveresponsetimevs.volumeofwater(Fig.2).

Theviscosityofcementgroutisdeterminedusingacoaxialrotatingcylinderviscometer(smoothcylinders,noserration)thatenabledthedeterminationofapparentviscosityatdi erentshearrates[17].Thetestiscon-tainedintheannularspacebetweenanoutercylinder(rotor)withradiusof18.415mmandabobwithradiusof17.245mmandheightof3.80cm.Therotorandthebobareplungedintoacupwhichcontains350mlofsample(Fig.3)[17].Viscositymeasurementsaremade

Fig.1.Platecohesionmeterapparatus[15].W=B¼0:35,SP¼1:2%,VA¼0:02%,LSP¼

45%.

Fig.3.Coaxialrotatingcylinderviscometer[17].

whentheoutercylinder,rotatingataknownspeed,causesaviscousdragtobeexertedbythe uid.Thisdragcreatesatorqueonthebob,whichistransmittedtoaprecisionspringwhereitsde ectionismeasuredandthencomparedwiththetestconditionsandtheinstru-mentÕsconstants.Themeasurementismadefor12speedsofrotorfrom0.9to600rpmwhenthevaluesofviscometerreading¼harerecorded.Thevalueofshearstress¼s(Pa)iscalculatedbyincludingk1¼torsionconstantofspringperunitde ection(Ncm/deg.),k2¼shearstressconstantforthee ectivebobsurface(cmÀ3)andk3¼shearrateconstant(sÀ1/rpm)[17].

Thespeedofrotorwasincreasedstepbystepfrom0to600rpmandreadingonviscometerwithincreasingrotatingspeedwasrecorded.Thereadingofhwastakenwhentheneedleintheviscometerwasstabilised,or30safterthechangeofspeedincaseswhentheneedlehasnotstabilisedwhichwascausedbythethixotropyofthecementgrout.Themeasurementofthereadingbyde-creasingrotatingspeedstepbystepallowedtheassess-mentofthethixotropyofgroutbetweentheascendinganddescendinglegsoftheshearstress–shearraterheo-grams.Theupcurvewaschosenfor nalevaluation

for