Strength development of concrete with ricehusk ashWord文件下载.docx
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1.Introduction
InUruguay,riceproductionhashadadramaticincreaseoverthepast10
years,becomingthemostimportantcropsince2001;
themainuseofricehuskisasfuelinthericepaddymillingprocess.Theuseofthisfuelgeneratesahugevolumeofash.Therice-huskash（RHA）hasnousefulapplication,isusuallydumpedintowaterstreamsandcausespollutionandcontaminationofsprings.Asaresult,theuseofrice-huskashhasarousedgreatinterestinUruguay.
Rice-huskashisamineraladmixtureforconcrete[1]and[2];
thebehaviorofcementitiousproductsvarieswiththesourceofRHA[3]and[4].ThebasicaimofthisstudyistoinvestigatetheinfluenceofresidualRHAfromthericepaddymillingindustryinUruguayandRHAproducedbycontrolledincinerationfromtheUnitedStates,usedforcomparison,onstrengthdevelopmentofconcretesatdifferentages.
2.Experimentalprogram
Thefollowingmaterialswereusedinthepreparationoftheconcretespecimens:
fineaggregate（localnaturalsand）withmaximumaggregatesizeof4.75
mm;
coarseaggregate（crushedgranite）withmaximumaggregatesizeof12.5
PortlandCementtypeI（normalportlandcement）;
andsuperplasticizerbasedonasulfonatednaphthaleneformaldehydecondensate.Twosourcesofashwereconsidered;
aresidualRHAfromtheuniquericepaddymillingindustryinUruguay（UYRHA）andahomogeneousashproducedbycontrolledincinerationfromtheUnitedStates（USARHA）,forcomparison.
TheresidualRHAusedforthisworkwasaprocessedwastedry-milledforthenecessarytimetoobtainamedianparticlesizeof8
μm,adefinedspecificsurfacebynitrogenadsorption[5],andwiththemaximumactivityindexaccordingtotheASTMC311-98b.Thisprocedureofoptimizationispresentedin[6].Table1showsthechemicalcomposition,physicalpropertiesandactivityindexofthecementitiousmaterials.
Table1.PhysicalpropertiesandchemicalanalysesofthecementandRHAused
Cement
RHA
UY
USA
Physicaltests
Specificgravity
3.14
2.06
2.16
Fineness
Specificsurface,Blaine,m2/kg
309
–
Nitrogenadsorption,m2/kg
28,800
24,300
Settingtime,min
Initial
145
Final
275
Compressivestrength,Mpa
1-day
10.1
3-day
22.8
7-day
33.1
28-day
45.1
ChemicalAnalyses,%
Silicondioxide（SiO2）
21.98
87.2
88
Aluminiumoxide（Al2O3）
4.65
0.15
Ferricoxide（Fe2O3）
2.27
0.16
0.1
Calciumoxide（CaO）
61.55
0.55
0.8
Magnesiumoxide（MgO）
4.27
0.35
0.2
Manganeseoxide（MnO）
Sodiumoxide（Na2O）
0.11
1.12
0.7
Potassiumoxide（K2O）
1.04
3.60
2.2
Sulphuroxide（SO3）
2.19
0.32
Lossonignition
2.30
6.55
8.1
Compounds
TricalciumsilicateC3S
44.0
DicalciumsilicateC2S
29.9
TricalciumaluminateC3A
8.5
TetracalciumaluminoferriteC4AF
6.9
Activityindex
ASTMC311-98b
100
92.93
92.4
Full-sizetable
ViewWithinArticle
ChemicalanalysisindicatethatthetwoashesaremainlycomposedofSiO2.Themedianparticlesizeofthetwoashesisthesame,andtheactivityindexaresimilar.X-raydiffractionanalysisindicatedthattheUSARHAcanbeconsideredtobenon-crystallineRHA;
buttheUYRHAshowedcrystallinematerials,whichwereidentifiedascristobalite.Arapidanalyticalmethodtoevaluateamorphoussilicainthericehuskashesaccordingto[7]hasbeenused;
thepercentageofreactivesilicacontainedintheUSARHAwas98.5%andintheUYRHAwas39.55%.
Atotalof15concretemixesweremade;
foreachRHA,sixconcretemixesweremade,andthreeconcreteswithoutRHAforcomparison.ThedifferentmixproportionsbymassofthematerialsusedaregiveninTable2.ThereplacementofcementbyRHAwasmadebyvolume,becausetheRHApresentslessspecificgravitythanthecementPortland,andthepastecontentinvolumewaskeptthesame（35%cementpastecontent）forthedifferentmixproportions.ThevaluesoftheslumptestarealsoindicatedinTable2,wheresuperplasticizerpercentagesareusedinrelationtoweightofcementitiousmaterials.Superplasticizerwasusedinverylowpercentagesaccordingtotheresultsobtainedintheslumps,toallowconsistencyadjustments（slump
=
60
±
20
mm）withoutchangingtheproportionoftheothermaterials.
Table2.Mixproportionsofconcrete
W/（c
+
RHA）
RHA（%）
Cement（kg/m3）
FineAgg.（kg/m3）
CoarseAgg.（kg/m3）
Superplast（%）
Slump（mm）
534
690
1050
0.40
47
10
481
0.20
0.70
45
56
20
427
0.80
48
63
462
723
1018
0.10
40
416
0.27
370
0.50
53
65
408
758
983
61
367
0.30
94
79
327
67
Cylindricalconcretetestspecimenswerecast.Theywerecompactedbyexternalvibrationandkeptprotectedaftercastingtoavoidwaterevaporation.After24
htheyweredemoldedandstoredinamoistroomuntilthetestingdate.
100
×
200-mmcylinderswereusedtoobservethecompressivestrengthat7,28and91
days.Inordertoobtainmoreinformationaboutthedevelopmentofstrengthoftheconcretes,splittingtensiletestsandairpermeabilityoncylindersof100
200
mmand150
300
mmrespectively,withlowerandhigherwater/cementitiousmaterialsratiosattheageof28
days,wereanalysed.Air-permeabilityforconcretewasdeterminedwiththe“Torrentpermeabilitytester”method[8]and[9].TheparticularfeaturesoftheTorrentmethodareatwo-chambervacuumcellandapressureregulator,whichensuresthatairflowsatrightanglestothesurfaceandisdirectedtowardstheinnerchamber;
thisallowsthecalculationofthepermeabilitycoefficientKtonthebasisofasimpletheoreticalmodel.Bycomparingtheresults[9]ofgaspermeabilitymeasuredbytheTorrentpermeabilitytester（Kt）andoxygenpermeabilityobtainedfortheCembureaumethod（K0）,thefollowingrelationispresented:
whereK0andKtareexpressedin10−16
m2.
3.Resultsanddiscussion
Table3showsthetestresults（strengthandpermeability）.Eachvaluerepresentstheaverageoffiveexperimentalobservations.Atlowerages（7
days）,concreteswithUYRHApresenthighercompressivestrengththatconcreteswithUSARHA.Athigherages（91
days）,theRHAconcretehadhighercompressivestrengthincomparisonwiththatofconcretewithoutRHA,andthehighestvaluesofcompressivestrengthswereachievedinconcreteswith20%USARHA.ThelongtermcompressivestrengthoftheconcreteswithUYRHAisnotashighastheoneobtainedwithUSARHA,whichalsoincreasesastheRHAcontentrises.
Table3.Testresults
w/（c
fc（MPa）
ft,d（MPa）28d
Kt（m2）28d
Type
%
7d
28d
91d
48.4
55.5
60.6
3.63
1.08
10−16
51.1
60.4
64.3
3.57
0.23
44.3
54.8
62.7
3.34
0.05
39.5
51.4
64.5
3.62
0.08
30.5
47.4
68.5
3.54
0.03
35.8
42.3
45.6
41.1
50.4
54.9
27.9
40.7
29.7
40.8
51.5
23.6
39.4
57.3
24.6
32.9
35.9
2.85
28.20
24.1
31.5
35.5
2.32
71.82
24.9
34.9
37.9
2.63
49.10
22.7
34.5
44.4
2.92
26.36
20.8
52.9
3.00
14.20
Keys:
fc
axialcompressivestrength;
ft,d
splittingtensilestrength;
Kt
permeabilitycoefficient.
TheresultsofsplittingtensilestrengthandairpermeabilityrevealthesignificanceofthefillerandpozzolaniceffectfortheconcreteswithRHA.Ontheonehand,theresultsareconsistentwiththecompressivestrengthdevelopmentat28
daysfortheUSARHA.Ontheotherhand,intheconcreteswithUYRHA,lowersplittingtensilestrengthsandlessairpermeabilityareobserved,whichcanbeduetothefactthatwithresidualRHA,thefillereffectofthesmallerparticlesinthemixtureishigherthanthepozzolaniceffect.
4.Conclusions
TheRHAconcretehadhigher
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