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Ondurabilityaspectsofconcretemembersformedagainstpermeableformwork
11
3.TESTRESULTSOFCONCRETEPROPERTIESATSURFACE
Thereductionofw/cratioinskinlayerofconcreteresultsinmanybene-
fits.Allofthemareimportantfromthedurabilitypointofview.Recentinvesti-
gationsweredoneusingdifferentspecimens,andfirstofall–differentconcrete
mixtures.Inthemajorityofcases,theconcretegradesfromC20/25toC40/45
weretested,withbasicw/cratiointherangeof0,40to0,60.
Ingeneral,thefollowingimprovementsofconcretepropertiesatsurface
wereobtainedbymeansofusingCPFincomparisontoclassicimpermeable
formwok(accordingto[10]):
•increaseofcompressiveconcretestrengthmeasuredonthesurfacewith
sclerometerfrom25to40%,
•increaseoftensilestrengthatsurface(pull-offmethod)from40to60%,
•reductionofw/cratioatsurfacefrom30to50%,
•decreaseofporosityupto30%,intherangeofgreaterporesmainly,
•decreaseofthedepthofcarbonation(inthetestofacceleratedcarbonation
underCO2pressure)from70to100%,
•decreaseofchloridediffusioncoefficientfrom50to70%,
•decreaseofabrasioncoefficient(Böhme’smethod)from30to70%,
•resistancetofreezingandtowing(RILEMtest):twentyormoretimeslessthe
weightloss.
SomeselectedresultsforconcretemixturesdescribedinTable1arepre-
sentedinFig.3onthebasisofourowntests’resultsandpresentedbyBarnewold
[8].Allthesetestsweredoneinasimilarway.Thecorespecimensweretaken
fromwalls300mmthick,formedagainstCPFononeside,andagainstplywood
ontheother.Therefore,eachcylindricalspecimenhaddifferentsurfacesonboth
bases,butitsconcretewasexactlythesame(noeffectsofcastinginthevertical
position).
Table1.Concretemixturesusedindurabilitytests
Concreteclassdesigned
Cementtype
Cement,kg/m
Fly-ash(fa),kg/m
Plasticizer(dry),kg/m
Water,kg/m
Aggregate(total),kg/m
Ratiow/(c+fa)
Compressivemean
strengthfcm,28,MPa
3
3
3
3
3
CEMI
C20/25
1765
32,5
0,60
31,4
335
201
-
-
C30/37
CEMI
42,5R
1845
0,51
40,4
280
175
0,5
60
C35/45
CEMI
42,5R
1805
47,1
0,47
350
180
0,6
30
CEMIIIB
C30/37h
1870
32,5
0,50
40,7
340
170
0,3
-