Treść książki
Przejdź do opcji czytnikaPrzejdź do nawigacjiPrzejdź do informacjiPrzejdź do stopki
10
AndrzejAjdukiewicz
•hydrostaticpressureofmixture,
•capillarysuctionfromabsorptivelining.
ThemainresultofcastingconcreteagainstCPFisasignificantchangein
thesurfaceappearance.Thevisibleeffectsonthesurfacescomparedtothecon-
ventionallyformedconcreteare:theeliminationofblowholesandotherfaults,
darkercolour,textureddullfinish.
Nowadays,inEuropetherearetwokindsofCPFinuse,bothbasedona
non-wovenpolypropylenefibrefabric.TheCPFsystemnamedZemdrainMD
(introducedin1996)isapropylenefour-layerspunbondedfabric,whilethe
secondonewithcommercialnameFormtex(2000)hasthermallybondedfibres
ononesideofthefabric.Thetestsconcerningthepropertiesofconcretewith
referencetodurabilityweredoneforbothkindsofCPFsystemsinseveralre-
searchcentres,butwithaverylimitednumberofconcretemixtures.
Allthoseinvestigationswerebasedonsmallspecimenstakenfromsimple
members,usuallyintheformofcorecylinders.Thegeneralaimofthetestspre-
sentedherewastoconfirmtheeffectsofCPFforconcretemixtureswithdiffer-
entw/cratio(includingHPC)andtoclarifyhowtheimprovedpropertiesofcon-
cretesurfacesmayaffectthebehaviourofmemberssubjectedtobendingand
shear,mainlyregardingthecrackingappearance.TheCPFsystemusedinthe
testswasbasedonthethermal-bondedfabricwithpolypropylenefibres.
ThemajortwoeffectsofformingconcreteagainstCPFare:significantre-
ductionofw/cratioatthesurfaceandclearlymoretightstructureoftheskin
layer(seeFig.2).Allthebenefitsmentionedbelowaredirectlyrelatedtothese
twoeffects.
Fig.2.SectionofconcreteclosetothesurfaceformedagainstCPF;darklayerofcement
concentrationisvisibleatthesurface;averagew/c=0.50,whileatsurfacew/c≤0,35