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AndrzejAjdukiewicz
aggressiveagents,gaseousorliquid,particularlychloridesorsulphates,should
beincreasedtotheextendofthestructureservicelife.Inmajorityofthepracti-
calcases,thediffusionofchloridesintotheconcreteisthedominatingfactorin
thedeteriorationofconcretestructures.Itiswellknownthatthedurabilityof
concreteisfirstofalldependentonthewater/cementratio(w/c)ormorepre-
ciselythewatertobinderratio(w/b).Thepropermixproportionsandthe
propertiesoftheconstituentmaterialsinfluencethebulkpropertiesofconcrete,
however,theperformanceofthesurfaceskinissignificantlyaffectedbythetype
offormworkusedduringtheconstruction,togetherwithcuringappliedtothe
concreteafterremovaloftheformwork.
Thecommonlyusedkindsofformwork,e.g.madefromimpregnated
plywoodorsteel,areessentiallyimpermeabletoairandwater,whichcausesthe
occurrenceofexcessiveblowholesandotherfaultsontheformedconcretesur-
face.Sometimes,thefaultsareinitiallynotvisible,buttheporousconcreteis
subjecttodeterioration.
Inthepast,severaldifferentmethodsofimprovementofconcretesurface
qualityhavebeenintroduced.Theinvestigationsstartedin1930sintheUnited
States.JohnEarleywasthefirstwhothesurfacesofconcretefacadeelements
effectively,usinggypsumexpandableformstoreducetheamountofwaterin
concretemixtureatthesurface.Thewideprogramofresearchandprototype
applicationswasundertakenintheUSin1938,andthemainresultswerepub-
lishedafewyearslater[1],[2].Intheearlyapplicationstheabsorbablefibre-
boardswereused,madefromcane,sawdustetc.Thosesimplemethodswere
effectiveforconcretemixturesusedinthepast(w/cover0,5)andeliminationof
voids,blowholesandotherfaultswasquitereasonablethen.Suchsimplesolu-
tionsarestillinuseinsomesystemsofformworks.
Intheearly1950sthespecialtestsforUSArmyweredone,takinginto
considerationtheeffectivenessofformworkfromtheconcretesurfacequality
pointofview[3].Anumberofdifferentinsertsintheformswerecompared,
sevennotpermeableandthirteenpermeable.Thesetestsgaveevidencethatin
allcasesofpermeableformworkthesurfacequalitywasbetterthanincaseof
notpermeableones,butontheotherside,theefficiencyofmaterialsavailablein
permeableformworksatthattimewasnotsatisfactory.
Whentheproblemswithdurabilityofconcretestructuresbecamecommon
andtherepairsconsumedgreaterandgreatercosts,theintensiveinvestigations
havebeenundertaken.Atfirst,thecostlymethodsofdurabilityimprovementby
meansofexternalconcreteimpregnation,electrochemicalcathodicoranodic
protectionofreinforcementorspecialcoversonreinforcingbarswereintro-
duced.
ApplicationsofmodernpermeableformworksstartedinJapan,inthelate
1980s[4].Thebasicprincipleofsuchsolutionsisthattheformworkactsasa
filterthroughwhichairandbleedwatercanpass,butnotthecementgrains.