Contents
Optimum sulphate content
–Why?
o to obtain a good workability
o silicates normal hydration
o better strength
–The optimal quantity of sulphates depends on
o % C3A & C4AF
o cement fineness
o sulphates reactivity
Sulphates
Optimum sulphate content Low alkaline sulphates level
Optimum sulphate content High alkaline sulphates level
Sulphates Action on hydration
Sulphates
o blocking ettringite
Alkaline sulphates
o accelerators
setting time (sometimes a little bit shorter)
higher initial strengths
lower 28 days strengths
o maintains high pH
protects reinforcement
but Ca++ lower
favorable effect on shrinkage
in plastic phase
in hardened phase
o reduces expansion
Sulphates Action on hydration
Alkaline sulphates
o favorable action in steam curing (increase strength)
o increase cement agglomeration
syngenite – gorgeyite
o alcali-aggregate reaction
o reaction with organic materials
stone staining
concrete staining…
efflorescences
Sulphates
Anhydrous sulphates of clinker
o Arcanite K2SO4
oLangbeinite 2 Ca SO4, K2SO4
o Aphtitalite Na2SO4, K2SO4
Hydrated sulphates
o Syngenite Ca SO4, K2SO4 , H2O
o Gorgeyite 5 Ca SO4, K2SO4 , H2O
Sulphates Compared solubility of some sulphates
