Optimum sulphate content

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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

 

 

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