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This
is a hydraulic cement produced by inter grinding or blending a mixture of granulated
blast furnace slag (80-85%), hard burnt Gypsum (10-15%) and a small amount of Portland
cement or Portland cement clinker( about 2-5%) or any other source of lime.
The product is ground finer than Portland Cement
(specific surface > 4000cm2/gm)
This
cement is known for its chemical resistance to most aggressive conditions
generally encountered in construction and particularly to the attack of
sulphates. The strength characteristics of this cement are little lower
than that for ordinary Portland cement.
The
hydration products of Super sulphated cement mainly comprise of Calcium
silicate hydrates and ettringite. The suitability of ettringite above 37oC
is sometimes questionable. So the use of super sulphated cement in the
tropical countries like India
is generally ruled out. This type of cement is mostly used in aggressive
conditions to resist the attack of aggressive waters.
Characteristics
It
has Low heat of hydration compared to OPC (only 40-45 cal/gm at 7days &
45-50 cal/gm at 28days). Hence it is suitable for mass concrete construction
but care must be taken if used in cold weather as the rate of strength
development is considerably reduced at low temperatures.
Has
high sulphate resistance: recommended for use in aggressive conditions like
sulphate bearing soils, marine water & other chemically aggressive
conditions.
More sensitive to deterioration during storage than OPC
Combines with more water on hydration than that is
required for Portland Cement .
Water/Cement ratio with such cement should not be less than 0.5. Wet curing
of not less than 3 days is essential to avoid formation of undesirable powdery
surface layer on account of premature drying.
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