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X2The rate of strength development is accelerated; a higher percentage of calcium
chloride causes excessive shrinkage. Strength gained after 1 day is 25 per cent more and after
7 days about 20 per cent more than the ordinary Portland cement.
X It is very suitable for cold weathers.
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@sX2VHRQAX It is also called hydrophobic cement. A small amount of
hydrophobic surfactants such as stearic acid, boric acid or oleic acid is mixed with the ordinary
Portland cement during grinding of clinker. These substances are added in amounts of 0.1 to
0.5% of the weight of cement in terms of dry admixtures. These acids form a thin
(monomolecular) film around the cement particles which prevent the entry of atmospheric
moisture. The film breaks down when the concrete is mixed, and the normal hydration takes place.
When concrete is being prepared, hydrophobic admixtures plasticize the mix and contribute
to the formation of uniformly distributed fine pores in concrete as it hardens and thus enhance
its frost resistance. Hydrophobic cement also features greater water resistance and water
impermeability.
The specific surface of hydrophobic cement should not be less than 350 m^2 /kg. The average
compressive strength should not be less than
72 ± 1 hour 1 15.69 N/mm^2
168 ± 2 hours 1 21.57 N/mm^2
672 ± 4 hours 1 30.40 N/mm^2The weak points of hydrophobic cement are its small strength gain during the initial period
because of the hydrophobic films on cement grains which prevent the interaction with water,
but its 28-day strength is equal to that of ordinary Portland cement.
X2It is most suitable for basements and for making water tight concrete.
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X It is manufactured by adding strearates of Ca and Al and gypsum
treated with tannic acid, etc. at the time of grinding.
X It is resistant to penetration of water.
XWater retaining structures like tanks, reservoirs, retaining walls, swimming pools,
bridge piers, etc.
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Portland cement is kept in sacks of 0.035 m^3 (50 kg) capacity for local use. These are stored for
short period of time in air tight room avoiding moisture and dampness, at some distance from
walls and at some height from floors. The stack should be covered with suitable coverings to
avoid circulation of air through the stack and not more than ten bags should be stacked one over
another.