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Concrete that needs to be watertight must have low
permeability. This can be achieved with a low water to cement ratio in
the cement paste and an extended moist curing time. The same procedure
along with hard aggregates can make the cured concrete abrasion
resistant.
The properties of concrete can be altered when supplementary cementing materials are added to Portland cement. Generally,
less water is needed in concrete mixes containing fly ash or ground
granulated slag. Air entraining admixtures should be added to concrete
containing slag, fly ash and silica fume because they reduce the amount
of entrapped air. Silica fume makes a concrete gummier and less
workable. Segregation and bleeding are reduced in concretes using fly
ash and silica fume. Plastic shrinkage
cracking in the concrete must be prevented if low bleeding concrete is subject to rapid
drying.
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