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Different types of
Portland cement can be used to regulate the amount of hydration
heat released when concrete sets. Type 10 Normal Portland cement
releases half of its heat in
three days. Type 20 Moderate Portland cement takes more than three days
to release half of its heat. Type 30 High Early Strength Portland
cement releases half of its heat in less than three days. Type 40
Low Heat of Hydration Portland cement releases very little heat of
hydration.
Type 50 Sulphate Resistant Portland cement is used to protect
concrete from degradation when it is placed in soils with high
sulphate
content.
Concrete must remain moist when it is curing. Hydration continues only
as long as there is moisture in the cement paste. Concrete
that has dried out before it is completely cured shrinks and
cracks, and can disintegrate into dust, especially at the
surface. Control joints and reinforcing steel can be used to control
cracking.
If concrete loses it's moisture or the relative humidity goes below
80 percent, or if it freezes, concrete stops curing and
gaining strength.
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