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Concrete
can be protected from freezing in cold weather by hydration heat,
and by using enclosures, windbreaks, portable heaters, insulated
forms and blankets to maintain the temperature and moisture
needed for curing. Forms, reinforcing steel and embedded fixtures also
need to
be clear of snow and ice before the concrete is placed. Thermometers
and storage for test cylinders should be made available. These measures
are important because concrete can lose
up to 50 percent of its strength if it is frozen within a few hours of
placement. Concrete that has been frozen once can be restored to nearly
normal
strength but it will not be as resistant to weathering or as watertight
as unfrozen concrete. Type 30 High early strength Portland
cement, reduces the time needed to harden concrete and remove
the cold weather insulation and other devices. Accelerators such as
Calcium Chloride can be used to reduce
the setting time and entrained air can provide protection from
freezing and thawing. Heating the mixing water and aggregates will help
protect the concrete from freezing. Gradually cooling the concrete,
after termination of the heating
period, will help prevent thermal cracking. |
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