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The curing period takes at least three
days and in cold weather this should
be extended to five. In freezing con-
ditions, the fresh concrete needs to
be well insulated from the effects of
cold weather.
When cement andwater aremixed
together to form a paste, a chemical
reaction occurs and the paste sets
and slowly hardens. In concrete, the
paste binds the other constituent
materials andwill continue to harden
and gain in strength as long as water
is present. This hydration will contin-
ue as long as there is sufficient water
available to support the process.
Curing is important to ensure that
concrete hydrates in a proper man-
ner. The gain in strength is initially
rapid but slows down progressively.
The purpose of curing is to control
the rate of loss of moisture and to
prevent plastic shrinkage cracking.
Lack of curing affects the strength,
durability and abrasion resistance of
the concrete.
FORMWORK
Formwork should be erected with
joints tight enough toprevent leakage
of cement paste. Surfaces of forms
that are in contact with fresh wet
concrete ought to be treated with a
coat of non-staining mineral oil, or a
suitable releasing agent. In the case
of timber forms, wetting the surface
is acceptable to ensure easy release
and prevent adhesion of the concrete
to the formwork.
The formwork can be removed
after the concrete has attained suf-
ficient strength to support its own
weight and any loads that may be
imposed on it.
REINFORCEMENT
Reinforcementmust at the time of the
placing of the concrete, be free from
rust, scale, oil and other coatings that
may reduce the bond between steel
and surrounding concrete, or affect
the durability, or initiate corrosion.
Ensure that water is used as a release
agent on the formwork, to prevent
contamination of the reinforce-
ment. It must be secured by tying at
intersections with annealed wire of
1,6mmor 1,25mmor suitable clips or
fixed in position bymeans of hangers
or saddles and aligned by spacers or
other supporting materials.
CEMENT PLASTER
Common problems with cement
plaster include crazing, cracking,
Continued
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Transporting bricks on site