Why Curing of Concrete is important?
Curing is the process
where the concrete surfaces are kept wet for a certain period after placing of
concrete so as to promote the hardening of cement. It consists of a control of
temperature and of the moisture movement from and into the concrete.
Contents:-
- Purposes
- Period
- Effects
- Methods
Purposes of curing of concrete:-
Following are the
objects or purposes of the curing of concrete:
- Curing protects the concrete surfaces from sun and wind.
- The presence of water is essential to cause the chemical action
which accompanies the setting of concrete. Normally, there is an adequate
quantity of water at the time of mixing to cause the hardening of
concrete. But it is necessary to retain water until the concrete has fully
hardened.
- The strength of concrete gradually increases with age, if curing is
efficient. This increase in strength is sudden and rapid in early stages
and it continues slowly for an indefinite period.
- By proper curing, the durability and impermeability of concrete are
increased and shrinkage is reduced.
- The resistance of concrete to abrasion is considerably increased by
proper curing.
Period of curing:-
This depends upon the
type of cement and nature of work. For ordinary Portland cement, the curing
period is about 7 to 14 days. If rapid hardening cement is used, the curing
period can be considerably reduced.
Effects of improper curing:-
Following are the
major disadvantages of improper curing of concrete:
- The chances of ingress of chlorides and atmospheric chemicals are
very high.
- The compressive and flexural strengths are lowered.
- The cracks are formed due to plastic shrinkage, drying shrinkage
and thermal effects.
- The durability decreases due to higher permeability.
- The frost and weathering resistances are decreased.
- The rate of carbonation increases.
- The surfaces are coated with sand and dust and it leads to lower
the abrasion resistance.
The above
disadvantages are more prominent in those parts of structures which are either
directly exposed or those which have large surfaces compared to depth such as
roads, canals, bridges, cooling towers, chimneys, etc. It is therefore
necessary to protect the large exposed surfaces even before setting. Otherwise
it may lead to a pattern of fine cracks.
Methods of curing:-
Following two factors
are considered while selecting any mode of method of curing:
- The temperature should be kept minimum for dissipation of heat of
hydration.
- The water loss should be prevented.
Thus all the methods
of curing of concrete are derived from the basic principle of lowering of the
surface temperatures and prevention of water evaporation. Several specialized
curing techniques are employed in the modern construction work, but the most commonly
employed methods of curing are as follows:
- Ponding with water.
- Covering concrete with wet jute bags.
- Covering concrete with water-proof paper of polythelene sheets and
holding it in position.
- Intermittent spraying with water and continuous sprinkling of
water.
- Applying curing compounds.
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