g PTIthan that which is exposed to dry air for the entire period. If the concrete is kept damp for one
month, the strength is about double than that of concrete exposed only to dry air.
w
2
2g
Concrete may be kept moist by a number of ways. The methods consist in either supplying
additional moisture to concrete during early hardening period by ponding, spraying, sprinkling,
etc. or by preventing loss of moisture from concrete by sealing the surface of concrete by
membrane formed by curing compounds. Following are some of the prevelent methods of
curing.
2 g is done by covering the concrete surface with gunny bags and then sprinkling
water over them regularly or with water proof paper. In membrane curing the surface is coated
with a bitumen layer to prevent loss of moisture by evaporation. Sealing compounds such as
rubber latex emulsion, resins, varnish and wax may also be used as an alternative to bitumen
layer. However, the concrete here may not achieve full hydration as in moist curing.
The horizontal surfaces are kept wet by storing water over them (ponding) or by damp
gunny bags, straw, etc. Ponding, may, affect the strength if the concrete is flooded too soon.
When sprinkling of water is done at intervals, care must be taken that the concrete does not dry
out between applications to prevent the possibility of crazing—the fine cracks that may occur
in the surface of new concrete as it hardens.
2 g X Curing can be also accomplished by artificial heat while the concrete is
maintained in moist condition. Both of these conditions can be fulfilled by the use fo steam
curing. This method of curing is also known as accelerated curing since an increased rate of
strength development can be achieved. The accelerated process of curing has many advantages
in the manufacture of precast concrete products; (a) the moulds can be removed within a
p 2IH II h/22 '20'2g" @A2h2 2e2
2 2w
2g