CURING
The concrete surface are kept wet for a certain period after placing of concrete so as to promote the hardening of cement. The process of applying the water on the concrete is known as curing.
Purpose of curing:
i. The curing protects the concrete surface from sun and wind.
ii. The presence of water is essential to concrete to cause chemical action which accompanies
iii. The strength of concrete gradually increases with age if curing is efficient.
iv. By proper curing the durability and impermeability of concrete are increased and shrinkage is reduced.
Methods of curing
The most common methods of Site curing of in-situ concrete are:
a. Form work retention,
b. suspension of covering above the surface before the concrete has set (horizontal surfaces),
c. spraying with water,
d. ponding with water,
e. covering with wet sand. earth, sawdust, straw, or periodically wetted hessian or cotton mats, or use of an absorbent covering with access to water.
f. application of a curing membrane. 
g. waterproof reinforced paper or plastic sheeting.
h. tenting or other shelter against drying winds,
i. sunshields,
j. covering with an insulating layer or heated enclosure.
1. Water curing : Immersion, Ponding, Spraying, Wet covering
a) The precast concrete members are immersed in curing tanks for a certain duration.
b) Pavement slabs, Roof slabs , etc are covered under water by making small pond . 
c) Vertical walls. columns , etc are cured by spraying water. In some cases covering with wet gunny bags, Hessian cloth, Jute matting, straw, etc.
d) For horizontal surfaces saw dust. earth or sand are used as wet covering .
2. Membrane curing
Concrete surface is covered with membrane or a sealing compound which Will effectively seal Off the evaporation of water from the concrete. The application of membrane should be after a short spell of water curing for one or two days. 
This method is useful where there is a acute shortage of water, concrete placed in inaccessible places, difficult or far off places.
The different sealing compounds used are:
a) Bituminous and asphaltic emulsion or cutbacks,
b) Coal tar thinned by means of a solvent,
c) Rubber latex emulsions,
d) Emulsions or solutions of resins, varnishes, waxes, drying oils and water - repellant substances,
e) Emulsion of paraffin or boiled linseed oil in water with stabilizers
3. Application of heat
When concrete subjected to higher temperature it accelerates the hydration process resulting in faster development of strength. Concrete cannot subjected to dry heat as the presence of moisture is also essential requisite. The higher temperature can be applied in following ways:
a. Steam curing at ordinary or high pressure- used for prefabricated concrete elements.
b. Curing with Infra-red radiation and Electrical curing- practiced in cold climatic regions.
0 Comments