Curing of concrete is the process of preventing the loss of moisture from the fresh concrete.
The main aim of curing of concrete is to maintain enough moisture content and favourable temperature in the concrete during hydration of the cementitious materials so that concrete can attain its potential strength and durability.
In India, curing is often neglected in the construction. There is a common wrong practise to start the curing only on the next day of concreting. Even on the next day, the curing delays in making arrangements of required materials.
Importance of Curing of Concrete
Hydration of cement is a long-term process. It depends upon available water and temperature. Thus, curing of concrete ensures continued hydration and, thus continued strength gain.
During the hydration process, the concrete shrinks. If we don’t cure the concrete, it will develop cracks on the surface. The surface cracks allow harmful ingredients to enter in the concrete which corrodes the reinforcement.
Hence, proper curing of concrete increases strength, durability, resistance to freeze and thaw, water tightness, resistance to harmful chemicals etc.
When should we start the Curing of Concrete?
Curing of concrete should start as soon as the final set of concrete occurs. It is when the bleeding water dry. Without the use of accelerators or retarders, the cement in concrete final sets in about six hours. So, we should start the curing of concrete after about 6 hours.
The starting of curing also depends upon various factors such as prevailing temperature, humidity, wind velocity, type of cement, fineness of cement, water-cement ration, size of that concrete member etc. However, the main idea is to keep the surface of concrete wet throughout the hydration phase.
The curing period should be as long as is feasible because the hydration of cement continues for a long time. In general, concrete must be cured until it attains about 70 % of its strength.
Curing Period of Concrete as per IS Code
As per Clause 13.5.1 of IS 456:2000,
- Curing should be continued for 7 days (with the temperature being maintained above 10-degree Celcius) for Ordinary Portland Cement.
- Curing should be continued for 10 days (with a recommendation to extend it to 14 days) where mineral admixtures or blended cement (such as fly-ash mixed) are used or when concrete is exposed to hot weather conditions.
- Curing should be continued at least for 14 days for mass concrete work, heavy footings, large piers.
At low temperature, the curing period must be increased.
Methods of Curing
Curing of Concrete can be performed by any of the following methods:
- By maintaining the presence of water in the concrete during early ages. Ponding or immersion, spraying or fogging, and wet coverings can be adopted to maintain the presence of water on a concrete surface.
- By preventing the loss of mixed water from the concrete by sealing the surface. Impervious sheets, membrane-forming compounds and leaving the forms in place prevents the loss of mixed water from concrete.
- By accelerating the strength gain by supplying heat and additional moisture to the concrete. Steam curing, insulating blankets or covers, and various heating techniques are available which accelerate the strength gain.