Importance of curing of concrete
Plenty has already been written about importance of curing of concrete yet we can not stress enough about its importance.
What is curing?
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 is the process to prevent the water used in concrete mix getting evaporated till certain period of time (28 days) and providing continuous moisture until it attains the required strength.
Science behind curing
Concrete is a mixture of sand, cement and aggregate. It is the chemical reaction between water and the cement that causes the concrete to set. Concrete strength depends on the growth of crystals within the matrix of the concrete. These crystals grow from a reaction between Portland cement and water—a reaction known as hydration. If there isn't enough water, the crystals can't grow and the concrete doesn't develop the strength it should. If there is enough water, the crystals grow out like tiny rock-hard fingers wrapping around the sand and gravel in the mix and intertwining with one another and thus giving concrete its strength
How long concrete should be cured?
Concrete gains maximum compressive strength within 28 days after placing of concrete and after 28 days compressive strength of concrete continues to increase for a long period of time but slowly. So, the minimum curing period for concrete should be 10 to 14 days. Since cement hydration is more rapid in first few days after fresh concrete is placed, it is important that enough water is retained within the concrete mass during this period.
Different 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.