What is concrete curing?
Curing is maintaining moisture in concrete following placement so that the concrete’s designed properties can develop. Curing influences the concrete’s ultimate durability, strength, water tightness, abrasion resistance, volume stability and resistance to freeze/thaw cycles and deicing salts. These properties are reduced significantly when curing is inadequate.
Why is curing necessary?
When Portland cement is mixed with water, a chemical reaction called hydration takes place. As cement hydrates, the strength, durability and density of the concrete increases. The more complete the hydration, the higher these properties become. Complete hydration of cement takes a very long time. The hydration process is complete when the surface of the concrete is hard. Theoretically, the hydration process continues for years. With sufficient water, the hydration process will be approximately 30% complete in 3 days, 60% complete in 7 days and 98% complete in 28 days.
Most freshly mixed concrete contains more water than is required to hydrate the cement in the mix. Water loss in the first few days due to bleed water and evaporation reduces the water content of the mix and slows or stops the hydration process. It is critical to the long term durability of the concrete that water evaporation be minimized. Excess loss of water causes the concrete to shrink, creating tensile stresses within the concrete. If these stresses develop before the concrete achieves adequate tensile strength, surface cracking results.
