Curing is the process of keeping freshly placed concrete moist and at a suitable temperature so the cement can continue to hydrate and the concrete can gain its full strength. It is one of the most important — and most neglected — steps on site: concrete that dries out too soon can lose a large fraction of its potential strength and develop surface cracks.
The cement-water reaction that hardens concrete continues for weeks, but only while moisture is present. If the surface water evaporates in the first few days, hydration stops near the surface and the concrete stays weak and porous there. Proper curing keeps water available during this critical early period.
Common methods are ponding (holding water on slabs), wet covering with hessian or gunny bags, continuous spraying, or curing compounds that seal in moisture. Concrete should be cured for at least 7 days (longer in hot, dry weather, and for blended cements). Good curing costs almost nothing yet directly determines whether the concrete reaches the strength it was designed and paid for.