In the early hours, when exposed to not saturated air (mild or dry climates), fresh concrete is subject to a quick evaporation of water from cement paste, with consequent shrinkage. Shrinkage is a contraction of the concrete volume and may induce cracking, thus reducing mechanical strength of concrete structures and facilitating corrosion of steel reinforcement.
During hydration and hardening, concrete must be cured to ensure the achievement of the expected strength and avoid cracking formation. Fast water evaporation from concrete surface must be avoided, for example by covering concrete surface with water retaining materials, plastic sheets or waterproof membranes, or keeping concrete surface continuously moist with water spray, or protecting newly cast concrete from direct sunshine and wind. This is due for at least for at least 1 up to some days after casting.
