Causes of Plastic Shrinkage Cracking
Loss of water from evaporation which leads to a built up tensile shrinkage stress when concrete is subjected to sufficient restraint.
When the rate of water loss due to evaporation exceeds the rate at which the bleed water is supplied to the surface, negative capillary pressures form which result in volume changes in the concrete.
Tensile stresses in the paste form due to the negative capillary pressure and the development of strength in the concrete. Cracking occurs if the tensile stresses are greater than the tensile strength of the concrete.