Water to cement ratio: A simple and effective approach to control plastic and drying shrinkage in concrete

Abstract

When water moves out of a porous body which is not fully rigid, contraction takes place. In Concrete, similar movement of water occurs from its fresh to hardened state which is known as Shrinkage. The loss of water by evaporation from the surface of the freshly laid concrete (i.e. plastic state) causes Plastic shrinkage. A similar loss can also occur by suction by the underlying subgrade or soil. Contracting of hardened concrete mixture due to loss of capillary water is called Drying Shrinkage. This shrinkage causes an increase in the tensile stress which may lead to cracking, internal warping and deflections. Several factors affect the plastic and drying shrinkage including temperature, water / cement ratio, curing materials and time. Concrete exhibiting high shrinkage can lead to serviceability problems in structures due to excessive deflections or warping (curling); if higher shrinkage leads to cracking, durability of the structure may also be impaired. Several studies and investigations have demonstrated that adequate and proper curing of concrete is the most appropriate step to prevent shrinkages and developing a high degree of the desirable properties of concrete. The best curing techniques and procedures depend upon the water-cement ratio of the concrete. This paper highlights the causes of the plastic and drying shrinkages with easier approaches to avoid or minimise them so as to prevent deterioration of concrete.