Effect of Addition of Silica Fume and/or Superplasticizer on Shrinkage of Cement Mortars

Abstract

The concrete undergoes some volume change due to the following: settlement of the fresh concrete, chemlcal com binations of high alkali cements with certain reactive aggregates, changes in moisture content, changes in temperatures and due io applied loads. During the process of the hydration of cement there occurs change in volume due to the reduction in volume of the cement paste. When the cement paste is plastic, it undergoes a volumetric contraction whose magnitude is about one per cent of the absoluie volume of dry cement. This shrinkage is known as plastic shrinkage, as it takes place while the concrete is still in the plastic staie. Plastic shrinkage occurs mainly due to the settlement of the cement paste and bleeding of water to the top, which finally waporates. Sometimes concrete may swell thus increasing the volume. This occurs when continued hydration takes place in the presence of water. Volume change of sealed concrete is due to the causes other than the moisture movement, change in tempemture, amount and rate of loading. Such shrinkage is known as autogeneous shrinkage This occurs in the interior of large concrete mass.