Shrinkage Characteristics of Cement Paste and Mortar at Very Early Ages
Yusuke BABA and Tetsurou KASAI
Abstract:At very early ages, plastic shrinkage is one of the causes of cracking of concrete. It has been believed that the plastic shrinkage of cementitious material occurs when the water drying rate from the surface is larger than bleeding rate. However, in recent studies, it was reported that negative pressure may occur due to hydration, without drying, in high-strength concrete with a low water-binder ratio. This suggests that the volume change of cementitious material at very early ages is influenced not only by drying from the surface but also by self desiccation due to hydration. The purpose of this study is to clarify the effects of water-binder ratios, volume fraction of fine aggregates and curing conditions on volume change of cement paste and mortar at very early ages. Effect of each factor on volume change of cement paste and mortar was investigated through experiments on the change in pore water pressure and the shrinkage behavior at very early ages. It was found that volume change of cement paste and mortar at very early ages was markedly influenced by self desiccation as well as by drying when the water-binder ratio is low. Key Words:Plastic shrinkage, Autogenous shrinkage, Pore water pressure, Self desiccation, Drying