Hydration-induced Thermal Stress and Autogenous Shrinkage in Early Age Concrete

Abstract

This thesis mainly dealt with the prediction of the thermal stress and autogenous shrinkage (AS) in early-age concrete. The main purpose of the present work is to improve and extend the existing knowledge of crack-inducing forces. The occurrence of restraint stress due to restrained thermal and autogenous deformations has been known as one of the major cause of early-age cracking in concrete. It is thus of utmost importance, to further study and improve the existing knowledge of material behavior in order to accurately predict the crack inducing forces subjected to in-situ temperature variations and restrained conditions. In the early hardening phase, thermal and autogenous deformations occurred simultaneously. This is because concrete goes through natural heating and cooling cycle due to hydration reaction between cement and water, which causes the temperature of concrete getting rise. In traditional massive concrete structures, thermal deformations (TD) will be dominant that would induce restraint thermal stresses due to restraining actions, where as in high strength or newly developing high performance concrete both thermal and autogenous deformations simultaneously occurred, which results in combined thermal and shrinkage induced stresses. This is because of high binder contents of high strength and high performance concretes (HSC/HPC) which increases not only shrinkage but also causes very high temperature rises in large cross-sectional members (such as HSC columns and shear wall in high rise buildings which are normally 0.6m thick or more) due to enormous amount of heat accumulation in the center that usually takes much longer time in dissipating depending on various influencing factors (i.e., size of member, distance of studied location from exposed surface, type of form work, its thickness and removal time, and ambient conditions). To improve the cracking resistance at early-age stage, an accurate assessment of the relevant property is indispensib...