ABSTRACT

Abstract This study aims to clarify the relationship between autogenous shrinkage and hydration by investigating the effects of hydration reaction on the autogenous shrinkage phenomenon and the relationship between the autogenous shrinkage and ratio of hydration, in order to set course for devising a model of autogenous shrinkage. The authors therefore measured autogenous shrinkage strain of cement paste with a W/C of 25 and 30% using an experimental laser measuring device. The pore size distribution and ignition loss were also measured to investigate the relationship between autogenous shrinkage and the microstructure in the hardened paste and hydration reaction. As a result, it was found necessary to quantify the time-related changes in the ratio of hydration and the intermolecular forces and surface forces resulting from the changes in the microstructure of hardened paste. Keywords: Autogenous shrinkage, Chemical shrinkage, Hydration ratio, Ignition loss, Pore size distribution

I Introduction

Autogenous shrinkage of hardening cement is said to be a phenomenon in which water in newly formed voids is lost by the reaction of cement with water and the low relative humidity in the voids causes a capillary tension, which causes a reduction in the volume of cement. This phenomenon can be considered from three levels of scale: a microscopic level of hydration of cement, intermediate level of pore structure, and macroscopic level of autogenous shrinkage development. Grasping such a macroscopic phenomenon from different levels of scale will lead to the formulation of a

more realistic and reliable evaluation model. Hydration of cement is impossible to explain with a simple parameter.