EFFECT OF CALCIUM HYDROXIDE ON TRIAXIAL BEHAVIOR OF CEMENT PASTE

Abstract

Hardened cement paste is a brittle material but known to deform in a ductile manner under confining pressure. However, the mechanism involved in ductile deformation is not well understood. Classification of deformation mechanisms based on strain rate-differential stress relationships indicate that dislocation creep is a possible mechanism for ductile deformation but that the main hydrate of hardened cement paste is C-S-H, which is a gel material. In addition, dislocation cannot be defined in a gel material because dislocation represents a linear defect in a crystal material. In this study, scanning electron microscopy （SEM） observation and a stepwise creep test were conducted to understand the hydrates that govern the deformation of hardened cement paste under confining pressure. A sample prepared by mixing synthesized hydrates and commercial chemicals and compacting showed a different deformation behavior from that of the crushed and compacted cement paste sample. SEM observation of crushed and compacted cement paste revealed crystals of calcium hydroxide larger than 100μm. Compacts composed of cement paste powder with additional crushing or leaching of calcium with ammonium nitrate showed a different deformation behavior from that of cement paste. These results indicate that assembled calcium hydroxide plays a critical role in the deformation of cement paste under confining pressure and that the assemblage of calcium hydroxide was lost by additional crushing and leaching.