Experimental study of micro/macro crack development and stress-strain relations of cement-based composite materials at elevated temperatures

This paper presents the results of observations of scanning electron microscope (SEM) micro/macro crack development and simultaneous measurements of temperature-dependent stress-strain relations of hardened cement pastes (HCP) and mortar under a steady thermal state (up to 500 °C) and a displacement-controlled loading process. The experimental results showed that the thermal damage of HCP was not only due to the recognized decomposition of the hydration products but also to the formation of dehydration-induced microcracks. These damage mechanisms, together with three other types of macrocracks arisen from the mismatch of expansion/shrinkage between the phase materials (HCP and aggregates) contributed to the thermal damage of the mortar. By comparing the evolution of the stress-strain curves for the HCP and the companion mortar specimens, the effects of the damage mechanisms could be separately quantified. In this study, the thermal damage of the mortar specimens was largely caused by the thermal mismatch mechanism.