Thermal resistance, water absorption and microstructure of high-strength self-compacting lightweight aggregate concrete (HSSC-LWAC) after exposure to elevated temperatures

Abstract

An experimental investigation on the influence of elevated temperatures on the thermal resistance, water absorption and microstructure of high-strength self-compacting lightweight aggregate concrete (HSSC-LWAC) is presented. In total, 315 concrete specimens from 7 different mixtures with different replacement ratios (0, 30 %, 50 % and 100 % by weight) of two kinds of LWAs, namely cloud concrete stone (CCS) and fly ash ceramsite (FAC), were prepared. The workability of fresh concrete mixtures including slump, J-Ring and T500 tests was first conducted aiming at meeting the requirements of self-compacting performance. Hardened concrete specimens were then exposed to different elevated temperatures (i.e. 200 °C, 400 °C, 600 °C and 800 °C) increased with a heating rate of 10 °C/min. A series of tests including the apparent morphology, ultrasound pulse velocity (UPV), residual compressive strength and capillary water absorption were carried out on unheated control concrete and after air-cooling period of heated concrete. Finally, the thermal analysis and microstructural observation were further conducted through the thermogravimetry (TG), differential scanning calorimetry (DSC), mercury intrusion porosimetry (MIP), laser scanning microscopy (LSM) and scanning electron microscope (SEM) to characterize the evolution of high temperature damage. Generally, the high temperature resistance of HSSC-LWAC shows an increasing trend as the LWAs content increases, while the residual mechanical strength increases and then decreases with an increase of the temperature gradient. The microstructural observation indicates that the evolution behavior of thermal damage promotes the continuous development of micropores in the interfacial transition zones (ITZ) to form wider microcracks, resulting in the degradation of residual mechanical properties.