Thermally-induced mechanical degradation analysis of recycled aggregate concrete mixed with glazed hollow beads

Abstract

The occurrence of fire often leads to the damage and deterioration of micro- and meso-structures of concrete materials, leading to the decomposition of hydrates, coarsening of porous structure, and thermal cracking induced by water vapor pressure, resulting in the decline of macro-physical and mechanical properties and durability. The meso-regulatory function of the lightweight, high-strength, internally porous and thermally stable glazed hollow beads (GHB) can improve the high-temperature resistance of concrete. In order to study the degradation characteristics of recycled aggregate concrete mixed with glazed hollow beads (RATIC), mechanical properties and internal meso-structural changes at high temperatures, the cube compressive strength test and CT test are carried. According to the improved image segmentation algorithm based on adaptive threshold and region growing methods, the influence of different recycled coarse aggregate (RCA) and GHB contents on the mesostructure of RATIC, such as thermal crack development and pore distribution, is systematically analyzed. Based on the self-compiled box dimension program, the corresponding relationship between compressive strength, fractal dimensions of mesostructure and temperature is obtained. The results reveal that the GHB can alleviate the stress concentration of coarse aggregates and cement paste caused by temperature expansion and deformation, provide a release channel for vapor pressure, alleviate cracks in the mortar area and pore boundaries, and slow down the spread of heat in the concrete. Overall, the GHB renders a positive effect on the heat-induced damage resistance of concrete.