Residual fracture energy of natural and recycled aggregate concrete after exposure to high temperatures

摘要

Fracture energy (G_F) represents the average total energy consumed in the whole process of crack propagation. Using one parameter of G_F, it is not sufficient to describe the fracture behavior during crack stable and unstable propagation periods. In this study, the G_F, stable fracture energy (G_(FS)) and unstable fracture energy (G_(FU)) of natural and recycled aggregate concrete (RAC) were investigated by using three-point bending tests. Totally, 128 cubic specimens (100 mm × 100 mm × 100 mm) and 64 notched beams with size of 510 mm × 100 mm × 100 mm were manufactured to test the compressive strength (f_(cu)), splitting tensile strength (ft), load–deflection (P-δ), and loadcracking mouth opening displacement (P-CMOD) curves, considering different replacement levels (0, 30, 70, and 100) of recycled coarse aggregate (RA) and high temperatures exposure (20, 100, 200, and 300℃). The effects of RA substitutions and temperatures on basic mechanical properties, G_F, G_(FS), and G_(FU) were analyzed. The results demonstrated that the f_(cu), f_t, and elastic modulus (E) decreased with the incremental temperature. The G_(FS) of concrete with different RA substitutions first decreased and then increased, and the minimum value appeared at 200℃. The G_F and G_(FU) of concrete with different RA substitutions increased with the elevated temperature, and the increase rate decreased with RA substitutions. When the temperature is less than 100℃, the G_F and G_(FU) of concrete remained mostly unchanged with the increase of RA substitutions, while the temperature reached 200 and 300℃, the G_F and G_(FU) of concrete increased and decreased with the increase of RA substitutions, respectively.