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

Abstract

Fracture energy (GF) represents the average total energy consumed in the whole process of crack propagation. Using one parameter of GF, it is not sufficient to describe the fracture behavior during crack stable and unstable propagation periods. In this study, the GF, stable fracture energy (GFS) and unstable fracture energy (GFU) 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 (fcu), splitting tensile strength (ft), load–deflection (P‐δ), and load‐cracking 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°C). The effects of RA substitutions and temperatures on basic mechanical properties, GF, GFS, and GFU were analyzed. The results demonstrated that the fcu, ft, and elastic modulus (E) decreased with the incremental temperature. The GFS of concrete with different RA substitutions first decreased and then increased, and the minimum value appeared at 200°C. The GF and GFU 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°C, the GF and GFU of concrete remained mostly unchanged with the increase of RA substitutions, while the temperature reached 200 and 300°C, the GF and GFU of concrete increased and decreased with the increase of RA substitutions, respectively.

The combined effect of load and corrosion on the flexural performance of recycled aggregate concrete beams

“…1,2 Therefore, recycled aggregate concrete has lower mechanical properties and poorer durability compared to those of natural aggregate concrete. [3][4][5][6] In chloride-laden environments, because the porosity of recycled aggregate concrete is larger than that of natural aggregate concrete, chloride ions can easily migrate into recycled aggregate concrete, which increases the possibility of steel corrosion. Zhao et al 7 found that the corrosion of steel bars initiated earlier in recycled aggregate concrete than in natural aggregate concrete, and the more recycled coarse aggregate the concrete contained, the more rapidly the steel corroded and the earlier corrosioninduced cracks appeared on the surface of concrete cover.…”

“…Due to a layer of old cement mortar attached on the surface of recycled coarse aggregate, a large number of defects and micro‐cracks are introduced into recycled aggregate concrete 1,2 . Therefore, recycled aggregate concrete has lower mechanical properties and poorer durability compared to those of natural aggregate concrete 3–6 . In chloride‐laden environments, because the porosity of recycled aggregate concrete is larger than that of natural aggregate concrete, chloride ions can easily migrate into recycled aggregate concrete, which increases the possibility of steel corrosion.…”