Durability of recycled aggregate thermal insulation concrete under combined flexural loading and freeze-thaw cycles

A testing program including freeze-thaw cycles and flexural-loading combined action was designed to investigate the durability of recycled aggregate thermal insulation concrete (RATIC). The volume replacement ratios of recycled coarse aggregates (RCAs) were 0, 30, 50, 70, and 100%, and the flexural-load ratios were 0, 15, 30, 45%, and the glazed hollow bead particles (GHBs) with volume percentage of 130% were added. To evaluate the performance of RATIC, the relative dynamic modulus of elasticity (RDME) and mass loss rate (MLR) were estimated. The results show that the flexural-load stress exhibited an obvious negative effect on the freeze-thaw resistance of RATIC. With a 45% flexural-load ratio, RATIC fractured even before the load cycles reached 30. The decrease in the RDME was accelerated by the flexural-load stress, whereas this stress exhibited little effect on MLR. The durability performance of RATIC under combined actions decreases with the increase in the RCA replacement ratio, whereas the performance increased with the increment in the thermal insulation aggregate GHBs. Further to reveal the mechanism of RATIC under double actions, scanning electron microscopy, X-ray diffraction, and a new method of fluorescence analysis were employed. The results showed the existence of more micropores and microcracks in the tensile area. Further, compared to the new interfacial transition zones (ITZs), the microcracks in old ITZs caused by combined actions aggravated the damage caused in the freeze-thaw cycles. (C) 2020 Published by Elsevier Ltd.