Multiscale study on high-temperature mechanical behaviors and durability of recycled concrete reinforced by polycarboxylate-modified 3D porous graphene

Polycarboxylate-modified 3D porous graphene (PG) is a highly porous graphene with an extremely large specific surface area, providing a novel approach for enhancing the mechanical and durability performance of recycled aggregate concrete (RAC). This study investigates the influence of PG on the high-temperature mechanical performance, crack development, durability of RAC from the perspective of multiscale. The results demonstrate that the enhancing effect of PG on RAC on the strength increases with curing age. Although high temperature can damage RAC, its mechanical properties at the same temperature first increase and then decrease with the increase of PG content, and the optimal content of PG is 0.03 %. In addition, the resistance of RAC to chloride ion penetration and freeze-thaw cycles also follows a similar trend, that is, it decreases after initial improvement with increasing PG content.From a microscopic perspective, the benefits brought by PG can be attributed to its capacity to densify the pore structure, reduce the thickness of the ITZ, enhance the elastic modulus and hardness of the ITZ, and promote cement hydration, as evidenced by the mercury intrusion porosimetry, nanoindentation test, microscopic observation and hydration analysis.