Study and mechanism analysis on fracture mechanical properties of steel fiber reinforced recycled concrete (SF-R-RC)

Recycled concrete has deficiencies in its overall performance due to the deteriorated properties of the recycled aggregate (RA) used. Based on the RA characteristics and fiber reinforcement mechanism, designing recycled concrete by adding steel fiber (SF) and enhancing RAs in a coordinated manner can effectively improve the overall performance of recycled concrete. Therefore, this paper considers the SF content and RA enhancement to study the fracture mechanical properties of steel fiber reinforced recycled concrete (SF-R-RC), and the main conclusions are as follows: the fracture mechanical properties of SF-R-RC are significantly affected by aggregate enhancement and SF content. Without the SFs, the strengthened coated recycled aggregate concrete (CRAC) was better than unreinforced recycled aggregate concrete (RAC) in terms of the unstable fracture load, fracture energy, initial fracture toughness and unstable fracture toughness, but weaker than normal aggregate concrete (NAC). The increase in the unstable fracture load, fracture energy, initial fracture toughness and unstable fracture toughness of NAC, RAC and CRAC with the increase in SF content was observed, with CRAC showing the most significant increase in these fracture parameters. Applying digital image correlation (DIC) and acoustic emission (AE) techniques, the effect of SF content and RA enhancement method on the crack evolution process and damage distribution law of SF-R-RC was studied. Meanwhile, the microscopic testing technique was used to reveal the mechanism of the influence of SF and RA enhancement on the fracture mechanical properties of SF-R-RC. The research results of this paper provide a theoretical basis for the application of RA enhancement and SF reinforcement methods of recycled concrete in practical engineering.