Damage Mechanism Investigation on Fiber Reinforced Recycled Cement Aggregate Concrete in a Cold Region

In order to investigate the internal damage mechanism of carbon fiber-reinforced recycled concrete, microscopic, mechanical, and freeze-thaw cycle experimental programs were conducted. Three categories of recycled concrete specimens with different recycled concrete admixtures and reinforcement modes were designed in this study. Axial compression tests and freeze-thaw cycles were conducted, combined with SEM and fracture surface observation and analysis, which were used to study the effects of the ratio of carbon fiber reinforcement and admixture of recycled aggregates on the mechanical properties of the concrete, the freezing resistance, and the microstructure. Research results indicate that carbon fiber reinforcement can effectively improve recycled concrete's strength and frost resistance. The increase in reinforcement ratio gradually increased mechanical strength and frost resistance. Compared with the unreinforced concrete, the axial strength of semi-reinforced and fully reinforced specimens was enhanced by 25% and 42.5%, respectively. The 100% recycled substitution rate specimens were treated with full reinforcement. Their compressive strengths were similar to those of unreinforced natural aggregate concrete. The compressive strength of the fully reinforced specimens was similar to that of the unreinforced natural aggregate concrete. Furthermore, the mechanism of strength loss in recycled concrete is obtained through microstructural analysis. A uniaxial compression numerical model of CFRP-reinforced recycled concrete was established, and a modified CFRP-reinforced cement-recycled concrete was proposed to accurately determine the ontological relationship for different reinforcement ratios and recycled aggregate admixtures. A BP neural network model was developed by MATLAB to effectively predict the compressive strength of recycled concrete with different mix ratios under different numbers of freeze-thaw cycles.