Mechanical Properties and Microstructure of Carbon Fiber-Reinforced Nano-Metakaolin Recycled Concrete

To make full use of recycled aggregate concrete (RAC), carbon fiber (CF) and nano-metakaolin (NMK) were mixed into RAC to improve its mechanical properties and microstructure. The effects of NMK content, CF content, recycled aggregate (RA) replacement rate, and CF length on the compressive strength, splitting tensile strength, and tension-compression ratio ofRAC were studied by the orthogonal test method; then, the test results were analyzed. The results show that the NMK content and RA replacement rate have significant effects on the compressive strength of RAC, while the CF content has significant effects on the splitting tensile strength and the tension-compression ratio. Through the synergistic effect of NMK and CF, the pore structure characteristics of RAC are improved, and the bond strength of the interfacial transition zone (ITZ) of CF-mortar is increased, which further enhances the strengthening effect of CF; thus, the mechanical properties of RAC are continuously enhanced.