Abstract: Recycled concrete enables resource reutilization of construction waste materials and mitigates the depletion of natural sand and gravel resources. This study investigates recycled concrete (RCA) with a 30% substitution rate to address its performance degradation caused by high porosity and strong water absorption in recycled fine aggregates (RFA), focusing on three treatment conditions－different silica fume dosages (0%, 6% and 12%), and three drying conditions－dry, semi-saturated prewetted, and fully saturated prewetted states. We conduct experimental tests on compressive strength, and make nuclear magnetic resonance (NMR) analysis and thermogravimetric analysis, examining the synergistic effects of silica fume and prewetting on RCA. The results show that in the case of the silica ash content of 6% and the semi-saturated and prewetted RFA, the recycled concrete is best in comprehensive performance－its hydration degree increased by 8.08%, porosity reduced by 16.64%, and compressive strength increased by 13.8%, compared with the RD of the recycled control group. Prewetted RCA provides a stable hydration environment in the early curing stage, while it facilitates hydration during mid-to-late stages through releasing its sustained water that results in an internal curing condition. And, correlations exist between its hydration degree, pore structure parameters, and mechanical properties.

Key words: recycled concrete, hydration degree, pore structure, fractal dimension, internal curing