Sulfate resistance of steel slag-ore slag-fly ash-based recycled concrete under dry-wet cycling conditions: Strengthening recycled aggregates with cement-silica fume

To address the insufficient sulfate resistance of recycled aggregate concrete in construction waste resource utilization, this study applied cement-silica fume treatment technology to steel slag-ore slag-fly ash-based cementitious solid waste concrete. By adjusting the replacement rates of recycled aggregate (RA) (70%, 100%) and cementitious material dosages (9%, 12%, 15%) to prepare specimens. Through mechanical property testing, sulfate dry-wet cycle testing, and microscopic characterization, the study investigated the effects and mechanisms of these factors. Results showed that cement-silica fume treatment increased the apparent density of recycled aggregates by 0.39%, reduced the crushing value by 4.5%, and elevated silicon and calcium content by 52% and 83%, respectively, thereby improving aggregate properties and the interfacial transition zone. Regarding mechanical properties, increased cementitious material content enhanced concrete strength at all ages. After cement-silica fume modification, strength loss at 100% RCA replacement rate was mitigated: the TR-100-15 group achieved 32.2 MPa compressive strength at 60 days, while the TR-70-15 group reached 6.5 MPa flexural strength at 60 days. Regarding sulfate resistance, the synergistic effect of high cementitious material content and cement-fly ash modification was significant. The TR-70-15 group achieved a corrosion resistance coefficient of 0.74 after 75 cycles, while the gap between the TR-100-15 group and the 70% replacement rate group narrowed. This study provides support for mix design and sulfate resistance optimization in high-replacement solid waste concrete.