Effects of cement-silica fume treated recycled aggregates on mechanical properties and sulfate resistance of all-waste concrete: Varying the dosage of recycled aggregates and gel materials

To address the issue of insufficient sulfate resistance in recycled aggregate concrete during the resource utilization of construction waste, this study applied the cement-silica fume treatment technology for recycled aggregates to steel slag-slag-fly ash-based cementitious material solid waste concrete. Test specimens were prepared by adjusting the replacement rate of recycled aggregates (RA) (70%, 100%) and the dosage of SSR (9%, 12%, 15%). Through mechanical property tests, sulfate dry-wet cycling tests, and microstructural characterization, the influence and mechanisms of each factor were investigated. The results showed that cement-silica fume treatment increased the apparent density of recycled aggregates by 0.39% and decreased the crushing value by 4.5%. The contents of silicon and calcium elements were increased by 52% and 83%, respectively, improving aggregate performance and the interfacial transition zone. In terms of mechanical properties, an increase in SSR dosage enhanced the strength of concrete at all ages. After cement-silica fume modification, the strength loss was mitigated at a 100% RA replacement rate. The 60-day compressive strength of the TR-100-15 group reached 32.2 MPa, and the 60-day flexural strength of the TR-70-15 group reached 6.5 MPa. Regarding sulfate resistance, the synergistic effect of high SSR dosage and cement-silica fume modification was significant. The corrosion resistance coefficient of the TR-70-15 group after 75 cycles was 0.74, and the gap between the TR-100-15 group and the 70% replacement rate group was reduced. Microscopically, the combination of these two factors hindered sulfate intrusion and suppressed the formation of expansive products. This study provides certain support for the mix design and optimization of sulfate resistance in high-solid-waste-content concrete.