The application of fully recycled aggregate concrete (FRAC) promotes sustainable construction, but its mechanical properties are often unstable due to the high absorption and variability of recycled aggregates. This study investigates the effect of saturation degrees of recycled coarse aggregate (RCA) and recycled fine aggregate (RFA) on FRAC’s mechanical performance and failure mechanisms. Results show that optimal strength is achieved at 70% RCA and 25% RFA saturation. Reducing RFA saturation from 100% to 25% increases compressive strength by 28.8% and tensile strength by 34.6%. RFA saturation has a greater influence than sand ratio or superplasticizer dosage, second only to water–cement ratio. Analysis indicates that excessive saturation leads to pores and microcracks in the interfacial transition zone, weakening bonding. A multiple linear regression model based on recycled aggregate saturation accurately predicts FRAC properties, supporting optimized use of recycled materials and cleaner construction practices.

Aiming at the critical problem that recycled concrete aggregate (RCA) has more cracks and severe defects on its surface than natural aggregate, resulting in an excessively weak interfacial transition zone (ITZ) between RCA and cement paste, this paper proposes a triple synergistic modification method combining calcium ion accelerating solution treatment, dopamine polymerization treatment and nanofiber reinforcement to improve the properties of recycled aggregate. Through in-depth research on the mechanical properties of basalt fiber-reinforced fully recycled concrete after triple modification, it is found that the triple modification technology can significantly optimize the structure of the recycled aggregate-cement paste ITZ. The 28-day compressive strength of the fully recycled concrete is increased by 56% (reaching 27.7 MPa), and the splitting tensile strength is improved by 129% (reaching 5.32 MPa). Microscopic analysis shows that the modified system realizes gradient strengthening of the ITZ structure through the synergistic mechanism of “pore filling, chemical bonding and fiber bridging”. This research provides a new idea for the high-performance modification of fully recycled concrete, and has important significance for promoting the sustainable development of the construction industry.