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.

To improve the workability and mechanical properties of Recycled Micro-Powder (RP) mortar, basalt fiber (BF) was used for modification in this study. Experimental groups with different BF contents (0%, 0.1%, 0.15%, and 0.2%) were designed to investigate the effects of BF on the flowability, flexural strength, and compressive strength of RP mortar. The microscopic reinforcement mechanism was further revealed through Scanning Electron Microscopy (SEM). Additionally, an early strength prediction model for the mortar considering the synergistic effect of BF and RP was established. The results show that the incorporation of BF significantly enhanced the mechanical properties of RP mortar. At the 28-day curing age, when the RP replacement rate was 10% and BF content was 0.15%, the flexural strength increased by 9.7%, and the compressive strength increased by 17.3%. At an RP replacement rate of 30%, the compressive strength still increased by over 30%, demonstrating a good “performance compensation” effect. However, the inclusion of BF also led to a decrease in flowability, with a maximum reduction of 25.5%. SEM analysis revealed that BF improved the matrix densification and interface bonding performance through crack bridging and physical anchoring. The established early strength prediction model achieved a high goodness of fit (R² > 0.92), indicating high accuracy and engineering applicability.

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.