Electric-Induced Curing of Carbon Fiber-Reinforced Recycled Aggregate Concrete Under Sub-Zero Conditions: Synergistic Effects of Curing Temperature and Aggregate Type on Electrical and Mechanical Performance

Recycled coarse aggregate (RCA) provides a sustainable approach to managing construction and demolition waste. However, its high porosity and water absorption pose challenges for electric-induced curing under sub-zero conditions, affecting electrical and mechanical performance. This study investigated the effect of curing temperature on carbon fiber-reinforced RCA concrete subjected to electric-induced curing at −20 °C. Three curing regimes with upper temperature limits of 20 °C, 40 °C, and 60 °C were applied for 7 days. Results showed that the initial electrical resistance of recycled aggregate concrete (RAC, 2.1–2.2 Ω) was lower than that of natural aggregate concrete (NAC, 5.4–6.0 Ω), but increased dramatically at elevated temperatures, reaching 2600 Ω at 60 °C. The 40 °C regime achieved the highest compressive strength (54.3 MPa for RAC, 53.7 MPa for NAC), while the 60 °C regime reduced RAC strength to 42.3 MPa. Equivalent age analysis revealed that the 40 °C regime provided an equivalent curing age of 10.0 days for RAC and 14.1 days for NAC, confirming optimal hydration acceleration. Microstructural analyses (TG–DSC, MIP, SEM) showed that higher curing temperatures increased the proportion of gel pores (< 10 nm) from approximately 7–38%, refining the pore structure. The 40 °C regime optimally balanced hydration promotion and electrical resistance stability, offering a practical solution for in situ construction in severely cold regions, such as winter road repairs, bridge deck overlays, and airport runway maintenance, where conventional curing methods are inefficient or impossible. These findings highlight the potential of optimized electric-induced curing to enable the use of RAC in cold-region infrastructure.