Gradient Joule Heating Curing Performance of Steel-Fiber-Reinforced High-Performance Concrete in Severe Cold Environments: A Preliminary Attempt for Deep-Cold Concrete Construction

Winter concrete construction in cold regions faces significant challenges due to extreme subzero temperatures, and the harsh environment presents new requirement for cement-based materials to resist this hostile external condition. To address this gap, this study proposes gradient Joule heating (GJH) curing for steel-fiber-reinforced high-performance concrete (SFR-HPC) in subzero environments (-20 °C to -60 °C). Compared to room-temperature (RT) curing, GJH enabled specimens at -20 °C to -50 °C to achieve equivalent mechanical properties within a short curing duration; the compressive strength of the specimens cured at such low environmental temperature still reached up to that of the specimen cured by RT curing. Moreover, the compressive strength of the specimens cured at -60 °C retained >60 MPa despite reduced performance. Specifically, the specimens cured at -20 °C, -30 °C, -40 °C, and -50 °C for 2 days exhibited compressive strengths of 75.8 MPa, 79.2 MPa, 77.6 MPa, and 75.4 MPa, respectively. FTIR/XRD confirmed that the specimens cured by GJH showed hydration product integrity akin to RT-cured specimens. Moreover, it should be noted that early pore structure deteriorated with decreasing temperatures, but prolonged curing mitigated these differences. These results validate GJH as a viable method for in situ HPC production in extreme cold, addressing critical limitations of conventional winter construction techniques.