Ohmic heating-induced microstructure refinement and multi-environment durability enhancement in seawater sea sand concrete under severely cold environment

To address the lack of reliable curing strategies for seawater sea-sand concrete (SSC) in extremely cold marine regions, this study proposes an ohmic-heating (OH) curing approach that enables self-generated internal heating through a percolation-based conductive network. This energy-efficient method simultaneously promotes rapid hydration, microstructural stabilization, and long-term durability. A percolation-controlled conductive network was achieved by incorporating 1.25 vol% carbon fibers (CFs), reducing electrical resistivity from 102.16 Ω·cm to 52.01 Ω·cm while maintaining a slump of 16.1 cm. The resulting internal temperature rise (65 ± 2 °C) accelerated hydration and produced a 2-day compressive strength of 65 MPa. Mercury intrusion porosimetry revealed that OH curing refined the pore structure, with total porosity decreasing to 13.1% and the fine-pore fraction (< 50 nm) increasing to 0.52. The ohmic-heating followed by freeze treatment (OHF) specimens exhibited superior microstructural stability after 300 freeze–thaw cycles. Chloride-exposure tests showed minimal penetration (≈ 3 mm) and over 90% strength retention after 90 days in OH-cured samples. Accelerated carbonation tests confirmed the lowest full and partial carbonation depths (1.2 mm and 16.9 mm, respectively), attributed to CaCO 3 precipitation within microcracks and pores observed by SEM. This study reveals a self-regulated pore stabilization and crystallization-filling mechanism, wherein ohmic heating promotes secondary C–S–H and AFm phase formation that dynamically heals microvoids and stabilizes the pore network. The findings establish OH curing as a multifunctional, low-energy, and durable curing strategy for SSC, providing a mechanistic foundation for sustainable construction in cold marine environments.