Stabilized electrical conductivity in nano-engineered ultra-high performance concrete under prolonged freezing exposure: Nano-reinforcement and cryo-induced water migration mechanism

Concrete with stable electrical conductivity is essential for critical intelligent infrastructure functions such as self-monitoring and deicing, but its performance under long-term freezing exposure remains a major challenge. This study developed a multifunctional carbon fiber strengthened ultra-high performance concrete (CFS-UHPC) by incorporating nano carbon blacks (NCBs) and carbon nanofibers (CNFs), achieving exceptional electrical conductivity under prolonged freezing exposure (-7.5°C). Results identified the benefits of low-content CNFs on improving the mechanical strength and highlighted NCBs as the pivotal component for electrical stability, yielding resistances of 455.5 Ω and 533.17 Ω at 28 and 135 days, respectively. A key finding was a dramatic 86.6% reduction in electrical resistance after 128-day freezing exposure. Microstructural and electrochemical analyses revealed that this enhancement was due to a coarsened pore structure and a unique cryo-pumping effect. Furthermore, machine learning models achieved highly accurate predictions of the electrical resistance, with an R-squared value of 0.9839, and confirmed NCBs and freezing exposure as the dominant controlling factors. This research provides a practical and mechanistic framework for engineering the next generation of durable and intelligent concrete composites for resilient infrastructure in cold climates.