Enhanced electrical-thermal conversion efficiency in electrically conductive heat-stored mortar: Role of carbon nanofiber hybrid microencapsulated phase change materials

To develop functional materials for cold climates, this study prepared an electrically conductive heat-stored mortar (ECHSM) containing microencapsulated phase change materials (MPCMs) and employed ohmic heating (OH) curing to enable strength stimulation at sub-zero temperatures. The microcapsules (PA@EC), with a paraffin core and an ethyl cellulose shell, were fabricated via solvent evaporation, and carbon nanofibers (CNFs) were incorporated to enhance heat transfer efficiency. Results demonstrated that CNFs significantly improved the phase change enthalpy and thermal conductivity. PA@EC with 10% CNFs (CNF10-PA@EC) achieved a melting enthalpy of 129.9 J/g, an encapsulation efficiency of 70.14%, and a thermal conductivity of 0.412 W/(m·K). Further, the heating efficiency, electrical characteristics, early-age strength, and microstructure of the ECHSM were analyzed. ECHSM containing CNF10-PA@EC displayed excellent electrical-thermal performance under OH curing, with a maximum temperature rise rate of 0.53 °C/min and a stable curing temperature within 48.8 °C–56.35 °C in the last 6 h. The compressive strength of OH@Mortar-MPCM4% was 24% higher than RT@Mortar and 51% higher than RT@Mortar-MPCM4%. Specifically, the enhanced mechanism of CNF-PA@EC on electrical-thermal properties was further elucidated. This study offered a novel potential pathway for functional ECHSM for cold-weather construction and intelligent maintenance.