Abstract: A thermal conductivity model of concrete under temperature variation is proposed in the purpose of exploring the influence mechanism of alternating positive and negative temperatures on the thermal conductivity of concrete. The calculation theory of thermal conductivity of liquid phase (ice-water phase) in concrete pore at different temperatures is proposed to characterize the phase transformation characteristics of pore solution in concrete at different temperatures.Concrete is regarded as a three-phase composite material consisting of equivalent solid phase, liquid phase (ice-water phase), and gas phase in concrete pore. The series-parallel calculation model for the thermal conductivity of concrete as a three-phase composite material varying with temperature, saturation, and pore distribution is established and compared with other models. The thermal conductivity of concrete calculated by the present series-parallel model is in good agreement with measured values, with the relative error ranging from 8.83% to 24.13%, indicating high accuracy. The calculated results of the model well reflect the correlation between thermal conductivity and saturation and temperature of concrete in cold region. In sensitive temperature (-10 ℃~0 ℃) zone, the thermal conductivity of concrete changes abruptly with an amplitude from 2.59% to 8.47%. The liquid-phase (ice-water phase) model effectively depicts the phase transformation of pore solution under temperature variation, and the series-parallel three-phase model also objectively reveals the evolution mechanism of thermal conductivity of concrete under alternating positive and negative temperatures.

Key words: concrete, alternating positive and negative temperatures, saturation, thermal conductivity, three-phase composite, calculation model