Thermal conductive properties of solid-liquid-gas three-phase unsaturated concrete

In order to study the thermal conductivity of unsaturated concrete, 8 groups of concrete samples with different porosity and water content were prepared. For comparative analysis, the porosity of samples by adding air entraining agents with different mass fractions, and the water-filled porosity is controlled by weight and humidity method. The actual porosity, water-filled porosity and gas-filled porosity of the specimens were measured by nuclear magnetic resonance technology (NMR), and the thermal conductivity is synchronously test in the corresponding state. Based on the experimental data, it is verified that the dispersion-continuous thermal conductivity model is feasible to determine the thermal conductivity of unsaturated concrete. Combining the calculated results with the test results, we obtain the variation of thermal conductivity with porosity and gas-liquid filling of pores. Furthermore, a two-dimensional mesoscopic model of porous media was established to analyze the mechanism of the three phases of solid, liquid and gas in the heat transfer process. The results show that both porosity and water content have great influence on the thermal conductivity of concrete. Thermal conductivity not only decreases with the increase of porosity, but also increases nonlinearly with the increase of water-bearing porosity at the same porosity. Compared with the elemental materials, the pore makes the distribution of temperature field change greatly. For three-phase unsaturated concrete, the connectivity of pores and the difference of solid-liquid-gas thermal conductivity will also cause temperature distortion in local areas. (C) 2019 Elsevier Ltd. All rights reserved.