Estimation Method of Thermal Conductivity at High Temperature Based on Mix Proportion and Water Content Ratio of Concrete

Abstract

In this study, methods for estimating the thermal conductivity of concrete under various temperatures are reviewed. Based on Maxwell’s model for predicting the equivalent thermal conductivity of composite materials, the constituent materials of hardened concrete are categorized into five types of materials: coarse aggregate, fine aggregate, skeleton, and voids. The voids, which include air and excess water, are considered to determine the effect of water reduction on thermal conductivity. The volume ratio of the constituent material to the cured concrete is estimated using a simple curing model, and the thermal conductivity of each constituent material is obtained from the literature. Air volume and excess water reduction are set as the estimation conditions, and the optimal method is devised by comparing the respective estimation results. The thermal conductivity range for concrete is estimated based a design strength of 21∼100 MPa (W/B60 to W/B15) and a temperature of 30 °C∼800 °C. The results reflecting the measured air volume and moisture reduction are similar to the measured values. A comparison between the optimal estimated value and measured value shows that both values are similar in the temperature range of 400 °C∼800 °C, and that the estimated value is lower than the measured value in the temperature range of 80 °C∼200 °C.