In recent years, the steady rise in global energy demand has drawn increasing attention to the development and use of renewable energy systems. At the same time, the expansion of thermal engineering projects has placed stricter performance requirements on insulation materials. To investigate how heat is transferred within mixtures containing waste tire rubber and kaolin, a series of laboratory thermal-probe tests was carried out. The tests covered a range of rubber contents, particle sizes, moisture contents, and dry densities, allowing the variation of thermal conductivity to be examined in a systematic manner. Using the measured data together with concepts from unsaturated soil theory, a corresponding theoretical model for rubber-kaolin mixtures was formulated. The results show a general decrease in thermal conductivity as the rubber content increases. For the two particle sizes studied, the mixture with 20-mesh rubber exhibits a noticeable dip in conductivity at a moisture content of about 35%, while the 40-mesh mixture shows its strongest decline at around 45%. When the moisture content becomes relatively high, the differences between the two particle sizes diminish, largely due to the progressive saturation of pore water. For both particle sizes, the conductivity rises with increasing moisture content and dry density, but not in a single trend; instead, it increases slowly at first, then more sharply, and eventually levels off, with the transition points shifting with changes in dry density and mixture proportion. The proposed model reproduces these patterns well, achieving a root-mean-square error of 0.111, which is lower than that of commonly used empirical models. This work adds to the understanding of the thermal behavior of soils modified with waste rubber and provides a technical basis for selecting insulation and energy-efficient materials in thermally activated foundations, buried pipe systems, and underground structures in cold regions.
Wang et al. (Fri,) studied this question.