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Shredded rubber tire is a geomaterial that is potentially useful in environmental and engineering projects. Here, we study the effect of particle size ratio on the thermal conductivity of granular mixtures containing rubber tire particles. Glass beads were mixed at various volume fractions with rubber particles of varying size. The 3D network model analysis using synthetic packed assemblies was used to determine the dominant factors influencing the thermal conduction of the mixtures. Results present that mixtures with varying size ratios exhibit different nonlinear evolutions of thermal conductivity values with mixture fractions. In particular, mixtures with large insulating materials (e.g., rubber particles) have higher thermal conduction that those with small ones. This is because the larger insulating particles allow better interconnectivity among the conductive particles, thereby avoiding the interruption of the thermal conduction of the conductive particles. Similar tests conducted with natural sand corroborate the significant effect of the relative size of the insulating particles. The 3D network model identifies the heterogeneity of local and effective thermal conductivity and the influence of connectivity among conductive particles. A supplementary examination of electrical conductivity highlights the significance of local and long-range connectivity on conduction paths in granular mixtures.

Microbially induced calcite precipitation is an emerging environmentally friendly ground improvement technique for a range of geotechnical applications. One of the remaining issues for field implementation of this technique is poor uniformity of calcite, with concentrated precipitation near the injection point, particularly for treatments with continuous injection or in fine sand. Therefore, the work described in this paper performed an experimental investigation to test the hypothesis that using kaolinite particles can increase the number of calcite nucleation sites throughout the sand medium to increase the mass of calcite deposited and provide better distribution of calcite. Both batch and column tests were performed to quantify the impact of kaolinite particles on calcite precipitation. The results indicated that the kaolinite particles may play a role as nucleation sites and facilitate the heterogeneous nucleation of calcite, with observed deposition profiles of kaolinite and breakthrough curves of both kaolinite and bacteria demonstrating that the uniform distribution of deposited kaolinite particles at relatively low inlet concentration (100 mg/l) most effectively increased the amount of calcite, producing a uniform calcite deposition profile. In addition, the results also showed that the well-predicted deposition profile of kaolinite correlated well with the deposited calcite profile.

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