Thermal conductivity of scrap tire rubber-sand composite as insulating material: Experimental investigation and predictive modeling

Abstract

Scrap tire rubber of good thermal insulating properties can be reused with soils as a new sustainable construction material. While the heat conduction mechanism of this tire rubber-soil composite has not been fully understood. The present study investigated the thermal behavior of scrap tire rubber-sand composite for using it as an insulating material in thermo-active applications. Several series of thermal conductivity tests were conducted on scrap tire rubber-sand composite prepared with different sand/shredded tire particle size ratios, shredded tire mixing ratios, and degrees of saturation. A predictive model was developed within the framework of normalized thermal conductivity concept that could capture the experimental data. The results showed that addition of shredded tires leads to a considerable reduction in thermal conductivity of sand, indicating great potential of using recycled scrap rubber tires in the construction of insulation layers. With an increase in degree of saturation, the order of thermal conductivity increase was found to be: sand > scrap tire rubber-sand composite > shredded tires. The spatial distribution of solid particles changed from ‘rubber-connected insulation layer’ to ‘sand-encompassed conduction path’ with increasing sand/shreds tire particle size ratio. The normalized thermal conductivity exhibited a linearly increasing trend with shredded tire mixing ratio, and the increase rate mainly depended on degree of saturation and particle size ratio. The predicted thermal conductivity showed satisfactory accuracy for engineering design, as reflected by the absolute percentage difference being controlled under 25%. The validity of the prediction model was also demonstrated based on the experimental results reported in the published literature. Additional research is recommended to assess the effects of particle morphology on thermal conduction of the binary-solid particle system.