Experimental Investigation of Sand-Rubber-Bitumen Mixtures as a Geotechnical Seismic Isolation Material

Waste tires, which are a serious environmental threat due to the ever-increasing number of on-road vehicles, must inevitably be effectively recycled. Many researchers have posited that granular soil and crumbed waste tire mixtures can be used to reduce seismic forces in so-called geotechnical seismic isolation (GSI) systems because of the high-energy absorption capacity of sand and rubber (SR) mixtures. However, there are concerns about the stability of superstructures due to the high compressibility of SR mixtures. Asphalt mixtures have also gained new application areas outside of transportation engineering, such as in hydraulic structures and seismic isolation, due to their ductile, cohesive and viscoelastoplastic properties in recent years. In this study, sand-rubber-bitumen (SRB) mixtures were produced by adding bitumen as a binder to SR mixtures containing crumbed rubber (CR) at different ratios (1%, 2%, 3%, and 4% of the sand weight). The dynamic properties of the SRB mixtures were determined by cyclic simple shear tests, depending on vertical and cyclic stresses. We found that the SRB mixture containing 3% CR had the maximum damping ratio (D) and that an increase in the rubber content of SRB mixtures causes a decrease in the secant shear modulus (Gsec). In addition, it was observed that the Gsec increased with the vertical stress and decreased with the cyclic stress ratio. In comparing the D and Gsec values of the SRB mixtures with those of SR mixtures under similar loading conditions, it was found that the SRB mixtures had both higher D and stiffness. As a result, SRB mixtures are more suitable than SR mixtures in terms of damping, and SRB mixtures can be an alternative material for use in GSI systems.