Compressibility Behavior of Soft–Rigid Granular Mixtures Bound with Polyurethane Binder

Abstract Mixtures of recycled tires and granular material have been used for a variety of applications in geotechnical engineering over the years. The characteristics and mechanical properties of sand–rubber mixtures as unbound soft–rigid mixtures have been extensively studied over the years. Research on bound soft–rigid mixtures, however, has been mainly focused on using a brittle binding agent, for example, Portland cement. A very limited number of studies over the last years have examined the behavior of soft–rigid mixtures bound with a nonbrittle binder. This study aims to provide a better understanding of the deformation mechanism of the soft–rigid mixtures bound with a polyurethane binder. Sixteen one-dimensional compression tests were conducted on bound and unbound samples to study the impact of the binding agent on the behavior of the soft–rigid mixture. In addition, computed tomography scan images of samples were used to visualize the deformation mechanism. A multiphased behavior, as opposed to single-phased behavior for unbound mixtures, was observed and each phase was explained in detail. The observed multiphased behavior is divided into up to four phases, that is, initial compression, normal compression, bond degradation, and secondary compression, with boundaries defined based on constrained modulus curve.