Granular Mixtures with Tailored Effective Properties

Noise and vibration/resonance constitute a drawback in many technical and geo-engineering applications. Acoustic waves produced on roads, railways or by earthquakes propagate through “granular” materials (like soil, concrete or asphalt), with the characteristics of the aggregate affecting the velocity, amplitude-damping and frequencies of the wave. Here, we focus on wave propagation and attenuation in biphasic granular mixtures made of soft and stiff particles subjected to various hydrostatic stress conditions, testing them with diverse modes of deformation. The properties of aggregates made of monodisperse glass and rubber bead mixtures are studied experimentally and numerically, varying the rubber content and the confining stress. Interestingly, the experiments show that for an optimal amount of soft inclusions one can obtain a tailored material, with the same (or even higher) stiffness than the original, yet lighter and with stronger damping. The experiments are complemented by particle-based numerical simulations to complement and understand the experiments; a future goal is improving and optimizing novel designs for materials, constructions, or landfills/soils.