Combined Effect of End-of-Life Rubber and a Hydrophobic Polymer on Coastal Saturated Sand: A Multiaspect Investigation

Nowadays, mass production of tires and construction operations adjacent to saturated soils have become a concern for engineers. The present study aimed to explore the potential of the combined effect of a waterproof polymer and rubber powder, confining pressure, and cyclic stress ratio on the static and dynamic properties of sand-rubber-polymer mixtures using a scanning electron microscope (SEM), attenuated total reflectance (ATR) analysis, unconfined compressive strength (UCS), and cyclic triaxial tests. The findings indicated that with the inclusion of 4% rubber, rough polymer chains are extended due to creating C─ CH3 bonds, uniform distribution of rubber particles between rigid materials, and interlocking rubbers in hydrocarbon chains. These chains increase adhesion with sand particles and prevent rubber flexibility, increasing UCS and shear modulus. In contrast, with the inclusion of 8% rubber, due to several mechanisms, including poor adhesion between particles because of the high surface area of the mixture and low polymer content (i.e., 2%), the dominance of weak rubber–polymer and rubber–rubber bonds over polymer–polymer and sand–polymer bonds, emerging free rubber particles (free CH2 groups), and creating the aromatic and double bond structures due to the nature of rubber flexibility, the trend is reversed.