Environmental Characterization of Lightweight Fill Materials in Road Applications

Abstract: Weak subgrade and excessive settlement of soft compressible soils can pose serious geotechnical challenges that threaten the integrity of roadways and other transportation infrastructures. Minimizing the stress imposed on these problematic soils is essential to address this issue. In these situations, conventional geomaterial aggregates are usually unsuitable in roadway and embankment applications due to their higher densities. Instead, the use of lightweight fill (LWF) materials, such as the tire-derived aggregates (TDA) from scrap tires, can address this problem. LWF materials are utilized in road applications due to their properties, including lower unit weight, higher strength, thermal insulation, and good drainage properties. Despite their advantages, several knowledge gaps exist regarding their long-term environmental performance, particularly in areas with high groundwater levels. While some studies report that TDA is non-hazardous, others have observed elevated concentrations of some metals above regulatory limits under saturated conditions. Specifically, the leaching behavior of TDA in road applications under fully submerged groundwater conditions and in fluctuating groundwater zones remains unclear. This study evaluates the environmental performance of TDA in roadways and embankment applications in areas with high groundwater levels. Batch leaching tests are performed following a modified version of the standard EPA LEAF Method 1315 to simulate the impact of different wet-dry cycles and groundwater flow conditions. The leachate is then analyzed for pH, electrical conductivity, and concentrations of metals such as cadmium, zinc, iron, manganese, lead, and copper over time to evaluate potential pollution risks and TDA leaching behavior under the various groundwater conditions. Ultimately, the research aims to provide data-driven recommendations on environmental viability and specific construction techniques that will guide TDA use in road system applications, ensuring environmental compliance.

Keywords: Lightweight fill materials, Environmental characterization, LEAF Method 1315, Leaching test