Mitigating Zinc Leachate from End-of-Life Tire Rubber in Stabilized Clayey Soils

Abstract

End-of-life tire (ELT) rubber has been widely researched to replace aggregates in construction materials such as asphalt concrete and cementitious composites. Although most studies paid attention to its effect on engineering properties and the durability of the materials, very few considered chemical reactions with pore solution and the potential for environmental leachate, especially rubberized stabilized soil, which was proposed recently to increase the use of ELT rubber in civil engineering. This study proposes the use of rubberized stabilized soil (RSS) in which clayey soils (e.g., kaolin and bentonite) were stabilized by portland cement (PC) and end-of-life tire (ELT) rubber particles. The authors previously developed a methodology to extract zinc from the ELT rubber; therefore, this study explores the potential for RSS to immobilize the leachate from the ELT rubber before and after this treatment. Three main topics are addressed in this study: (1) the capability of clay to capture leached zinc under ambient and alkaline aqueous conditions; (2) engineering properties of RSS [i.e., unconfined compressive (UCS), flow] with 0%, 10%, 30%, and 50% ELT rubber added by clay volume; and (3) pore solution and leachability tests of RSS. A leaching experiment was employed for Topic 1, UCS and flow tests were conducted for Topic 2, and pore solution extraction and leaching tests were performed for Topic 3. The results showed that the clayey soils and ELT rubber are synergistic in terms of engineering properties and the capturability of zinc and total organic carbon (TOC). Although the ELT rubber and PC strengthen the clay structure, the clay absorbs leached zinc and TOC from the ELT rubber particles. Adding untreated ELT rubber into PC-stabilized clays significantly increased the RSS strength; however, this improvement was less significant for the treated ELT rubber. Ultimately, the results proved that the environmental and mechanical performance of RSS makes it a viable construction material.