Impact of stabilisation on mechanical properties of recycled concrete aggregate mixed with waste tyre rubber as a pavement material

Abstract

The rising demand for the construction of pavement infrastructure creates great pressure on the production and transportation of virgin aggregates, which consumes high energy and natural resources. Therefore, the possibility of using recycled materials in pavements has generated wide interest in the growing economies of developed and developing countries. The wastes produced by construction and demolition materials such as recycled concrete aggregate (RCA) enter landfills every year. Similarly, wastes generated by end-of-life tyres are non-biodegradable and poses an environmental challenge. However, the research on the mechanical performance of waste tyre rubber (TR) in pavement applications is very limited. Therefore, finding innovative ways to incorporate these solid wastes could improve the sustainability of pavements. Meanwhile, the use of major binder (i.e., portland cement) for stabilisation of pavements contributes to carbon footprint issues. Hence, there is a need to use environmentally friendly binders such as ground granulated blast furnace slag which is a promising way to process these waste materials with significant environmental benefits. Therefore, this study investigates the feasibility of RCA and TR as a substitute for quarried pavement material, stabilised with slag (S) to improve the binding action between waste tyre rubber and surrounding aggregates. The main objective of the study was to evaluate the physical and mechanical characteristics of combined TR + RCA mixes by undertaking extensive laboratory tests. Firstly, unconfined compressive strength (UCS) test studies were conducted at 7 days of curing period at 21 °C to determine the efficacy of mixing two types of wastes by slag stabilisation at three different binder contents (10 %, 15 %, and 20 %). Subsequently, a series of resilient modulus (RLT) tests were performed to determine the stiffness of the mixes using a repeated load triaxial setup. Finally, the hydration mechanism was studied by microstructural studies (SEM) to understand the inter-particle bonding of TR + RCA mixes. It was found that stabilised mixes with 10 %TR could satisfy the minimum road requirements for pavement base layers in terms of compressive and resilient moduli characteristics. Besides, the study provided a mathematical model equation by response surface methodology to predict the values of UCS. Predicted values were found to be in good agreement with experimental values. The research offers a sustainable solution with the help of stabilisation technique in increasing the volume of combined TR + RCA wastes in pavements by satisfying road requirement criteria.