Hydrated Lime Treatment of Recycled Concrete Aggregate for Use in Hot Mix Asphalt Production

The reuse of recycled concrete aggregate (RCA) in hot mix asphalt (HMA) is an environmentally friendly and economically affordable procedure. However, the quality of RCA is generally lower than the virgin aggregate due to adhered mortar; hence, treatment methods have been utilized to improve RCA characteristics. Among different treatment methods, soaking in hydrated lime slurry is a practical approach regarding its multiple merits. Nevertheless, the optimum concentration of the hydrated lime slurry can impact the properties of RCA and HMA and therefore needs to be determined. Moreover, fracture resistance of asphalt mixtures containing RCA has not been studied. In this paper, the effects of 1%, 2%, 4%, 6%, 8%, and 10% slurry concentrations on physical, mechanical, and morphological properties of RCA were assessed to determine the optimum concentration. The Marshall HMA mix design method was then employed to determine the optimum binder content, mixture volumetrics, and Marshall parameters of asphalt mixtures containing 0%, 25%, 50%, 75%, and 100% coarse treated and untreated RCA. In addition, the resistance of the HMA mixtures to fracture at intermediate and low temperatures as well as rutting was examined using edge notched disc bend (ENDB) and Marshall rutting test (Marshall-RT) tests, respectively. The long-term durability of the mixtures was further assessed against freeze–thaw cycles. The results show that slurry concentration substantially affects the properties of RCA treated by hydrated lime slurry. The optimum slurry concentration in this study was found to be 6%. Furthermore, it was concluded that this treatment method reduces the optimum binder content and enhances volumetrics, Marshall parameters, intermediate- and low-temperature fracture tolerance, rutting resistance, and long-term durability of the asphalt mixtures.