Life cycle assessment of rubberized semi-dense asphalt pavements; A hybrid comparative approach

Abstract

This study employed the methodology of life cycle assessment (LCA) to assess the environmental impacts of rubberized semi-dense asphalt (SDA) pavement. Asphalt mixtures were prepared at the asphalt plant, followed by hybrid approach of mechanical and leaching tests in the laboratory to assess the possible service life and PAH leaching. The LCA was carried out considering two scenarios: (1) the reference scenario focuses on standard SDA produced of only virgin materials; (2) the test scenario refers to rubberized SDA using crumb rubber, a secondary material from waste tires. In the reference scenario, waste tires were assumed to be used as fuels for clinker production; while in the test scenario, waste tires were applied for SDA and primary fuels were used for clinker production (system expansion approach). In a sensitivity analysis, a scenario with waste tire treatment in municipal solid waste incinerators (MSWI) was also assessed. The impact assessment includes greenhouse gasses (GHG) emissions, nonrenewable cumulative energy demand (CED), human and ecotoxicity (USEtox), and the Swiss method of ecological scarcity. The results indicate that the investigated impacts were not improved by the test scenario. The USEtox results also reveal that the leaching impacts can be as serious as binder production and material transport if PAHs emit to groundwater. From an environmental point of view in Switzerland, it is not recommended to promote rubberized SDA by reducing the waste tires used for clinker production. However, if there are waste tires used for MSWI, the rubberized SDA is still an environmentally viable option.