A combined LCA–circular economy approach for investigating the effect of additives on sustainability of cold recycled asphalt mixtures

Abstract

This study investigates the effects of high reclaimed asphalt pavement (RAP) content and the incorporation of different additives, including ground granulated blast furnace slag (GGBFS), Portland cement, and glass fibers on the performance, moisture susceptibility, and sustainability of cold recycled asphalt mixtures (CRMs). GGBFS and Portland cement contents were fixed at 2 % by aggregate weight, while glass fibers were added at varying dosages of 0.2, 0.3, and 0.4 % by aggregate weight. Results showed that CRMs without additives lacked sufficient moisture susceptibility. While glass fibers enhanced Marshall stability by up to 10.3 %, they significantly reduced the dry indirect tensile strength (ITS). Portland cement and GGBFS increased Marshall stability (50 % and 40 %) and dry ITS (36.3 % and 16.4 %) at 28 days. Fatigue resistance and resilient modulus also improved significantly, with both Portland cement and GGBFS increasing modulus by 82 % and 42 %, respectively, after 42 days. Flow number at 28 days was 1796 cycles for Portland cement, 391 cycles for GGBFS, and zero for the Base mix design. An integrated approach combining life cycle assessment and the Material Circularity Indicator (MCI) revealed that, although the CRM containing Portland cement had the highest environmental impact, it achieved the highest Environmental Sustainability and Circularity Assessment Indicator (ESCi) due to its superior performance and MCI. In two RAP reuse scenarios, ESCi increased by 98.1 % and 99.3 %. The study also highlights that MCI values depend on the expected performance of the mixture, underscoring the importance of considering both performance and environmental sustainability when selecting additives. The proposed assessment method is applicable to any additive.