Performance Evaluation of Hot-mix Asphalt, Modified with Reclaimed Asphalt Pavement (RAP) for Wearing Course: A Case Study at the Adama-Awash Road Project in Ethiopia

The raising cost of virgin pavement materials and the growing need for sustainable road maintenance practices have driven the adoption of reclaimed asphalt pavement (RAP) in road construction. However, in Ethiopia, the utilization of RAP remains limited due to the absence of localized performance data and mechanistic design guidelines. This study was aimed to evaluate the engineering performance and long-term structural behavior of hot-mix asphalt (HMA) integrated with varying RAP percentage increments (0%, 20%, 25%, and 30%) without chemical additives/rejuvenators. RAP materials were sampled from the milling operations of the heavily trafficked Adama-Awash heavy maintenance road project. Marshall mix design and advanced Superpave performance tests such as indirect tensile strength (ITS), Resilient modulus (M R ), and Hamburg wheel-tracking (HWT) were conducted. Additionally, the KENPAVE mechanistic-empirical software was used to predict the fatigue and rutting life of the pavement structures under the actual design traffic of 205 million ESALs found by forecasting up to 2040 during the research study. Laboratory results indicated that increasing the RAP percentage up to 25% enhanced mixture stiffness, with peak M R value of 5.45 GPa and rut depth lowered to 3.9 mm. However, at 30% RAP content, the mixture experienced a sever drop in tensile strength and modulus due to the aged binder excessive stiffness and brittleness. KENPAVE analysis confirmed that while all mixtures exceeded the actual design traffic volume of 205 million ESAL requirement for structural rutting, all RAP percentages did not achieve the required fatigue life, suggesting bottom-up fatigue cracking as the governing failure mode. Ultimately, 25% RAP was identified as the optimum RAP content, providing the best balance between structural performance, rutting resistance, and an approximate 18% reduction in virgin material costs. The study recommends adopting polymer-modified binders and/or lane distribution factors to meet the project’s full fatigue life.