Investigation of deformation characteristics of asphalt mixtures containing Reclaimed Asphalt Pavement (RAP) binders using laboratory simulations

Asphalt pavement deterioration, particularly in developing countries such as Nigeria, has led to a significant increase in waste asphalt, presenting environmental and sustainability challenges. Despite the growing application of Reclaimed Asphalt Pavement (RAP) in new asphalt mixtures, the understanding of its performance under varying environmental and loading conditions remains limited. This gap in knowledge is critical, as optimizing RAP utilization could significantly reduce the demand for virgin materials, lower costs, and mitigate environmental impacts. This study investigates the feasibility of incorporating RAP, focusing on the performance of RAP-modified asphalt mixtures under different environmental conditions. Key factors such as stress level, temperature, and moisture content were analyzed to understand the influence on the permanent deformation behavior of these mixtures. To achieve this, virgin and RAP binders were blended at varying RAP contents (15 %, 30 %, and 60 %) and subjected to advanced laboratory tests. These tests included Fourier Transform Infrared Spectroscopy (FTIR) to assess binder blending, Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) for rheological properties, Hamburg Wheel Tracking Test (HWTT), and uniaxial repeated loading test to evaluate deformation resistance and durability. Specimens were evaluated under varying stress levels, temperatures, and moisture conditions to simulate real-world scenarios. The results revealed that a 30 % RAP content optimized blending, while higher RAP contents of 60 % improved resistance to permanent deformation at lower stress levels. However, at higher stress levels of 0.6 MPa, the performance improvement became less pronounced. Specifically, at a higher temperature of 60 °C, the number of cycles required to cause permanent deformation increased by 77.7%, 187%, and 288.8% for 15%, 30%, and 60% RAP content, respectively, compared to the virgin binder. Nevertheless, challenges such as moisture infiltration and low temperatures reduced the mixtures' durability. This study underscores the potential of RAP in promoting sustainable asphalt pavement construction and highlights the importance of addressing gaps in current research, particularly in mitigating environmental impacts and enhancing the durability performance of RAP-modified mixtures.