Doctor of Philosophy (PhD)


Civil and Environmental Engineering

Document Type



Due to the critical role of asphalt pavements in national infrastructure development, there is a pressing need to investigate more sustainable materials and approaches. The use of natural aggregates and asphalt binders in asphalt pavement presents sustainability challenges due to the depletion of finite resources. Recycling Asphalt Pavement (RAP) offers a promising sustainable solution by substituting virgin aggregates and asphalt binders with recycled ones. However, increasing RAP contents in asphalt mixtures (>25%) can lead to premature cracking, insufficient durability, and limited longevity due to the presence of aged RAP-asphalt binder. To address these concerns, the application of novel recycling agents (RAs) was evaluated to enhance the cracking resistance of high-RAP mixtures. The RAs considered were petroleum-based and bio-derived. The objectives of this study were: 1) increase RAP contents in asphalt mixtures to comply with Louisiana Balanced Mixture Design (BMD) framework; 2) develop a framework for blending additives into high-RAP asphalt mixtures and optimizing the additives’ dosages, 3) develop a prediction model to forecast High-RAP asphalt mixtures’ cracking performance, and 4) quantify the environmental benefits of the use of the proposed RAs and high-RAP content in asphalt mixtures. The RAs evaluated include petroleum-derived aromatic oil, soy oil, and four types of tall oil-derived phytosterol (industrial by-product, intermediate, purified, and fatty acid-based). A total of 66 asphalt mixtures with various compositions of unmodified asphalt binder PG 67-22, RAP, and RAs were prepared and tested mechanically against cracking and permanent deformation. The mechanical responses of asphalt mixtures containing RAP were compared to LaDOTD conventional mixtures for high-traffic volume roads containing asphalt binders PG 70-22 and PG 76-22 without RAP and RAs. Two different RAP sources with different characteristics were considered in this study at three RAP levels, namely, 0-, 30%, and 50%. Results showed that the RAs evaluated were effective in asphalt mixtures containing up to 50% RAP to meet the required Louisiana BMD specifications for rutting and cracking performances. Further, asphalt mixtures containing 50% RAP reduced global warming potential by 41% and 42.9% for petroleum and bio-oil RAs, respectively, when compared to the conventional asphalt mixture.



Committee Chair

Mohammad, Louay