<p>Premature failure in flexible pavements is driven by several factors including heavy traffic and environmental stresses due to moisture, temperature and ultraviolet radiation. Enhancing material properties, particularly through binder modification, has proven to be the most effective solution. Recent studies have increasingly emphasized the use of modified bitumen, particularly incorporating recycled plastics, to enhance pavement performance while reducing cost and environmental impact. With limited research on the impact of crystalline form of polypropylene and its associated aged performance of the binder, this study aims to examine its effect on the performance of bituminous concrete mix under short and long-term aged conditions. Bitumen was blended with varying dosages of polypropylene through wet process. Incorporation of polypropylene enhances the stiffness and brittleness of the binder, while diminishing its ability to deform plastically. Mixes with varying dosages of polypropylene were tested for Marshall properties, indirect tensile strength and semi-circular bending test under unaged and aged conditions wherein laboratory aging of was performed using normal oven. Results suggest that incorporation of polypropylene enhances the stability whereas minimizes the flow and rupture of mix in the presence of moisture, leading to enhanced thermodynamic stability to the mix up to a dosage of 0.4%. Incorporation of 0.4% polypropylene enhances the mix stability by 16.54% and reduces flow by 9.05% compared to conventional mix under long-term aged condition. However, beyond this threshold further increasing the polymer content intensifies particle collisions, causing agglomeration which disrupt binder homogeneity and reduce effective dispersion, which degrades performance of the mix. The increase in non-polar surface free energy of bitumen due to the incorporation of polypropylene promotes the formation of covalent and non-polar bonds that are more resistant to moisture thereby reducing the moisture induced damages. Incorporation of polypropylene leads to an enhancement in strain energy and enhanced resistance to cracking and deformation of the mix under loading. Polypropylene modification notably enhances the fracture resistance of bituminous mixes, reflected by higher peak load, strain energy, and critical strain energy, especially after aging. The improved response across different notch depths confirms better durability against crack propagation. Polypropylene modified mixes also exhibited increased stiffness and superior cracking resistance under long term aged conditions, making them more suitable for durable pavement applications. A 0.4% dosage of crystalline polypropylene is recommended for binder modification, as it significantly enhances the Marshall stability, rutting resistance, tensile strength and resistance to aging of the mix. However, this recommendation is based on laboratory studies and should be validated under field conditions.</p>