Abstract
This study investigates the performance of hot mix asphalt (HMA) modified with 7% natural rubber (SIR-20) and incorporating five new aggregate gradations, compared to a standard control mix. The objective is to identify an optimal gradation that maximises mechanical performance and durability of rubberised asphalt under tropical climate and heavy traffic conditions. A total of 300 laboratory specimens were evaluated using the Marshall method, volumetric analysis (VMA, VIM, VFB), wheel tracking test, and resilient modulus test. Results indicate that Gradation B at 6.5% asphalt content provides the most balanced performance, achieving high Marshall stability (>1,200 kg), acceptable flow (~3.4 mm), an optimal Marshall Quotient (>375 kg/mm), excellent rutting resistance (Do = 1.59 mm), and resilient modulus values exceeding 2,600 MPa. The findings confirm that optimised gradation design significantly enhances the effectiveness of rubber-modified asphalt and supports the implementation of performance-based mix design in sustainable pavement technologies.