How Rubber Percentage and Size Affect Water Stability and Resistance in Hot Asphalt Pavements

The premature deterioration of asphalt pavements in urban areas, especially in contexts of an arid coastal climate such as that of Trujillo (Peru), raises the need for sustainable and technically feasible solutions. This research aimed to evaluate the effect of the percentage and granulometry of recycled rubber from end-of-life tires (ELT) on the mechanical performance of hot-dense asphalt mixtures. A two-factor experimental design was applied with three levels of granulometry (75 μm, 150 μm and 300 μm) and four percentages of addition (0%, 1%, 2%, 3%), analyzing the stability and Marshall flow, and the tensile strength ratio (TSR) as an indicator of resistance to moisture damage. The mixtures were molded and compacted in the laboratory under modified ASTM and AASHTO standards, using local aggregates and asphalt cement. The results showed that the combination of 2% recycled rubber with a grain size of 75 μm offered the best performance: stability of 13.43 kN, flow of 12.57 mm and TSR of 86.4%—values that exceed the MTC standards and international references. This combination did not affect the workability or compactness of the mix and represents a viable technical and environmental improvement. It is concluded that the use of thin rubber in moderate proportions significantly improves structural behavior and durability against moisture, with potential for practical implementation in similar urban contexts. It is recommended to evaluate its long-term behavior in real conditions and complement this evaluation with life cycle analysis to validate its integral sustainability.