Interactive Effects of Limestone/Basalt Mineral Fillers and Dry-Processed Crumb Rubber on Hot Mix Asphalt Performance
Road networks in developing regions such as Yemen suffer from premature deterioration for many reasons, including the use of basalt asphalt mixtures in the design of pavement layers; however, these mixtures exhibit poor resistance to rutting and moisture damage, particularly under excessive axle loads. This study investigates the performance of hot mix asphalt (HMA) modified with crumb rubber (CR) from scrap tires using the dry mixing technique, with a focus on the influence of mineral filler type and rubber gradation. Two locally sourced fillers- limestone and basalt-were evaluated using three CR gradations (coarse, fine, and powder) at concentrations of 0%, 5%, 10%, 15%, 20%, and 25% by weight of the asphalt binder. A total of 210 Marshall specimens were tested. The results showed that the limestone reference mixture exhibited critically low voids in mineral aggregate (VMA=12.40%), below the 13% specification requirement, while excessive stability suggested susceptibility to premature aging. The addition of 15% fine crumb rubber to the limestone mixture yielded optimal performance: a stability of 14.7 kN, a VMA of 14.8%, and an optimum asphalt content of 4.0% at 4% air voids, satisfying the Marshall mix design criteria for a heavy-traffic wearing course. In contrast, the basalt mixture showed continuous performance degradation upon crumb rubber addition. A two-way ANOVA confirmed a significant interaction between filler type and rubber content (p < 0.001). The study concludes that the optimal formulation-limestone filler with 15% fine crumb rubber -offers a practical solution for sustainable pavement infrastructure development in Yemen.
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