Performance of Hot Mix Asphalt Using Blended Cinder–Basalt Aggregates for Low-Volume Roads in Mbeya Region, Tanzania

The limited availability of high-quality aggregates in volcanic regions has increased interest in using locally available marginal materials for asphalt pavement construction. This study evaluates the suitability of blended cinder–basalt–sand aggregates for AC20 hot mix asphalt (HMA) surfacing of sealed low-volume roads in Mbeya Region, Tanzania. Physical and mechanical properties of cinder, basalt, and blended aggregates were determined, followed by Marshall mix design using 60/70 penetration grade bitumen. Natural cinder aggregates exhibited inadequate strength and durability, with low ten percent fines values and high crushing values, confirming their unsuitability for direct use in HMA. Blending with basalt significantly improved aggregate performance, with ten percent fines values increasing to 128–202 kN and aggregate crushing values reducing to 12.5–19%. Marshall test results showed that all blended mixtures satisfied specification requirements, with stability values of 10–12 kN, flow values of 2.5–3 mm, air voids of 4–7%, and voids in mineral aggregate of 18.5–22.4%. Optimum binder content increased with cinder content, ranging from 6.7% to 8.6%, reflecting the porous nature of cinder aggregates. The results of this study are based solely on Marshall mix design parameters and are therefore specific to low-volume road applications under moderate environmental exposure conditions. Performance-related properties such as moisture susceptibility, rutting resistance, and aging behavior were not evaluated and require further investigation before broader application.