Mechanical performance and stiffness characteristics of plantain leaf ash and quarry dust modified asphalt concrete towards a sustainable pavement construction

The increasing demand for sustainable construction materials has driven the exploration of agricultural and industrial wastes as alternative fillers in asphalt concrete. This study investigates the effect of Plantain Leaf Ash (PLA), an agricultural waste, and Quarry Dust (QD), an industrial by-product, as composite fillers on the mechanical properties of asphalt concrete. The research aimed to determine the optimal blend that balances sustainability with structural performance. Initially, the physical properties of the base materials—including the specific gravity of aggregates, the grading of the bitumen (60/70 penetration grade), and the particle size distribution of the aggregates were characterized. The control aggregate (gravel) was found to be gap-graded, deficient in intermediate particles. Asphalt concrete specimens were prepared with varying proportions of PLA (0%, 2%, 4%, 6%, 8%, and 10% by weight of filler) and QD (0%, 2%, 4%, 6%, 8%, and 10%) in a full factorial design. The specimens were evaluated for Marshall Stability, Tensile Strength (TS), and Young's Modulus (Stiffness). The results revealed a clear trade-off: increasing PLA content consistently degraded mechanical performance due to its low specific gravity (1.80) and organic nature, while increasing QD content (Specific Gravity 2.62) proportionally enhanced all properties. The highest absolute performance was recorded for the control mix with 10% QD (Stability 42.2 kN; TS 4.16 N/mm²; Modulus: 1.487 N/mm²). However, a significant interaction was identified at moderate replacement levels. The combination of 4% PLA with 10% QD yielded superior mechanical properties (Stability 39.0 kN; TS: 3.85 N/mm²; Modulus: 1.284 N/mm²) compared to the baseline mix containing no fillers (Stability 35.6 kN; TS: 3.51 N/mm²; Modulus: 1.066 N/mm²). This represents improvements of 9.6%, 9.7%, and 20.5% in stability, tensile strength, and stiffness, respectively. In conclusion, up to 4% of conventional mineral filler can be replaced with Plantain Leaf Ash without compromising, and indeed enhancing, pavement performance, provided it is combined with an optimal dose of Quarry Dust (10%). This approach offers a viable pathway for the use of agricultural waste in pavement construction, contributing to sustainability while improving the structural integrity of asphalt concrete.