The growing demand for sustainable road infrastructure has intensified the interest in alternative mineral fillers that reduce natural resource consumption and environmental impacts. This study investigates the use of Sugarcane Bagasse Ash (SBA), an abundant agricultural by-product in sub-Saharan Africa, as a partial replacement for conventional mineral fillers in hot-mix asphalt (HMA). Unlike previous studies that considered SBA primarily as a minor additive, this study provides a systematic evaluation across a wide replacement range (0–16 %), combined with experimental testing and numerical validation. Marshall and indirect tensile strength (ITS) tests were conducted on HMA mixtures produced using locally sourced Nigerian aggregates and 60/70 penetration-grade bitumen. A three-dimensional finite element model (FEM) of the ITS configuration was developed to corroborate the experimental response and identify stress concentration zones. results indicate that SBA improves both mechanical and volumetric performance within an optimal replacement range of 6–10 %, with peak performance of approximately 8 % SBA. Within this range, Marshall stability increased from 7.6 kN to 9.0 kN, the Marshall quotient reached 3.3 kN/mm, bulk density increased to 2.51 g/cm³, and air voids decreased from 4.9 % to 3.5 %, remaining within standard design limits. Microstructural analyses confirmed the predominance of amorphous silica and porous SBA morphology, which promoted enhanced filler–binder interactions and mixture densification. FEM predictions of peak tensile stress agreed with laboratory ITS results within 10 % and successfully reproduced observed crack initiation zones. Excessive SBA content (> 10 %) led to reduced stability and density owing to over-filling effects. The findings demonstrate that 6–10 % SBA is a technically viable and sustainable filler replacement for HMA, particularly in sugarcane-producing regions, offering improved performance alongside waste valorization and reduced reliance on quarry-derived fillers.

The increasing accumulation of plastic waste and the persistent durability challenges associated with conventional asphalt pavements have prompted the search for sustainable material modifications. Among potential additives, recycled polyethylene terephthalate (RPET) has emerged as a promising modifier capable of enhancing pavement performance while supporting environmental sustainability. This study investigated the mechanical and microstructural behavior of hot-mix asphalt (HMA) modified with RPET using a drying process. RPET was incorporated at proportions ranging from 0% to 10% of the total mix mass, and the mixtures were evaluated through Marshall stability and flow, uniaxial compressive strength, indirect tensile strength, rutting resistance, dynamic modulus, semi-circular bending, moisture sensitivity, and scanning electron microscopy. Results indicate that RPET significantly improves HMA performance up to an optimal content of 8%. At this dosage, Marshall stability increased from 6.40 to 11.97 kN, while flow decreased from 11.67 to 5.17 mm, demonstrating enhanced stiffness and resistance to permanent deformation. UCS and ITS rose from 1.10 to 1.85 MPa and 0.165 to 0.278 MPa, respectively, and rutting depth declined from 5.0 to 3.0 mm. Additionally, the dynamic modulus increased from 1500 to 2500 MPa, and the SCB increased from 320 to 590 J/m², confirming the enhanced cracking resistance. SEM analysis revealed stronger binder–aggregate interaction at intermediate RPET levels, whereas excessive RPET (10%) caused particle agglomeration and slight performance reductions. The findings show that RPET improves hot mix asphalt mainly through physical reinforcement and microstructural densification, with optimal dosage offering a sustainable way to enhance pavement durability while reducing plastic waste.