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.

Incorporating recycled polyethylene terephthalate (PET) into asphalt mixtures offers a sustainable approach to enhance pavement performance while reducing plastic waste. However, the mesoscale mechanisms governing the influence of PET on stiffness, deformation resistance, and fracture behavior remain unclear. In this study, a three-dimensional Discrete Element Method (DEM) framework was developed to investigate the constitutive response of PET-modified asphalt concrete through the explicit representation of aggregates, asphalt mortar, PET inclusions, and air voids. Two bonding schemes, the Contact Bond Model (CBM) and Parallel Bond Model (PBM), were implemented and compared in terms of stiffness, tensile strength, damage evolution, and crack propagation. The experimental dynamic modulus (|E*|), indirect tensile strength (ITS), resilient modulus (Mr), rutting, and moisture susceptibility tests were conducted for mixtures containing 0–10% PET by volume. The DEM microparameters were calibrated using |E*| and ITS data, whereas Mr, rut depth, and tensile strength ratio (TSR) were used for independent validation. The results show that PET incorporation increases the mixture stiffness, with the dynamic modulus rising from 3500 to 5159 MPa and improves the resilient response under repeated loading. ITS increased from 0.44 MPa for the control mixture to a peak value of 1.15 MPa at 6% PET before decreasing to 0.89 MPa at 10% PET due to interfacial weakening. The rut depth decreased consistently with increasing PET content, indicating enhanced resistance to permanent deformation, whereas the TSR values confirmed acceptable moisture durability. Mesoscale analyses revealed that PET modified the force-chain distribution and promoted interface-controlled damage at the PET–mortar contacts. Compared with CBM, PBM more accurately reproduces progressive stiffness degradation and distributed cracking. An optimum PET content of approximately 6% was identified, providing the best balance between stiffness enhancement, tensile resistance and durability. These findings provide mechanistic insights into PET-modified asphalt mixtures and support the development of performance-based sustainable pavement materials.

The increasing generation of plastic waste and the growing demand for sustainable pavement materials have encouraged the incorporation of recycled polymers into asphalt mixtures. This study evaluates the engineering performance, microstructural characteristics, numerical response, and preliminary environmental implications of recycled polyethylene terephthalate (RPET)-modified asphalt concrete. RPET obtained from post-consumer plastic bottles was incorporated into asphalt mixtures through the dry process at dosages of 0–9% by weight of binder. Marshall stability, indirect tensile strength (ITS), repeated load dynamic creep (RLDC), scanning electron microscopy (SEM), and finite element modelling (FEM) were employed to assess the influence of RPET content on mixture behavior. Experimental results showed that increasing RPET content improved stiffness-related properties and rutting resistance. Marshall stability increased from 5.5 kN for the control mixture to 14.3 kN at 9% RPET, while ITS increased from 0.72 MPa to 1.02 MPa. RLDC results indicated a reduction in accumulated permanent strain from 3.20% to 1.85%, demonstrating enhanced resistance to deformation under repeated loading. SEM observations revealed comparatively uniform RPET dispersion at moderate dosages (3–5%), whereas higher contents showed localized particle agglomeration. FEM simulations demonstrated reduced surface deflection and improved stress distribution with increasing RPET-related stiffness. Preliminary life cycle assessment indicated modest embodied carbon reduction and potential cost savings. The findings suggest that RPET incorporation can enhance the mechanical and deformation-resistant characteristics of asphalt mixtures while contributing to plastic waste valorization and sustainability objectives. However, the results should be interpreted as comparative laboratory and numerical indicators rather than direct predictors of long-term field performance.