This study investigates the combined use of waste glass cullet (WGC) and snail shell powder (SSP) as a sustainable binary cementitious system to enhance the mechanical performance and durability of concrete, particularly for rigid pavement applications. Nine concrete mixes were formulated: a control mix, four mixes with 5%, 10%, 15%, and 20% WGC as partial cement replacement, and four corresponding mixes with 1% SSP addition. Slump, compressive strength, and flexural strength were evaluated at various curing ages. Results showed that while WGC reduced workability due to its angular morphology (slump decreased from 30 mm to 20 mm at 20% WGC), the inclusion of SSP slightly mitigated this reduction (21 mm at 20% WGC + 1% SSP). At 28 days, compressive strength increased from 40.0 MPa (control) to 45.0 MPa with 20% WGC and further to 48.0 MPa with the addition of SSP. Flexural strength also improved from 7.0 MPa (control) to 7.8 MPa with both WGC and SSP. These improvements were statistically significant (p < 0.05) and supported by correlation analysis, which revealed a strong inverse relationship between WGC content and slump (r = −0.97) and strong positive correlations between early and later-age strength. Microstructural analyses (SEM/EDX) confirmed enhanced matrix densification and pozzolanic activity. The findings demonstrate that up to 20% WGC with 1% SSP not only enhances strength development but also provides a viable, low-cost, and eco-friendly alternative for producing durable, load-bearing, and sustainable concrete for rigid pavements and infrastructure applications. This approach supports circular economic principles by valorizing industrial and biogenic waste streams in civil construction.

This study presents a mechanistic and comparative laboratory assessment of lime stabilization and uniaxial geogrid reinforcement, applied independently and in combination, to improve the engineering performance of a classified A-7-6 (CL–ML) lateritic subgrade from Ogun State, Nigeria. The objective was to evaluate the effect of lime dosage and geogrid inclusion on the short- and long-term California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), and Resilient Modulus (MR), and to test the hypothesis that chemical and mechanical stabilization mechanisms act synergistically to enhance stiffness and durability. Quicklime (CaO > 90%) was added at 2–8% by dry weight, while the geogrid used was uniaxial polypropylene with an aperture size of 30 mm and tensile strength of 22 kN/m. Specimens were prepared by mixing, compacting, and curing at 25 ± 2 °C and 95 ± 2% RH for 7, 14, and 28 days, then tested according to ASTM and AASHTO standards. Each condition was replicated thrice, and the data were analyzed using one-way ANOVA (p < 0.05). Results showed that lime treatment reduced the plasticity index from 30 ± 1.2 to 6 ± 0.5%, increased UCS from 300 ± 15 to 950 ± 40 kPa and improved soaked CBR from 23 ± 1.1 to 57.5 ± 2.3% after 28 days. Single and double geogrid layers enhanced soaked CBR to 33 ± 1.4% and 43 ± 1.7%, respectively, with negligible strength loss after three moisture cycles, confirming durability under wetting–drying conditions. Combined lime–geogrid stabilization achieved the highest performance, with CBR > 65%, MR > 90 MPa, and UCS > 1.0 MPa, exceeding AASHTO subgrade requirements. The findings demonstrate that lime primarily enhances chemical bonding, whereas geogrid reinforcement improves mechanical confinement; their combination offers a durable, cost-effective, and low-carbon alternative to conventional cement stabilization for tropical lateritic subgrades.

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.