Multi-criteria assessment of recycled polyethylene terephthalate (PET) incorporation in bituminous mixtures: application to the cameroonian context

• The study evaluates the incorporation of recycled PET into bituminous mixes in line with French (NF) standards. • Adding 5% PET reduces the overall cost of producing asphalt concrete by 8–10%. • Approximately 2 tonnes of plastic bottles are recycled per kilometre of road built. • The multi-criteria analysis combines mechanical, economic and environmental performance. • The results confirm the viability of recycled PET for tropical road infrastructure. The valorization of plastic waste in road construction represents a promising solution to both environmental and infrastructure challenges in developing countries. This study investigates the mechanical, economic, and environmental performance of asphalt mixtures modified with recycled polyethylene terephthalate (PET) in the Cameroonian context. PET was incorporated into asphalt mixtures at different contents (0–7% by weight of bitumen), and the resulting mixes were evaluated using standard mechanical tests, including Marshall stability, flow, compactness, Marshall creep, and water sensitivity. The results show that PET modification significantly improves the mechanical performance of asphalt mixtures up to an optimal content of 5%, with an increase in Marshall stability, a reduction in permanent deformation, and satisfactory resistance to moisture damage compared to conventional asphalt. Beyond this threshold, mechanical performance decreases due to reduced workability and excessive stiffening of the mixture. An economic assessment indicates that PET-modified asphalt can reduce material costs by partially substituting bitumen, assuming local collection and processing of plastic waste. A simplified life cycle assessment (cradle-to-gate) focusing on energy consumption and greenhouse gas emissions highlights a net environmental benefit at optimal PET content, despite increased processing energy. The combined multicriteria analysis demonstrates that a PET content of approximately 5% provides the best compromise between mechanical performance, cost efficiency, and environmental impact. This study highlights the feasibility of integrating recycled PET into asphalt mixtures for tropical regions and provides practical guidance for sustainable road construction in sub-Saharan Africa.