Material Valorisation of Post-Consumer Plastic Waste into Plastic–Sand–Gravel Composite Paving Blocks: Experimental Formulation and Mechanical Characterisation in Kinshasa, DRC.

Introduction: The accumulation of plastic waste in rapidly urbanising cities represents a major environmental and resource-management challenge. In Kinshasa, where solid waste collection remains limited in several neighbourhoods, transforming post-consumer plastics into construction materials could contribute to both urban sanitation and circular material recovery. This study investigates the feasibility of producing plastic–sand–gravel composite paving blocks from locally collected plastic waste in the Musey neighbourhood, Ngaliema municipality, Kinshasa.

Methods: An experimental and quantitative approach was adopted. Household waste generation was estimated using demographic data, local administrative records and field sampling. Three plastic-based paving block formulations were prepared by heating collected plastic waste until a viscous binder was obtained, then incorporating sand and gravel in varying proportions before moulding. The produced specimens were evaluated through physical measurements and compressive testing at the Office des Routes.

Results: The average specific waste generation was estimated at 0.11 kg per inhabitant per day. For the 2024–2034 projection period, weekly, monthly and annual waste quantities could reach 46,426.24 kg, 198,369.6 kg and 2,420,796.8 kg, respectively. The best-performing formulation contained 27.4% plastic waste, 54.9% sand and 17.7% gravel, corresponding to 3.8 kg, 5.0 kg and 1.2 kg, respectively. The resulting paving block had a volume of 4,880 cm³, a mass of 7,441 g, a density of 1.52 g/cm³ and a compressive failure load of 29 kg/cm². Compared with preliminary formulations, this mixture showed better cohesion, dimensional integrity and practical suitability for common non-structural paving applications.

Conclusions: The results demonstrate the technical feasibility of converting post-consumer plastic waste into composite paving blocks using a simple thermal recycling route. This approach may help reduce uncontrolled plastic disposal while supporting local circular economy initiatives and the production of low-cost alternative construction materials.