Influence of Physical Parameters on the Mechanical Properties of a Material Produced from PET Plastic Waste into Paving Blocks

This study is part of a circular economy approach aimed at valorizing polyethylene terephthalate (PET) waste in cementitious matrices through a materials science and engineering approach. PET waste from used containers underwent a controlled thermomechanical transformation (melting at 260°C, cooling, grinding, and sieving), yielding two distinct fractions: plastic aggregates (> 5 mm) and a fine powder. These two forms were incorporated into hydraulic concrete using two formulation strategies: (i) partial substitution of natural gravel with PET aggregates and (ii) partial substitution of sand with PET powder, at rates ranging from 0 to 18% by mass. The concrete's performance was evaluated after 7 days by measuring uniaxial compressive strength and water absorption capacity. The results show that the morphology and incorporation rate of PET significantly influence the concrete's properties. Substituting gravel with PET aggregates leads to a progressive decrease in mechanical strength and, at high concentrations, an increase in water absorption. Conversely, substituting sand with PET powder exhibits more favorable behavior at low concentrations (≤ 6–8%), characterized by a densification effect on the cementitious matrix. An optimal range of 5 to 8% PET powder is thus identified for non-structural hydraulic concrete applications.