Experimental Investigation on the Performance of Masonry Walls Made of Concrete Units with Plastic Waste Aggregates

The growing and uncontrolled accumulation of plastic waste has emerged as an environmental emergency requiring effective strategies to mitigate the threats associated with plastic pollution. In this context, several approaches have been proposed to promote the reuse of plastic waste as a secondary raw material. In particular, its incorporation into construction materials has proven to be a promising strategy for waste valorization. This study investigates the effects of incorporating plastic waste into concrete mixes used for the production of masonry units. Specifically, the experimental campaign evaluates how replacing part of the conventional mix constituents with two types of plastic waste aggregates, namely granules and flakes, at different percentages affects the mechanical performance of the resulting concrete units and masonry walls. Compressive and flexural tests were first performed on concrete units containing plastic granules and flakes at replacement percentages ranging from 2.5% to 10% by volume, with the aim of identifying representative mixes for the subsequent tests on the masonry walls. Based on these results, masonry walls were manufactured using a control mix and two mixes containing 5% plastic aggregates (flakes or granules) and tested under vertical and diagonal compression according to standard procedures. The results show that the incorporation of plastic aggregates generally reduces the mechanical strength, depending on both the replacement percentage and the type of plastic aggregate adopted. However, despite the reduction in strength, some walls containing plastic aggregates exhibited a more ductile post-peak response, characterized by greater deformation capacity and a more gradual degradation of the load-carrying capacity. These findings indicate that the incorporation of recycled plastic aggregates into concrete masonry units can be considered a valuable strategy for the reuse of plastic waste in masonry construction, particularly when an appropriate balance between load-carrying capacity and deformation capacity can be achieved.