Investigation Using Granular Material Obtained from High-Density Polyethylene and Polypropylene Plastic Waste as Aggregate in Cementitious Systems

The accumulation of plastic waste represents a significant environmental challenge worldwide, and its reuse in construction materials offers a sustainable management alternative. This study investigates the use of recycled high-density polyethylene (HDPE) and polypropylene (PP) granules as partial volumetric replacements (10%, 20%, and 30%) for limestone aggregate in mortar mixtures. A total of seven mixtures were produced and evaluated in terms of flow value, unit weight, water absorption, porosity, compressive strength, flexural strength, and capillary water absorption. In comparison to the control mixture, it was found that the use of plastic aggregate improved the workability. It was found that the flexural and compressive strengths of mixtures decrease when plastic aggregate is added. Additionally, it was understood that utilization of plastic aggregate in mixtures caused an increase in water absorption rate and porosity values. HDPE and PP plastic aggregates increased flow by 9% to 13% and reduced unit weight by 15 to 15.3%, while compressive and flexural strengths decreased by 48 to 30% and 46 to 54%, respectively. The optimum replacement level was 10% for both HDPE and PP mixtures.