Recycling plastic waste into bricks: A sustainable approach using HDPE, PET, RFA, and PP

Plastic waste poses a significant environmental challenge due to its resistance to degradation. One promising solution is its utilization as a construction material, such as lightweight or floating bricks. This study investigates the feasibility of using High-Density Polyethylene (HDPE), Polyethylene Terephthalate (PET), and Polypropylene (PP) combined with Recycled Fine Aggregate (RFA) to produce sustainable bricks. A total of 39 specimens and 3 control samples (100% HDPE) were tested through three experimental series. The first series examined HDPE–RFA mixtures (100–70% HDPE; 0–30% RFA). Increasing RFA content significantly improved the compressive and shear strengths, reaching maximum values of 47.43 MPa and 0.700 MPa, respectively. The second series evaluated HDPE–PET blends (90:10 to 70:30). Although pure HDPE showed the highest compressive strength (30.43 MPa), the 80:20 ratio provided an optimal balance between performance and efficiency. The third series analyzed HDPE–PP mixtures, with the 90:10 ratio yielding the highest strength (30.13 MPa), while the 80:20 ratio demonstrated more stable overall performance. All specimens met lightweight brick criteria and exhibited low water absorption. Increased PET content improved moisture resistance, making HDPE–PET blends suitable for water-sensitive applications. Density values ranged from 0.088 to 0.101 g/cm³, with HDPE–RFA mixtures showing the highest density. Overall, the results indicate that incorporating PET or RFA enhances mechanical strength, while PP improves stability. These findings demonstrate the strong potential of HDPE-based composite bricks as sustainable and eco-friendly alternatives for construction and floating applications.