Effect of HDPE and PET Plastic Waste Use in The Manufacture of Lightweight Concrete

Abstract

Plastic waste poses a persistent environmental problem because it degrades very slowly. This study evaluated polyethylene terephthalate (PET) and high-density polyethylene (HDPE) waste as partial aggregate substitutes in lightweight concrete. Three substitution schemes were examined: PET, HDPE, and combined PET–HDPE. Individual PET and HDPE substitutions ranged from 0% to 50%, while combined substitutions ranged from 0%:0% to 25%:25% by aggregate volume. Pumice was used as the natural coarse aggregate, and silica fume was added at 10% of the cement mass. The specimens were tested at 28 days for density, compressive strength, splitting tensile strength, flexural strength, and elastic modulus in accordance with applicable Indonesian concrete standards. Increasing plastic content reduced slump, unit weight, compressive strength, splitting tensile strength, flexural strength, and elastic modulus. The lower workability was associated with the flat and irregular geometry of the plastic particles, while the reduction in mechanical properties was attributed to weaker bonding between the plastic surfaces and cement paste. PET substitutions of 20–50% and HDPE substitutions of 30–50% met the density criterion for lightweight concrete. The findings indicate that PET and HDPE waste can reduce concrete density and support plastic-waste utilization, although the substitution level must be controlled to limit losses in mechanical performance.