Pemanfaatan Hasil Peleburan Sampah Kantong Plastik sebagai Substitusi Parsial Agregat Halus pada Beton Mutu Sedang

Abstract

The utilization of melted plastic bag waste as a partial substitute for fine aggregate in medium-strength concrete is an innovative solution to address environmental issues caused by plastic waste, which is difficult to decompose, and the increasing exploitation of natural sand. This research aims to determine the effect of partial fine aggregate substitution using melted plastic bag waste on the compressive strength, splitting tensile strength, and flexural strength of medium-strength concrete. Laboratory testing was conducted using LDPE substitution variations of 0%, 5%, 10%, and 15%, in accordance with SNI standards, at 28 days of concrete age. The results show that the use of LDPE aggregate significantly reduces compressive strength, from 18.90 N/mm² in normal concrete to 11.89 N/mm² (LDPE 5%), 10.21 N/mm² (LDPE 10%), and 9.77 N/mm² (LDPE 15%), with the relationship between LDPE content and compressive strength modelled through a quadratic regression equation (R² = 0.9845). Splitting tensile strength also decreased consistently, from 1.6 N/mm² to 0.9 N/mm² at 15% LDPE. Flexural strength showed a different pattern: at 5% LDPE, the value remained equivalent to normal concrete (2.933 N/mm²), before decreasing to 1.732 N/mm² at 15% LDPE. The decline in all three mechanical parameters is indicated to result from sub-optimal bonding between the plastic aggregate and cement paste, along with increased porosity in the concrete matrix. This research complements previous studies that generally focused on non-structural products, by providing a comprehensive mechanical characterization of medium-strength concrete with LDPE plastic aggregate substitution.