Optimization of the Compressive and Split Tensile Strength of Lightweight Concrete Containing Recycled Expanded Polystyrene Using Response Surface Methodology

This study optimized the compressive and split tensile strengths of lightweight concrete containing recycled expanded polystyrene (EPS) using Response Surface Methodology (RSM). EPS, a non-biodegradable polymer commonly used in packaging, was recycled from computer packaging waste and used as a partial replacement for coarse aggregates. A central composite design with three factors—EPS particle size (12, 16, 19 mm), replacement level (25%, 35%, 45%), and density—was generated using Design Expert (v.11). Ten experimental runs with five replicates each for compressive and split tensile strength were conducted. Results showed that compressive strength decreased from 8.52 MPa for the control (clay balls) to 3.78–5.80 MPa for EPS concretes, while split tensile strength ranged from 1.02–1.42 MPa compared with 1.162 MPa for the control. Replacement level significantly affected both properties, while particle size showed an interaction effect with replacement level for compressive strength. The optimal mix consisted of 13.53 mm EPS at 25% replacement and a density of 1.73 g/cc, achieving 5.80 MPa compressive strength and 1.33 MPa split tensile strength values suitable for non-structural lightweight concrete. These findings demonstrate the potential of recycled EPS for sustainable construction and highlight the effectiveness of RSM in optimizing lightweight concretes.