Preliminary experimental investigation of concrete incorporating minimally processed recycled concrete aggregate, waste plastic, and styrofoam

Concrete is widely used; however, its high density, largely associated with conventional aggregates, increases structural dead loads, transportation demands, and material consumption, highlighting the value of recycled waste as alternative aggregates for lightweight concrete. This study evaluates minimally processed recycled plastic, styrofoam, and recycled concrete aggregate (RCA) as partial or complete natural-aggregate replacements to reduce concrete density and assess their potential as alternative aggregate materials. Five mixtures were prepared: control, plastic-modified, styrofoam-modified, 50% RCA, and 100% RCA. After 28 days of curing, three specimens per mixture were tested for compressive strength and dry density. The control exhibited the highest compressive strength (35.11 ± 0.61 MPa) and density (2374.42 ± 42.77 kg/m³). Plastic and styrofoam incorporation reduced compressive strength to 15.50 ± 0.38 and 12.01 ± 1.30 MPa and density to 2261.93 ± 77.13 and 1969.87 ± 31.83 kg/m³, respectively. The 50% and 100% RCA mixtures achieved compressive strengths of 23.72 ± 1.62 and 19.21 ± 0.79 MPa, with corresponding densities of 2205.66 ± 15.33 and 2065.46 ± 9.02 kg/m³. The plastic-modified mixture approached the International Building Code Sect. 1904.2 compressive-strength range for non-structural applications (17.23–24.13 MPa), while both RCA mixtures fell within this range. Overall, RCA provided a more favorable strength–density balance than plastic and styrofoam. Long-term durability, life-cycle assessment, and microstructural evaluations were beyond the scope of this preliminary study. The findings indicate that minimally processed waste-derived aggregates can reduce concrete density and natural-aggregate consumption, with RCA showing greater potential for non-structural applications under the investigated conditions.