Integrated mechanical, environmental, and cost assessment of recycled polypropylene–silica fume concrete under moderate thermal exposure

Abstract

Concrete production contributes substantially to CO 2 emissions and depletion of natural aggregates. This study investigates concrete incorporating recycled polypropylene (PP) granules as a partial fine-aggregate replacement (0–50%) under moderate thermal exposure (25–200 °C). PP-modified mixtures contained 10% silica fume (SF) by mass of cement, while the control mixture contained no SF. Workability and performance were assessed via slump, density, compressive strength, and splitting tensile strength at 28 days, supported by analysis of variance (ANOVA) and scanning electron microscopy (SEM)-based interfacial transition zone (ITZ) observations. At 25 °C, slump decreased from 97 to 87.33 mm and density declined from 2266.88 to 2044.80 kg/m 3 (−9.8%) as PP increased to 50%. Compressive and splitting tensile strengths reduced from 32.89 to 20.37 MPa and from 2.83 to 1.89 MPa, respectively. After 200 °C exposure, compressive strength retention was 63.87% for the control and 82.94% for the 25% PP–10% SF mixture. SEM indicated more pronounced interfacial discontinuities at higher PP contents. Screening-level life cycle assessment (LCA), unit-cost indicators, and multi-criteria scoring suggest that 10–25% PP (within the fixed 10% SF system) provides the most balanced trade-off among the PP-modified mixtures.

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