Sustainable concrete incorporating bagasse ash and plastic waste as fine aggregate

The construction industry is increasingly adopting sustainable materials to reduce environmental impacts while maintaining structural performance. This study investigates the combined use of sugarcane bagasse ash (BA) and polyethylene terephthalate (PET) aggregates in M30-grade concrete. BA replaced cement at 0%–15%, while PET replaced natural sand at 0%–20%. The control mix achieved a compressive strength of 37.25 MPa, while the 5%BA + 10%PET mix attained 36.46 MPa (≈2% reduction). At 20% PET replacement, compressive strength decreased to 33.81 MPa (≈9% reduction). Similar trends were observed for split tensile strength (3.45–3.27 MPa) and flexural strength (3.79–3.62 MPa). The optimum mix (BA10–PET10) exhibited a modulus of elasticity of 28 525 MPa and UPV of 4.05 km/s, indicating good-quality concrete. Durability improved significantly, with rapid chloride permeability test values decreasing from 3150 to 2045 Coulombs and water penetration reducing from 22 to 15 mm. Sorptivity decreased from 0.0060 to 0.0041 mm/min^0.5, while effective porosity reduced from 15.2% to 12.3%. Abrasion resistance improved by 18.8%, and marine-exposure strength loss decreased from 22.95% to 19.02%. Furthermore, BA and PET reduced cost by 10% and carbon dioxide emissions by 30.6%. Overall, mixes containing 10%–15% BA and 5%–10% PET achieved the best balance of performance, durability and sustainability.