Valorization of Industrial Byproducts in Concrete: Synergistic Effects of Sewage Sludge Ash and Silica Fume with Recycled Plastic Fine Aggregates

Plastics are inexpensive, lightweight, adaptable, and easily available. The manufacture of plastic has increased dramatically over the past 50 years, and its use has become an essential part of our daily life. Consequently, the production of plastic-related waste is rising, which threatens the ecosystem. Sewage sludge ash (SSA) is an inevitable waste product of wastewater treatment, and it poses a serious danger of contamination due to its high concentration of heavy metals. Various strategies are put forth globally to dispose of SSA in a sustainable and safe manner. One such method is using SSA, together with other industrial by products, to substitute cement in the creation of cementitious composites. This study explores the use of recycled plastic, sewage sludge ash, and silica fume as cement and fine aggregate substitutes. Using these materials, the study assesses the mechanical properties, workability, durability and environmental assessment of concrete, highlighting their sustainability and potential to reduce waste in the construction sector. A total of eight mixes were prepared, incorporating varying proportions of sewage sludge ash (SSA) and silica fume (SF) as partial replacements for cement, along with recycled plastic as a substitute for fine aggregate in concrete. The control mix demonstrated the best slump value among all mixes. However, mix 3 (containing 10% SF and 5% SSA) achieved the highest compressive and splitting tensile strength with an 18% and 6% increase in strength compared to the control mix after 28 days curing period. Additionally, mix 3 showed superior performance in water absorption and acid resistance tests. The environmental effect, embodied energy, and CO ₂ emissions are reduced when SF, SSA, and RP are added to the concrete as an aggregate and binder.