A study on durability and microstructural analysis of high-strength concrete utilizing rice husk ash and non-biodegradable polyethylene

The increasing need for green building materials has prompted research into alternative aggregates and binders that reduce the environmental footprint. This research explores the strength and microstructural characteristics of high-strength concrete (HSC) using rice husk ash (RHA) as a partial cement substitute and non-biodegradable polyethylene (PET) as a substitute for fine aggregates. The aim is to minimize cement consumption, make use of agricultural waste, and reuse plastic waste in order to counter environmental issues. Experimental program comprises the partial replacement of cement by PET at 0%, 5%, 10%, and 15% and fine aggregate by RHA at 10%, 20%, 30%, and 40%. Thorough tests were carried out such as compressive strength, water absorption, permeability, sulphate resistance, and chloride penetration. Scanning Electron Microscopy (SEM) analysis was used to study the microstructural impacts. Results show that the optimal mix—10% RHA and 5% PET replacement—achieved a compressive strength of 72 MPa at 28 days, representing a 5% increase compared to the control mix (68.5 MPa). Additionally, permeability was reduced by 15%, chloride penetration decreased by 20%, and water absorption dropped by 12%. While PET replacement beyond 10% caused a 10–18% reduction in compressive strength, it improved resistance to environmental degradation. The incorporation of RHA enhanced microstructural densification, reducing porosity by 22% and increasing sulphate resistance by 25%. SEM analysis confirmed the formation of additional C–S–H gel, leading to a refined pore structure. Higher levels of PET replacement diminished compressive strength but considerably enhanced resistance to the environment. RHA pozzolanic reaction enhanced microstructural densification, which diminished porosity and improved durability. This research illustrates how the use of RHA and PET in concrete offers a satisfactory compromise between environmental sustainability and mechanical performance, being a potential pathway for green building.