Sustainable Utilization of Corn Stalk Ash and Used Engine Oil as Hydrophobic Admixtures in Cement based composites

Abstract: The penetration of water into concrete remains a critical durability concern, as moisture ingress initiates and accelerates a wide range of deterioration mechanisms. At the same time, environmentally harmful waste materials such as cornstalk ash and used engine oil pose significant risks due to air emissions, soil contamination, and water toxicity. This study investigates the potential utilization of corn stalk ash and used engine oil as hydrophobic admixtures in cement-based composites, thereby offering both performance enhancement and sustainable waste management. Concrete specimens were prepared with corn stalk ash contents of 0%, 2%, 4%, and 8% and used engine oil contents of 0%, 0.5%, 1%, 2%, and 4%. Sorptivity, ultrasonic pulse velocity, and visual assessments were conducted to evaluate water ingress and material integrity. Increasing corn stalk ash content generally resulted in higher sorptivity and lower UPV, primarily due to its intrinsic porous structure. The combined effects of corn stalk ash, used engine oil, and curing age produced nonlinear trends across all measured properties, highlighting the importance of mixture proportions. Overall, the composite containing 2% corn stalk ash and 0.5% used engine oil demonstrated the most effective hydrophobic response, reducing moisture penetration while simultaneously diverting waste materials from environmentally harmful pathways. These findings demonstrate that corn stalk ash and used engine oil can serve as viable sustainable admixtures, contributing to improved concrete durability and reduced environmental impacts.