Upcycling used engine oil into concrete: Ecological and mechanical performances in coastal applications

The accumulation of used engine oil (UEO) poses significant environmental risks, particularly through soil contamination and water pollution in urban areas. Incorporating UEO into concrete as a chemical admixture offers a promising and sustainable disposal method, as it can function similarly to conventional water-reducing and air-entraining agents, contributing to the development of durable and eco-friendly concrete materials. The ecological assessment revealed negligible differences between UEO and traditional tiles in terms of overall species richness, coverage percentage of sessile organisms, and biomass accumulation. Interestingly, UEO demonstrated potential in terms of fostering a more habitable environment for marine biofilm formation and larval settlement through a relative reduction in concrete surface pH levels from 12.5 to 9.8. Mechanically, UEO concrete exhibited a progressive increase in compressive strength over time and demonstrated a decreased susceptibility to chloride penetration when optimally dosed at 2 %. Furthermore, the microstructural analysis accentuated the criticality of determining the optimal UEO dosage for densifying the microstructure of UEO concrete and maximizing its durability and chloride resistance.