Recycling used engine oil in concrete: Fire performance evaluation

Recycling used engine oil (UEO) into concrete is a viable and clean solution, as UEO has functions similar to chemical additives (i.e. as a water reducer and air entrainer) for concrete production. However, prior to the use of this ecofriendly concrete within the building industry, its fire performance should be thoroughly evaluated to further prove the technical feasibility and promote its safe application. Here, the fire performance of UEO concrete following exposure to elevated temperatures was assessed by measuring its compressive strength and elastic modulus. Experimental outcomes suggest that concrete admixed with 2% UEO by mass of cementitious materials shows enhanced fire performance and that concrete admixed with 5% UEO exhibits comparable mechanical properties to reference concrete. In ascertaining the microstructural origins behind the mechanical performance changes, scanning electron microscopy (SEM) analysis was conducted to analyze the surface morphology of UEO concrete. The analysis demonstrates that concrete with 2% UEO features densely packed fibrous calcium silicate hydrates (C–S–H) at 200 °C that contribute to strength increase. In addition, the surface characteristics of UEO concrete in terms of color changes, cracks, and pore density were analyzed to supplement the fire performance information, with the intention of facilitating structural health assessments following fire attacks. Moreover, the environmental and economic assessments of the proposed UEO disposal approach concerning carbon dioxide emissions, energy consumption, and costs, respectively, are discussed and contrasted with the mainstream disposal options. The discussion suggests that the present recycling strategy can reduce carbon dioxide emissions by 8050–10750 kg, energy consumption by 2.87–4.13 billion MJ, and disposal costs by HK$3250–9450 per tonne of UEO. These findings will contribute to advancing a clean UEO management strategy and to engineering waste-enhanced concrete with desired fire performance for sustainable civil infrastructure. © 2022 Published by Elsevier Ltd.