A way to reuse petrochemical wastes through the partial substitution of cement by spent cracking catalyst and its effect on cement pastes

This study examined the recycling of spent catalyst from Fluid Catalytic Cracking (FCC) process derived from Polish petroleum industry in cementitious materials. FCC is a basic process in converting crude oil into refinery products, utilizing zeolite catalyst. Nevertheless, owing to petroleum coke formation on its surface, such catalyst ends its life cycle in landfill as general solid waste (code 16 08 01) called spent Equilibrium Catalyst (E-Cat), which brings about serious environmental and health risks. Therefore, alternative approaches for E-Cat management are under development, one of which is recycling in cementitious materials. Nevertheless, there are still limitations in that scope arising from variable characteristics of E-Cat from different refineries and research gaps in terms of its influence on cementitious materials. Therefore, the current paper presents correlations between characteristics of Polish E-Cat, its superior pozzolanicity and impact of its usage as a 0–20% substitute of Portland cement, by mass, on fresh and hardened state performances of cement pastes at w/c ratios of 0.30, 0.35 and 0.40. It was demonstrated that the SiO2 and Al2O3 content in Polish E-Cat exceeds 87% of its mass, which contributes to its vital direct pozzolanic activity measured by Chapelle test (870.3 mg of Ca(OH)2/g E-Cat) and rapid, relevant and reliable (R3) test (497 J/g of E-Cat). Those performances contributed to the enhancement of pastes’ compressive strength for up to 16.7%, where the E-Cat was substituting 10–20% of cement, by mass, without application of any admixture. Simultaneously, other performances, such as consistency, flexural strength and water absorptivity were not significantly deteriorated. The partial substitution of cement with waste materials, such as E-Cat, brings about vital environmental benefits, which was additionally underlined in this paper.