Spent fluid cracking and spent alumina catalysts as sustainable construction materials in concrete

Spent catalysts are the industrial by-product generated from oil refineries. These deactivated catalysts are disposed of in landfills posing a substantial burden on the environment. Given their physical and chemical properties, spent catalysts have the potential to be used as a construction material in concrete production. Therefore, this study investigates the alternative use of spent fluid cracking catalyst (SFCC) and spent alumina catalyst (SAC) in concrete production. These spent catalysts were used in concrete as a partial replacement of sand (up to 25%) or cement (up to 10%). The physico-mechanical properties and durability of concrete with these spent catalysts were studied. Results indicate that concrete setting time decreased by increasing spent catalyst content of any type in concrete. Improvement in mechanical properties was observed in mixtures made with SFCC as a sand replacement. Conversely, no improvement was recorded when SAC was used as a sand replacement. Concrete with SFCC or SAC as a cement replacement exhibited similar strength to that of the control mixture when used only in small quantities at a water-to-binder (w/b) ratio of 0.7. The use of SFCC as a partial replacement of sand has a positive effect on the concrete's corrosion resistance. However, the inclusion of SAC in concrete has a detrimental effect on corrosion resistance. The study concluded that both spent catalysts are a good alternative as a partial replacement of cement in concrete. Furthermore, SFCC is one of the good options to be used as a green fine aggregate and cement additive material in concrete.