Mix design and moisture susceptibility of asphalt concrete mixes containing waste catalyst from oil refineries

The main objective of this study was to investigate the potential of using spent catalysts produced from the process of refining crude oil as a constituent material in hot mix asphalt (HMA). Two types of spent catalyst; equilibrium catalyst (ECat) and zeolite catalyst (ZCat) were used to partially replace some selected sizes of aggregate in the HMA. Chemical analysis of the raw catalysts indicated that both catalyst types used in this study comprised mainly of Al₂O₃ and SiO₂. Marshall Method of mix design was followed to determine the optimum asphalt content of the aggregate structure containing waste catalyst. Volumetric and stability data indicated that there is a good potential for using spent catalyst in road applications. Environmental analysis and moisture damage potential were also carried out to further characterize the designed mixes. It was observed that the level of all toxic elements in both ECat and ZCat spent catalysts samples were within the acceptable limits. ECat mixes proved to be less susceptible to moisture damage compared to the ZCat mixes. For the amounts of catalyst used in this study, the ZCat mixes failed to meet the moisture resistance requirements of 80% retained strength and hence it is not recommended to be utilized as a filler material.