The use of oily contaminated sand in geopolymer and concrete cement is being explored as a cost-effective method to mitigate environmental impacts. However, further understanding of certain phenomena is needed to ensure the longevity of this material. Carbonation, or the development of salts on the surface of geopolymers, has been seen in several industrial applications and laboratory studies. The presence of carbonation may have detrimental effects on the performance of materials since it leads to microstructural alterations caused by the leaching and carbonation of alkalis. This study examines the carbonation process in geopolymer pastes polluted with varying proportions of crude oil. Additionally, it examines methods to reduce the quantity of unbound or movable alkali cations, the connectedness of the pore network, and the process of carbonation. The mechanical and microstructural characteristics of geopolymer cement, produced from fly ash, are examined at oil contamination levels ranging from 0% to 10%. The study found that at 1% oil contamination, geopolymer paste had a 10% strength gain compared to control samples. However, it experienced a decrease in compressive strength at 4% or higher oil contamination. The carbonation formation decreased with increasing oil contamination, indicating that controlling oil contamination up to a certain level can enhance performance and durability in geopolymers.