Calcareous fly ash refers to a type of fly ash containing a higher amount of calcium compounds than typical fly ashes, which predominantly contain silicon, aluminum, and iron. This variation makes calcareous fly ash highly reactive and beneficial in cement and concrete applications, particularly as a supplementary cementitious material. It enhances the properties of concrete by contributing to the hydration process and improving the final product’s mechanical strength and durability. The utilization of calcareous fly ash is especially advantageous in regions with harsh environmental conditions, as it helps in mitigating the issues related to durability and longevity of concrete structures.