Investigation on blending CFB ash with blast furnace slag as replacement for portland cement used in concrete binders

Circulating Fluidized Bed (CFB) Boiler is a means of energy-generating process by burning petroleum coke. The residue collected from the boiler is called CFB ash. According to the position of the boiler where the ash is collected, CFB ashes can be classified as fly ash and bed ash, and both have similar chemical compositions, with high contents of gypsum and calcium oxide. In this study, CFB ash (fly ash) is mixed with blast furnace slag (BFS) as a substitute for cement in making concrete. Experiments results show that CFB ash will bring the activation of blast furnace slag and reacts with cement to produce hydration products. The findings suggest that the incorporation of CFB ash in various cement-BFS mixtures produces good compressive strength development and proves CFB ash an effective activator in the blend. The CFB ash contents of 18% to 22% by weight are suggested in a cement-BFS binding system. The high free lime contents in CFB ash are found to cause no soundness expansion as a binding material.