Utilisation of cement kiln dust for the activation of fly ash in low strength applications

Abstract

Cement kiln dust (CKD) is a by-product of the cement manufacturing process, the composition of which can vary widely. Recent years of using alternative fuels have resulted in higher chloride and alkali contents within CKDs; as such, this limits the applications in which CKDs can be utilised. Due to the high alkalinity of CKDs, they can potentially be utilised in the activation of pulverized fuel ash (PFA) for low strength un-reinforced applications. The potential reactivity of a CKD can be estimated from its composition; mainly, that which contains higher free-lime content will be more reactive than that containing higher unreactive calcium carbonate content. This study focuses on the hydration kinetics and mechanical properties of a CKD with 29.5% free lime blended in various proportions with PFA and Portland cement. Paste samples using a water to binder ratio of 0.35 were cast in 40 x 40 x 160 mm moulds, and the resulting compressive strengths measured at 28 and 56 days. The hydration products at 56 days were investigated by X-ray diffraction and thermogravimetric analysis. The results show that the CKD, containing high free-lime content, has the potential to activate PFA and provide sufficient mechanical properties for low strength applications.