Aqueous carbonation of cement bypass dust for reuse in cement: Potassium chloride removal, hydration reactivity and mechanical properties

At present, Cement Bypass Dust (CBPD) is landfilled even if characterised by elevated levels of free lime because of high chlorides and sulphates contents. Thus, this study investigated the possibility of reusing CBPD in cement mortars after an aqueous carbonation treatment. Emphasis was given on the optimisation of KCl removal during the carbonation process. To this end, a range of liquid-to-solid ratios and washing-carbonating cycles were investigated. Subsequently, isothermal calorimetry and compressive strength tests on mortars, were done on the as received and carbonated CBPD. Finally, a comparative analysis of CO₂ emissions, substitution percentage and strength class, based on the data from different types of standard cement, was conducted to frame CBPD-based cements within the current commercial classifications. The samples with reduced chlorides content, showed similar reactivity when analysed with calorimetry. However, CBPD first hydrated then, carbonated (CBPDhc), stood out as the material with higher heat rate and the better mechanical performances with a relative strength of −26.9 % respect to the reference sample.