Sustainable concrete incorporating cement kiln dust: effects of mineral admixtures and data-driven strength prediction models with mechanical and microstructural assessment

Cement kiln dust (CKD), a by-product, is typically disposed of in landfills, but landfilling poses risks of leachate formation and the transport of aggressive substances to groundwater and soils. In this study, the properties of cement paste and concrete, with or without a Mineral admixture (MA), were evaluated, with CKD added at 0, 5, 10, and 20% as a cement replacement. Results show that CKD had a limited influence on the setting time of cement paste, with only minor variations observed across different replacement levels of cement paste or the ultrasonic pulse velocity (UPV) of concrete. Some loss of compressive strength and increased absorption were observed. No significant benefit was found from using MA, especially silica fume added at 15% as a cement replacement, in enhancing concrete properties. CKD was added at 5%, 10%, and 20% as a cement replacement, with a control mix without CKD (0%). Generally, the microstructures of mixes with different mineral admixtures and CKD ratios were homogeneous, and adding up to 20% CKD had no significant adverse effect on concrete properties. These findings may encourage concrete producers to consider using CKD in mixes instead of landfilling. Additionally, regression analysis was performed on data collected from the literature to predict the compressive, splitting tensile, and flexural strengths of concrete with or without MA-containing CKD. Among the developed models, the highest coefficient of determination (R2 ≈ 0.97) was achieved for predicting the compressive strength of concrete containing CKD and mineral admixtures.