Experimental study on sustainable utilization of CKD for improvement of collapsible soil

Heavy structures built on untreated collapsible soil remain susceptible to failure due to abrupt changes in the soil structure upon wetting. Industrial wastes like cement kiln dust (CKD) can be used to solve this problem. For this study, undisturbed and disturbed collapsible soil samples were collected from Thal Haro arid area, Punjab, Pakistan. CKD was mixed up to 20% to stabilize the collapsible soil with a maximum of 28 days of curing time. To perform strength tests and collapsible potential tests, samples were remolded at optimal water content and maximum dry unit weight. The CKD content exponentially improves the unconfined compression strength, deformation modulus, and soaked California bearing ratio; however, it marginalizes the ductility of treated soil. With the addition of CKD, the strain at failure and deformability index is significantly decreased. Moreover, for microstructural characteristics comparison, X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDAX) analyses were performed on untreated and treated samples. Due to the addition of CKD, XRD and EDAX results show the new peaks of calcium and calcium silicate, respectively, in treated samples. The formation of the new element and compound indicates the generation of bonds among soil partials owing to the hydration and pozzolanic reactions which is also verified by the SEM results. The SEM analyses manifest the conversion of the dispersed and silt-dominated structure of the native collapsible soil to a reticulated structure without micropores due to the addition of CKD.