Physicochemical Behavior of Cement Kiln Dust–Treated Kaolinite Clay

Abstract

The physicochemical responses induced in kaolinite clay treated with 25% of a high free lime content cement kiln dust (CKD) were investigated. Atterberg limits, unconfined compressive strength, and stiffness of the compacted, CKD-treated kaolinite were measured as functions of the curing period. These properties were compared with those of the untreated clay and of the clay treated with quicklime, so as to determine the comparative extent of enhancement induced by the CKD treatment. The CKD-treated clay developed significantly higher strength than quicklime-treated clay containing the same amount of lime. The remarkable enhancement in clay properties observed suggests significant potential for use of some CKDs as soil stabilizers. The mineralogi-cal and morphologic changes induced in the clay by the CKD addition were characterized using X-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive X-ray analyses, so as to help provide an understanding of the CKD-clay interaction mechanism. These examinations indicated that the preexisting stacks of kaolinite clay particles were disaggregated and that the individual clay flakes had absorbed calcium hydroxide that had been previously generated by the hydration of quicklime in the CKD. However, direct evidences for production of calcium silicate hydrate (C-S-H) by pozzolanic reaction between the clay and the calcium hydroxide was not found, despite high likelihood that this had occurred. The same basic interaction mechanisms appeared to operate in both the CKD-treated and the lime-treated clays. The 90-day cured specimens were found to be well cemented and not affected by water immersion.