Fundamental study of clay-cement kiln dust (CKD) interaction to determine the effectiveness of CKD as a potential clay soil stabilizer
Abstract
Cement kiln dusts (CKDs) are by-products of the cement manufacturing process that are removed from the stream of kiln gases as they pass through the kiln’s dust collection system during clinker production. The feasibility of using cement kiln dusts (CKDs) as potential stabilizing agents for kaolinite, Na-montmorillonite and Ca-montmorillonite clay was investigated in this research. A suite of four CKDs with different chemical and physical characteristics were used in the study. The amount of free lime, which is expected to play a major role in the stabilization, was high in two of the CKDs and was low in the remaining two CKDs. The dry clays, dry CKD powders and the hydration products of compacted CKDs were characterized in detail using different characterization techniques. The physical properties such as, particle size distribution and the surface areas were also determined. The evaluation of the hydration products of the high free-lime CKDs, indicated that they contained calcium hydroxide, syngenite, ettringite and gypsum. The content of the same components in the hydration products of the low-free lime CKDs was significantly lower. The compressive strengths and temperatures of hydration of the two hydrated CKDs with high free-lime content were significantly higher than the remaining two CKDs. The engineering properties of CKD-treated clays were determined and compared with that of the untreated and lime-treated clays. The Atterberg limits, pH values and unconfined compressive strength (UCS) were determined as a function of CKD content and curing period. It was found that effectiveness of a particular CKD in stabilizing clay is mainly a function of its chemical composition, specifically, the free-lime (CaO) content. In each case, the CKD with higher free-lime content was found to be more effective in improving various engineering properties. Finally, a chemical interaction study of the CKD-clay system was conducted. The presence of ettringite, gypsum and C-S-H was confirmed and the amount of these products appeared to be a function of chemical characteristics of the particular CKD. Irrespective of the type of clay mineral, the main mechanism of stabilization appeared to be a pozzolanic reaction between a small part of the clay and the calcium hydroxide produced from the free-lime during the hydration of the CKD. The SEM examinations gave conclusive evidence of the adsorption of the calcium hydroxide on to the surfaces of the kaolinite clay treated with CKDs, a process that may promote formation of C-S-H in the system. In addition to the evidences of the adsorption of the CH on the Na-montmorillonite clay, more C-S-H formation was also indicated by SEM and EDX analysis. Although CH adsorption was observed in Ca-montmorillonite clay no indication of formation of C-S-H was observed. Other hydration products, which may have contributed to the improvement of the CKD-treated compacted clays, were ettringite and probably gypsum.
Degree
Ph.D.
Advisors
Olek, Purdue University.
Subject Area
Civil engineering
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