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The interaction of cement with clay or clay with cement and the stability of both materials is of special interest in many cases of environmental concern. Possible interactions of these materials happen in waste deposits of various kinds. Clay-cement suspensions are used in slurry walls for remediation of hazardous waste sites. Here the high pH may cause a destabilization of certain clay minerals and also a decrease in the clay-concrete strength compared to clay-free concretes. The setting of the cement has been showed to be strongly influenced by the kind of clay used in the suspension. The interaction of setted cement and clay is of interest in cases where for example a clay barrier is built in connection with existing concrete constructions in a waste disposal. For a better understanding of the clay cement reactions compacted mixtures of setted finely grinded cement or calcium hydroxyde were examined after being allowed to swell under constant volume condition at elevated temperatures for 4 to 16 weeks. The interface of setted cement and Na- and Ca-bentonite was investigated in relevance to changes in mineralogy and microstructure. The most obvious reaction is the replacement of exchangeable sodium ions in the Na-bentonite with calcium ions from the cement pore water. However, results also indicate a beginning structural alteration of the Montmorillonite. In this case leaching of alumina from the octahedral sheet produces a silica-rich residual phase (possibly Cristobalite) and a tetra-calcium-alumina-hydrate (4CaO Al2O3 13H2O).
Authors:Kahr, Günter and Madsen, Fritz
Index Terms:Clay; ClayGroup; cement
Further Information:Date published: 1995