Of the cohesive soils the property of plasticity is usually of the most concern to the engineer. The clay minerals rather than the clay size material present in a soil determine the degree and magnitude of plastic properties. In turn, the plasticity of the clay minerals varies according to their mineralogy and particle size. Of the various types of clay minerals present in a soil, only kaolinite, illite and montmorillonite occur in sufficient abundance to be of general engineering significance.

Much prior work has been performed to alter these plastic properties of clay soils. This has been accomplished in some instances by the use of solidifiers and cationic modifiers. Although these methods have proved effective in many instances; they have shown definite difficulties and limitations. All of these efforts have been directed toward one principal objective: soil stabilization -- that is, rendering clay particles into larger aggregates or otherwise rendering them non-plastic. One such method which may be feasible in the near future is thermal treatment. Perhaps ultimately a technique may be devised for transforming soil into a continuous vitreous roadway base or pavement. Although such a method is still visionary, there are considerable possibilities at the present for more limited techniques of thermal treatment of soils.

Since the noncohesive components of a soil have rather definite physical properties in relation to moisture contents and have high heats of transformation, it seems logical to approach the method of thermal treatment as a means of stabilization by treating materials having physical properties which vary greatly in relation to moisture content but which have low heats of transformation.

The purpose of this study was to further explore the effects of thermal treatment on the physical properties and mineralogy of the clay minerals: kaolinite, illite and montmorillonite.

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No. 141

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