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Particle-size fractions of several Georgia kaolins, which were prepared by sedimentation procedures, were examined from the standpoint of crystallinity, cation-exchange capacity, and surface area. Crystallinity was studied using X-ray techniques, exchange capacities were measured using the manganese saturation method, and surface areas were determined using glycerol adsorption techniques. A linear relation was obtained between surface areas and exchange capacities when areas were increased by decreasing the particle size or by changing from wellcrystallized to poorly crystallized kaolins. In most cases, the empirically determined crystallinity ratios indicated a change in crystallinity with change in particle size, the crystallinity generally increasing with decreasing particle size in individual samples. Unlike, however, the relation noted for exchange, the crystallinity did not consistently correlate with area changes both among the various samples and within the various particle-size fractions of a single sample. These results suggest that the relatively high cation-exchange capacity of poorly ordered kaolins is more directly a result of high surface area with crystallinity playing, at most, a very minor role.

The influence of varying degrees of crystal perfection of several Georgia kaolins on the flow properties of aqueous systems containing these clays was studied. The fractionated clay samples were characterized with respect to clay mineral composition, crystallinity, surface area, and cation-exchange capacity. In general, results indicated that dilatant and associated properties were controlled by the degree of crystal perfection whereas the viscous and plastic properties, at a given water content, were usually dependent on particle size.

Textural and compositional features of reaction products in the system kaolin-lime-water were examined by electron microscopy and electron di&action. Electron micrographs of replicas of fracture surfaces of compacted mixtures and transmission electron micrographs of powdered compacts showed considerable attack of kaolinite particles by hydrated lime and indicated formation of significant amounts of calcium silicate hydrate phases. Electron diiTraction of reaction products confirmed the presence of calcium silicate hydrates. The presence of these hydrates is undoubtedly responsible for the stabilizing effects of lime which have previously been reported in the literature.HE use of hydrated lime as a soil stabilizing agent has T developed rapidly in recent years. Many of the applied aspects of the stabilization process are well documented' but few detailed studies of reactions and reaction products have been made. The present investigation was undertaken to study some of the reaction products in the system kaolinlimewater by electron microscopy and electron diffraction. Electron microscope pictures of replicas of fracture surfaces were also taken to obtain information about the fabric and microtexture of kaolin-lime combinations. Well-characterized Georgia kaolinites, designated H and E by previous investigators,* were used in this study. Samples for investigation were small, cylindrical specimens recovered from strength experiments. The specimens were made from kaolin-water mixtures which were compacted by hand in a small cylindrical brass mold using a compactive effort approximating that prescribed by ASTM specification D69& 58T.a The specimens, 0.35 in. in diameter and 0.70 in. high, were cured for different periods of time and then tested in compression using an Instron tester Model TM equipped with a 50 CCTM Model T M compression cell. Other details of specimen preparation and strength tests are reported elsewhere.4 Electron micrographs were taken of fracture surfaces of strength specimens of kaolin E which contained 0, 0.8, and (3.0 wt% lime. Transmission electron micrographs and electron diffraction patterns were taken of specimens of kaolins H and E which contained 6 wt% lime. Replicas were prepared according to the method of Comer and Turley6; specimens for transmission and electron diffraction studies were prepared from -80 mesh material which was picked up on the surface of a droplet of mercury and then transferred to microscope specimen grids. All the specimens were examined using a JEM model 5A electron microscope using voltages of 80 and 100 kv. a characteristic reticular structure suggesting that the lime had a considerable effect on the clay, attacking both particle basal surfaces and edges.Figure 1 (C) shows the fine structure of plate basal surfaces. Small hexagonal plates seem to be forming from larger plates as a result of surface attack. Progressive deterioration may result in the development of cleavages and fissures perpendicular to the basal plane and in the fragmentation of the larger partic...

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