The thermogravimetric method offers a new approach to the study of clay and clay-like minerals as well as other minerals and compounds that gain or lose weight upon heating. This method is complementary to differential thermal analysis, which records energy gains or losses upon heating. Thermogravimetric curves for clay and clay-like minerals are presented and correlated with curves obtained by the differential thermal method. The apparatus, procedures, limitations, and application of the method are described and illustrated.
Fabric (texture and structure) and minpralogic compofsition determine the response of clays and shales to events occurrins during construction and oi)eration of engineering works. A new system of classification of the fabric of earth materials is proposed. Characteristic minpralogic composition of clays and shales, especially in the western United States, is described. Fabric and composition are correlated with soil mechanics properties and engineering performance. Needed research on clays and shales as a basis for design, construction, and maintenance of engineering strticturcs is emphasized. * Head, Petrographio Laboratory, and Petrographer, respectivel.v, Engineering-Laboratories, U. S. Bureau of Reclamation, Denver, Colorado. Part V] Cr.AY TECHNOLOGY IN SOIL MECHANICS Tiihle 2. A cldnsification of fahric of clastic earth materials based on discontinuities.
The petrographic and mineralogic characteristics and geologic occurrence of rock formations and sand and gravel deposits determine the composition, gradation, and quality of aggregates. Thus, because of their several modes of origin—igneous, sedimentary, and metamorphic—rock formations present different problems to the quarryman and produce aggregates of differing serviceability. The suitability of natural aggregates for any purpose also depends upon the geologic processes involved in their formation and subsequent history. Petrographic and mineralogic composition and internal texture and structure of the particles control the physical and chemical properties of the aggregate. Consequently, the suitability of aggregates for proposed uses can be evaluated by petrographic methods. The physical properties of particles important to the quality of aggregate are: porosity, permeability, and absorption; surface texture; volume change with wetting and drying; thermal characteristics; strength and elasticity; density; hardness; shape; and coatings. The important chemical properties are: solubility, susceptibility to oxidation, hydration, and carbonation; and reactivity with constituents of portland cement. The interrelation of petrographic character and serviceability of concrete aggregate is demonstrated by several case histories.
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