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The measured density of smectites, using ASTM Test Method for Specific Gravity of Soils (D 854) and ASTM Method for Laboratory Determination of Water (Moisture) Content of Soil, Rock, and Soil-Aggregate Mixtures (D 2216), vary as a function of heating temperature and time. For example, the measured moisture content of air-dry Otay bentonite, heated to 110°C, varied from 16.48% moisture to 19.0% moisture for 18- to 96-h heating time giving a calculated specific gravity varying from 2.679 to 2.785, and a measured variation in equilibrium temperature from 100 to 130°C gave a calculated specific gravity varying from 2.744 to 2.857. Measured specific gravity values of these smectite clays, for constant mass at 110°C, range from 2.785 to 3.150, whereas the calculated values for the smectites, including the essential bound water, range from 1.98 to 2.14. The maximum oven-dry density of compacted Otay bentonite varied from 1354 to 1384 kg/m3 (84.5 to 86.4 lb/ft3), with optimum moisture contents from 29.0 to 27.2% when possible temperature and time variations in moisture determination were observed, using ASTM Test Method for Moisture-Density Relations of Soils and Soil-Aggregate Mixtures Using 10-lb (4.54-kg) Rammer and 18-in. (457-mm) Drop (D1557). The bound water of the smectite is considered part of the moisture content when a compaction curve is prepared.
Professor of civil engineering, California State University, Sacramento, CA
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