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Title: Precision of quartz crystal and mercury differential thermometers in heat-of-hydration test
Authors: United States. Assistant Secretary of the Army (R & D)
Pepper, Leonard.
Keywords: Calorimeters
Heat of hydration
Heat of solution
Portland cements
Issue Date: Jul-1969
Publisher: Concrete Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; C-69-11.
Description: Miscellaneous paper
Abstract: The precision of a quartz crystal thermometer was directly compared with that of a mercury differential thermometer in the determination of the heat of solution of a type II low-heat portland cement and a hardened paste made with the cement. Test procedures prescribed in Method 3101.1 of Federal Test Method Standard No. 158a were followed. The standard calorimeter apparatus was altered to permit (a) the insertion of one crystal probe into the calorimeter and a second crystal probe into the thermal jacket of the calorimeter and (b) the storage of the sample within the calorimeter enclosure. The calorimeter temperature rise was determined during solution of zinc oxide, dry cement, and 7-day hydrated paste. Three rounds were conducted for each material and four runs were made per round. Only one round was made on any one day. The heat-of-hydration test results, whether obtained with the quartz crystal thermometer or the differential thermometer, calculated using the alternate or the regular method of the Federal Standard, were essentially the same. The test precision obtained using the quartz crystal thermometer was far poorer than expected, due to its low thermal mass in contrast to the high thermal mass of the rest of the calorimeter system. It is concluded that improved precision would require a low thermal mass calorimeter and closely controlled ambient temperature. The precision obtained with the differential thermometer was better than expected and was improved by storage of the sample within the calorimeter enclosure. The test results indicated that calibrated differential thermometers are not needed for this test procedure. The test results also indicated that properly prepared zinc oxide does not dissolve at the same rate as dry cement, but dissolves at a rate two to three times as fast as the dry cement.
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