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Cement: Specific Gravity Test
The specific gravity of hydraulic cement is obtained using Le-Chatelier flask shown in Fig. 5.13.
Conditions Affecting Specific Gravity: Long seasonig is the chief cause of a low specific gravity in unadulterated cement. This is because the freshly ground cement when exposed to air rapidly absorbs moisture and carbon dioxide. Cements with high contents of iron oxide have a higher specific gravity. The effect of fineness of grinding upon specific gravity is slight. Very finely ground cements are likely to have lower specific gravities.
Test Procedure: The flask is filled with either kerosene free of water, or naphtha having a specific gravity not less than 0.7313 to a point on the stem between zero and 1-ml mark. The flask is immersed in a constant temperature water bath and the reading is recorded. A weighed quantity of cement (about 64 g of Portland cement) is then introduced in small amounts at the same temperature as that of the liquid. After introducing all the cement, the stopper is placed in the flask and the flask rolled in an inclined position, or gently whirled in a horizontal circle, so as to free the cement from air until no further air bubbles rise to the surface of the liquid. The flask is again immersed in the water-bath and the final reading is recorded. The difference between the first and the final reading represents the volume of liquid displaced by the weight of the cement used in the test.
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