Cement: Specific Gravity Test
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.