The specific gravity is normally defined as the ratio between the weight of a given volume of material and weight of an equal volume of water. The portland cement have a specific gravity of value around 3.15. When it comes to portland pozzolan cements and portland blast furnace cements the value will come near to 2.90 (As per Portland Cement Association (PCA) 1988).
To determine the specific gravity of cement, kerosene which does not recent with cement is used.
Significance of Specific Gravity of Cement
Based on the moisture content present in the cement, the specific gravity can either increase or decrease. The cement particles have pores or particles that can contain water within it. A nominal mix is prepared with a cement of specific gravity 3.15. Any change in this value of specific gravity will affect the mix design. Hence, it is necessary to test the specific gravity of the cement procured before mixing process.
This is the main reason why we ignore the use of old stock cement. Old stock cement may be affected by external moisture content.
A value of specific gravity of cement greater than 3.19 shows that the cement was not properly minced into fine powder during its production or the cement has more moisture content. The presence of moisture content in cement is easily identified by the presence of chunks in cement.
Specific Gravity Test on Cement
Equipment and Apparatus
- Le Chaterlier”s flask
- Weighing balance
- Kerosene (free from water).
- Weighing Balance
Le Chaterlier”s flask, is made of thin glass having a bulb at the bottom. The capacity of the bulb is nearly 250 ml. The bulb is 7.8 cm in mean diameter. The stem is graduated in millimeters.
The zero graduation is at a distance of 8.8 cm from the top of the bulb. At 2 cm from the zero, there is another bulb is of length 3.5cm and capacity of 17 ml. At 1 cm from the bulb, the stem is marked with 18 ml and is grated up to 24 ml. The portion above 24ml mark is in the form of a funnel of diameter 5cm.
Procedure for Specific Gravity Test on Cement
- The flask is allowed to dry completely and made free from liquid and moisture. The weight of the empty flask is taken as W1.
- The bottle is filled with cement to its half ( Around 50gm of cement) and closed with a stopper. The arrangement is weighed with stopper and taken as W2.
- To this kerosene is added to the top of the bottle. The mixture is mixed thoroughly and air bubbles are removed. The flask with kerosene, cement with stopper is weighed and taken as W3.
- Next, the flask is emptied and filled with kerosene to the top. The arrangement is weighed and taken as W4.
Observations and Calculations
Specific Gravity of Cement Sg is given by the formula,
Here, the specific gravity of kerosene is 0.79g/cc
- Duplicate determination of specific gravity should agree within 0.01.
- To get an accurate result, the flask should be held in a constant temperature before each reading is taken.
The specific gravity of a sample of cement =