Determination of Normal or Standard Consistency of Cement | Vicat Apparatus

Definition of Consistency of Cement

The standard consistency / normal consistency of cement paste is defined as that consistency which will permit a Vicat plunger having 10 mm diameter and 50 mm length to penetrate to a depth of 33-35 mm from the top of the mold. It is the amount of water required to make the cement paste plastic. It is used to find out the initial setting time, final setting time, soundness, and strength of cement.

In case, if less amount of water is added than normal consistency of cement, less water will be available for hydration reaction and un-hydrated cement will left behind. If more amount of water is added to cement, extra water will result in pores in cement. In both the cases strength of the cement will be reduced. Thus standard consistency helps us to choose the right amount of water.

Standards Used

• ASTM C187
• IS 4031 (Part 4) 1988
• BS EN 196-3

Apparatus

1. Vicat apparatus
2. Glass Graduates, 200 mL or 250 mL capacity
3. Balance
4. Flat Trowel
5. Stop Watch, etc.

Materials

• Water
• Cement

Procedure

1. The standard consistency of cement paste is defined as that consistency which will permit the Vicat plunger to penetrate to a point 5 to 7 mm from the bottom of the Vicat mold.
2. Initially a cement sample of about 300 g is taken in a tray and is mixed with a known percentage of water by weight of cement, say starting from 26% and then it is increased by every 2% until the normal consistency is achieved.
3. Prepare a paste of 300 g of Cement with a weighed quantity of potable or distilled water, taking care that the time of gauging is not less than 3 minutes, nor more than 5 min, and the gauging shall be completed before any sign of setting occurs. The gauging time shall be counted from the time of adding water to the dry cement until commencing to fill the mold.
4. Fill the Vicat mold (E) with this paste, the mold resting upon a non-porous plate. After completely filling the mold, smoothen the surface of the paste, making it level with the top of the mold. The mold may be slightly shaken to expel the air.
5. Place the test block in the mold, together with the non-porous resting plate, under the rod bearing the plunger; lower the plunger gently to touch the surface of the test block, and quickly release, allowing it to sink into the paste. This operation shall be carried out immediately after filling the mold.
6. Prepare trial pastes with varying percentages of water and test as described above until such amount of water is achieved which allow the Vicat plunger to penetrate to a depth of 33-35 mm from the top of the mold.

Observations

Express the amount of water as a percentage by mass of the dry cement to the first place of decimal.

Precautions

Following points should be kept in mind while performing consistency of cement test:

• Keep the temperature between 26 ± 2 °C
• Humidity should be 90%
• Avoid vibrations while performing the test
• Clean the plunger after every trial
• Gauging time should be between 3 to 5 min.

Conclusion/Result

The normal consistency of cement of a given sample is _________%

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