Determining Normal Consistency of Cement: Standard Procedure

Experiment No. 1: Normal Consistency of Cement

Objective

To determine the normal consistency of a given sample of cement.

Apparatus

• Vicat apparatus (conforming to IS: 5513-1976)
• Balance
• Gauging trowel
• Stopwatch

Theory

To determine the initial setting time, final setting time, soundness, and strength of cement, a parameter known as standard consistency must be used. The standard consistency of a cement paste is defined as the consistency that permits a Vicat plunger (10 mm diameter and 50 mm length) to penetrate to a depth of 33–35 mm from the top of the mould.

Procedure

1. The standard consistency of a cement paste is defined as the consistency that permits the Vicat plunger to penetrate to a point 5 to 7 mm from the bottom of the Vicat mould.
2. Initially, a cement sample of about 400 g is taken in a tray and mixed with a known percentage of water by weight of cement (starting from 28%, increasing by 2% increments until normal consistency is achieved).
3. Prepare a paste of 400 g of cement with a weighed quantity of potable or distilled water. Ensure the gauging time is between 3 and 5 minutes, and complete the process before any signs of setting occur. The gauging time is counted from the moment water is added to the dry cement until the mould is filled.
4. Fill the Vicat mould with the paste, ensuring the mould rests on a non-porous plate. After filling, smoothen the surface level with the top of the mould. The mould may be slightly shaken to expel trapped air.
5. Place the test block in the mould, along with the non-porous resting plate, under the rod bearing the plunger. Lower the plunger gently to touch the surface of the test block, then quickly release it to allow it to sink into the paste. This operation must be performed immediately after filling the mould.
6. Prepare trial pastes with varying percentages of water and repeat the test until the amount of water necessary for standard consistency is achieved.

Observation

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

Engineering and Engineering Mechanics