Normal Consistency Test By Vicat Apparatus

The normal (standard) consistency of a cement paste is defined as that consistency which will permit a Vicat plunger having 10 mm diameter and 50 mm length to penetrate a depth of 33 to 35 mm from the top (or 5 to 7 mm from the bottom) of the mould.

Vicat Apparatus:

Vicat apparatus assembly consists of a plunger 300 gm in weight with a length of 50 mm and diameter of 10 mm and a mould which is 40 mm deep and 80 mm in diameter.

There are two attachments for the plunger viz:
(i) A square needle with a 1 mm2 cross-section which is attached to the plunger for the initial setting time
test.
(ii) A needle with an annular collar of 5 mm diameter is used for the final setting time.

Test Procedure:

• To prepare the paste, take weighed quantity (300 g) of cement and place it in a crucible.
• Mix a weighed quantity of water (approximately 24% by weight of cement) for the first trial.
• The time of mixing or gauging should not be less than 3 minutes nor more than 5 minutes and gauging time should be counted from the time of adding water to the dry cement until commencing to fill the mould.
• The Vicat mould is filled with the paste, which is levelled off at its top.
• The mould is placed under the Vicat plunger.
• The Vicat plunger is brought down to touch the surface of the paste in the mould and quickly released allowing it to sink into the paste by its own weight.
• Take the reading by noting the depth of penetration of the plunger.
• Similarly, conduct the trials with increasingly water/cement ratios till such time the plunger penetrates for a depth of 33 to 35 mm from the top (or 5 to 7 mm from the bottom).
• That particular percentage of water that allows the plunger to penetrate only to a depth of 33 to 35 from the top (or 5 to 7 mm from the bottom) is known as the percentage of water required to produce a cement paste of normal (standard) consistency.
• This percentage is generally denoted by P.
• This test should be conducted at a constant temperature of 27° +2°C and a constant humidity of 90%.