Theory: This test is conducted to calculate the amount of water to be added to the cement to get a paste of standard consistency which 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 mould. This experiment is done with the help of Vicat apparatus (Figure 1). The time taken between adding of water to the cement and filling of mould of Vicat apparatus is called as gauging time which should be between 3 to 5 minutes.
For finding out initial setting time, final setting time, soundness of cement and
compressive strength of cement, it is necessary to fix the quantity of water to be mixed in cement in each case. Since different batches of cement differ in fineness, pastes with some water content may differ in consistency when first mixed. For this reason the consistency of
the paste is standardized by varying the water content until the paste has a given resistance to penetration.
Objective:
Determination of percentage of water by weight of cement required to prepare
a standard acceptable (consistent) cement paste.
Reference:
IS 4031 (Part-4):1988.
Apparatus:
Vicat apparatus conforming to IS: 5513-1998; Weighing balance; Gauging
trowel; measuring cylinder.
Material:
Ordinary Portland cement; Water.
Procedure:
1. Take 400 g of cement sieved through 90 micron IS sieve and keep it on a nonporous, non-absorbent plate.
2. Add 120 ml of water (i.e. 30% by weight of cement) to the cement and mix
thoroughly with two trowels for 3 to 5 minutes till a uniform cement paste is
achieved.
3. Fill the past in mould and level with trowel. Shake or tap to remove air
bubbles.
4. Place the nonporous plate and the mould under the plunger.
5. Release the plunger gently to touch the surface of paste. Record the initial
reading.
6. Release the plunger quickly and allow penetrating into the paste. When the
plunger comes to rest, note the final reading.
7. Repeat the procedure with fresh paste varying the water percentage until the
plunger penetrates to a depth 5 to 7 mm from the bottom of the Vicat mould.
Table
Result:
Percentage of water required to achieve normal consistency of cement paste is ___________.
Precautions:
(Discuss about the precautions to be taken while conducting this experiment)
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Questions:
1. What is meant by normal consistency? Why it is determined.
2. What are the factors which affect the consistency of cement?
3. Discuss the effect of different cement grades on normal consistency.
4. What is gauging time?
