Consistency Test is conducted to find the setting times of cement, viz., initial setting time and final setting time. The test is conducted using a standard consistency test apparatus, viz., Vicat’s apparatus (Fig. 6.6).
Figure 6.6 Vicat apparatus with various plungers
Standard or normal consistency of cement paste is defined as that water content which will permit a Vicat plunger of 10 mm diameter and 50 mm length to penetrate depths of 33–35 mm within 3–5 minutes of mixing. The test has to be repeated thrice. Each time the cement is mixed with water varying from 24 to 27% of the weight of cement. It is required that the test be conducted at a constant temperature of 27 ± 2°C and at a constant humidity of 20%.
The test procedure is simple. The paste prepared within 3–5 minutes is filled into the Vicat mould and shaken to expel air. The standard needle is brought down to touch the surface of the paste and quickly released allowing to sink into the paste by its own weight. The depth of the penetration is noted. Then that percentage of water which allows the plunger to penetrate only to a depth of 33–35 mm is known as the percentage of water required to produce a cement paste of standard consistency.
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