What is the approximate depth of penetration of the plunger in Vicat Apparatus (IS : 5513 – 1976) from the bottom of the Vicat Mould, when the cement paste is tested for standard consistency, according to IS 4031-1988 ?
🔬 Understanding Standard Consistency Test
The standard (or normal) consistency of cement is the specific percentage of water required to make a cement paste of a standard, plastic-like consistency. This test is fundamental because the water content determined here (denoted as 'P') is used as a reference for other important tests like setting time and soundness. The test is performed using the Vicat apparatus, which measures the penetration of a standard plunger into a cement paste.
📝 Detailed Analysis of the Penetration Depth
The key to this question is understanding the dimensions of the Vicat mould and the definition of standard consistency as per IS 4031.
- The height of the Vicat mould is 40 mm.
- Standard consistency is achieved when the 10 mm diameter plunger penetrates to a depth of 33 to 35 mm from the top of the paste.
The question asks for the reading from the bottom of the mould. This can be calculated as:
Distance from bottom = Total height - Penetration from top
(d) 5 to 7 mm
This is the correct answer. Using the formula above:
• For 33 mm penetration from top: 40 mm - 33 mm = 7 mm from bottom.
• For 35 mm penetration from top: 40 mm - 35 mm = 5 mm from bottom.
Therefore, the plunger stops at a height of 5 to 7 mm from the bottom of the mould.
(a) 11 to 15 mm, (b) 8 to 10 mm, & (c) 15 to 17 mm
These are incorrect. These ranges do not match the calculated distance from the bottom based on the standard penetration depth from the top.
📊 Summary: Vicat Test for Standard Consistency
| Parameter | Dimension / Value |
|---|---|
| Vicat Mould Height | 40 mm |
| Vicat Mould Diameter | 80 mm |
| Plunger Diameter | 10 mm |
| Penetration from Top | 33 to 35 mm |
| Reading from Bottom | 5 to 7 mm |
💡 Study Tips
- Top vs. Bottom: Always read the question carefully to see if it asks for penetration "from the top" or the reading "from the bottom". This is a common trick in exams.
- The 40 mm Rule: Remember the mould height is 40 mm. If you know the penetration from the top (33-35 mm), you can always calculate the distance from the bottom by subtracting from 40.
- Visualize the Plunger: Imagine the 40 mm tall mould. The plunger sinks almost all the way down, leaving just a small 5-7 mm gap at the bottom.