Clay and silt content in a good brick earth must be at least
Try it first: pick an option, then read the explanation.
Understanding Brick Earth Composition
Good quality brick earth is a balanced recipe of different ingredients. Each component plays a vital role in creating a strong and durable brick. The main constituents are Silica (sand), Alumina (clay), Silt, Lime, and Iron Oxide.
This question focuses on the combined percentage of the two finest particles: Clay and Silt. These ingredients are responsible for giving the brick its plasticity, which allows it to be moulded, and its strength after firing.
Detailed Analysis of the Options
C. 50%
This is the correct answer. For good brick earth, the combined percentage of clay (alumina) and silt should be around 50%. Let's break it down:
- Alumina (Clay): The ideal range is 20-30%. This is the chief ingredient that imparts plasticity to the earth, making it easy to mould.
- Silt: The ideal range is 20-35%. Silt also contributes to plasticity and helps improve the density and strength of the brick.
Adding the lower limits (20% clay + 20% silt = 40%) and the upper limits (30% clay + 35% silt = 65%) shows that a combined content of at least 50% is a perfect requirement for a good quality brick.
A. 20% & B. 35%
These values are too low. If the combined clay and silt content is only 20% or 35%, the earth would be too sandy. It would lack the necessary plasticity to be moulded properly and would result in weak, brittle bricks.
D. 70%
This value is too high. If the clay and silt content is 70% or more, the brick earth would be excessively plastic. This would cause the bricks to shrink, warp, and crack severely during drying and firing.
Ideal Composition of Good Brick Earth
| Constituent | Ideal Percentage | Function |
|---|---|---|
| Silica (Sand) | 50 - 60% | Prevents cracking, shrinking, and warping. |
| Alumina (Clay) | 20 - 30% | Imparts plasticity for moulding. |
| Silt | 20 - 35% | Adds to plasticity and strength. |
| Lime | < 5% | Acts as a flux, helps binding. |
| Iron Oxide | 5 - 6% | Gives red color, improves strength. |
Study Tips
- The 50/50 Rule: A simple way to remember is that good brick earth is roughly 50% fine particles (clay/silt) and 50% coarse particles (sand). This balance is key.
- Too Little Clay = Crumbly: Not enough clay/silt means the brick won't stick together.
- Too Much Clay = Cracks: Too much clay/silt means the brick will shrink and crack as it dries.