Silt content in fine aggregates leads to
- Adecreased permeability
- Bincreased durability
- Cincreased shrinkageCorrect
- Dexcellent bond characteristics
Solution
Concept
Silt and clay in sand increase the water demand of concrete. This leads to more shrinkage and a weaker bond.
Step-by-step solution
1. Silt is a very fine material with a large surface area. 2. A large surface area needs more water for the same workability. 3. More water means more drying shrinkage. 4. Silt also coats the aggregate and reduces the bond with the cement paste. 5. So silt causes increased shrinkage, and the answer is (C).
Explanation
Silt particles are very fine, so they absorb more water and need more mixing water. Extra water causes more drying shrinkage in concrete. Silt also weakens the bond and reduces durability.
Why the other options are wrong
A: Silt does not improve concrete quality, so decreased permeability is not its expected effect. B: Silt reduces durability, it does not increase it. D: Silt coats the aggregate and gives a poor bond, not an excellent one.
Shortcut
Silt is a harmful material, so pick the only bad effect in the options: shrinkage.
Common mistake
Students may think that fine silt fills the voids and makes concrete denner. In fact, it increases water demand and weakens the concrete.
Correct answer: C) increased shrinkage