For maximum strength, the desired workability of fresh concrete can be attained by which one of the following measures?
- AThe proportion of coarse aggregate may be increased
- BThe proportion of fine aggregate may be reduced
- CThe process of mixing concrete can be repeated second time by the use of vibrators
- DThe quantity of cement may be increased while quantity of water may be reducedCorrect
Solution
Concept
Strength depends on a low water–cement ratio at the required workability
Formula
Strength ∝ 1 / (w/c)
Step-by-step solution
1. Strength is governed mainly by the water–cement ratio. 2. A richer mix with less water (lower w/c) gives higher strength; the required workability is then obtained with the help of the larger paste content (and a plasticiser). 3. The measure that directly lowers w/c is increasing cement while reducing water.
Explanation
For the highest strength the water–cement ratio should be as low as possible while the mix remains workable. Increasing the cement content and reducing the water content lowers the w/c ratio.
Why the other options are wrong
Changing the proportions of coarse or fine aggregate changes workability and water demand but does not by itself reduce w/c. Re-mixing with vibrators is a compaction operation.
Shortcut
Max strength → lowest practical w/c.
Common mistake
Thinking that more coarse aggregate always increases strength.
Correct answer: D) The quantity of cement may be increased while quantity of water may be reduced