Question

In cement concrete mix design, with the increase in water-cement ratio, which one of the following statements is TRUE?

• A. Compressive strength decreases but workability increases
• B. Compressive strength increases but workability decreases
• C. Both compressive strength and workability decrease
• D. Both compressive strength and workability increase

Hint:

Remember Abrams' law: higher water-cement ratio \(\Rightarrow\) lower strength but higher workability.

Answer 1

The Correct Option is A

Step 1: Effect of water-cement ratio on workability.
- Workability of concrete refers to how easily it can be mixed, placed, and compacted without segregation.
- When the water-cement ratio increases, more water is available in the mix, which improves flow and lubrication of particles.
\(\Rightarrow\) Hence, workability increases.

Step 2: Effect of water-cement ratio on compressive strength.
- According to Abrams' law, compressive strength of concrete is inversely proportional to the water-cement ratio.
- Higher water content dilutes the cement paste, increases porosity after hardening, and reduces the bond strength.
\(\Rightarrow\) Hence, compressive strength decreases.

Step 3: Match with options.
- (A) Correct: Strength decreases, workability increases.
- (B) Incorrect: Opposite of the true behavior.
- (C) Incorrect: Workability does not decrease.
- (D) Incorrect: Both do not increase together.
Thus, the true statement is option (A).
\[ \boxed{\text{Compressive strength decreases but workability increases.}} \]