Strength of concrete increases with …………….
Correct Answer: B. Decrease in water cement ratio
📚 Detailed Explanation: Strength and W/C Trend
This is a direct application of Abrams' Law and one of the most fundamental relationships in concrete technology.
Why B (Decrease in w/c ratio) is correct: Abrams' Law: lower w/c = fewer capillary pores = denser paste = higher compressive strength. Option A (increase w/c) is the opposite. Option C (decrease aggregate size) — changing aggregate size affects workability and bond but strength at the same w/c is not governed by aggregate size alone. Option D (decrease curing time) — less curing gives less hydration, so strength would decrease, not increase.
W/C vs. 28-Day Strength (Typical OPC 43 Grade)
| W/C Ratio | Approx. 28-Day Strength (MPa) |
|---|---|
| 0.35 | ~55–65 |
| 0.40 | ~45–55 |
| 0.50 | ~35–45 |
| 0.60 | ~25–35 |
| 0.70 | ~18–25 |
Key Concepts for Students
- Lower w/c = higher strength — the most important single relationship in concrete mix design.
- Adequate curing is also essential: the concrete must remain moist for hydration to continue and develop full strength.