For proper workability of concrete, the water cement ratio varies from ………
Correct Answer: C. 0.4 to 0.6
📚 Detailed Explanation: W/C Range for Proper Workability
Workability refers to the ease with which concrete can be mixed, transported, placed, compacted, and finished. The water-cement ratio is the primary lever for adjusting workability, but it has practical upper and lower bounds.
Why C (0.4 to 0.6) is correct: Below w/c = 0.4: insufficient free water to lubricate aggregate particles and cement grains; the mix is harsh, unworkable, and cannot be properly compacted by hand or even vibration without special techniques. Above w/c = 0.6: excessive bleeding and segregation occur; strength drops sharply; durability is compromised. The range 0.4–0.6 covers practical structural concrete. Option A (0.1–0.2) is so dry the mix cannot be placed at all. Option D (0.6–0.8) gives high workability but also high porosity and poor durability.
W/C Ranges and Workability
| W/C Range | Workability | Application |
|---|---|---|
| <0.35 | Very stiff (VB >20 sec) | Precast under vibration/pressure |
| 0.35–0.40 | Stiff (slump 0–25 mm) | Road slabs with vibration |
| 0.40–0.55 | Medium (slump 25–75 mm) | General structural concrete |
| 0.55–0.65 | High (slump 75–125 mm) | Columns, thin walls |
| >0.65 | Very high (slump >125 mm) | Not recommended without admixture |
Key Concepts for Students
- 0.4–0.6 is the standard workability range for hand-mixed and vibration-compacted structural concrete.
- IS 456 specifies a maximum w/c of 0.55 for mild exposure and 0.40 for extreme exposure — both within or at the edge of this range.
- Superplasticisers allow w/c as low as 0.25–0.30 while maintaining workability for high-performance concrete.