Pick up the correct statement from the following
Correct Answer: D. All options are correct
📚 Detailed Explanation: Three Roles of Water in Concrete
Water is the second most important ingredient in concrete after cement. It serves multiple essential functions simultaneously — chemical, physical, and rheological — all of which must be satisfied for quality concrete.
Why D (All options are correct) is correct:
Statement A — Water is the reactant in cement hydration. Without water, the silicate and aluminate compounds in cement cannot react to form C-S-H gel (the main strength-giving phase).
Statement B — Water acts as a lubricant between aggregate particles and cement grains, reducing inter-particle friction and giving the mix workability for placement and compaction.
Statement C — Only w/c ≈ 0.23 is needed for complete chemical reactions. The additional water (bringing practical w/c to 0.40+) is for workability, not hydration.
Statement A — Water is the reactant in cement hydration. Without water, the silicate and aluminate compounds in cement cannot react to form C-S-H gel (the main strength-giving phase).
Statement B — Water acts as a lubricant between aggregate particles and cement grains, reducing inter-particle friction and giving the mix workability for placement and compaction.
Statement C — Only w/c ≈ 0.23 is needed for complete chemical reactions. The additional water (bringing practical w/c to 0.40+) is for workability, not hydration.
Functions of Water in Concrete
| Function | Mechanism | W/C Required |
|---|---|---|
| Hydration (chemical) | Reacts with C3S, C2S, C3A, C4AF | ~0.23 (minimum) |
| Gel formation (physical) | Fills gel pores in C-S-H | ~0.19 additional |
| Lubrication (rheological) | Reduces friction, gives workability | ~0.20+ additional |
| Practical total | All three purposes | 0.40–0.60 |
Key Concepts for Students
- Water serves three roles: reactant, gel-former, and lubricant.
- The minimum water for chemistry (w/c=0.23) is far less than the minimum for workability (w/c=0.40+).
- Adding excess water (above workability need) creates capillary pores — every extra litre reduces strength.