Presence of oil in water for concrete:
Try it first: pick an option, then read the explanation.
Correct answer: D. Reduces strength
Detailed Explanation: Effect of Oil in Mixing Water
Why D (Reduces strength) is correct: Oil in mixing water:1. Coats cement particles — forming a film that inhibits hydration of C&sub3;S, C&sub2;S, C&sub3;A, and C&sub4;AF phases.
2. Reduces paste bond strength — oil acts as a barrier at the aggregate-paste interface, reducing bond.
3. Does NOT improve slump — while oil reduces surface tension slightly, its primary effect is chemical interference with cement hydration, not workability improvement.
4. Does NOT give smooth surface — oil causes surface defects and discolouration.
IS 456 specifies that mixing water should be free from oils, salts, acids, alkalis, organic matter, and other contaminants.
Effect of Common Water Contaminants on Concrete
| Contaminant | Effect |
|---|---|
| Oil (petroleum) | Reduces strength (inhibits hydration) |
| Silt / clay | Reduces strength, increases water demand |
| Chlorides | Corrodes reinforcement; may increase early strength |
| Sulphates | Sulphate attack on hardened concrete |
| Sea water | Reduces long-term strength; dangerous for reinforcement |
- Oil in mixing water = reduces concrete strength by inhibiting cement hydration.
- IS 456 mandates potable / clean water for mixing concrete.