Which problems are observed during pouring of fresh concrete in hot weather? (i) Rapid hydration (ii) Quick setting and early stiffening (iii) Greater plastic shrinkage (iv) More finishing times
Correct Answer: D. Only (i), (ii) and (iii)
📚 Detailed Explanation: Problems in Hot Weather Concreting
Why D (only i, ii, iii) is correct: Elevated temperature accelerates all hydration-related processes. Statement (iv) about more finishing time is wrong — hot weather actually gives the finisher less time because concrete stiffens faster. All other three effects are real and well-documented adverse consequences of hot weather concreting.
Verification of Each Statement
| Statement | Verdict | Technical Reason |
|---|---|---|
| (i) Rapid rate of hydration | Correct | Higher temperature accelerates the chemical reaction rate of cement hydration (Van't Hoff rule: reaction rate ≈doubles for every 10°C rise) |
| (ii) Quick setting & early stiffening | Correct | Faster hydration leads to earlier and more rapid stiffening, reducing workability life of the mix |
| (iii) Greater plastic shrinkage | Correct | High temperature increases surface evaporation rate; if evaporation rate > bleeding rate, plastic shrinkage cracks form |
| (iv) More finishing time | WRONG | Hot weather gives LESS finishing time — concrete sets faster, leaving a shorter window for surface work |
Full List of Hot Weather Concreting Problems
| Problem | Effect |
|---|---|
| Faster hydration | Higher heat of hydration → thermal cracking risk |
| Rapid slump loss | Workability drops quickly; may need re-tempering (undesirable) |
| Early stiffening | Cold joints form if placement is not continuous |
| Plastic shrinkage cracking | Surface cracks appear before the concrete hardens |
| Higher w/c demand | More water needed for same workability → lower strength |
| Reduced long-term strength | Rapid early hydration leaves less hydration product potential |
| Increased chemical attack risk | Higher temperature accelerates chemical reactions in aggressive environments |
IS 7861 (Part 1) Precautions for Hot Weather Concreting (>40°C)
- Shade aggregates and use chilled/iced water.
- Store cement in a cool area; avoid over-stacking bags.
- Schedule concrete pours in early morning or night.
- Use retarders to extend setting time and maintain workability.
- Cure immediately after finishing — at least three times a day.