Which of the following problems are observed during the pouring of freshly prepared concrete in hot weather? (i) Rapid rate of hydration of cement (ii) Quick setting and early stiffening (iii) Greater plastic shrinkage (iv) More finishing times
- A(i), (ii), (iii), and (iv)
- BBoth (i) and (iii)
- COnly (i)
- DOnly (i), (ii) and (iii)Correct
Solution
Concept
High temperature speeds up hydration and evaporation. This gives quick setting, early stiffening, plastic shrinkage and LESS time for finishing.
Step-by-step solution
1. Hot weather means high air and concrete temperature, plus fast evaporation. 2. (i) Rapid rate of hydration: correct, because heat speeds up the chemical reaction. 3. (ii) Quick setting and early stiffening: correct, because slump is lost fast. 4. (iii) Greater plastic shrinkage: correct, because surface water evaporates fast and causes plastic shrinkage cracks. 5. (iv) More finishing time: wrong. Concrete sets fast, so the time available for finishing is LESS. 6. So (i), (ii) and (iii) are correct. Answer is (D).
Explanation
In hot weather, cement hydrates faster and water evaporates quickly. Concrete sets and stiffens early, and plastic shrinkage cracks increase. Because setting is fast, workers get less time for finishing, not more.
Why the other options are wrong
A: includes (iv), but finishing time actually decreases. B: misses (ii), quick setting is a main problem. C: misses (ii) and (iii), which are also true problems.
Shortcut
Hot weather means everything happens FASTER, so finishing time gets SHORTER.
Common mistake
Students read 'more finishing time' as 'more finishing difficulty' and wrongly select option A.
Correct answer: D) Only (i), (ii) and (iii)