Q.88 Proper experimental knowledge about the porosity and water absorption capacity of a coarse aggregate is required as its affects the durability of concrete because of: I. Freezing and thawing II. Reaction with chemically reactive fluids III. Increasing the workability of concrete
- ABoth (i) and (ii)Correct
- B(i), (ii), and (iii)
- COnly (i)
- DOnly (ii)
Solution
Concept
Porous aggregates with high water absorption reduce durability through freeze-thaw damage and entry of chemically aggressive fluids.
Formula
Water absorption (%) = (Wssd - Wdry) / Wdry × 100
Step-by-step solution
1. Porosity and absorption control how much water or fluid enters the aggregate. 2. Water in the pores freezes and expands, so freezing and thawing causes cracking (I is correct). 3. Pores let chemically reactive fluids enter and attack the aggregate (II is correct). 4. Workability is a fresh concrete property, not a durability cause. High absorption actually reduces workability (III is wrong). 5. So the answer is I and II.
Explanation
Porous aggregates absorb water and fluids. Freezing of this water and attack by chemical fluids reduce the durability of concrete. Workability is not a durability factor, so statement III is wrong.
Why the other options are wrong
B: Includes III, but workability is not a durability factor and high absorption reduces workability. C: Misses chemical attack (II). D: Misses freeze-thaw (I).
Shortcut
Durability effects of porosity = freeze-thaw + chemical attack. Workability is not one of them.
Common mistake
Thinking absorption increases workability. Absorbent aggregate takes mix water and reduces workability.
Correct answer: A) Both (i) and (ii)