How does the age of concrete affect its compressive strength? Consider the age limit as 28 days with continued curing.
- ACompressive strength increases upto an age 14 days and continues to decrease on further curing
- BCompressive strength increases as the age of concrete increasesCorrect
- CAge of concrete does not affect the compressive strength of concrete
- DCompressive strength decreases upto an age 7 days and continues to decrease on further curing
Solution
Concept
With continued curing, cement hydration continues, so concrete strength keeps increasing with age.
Step-by-step solution
1. Concrete gains strength by hydration of cement. 2. Hydration continues as long as moisture is available (continued curing). 3. So strength keeps increasing with age: about 65-70% at 7 days, about 90% at 14 days, and 100% (design strength) at 28 days. 4. So compressive strength increases as age increases. Answer is B.
Explanation
Concrete becomes stronger with time because cement keeps reacting with water. With proper curing, strength at 28 days is higher than at 7 or 14 days. Gain continues slowly even after 28 days.
Why the other options are wrong
A: Strength does not decrease after 14 days. It keeps increasing. C: Age clearly affects strength because hydration is time dependent. D: Strength does not decrease in early days. It increases fast in the first 7 days.
Shortcut
Remember 7 days ≈ 65%, 14 days ≈ 90%, 28 days = 100%. Strength always goes up with proper curing.
Common mistake
Thinking strength stops or drops after 14 or 28 days. It only slows down; it does not decrease.
Correct answer: B) Compressive strength increases as the age of concrete increases