As per IS 10262 : 2019, what is the approximate amount of entrapped air to be expected in normal (non-air-entrained) concrete, when 10 mm Nominal Maximum Size of Aggregate is used in making concrete?
- A1.5%Correct
- B1.0%
- C0.5%
- D2.0%
Solution
Concept
In non-air-entrained concrete, entrapped air decreases as the nominal maximum size of aggregate increases.
Step-by-step solution
1. IS 10262:2019 gives approximate entrapped air for non-air-entrained concrete. 2. Values: 10 mm aggregate = 1.5%, 20 mm = 1.0%, 40 mm = 0.8%. 3. For 10 mm aggregate, entrapped air = 1.5%. 4. Answer is (A).
Explanation
Smaller aggregate gives more surface area and more fine voids, so more air gets trapped. IS 10262:2019 takes about 1.5% entrapped air for 10 mm aggregate. This value is used when finding the volume of aggregates in mix design.
Why the other options are wrong
(B) 1.0% is for 20 mm aggregate. (C) 0.5% is too low and is not a code value for 10 mm. (D) 2.0% is higher than the code value.
Shortcut
Remember 10-20-40 mm = 1.5-1.0-0.8 % air.
Common mistake
Students often take 1.0%, which is the value for 20 mm aggregate.
Correct answer: A) 1.5%