Question

As per IS: 456 – 1978, the concrete mixes have been designated into 7 grades. Which one out of the following seven grades (given below) is not the correct grade of concrete mix?

M₁₀₀, M₂₀₀, M₂₅₀, M₁₅₀, M₅₀, M₃₅₀, M₃₀₀

1. M100
2. M50
3. M350
4. M300

Answer 1

Correct Answer - Option 2 : M50

Explanation:

Grade of concrete: As per IS: 456-1978, the different grades of concrete are given as M10, M15, M20, M25, M30, M35, and M40. The letter M denotes the Mix and the numbers 10, 15, 20, 25, 30, 35, 40 represent the predetermined cube strength of 15 cm cube after curing of 28 days in N/mm². The list of specified concrete grades are given below:

Grade of concrete	Specified compressive strength at 28 days ( N/mm2)
M10	10
M15	15
M20	20
M25	25
M30	30
M35	35
M40	40

 

In the question, the value of M100, M200, M250, M150, M50, M350, M₃₀₀ is given in kg/cm², Not in N/mm². Hence the correct answer is option 2 for the question.

Note: M5 and M7.5 concrete mixes also exist which can be used in lean concrete work and for ordinary masonry wall foundation.