Question

In mix design for M25 concrete, the assumed standard deviation for estimation of target mean strength of concrete mix, as recommended by IS 456 ∶ 2000 is (in N/mm²):
1. 4.5
2. 4.0
3. 5.0
4. 3.5

Answer 1

Correct Answer - Option 2 : 4.0

The assumed value of standard deviation for initial calculations as per IS 456 – 2000 are given below in the table:

Sl. No	Grade of Concrete	Characteristic compressive strength (N/mm2)	Assumed standard deviation (N/mm2)
1.	M10	10	3.5
2.	M15	15
3.	M20	20	4.0
4.	M25	25
5.	M30	30	5.0
6.	M35	35
7.	M40	40
8.	M45	45
9.	M50	50
10.	M55	55