It is designation of grades of concrete mix. Letter M refers to the mix and number to specified characteristic compressive strength of 15 cm cube at 28 days expressed in N/square mm. Thus M 15 concrete means a concrete of characteristic strength 15N/square mm. Grades of concrete lower than M 15 shall not be used in reinforced concrete. (Note - N = Newton, mm = milimetre)
Mixing Ratio for Concrete in:
M5
* Mix ratio for M5 concrete is 1:5:10
* compressive strength is 5N/mm2 @ 28 days.
* 1 part of cement, 5 parts of sand, 4 parts of coarse aggregate.
M10
Ratio used in M10 concrete is 1:3:6 1 Cement, 3 Sand & 6 Aggregate
M15
1:2:4
M25
(1:1:2)
M30
1:1:2 (Nominal Mix)
M35
3.15 : 2.62 : 2.67
M- 40 is strongest It depends upon the design mix, . M-40
means its strengthis 40n/mm2
Water: cement: F.A.: C.A. = 0.4: 1: 1.65: 2.92
Strengh of M20 = 20 MPa
Strengh of M25 = 25 MPa
Strengh of M30 = 30 MPa
Strengh of M35 = 35 MPa
Strengh of M40 = 40 MPa