Grades of Concrete

Concrete is graded or designated on the basis of its compressive strength. As per IS456:2000 concrete is graded into fifteen types as given in the table (Table 2, IS456:2000)

Group Designation Compressive Strength (N/mm2)
Ordinary Concrete M10

M15

M20

10

15

20

Standard Concrete M25

M30

M35

M40

M45

M50

M55

25

30

35

40

45

50

55

High Strength Concrete M60

M65

M70

M75

M80

60

65

70

75

80

Concrete grades are expressed by letter M followed by a number. The letter ‘M’ refers to the mix and the number represents the characteristic compressive strength of concrete in N/mm2.

The specified characteristic strength is determined for 150 mm size cube at 28 days.

The characteristic compressive strength of concrete is defined as that strength below which not more than 5 percent of the test results are expected to fall. The various grades of concrete as per their use are listed below:

  1. For R.C.C. work – not lower than M20
  2. For post tensioning works – M35 and above
  3. For pretensioned and prestressed concrete – M40 and above

Concrete of grades lower than M20 may be used for plain concrete works, lean concrete, simple foundations, masonry walls and other simple constructions works.

 

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