Concrete mix ratio for different grades & characteristic compressive strength of concrete.

What is the grade of concrete?

The grade of concrete is the classification of the concrete according to the characteristic compressive strength of the 150 mm cube in N/mm2 (Mpa) after 28 days of curing.

 The following table shows the concrete mix ratio for the different grades of concrete.

Concrete type	Grade of concrete	Mix ratio	Characteristic compressive strength in N/mm2(Mpa)
Ordinary concrete	M5	1:5:10	5.0
Ordinary concrete	M7.5	1:4:8	7.5
Ordinary concrete	M10	1:3:6	10
Ordinary concrete	M15	1:2:4	15
Ordinary concrete	M20	1:1.5:3	20
Standard concrete	M25	1:1:2	25
Standard concrete	M30	Design mix	30
Standard concrete	M35	Design mix	35
Standard concrete	M40	Design mix	40
Standard concrete	M45	Design mix	45
Standard concrete	M50	Design mix	50
High strength concrete	M55	Design mix	55
High strength concrete	M60	Design mix	60
High strength concrete	M65	Design mix	65
High strength concrete	M70	Design mix	70
High strength concrete	M75	Design mix	75
High strength concrete	M80	Design mix	80

The design mix refers to the ratios which are calculated by the engineer.

Let us now see the full form of M15  with a 1:2:4 ratio
where    M ⇨ Mix

     15⇨Characteristic compressive strength in N/mm2(MPa)

1:2:4⇨cement:sand: coarse aggregate

What is the characteristic compressive strength?

Now, the next question which comes to mind is why the word "characteristic" is used instead of simply using compressive strength? right!

Suppose, we test 100 cubes of M15 grade concrete for its compressive strength after 28 days of curing, then practically there will be chances of the failure of one or two cubes out of the total 100 Nos. In such cases, we ignore the negligible percentage of failures and consider it as a success only. So we call it a characteristic compressive strength due to such considerations.

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Thank you for going through this article❤. Have a good day 😄.

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