Concrete Mix Ratio and Concrete Grades

Strength of concrete is designated by its grade. As per Indian Standards, concrete grades are denoted like M20, M25, M30, M35 etc. Here, M20 grade concrete is having 20 Newton per mm² strength. And so does for others. These strengths are also known as the characteristic compressive strength of concrete. This is measured at 28 days after casting the concrete.

The necessity and selection of different grades of concrete depends on many factors. Few factors include exposure condition of the concrete, required strength of the concrete, purpose of the structure etc.
M20 means Mix 20, whereas M30 means Mix 30. Strength of concrete is primarily influenced by its mix proportions.

Different Mix Proportions for Different Grade of Concrete

As per Is:456-2012, the following mix proportions are suggested for nominal mix concrete.
The ratio of Cement : Sand : Aggregate

Concrete Grade	Mix Ratio	Compressive Strength
Concrete Grade	Mix Ratio	MPa (N/mm²)	psi
Normal Grade of Concrete
M5	1 : 5 : 10	5 MPa	725 psi
M7.5	1 : 4 : 8	7.5 MPa	1087 psi
M10	1 : 3 : 6	10 MPa	1450 psi
M15	1 : 2 : 4	15 MPa	2175 psi
M20	1 : 1.5 : 3	20 MPa	2900 psi
Standard Grade of Concrete
M25	1 : 1 : 2	25 MPa	3625 psi
M30	Design Mix	30 MPa	4350 psi
M35	Design Mix	35 MPa	5075 psi
M40	Design Mix	40 MPa	5800 psi
M45	Design Mix	45 MPa	6525 psi
High Strength Concrete Grades
M50	Design Mix	50 MPa	7250 psi
M55	Design Mix	55 MPa	7975 psi
M60	Design Mix	60 MPa	8700 psi
M65	Design Mix	65 MPa	9425 psi
M70	Design Mix	70 MPa	10150 psi

Download – IS 10262-2019 [PDF] Guidelines to Concrete mix design

The ratio is often denoted as CSA ratio, also known as cement, sand, and aggregate ratio.

As per Indian Standards, M10, M15 and M20 are recognized as ‘Ordinary Concrete’
M25, M25, and up to M60 grades of concrete are recognized as ‘Standard Concrete’
From M65 to M100 grades of concrete are known as high performance concrete as per IS 456-2000.

Interesting Facts About Concrete Grade and Ratio

In 4th Amendment of IS 456-2000 the M60 grade concrete has been shifted to standard concrete from high strength concrete.
It is advisable to use design mix concrete for M25 or higher grade.
Download this Concrete Mix Design Indian Standard IS:10262-2019 (PDF)
Download IS 456-2000 Design Of Plain And Reinforced Concrete