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 mm^{2} 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 | |
MPa (N/mm^{2}) | 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
Important Websites for Concrete Engineers
Indian Concrete Institute Official Website
American Concrete Institute Official Website
The Concrete Society – Great Britain
Relevant Posts
IS 456:2000 Plain And Reinforced Concrete-Code of Practice(pdf download)
Criteria For Selection Of The Repair Material
Structural Health Monitoring – Bird Eye View
FAQs-
M20 is the minimum concrete grade for RCC works as per IS 456-2000.
It is the permanent strain in concrete members (particularly RCC member) under constant stress.
The minimum grade for extreme exposure conditions is M40.
ACI 318-19 is code for Structural Reinforced Concrete.