What is meant by the Grade of Concrete?
The grade of concrete is defined as the minimum strength the concrete should have after the completion of 28 days of the construction period with proper quality control. It is denoted by MPa, where M stands for Mix and MPa denotes the overall strength.
For example, for a grade of concrete with a strength of 20 MPa, would be denoted by M20, where M stands for Mix and 20 is the overall strength of the concrete in Newton.
Major ingredients of concrete are binding material (like cement, and lime), fine aggregate (sand), coarse aggregates (crushed stone, jelly), and water.
Depending on the proportion of the material, the strength of the concrete varies. And it is possible to determine the proportion of the ingredients for a particular strength by the mix design procedure.
Different Grades of Concrete
Generally, the grade of concrete is divided into three different categories viz. normal grade of concrete, standard grade of concrete, and high strength grade of concrete. The table below shows the grade of concrete and its mixing ratio and its corresponding compressive strength after 28 days of construction.
Normal Grade of Concrete:
Concrete | Mix Ratio | Characteristic | Characteristic |
|---|---|---|---|
| M5 | 1:5:10 | 05 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:
Concrete | Mix Ratio | Characteristic | Characteristic |
|---|---|---|---|
| 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 Grade of Concrete:
Concrete | Mix Ratio | Characteristic | Characteristic |
|---|---|---|---|
| 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 |
Uses of Different Grades of Concrete
1. Ordinary Grade:
M5, M10, and M15 grades of concrete are mostly used in Plain Cement Concrete (PCC) works as bed concrete below column footing. While M20 grade concrete is used for RCC works (for mild exposure) such as the construction of slabs, beams, columns, footings, etc.
2. Standard Grade:
M25, M30, M35, M40, and M45, fall in the category of the standard grade of concrete. Concrete grades ranging from M25 to M35 are mostly used to construct RCC works such as footings, columns, slabs, beams, etc. Whereas the higher grades like M40 & M45 are used for the construction of commercial structures, pre-stressed concrete members, Runways, Concrete Roads (PQC), Pressurised Concrete Girders, RCC Columns, Pressurised beams, etc.
3. High Strength Grade:
High strength grade of concrete is used in RCC work where high compressive strength is required such as tall buildings, long-span bridges, construction in aggressive environments, spillways of dams, etc.
