Generally, concrete is denoted as M20, M25, M30 so on.
They are decided by their requirements. But what exactly M** concrete is?
What is meant by Grade of Concrete?
Grade of concrete is nothing but their compressive strength measurement after 28 days of setting.
Why is it mentioned like M**?
M denotes concrete mix and the number followed by that is known as concrete compressive strength. For instance, M20 means concrete mix ratio that has 20 N/mm2 or Mpa compressive strength.
So M30 means concrete mix ratio that has 30 N/mm2 compressive strength. As simple as that.
Mix Ratio is a proportion of concrete micro-ingredients such as Cement, Sand and Coarse Aggregate.
For Example, M20 means a mix ratio of 1:1.5:3 (1 part cement, 1.5 part sand & 3 part coarse aggregate) concrete which has a compressive strength of 20 N/mm2.
Concrete Grade And Mix Ratio Table
|Type of Concrete||Grade of Concrete||Mix Ratio||Compressive strength of 150mm cube @ 28 Days|
|High Strength Concrete||M55||Design Mix||55|
As you can see from the table, up to M25 only we can do site mixing. Above that is a design mix since we can’t measure materials infractions by hand measurement.
How to select suitable concrete grade for construction?
Selection of concrete depends on the requirement of structural need.
That means it is based on types of loads that are going to act on the structure. It includes
- Dead load
- Live Load
- Earthquake Force
- Snow load
- Wind load
As per IS 456, the recommended minimum grade of concrete for RCC is M20.
|Grade of Concrete||Uses|
|M5, M7.5 – Lean Mix concrete||Used as filling material such as basement filling|
|M10 & M15||Used for PCC and non-structural members such as foundation bed|
|M20||Used for RCC structural members such as beam, column & footing|
|M25||Used for small construction residential or 3 floors residential|
|Other Design Mix||Design mixes are used where high compressive strength is demanded by structure|
Up to M20 grade concrete, we use general types of cement.
There are some other special grades of cement available for specific needs. Like seashore building, industrial concrete, precast works, nuclear power plants. In these areas, special grades of concrete will be used which are chemical resistant, corrosion-resistant.
Happy Learning 🙂