What is the meaning of M in M15, M20 etc, grade of concrete?

 

The letter "M" in the grades of concrete M15, M20, etc. stands for "Mix". It refers to the mix design of the concrete, which is the proportion of cement, sand, and aggregate used to make the concrete. The number that follows the "M" represents the characteristic compressive strength of the concrete mixture in megapascals (MPa) after 28 days.

For example, M15 concrete has a characteristic compressive strength of 15 MPa after 28 days. This means that 95% of the concrete cubes made with this mix design will have a compressive strength of at least 15 MPa after 28 days.

The higher the number after the "M", the higher the compressive strength of the concrete. So, M20 concrete has a compressive strength of 20 MPa after 28 days, and M30 concrete has a compressive strength of 30 MPa after 28 days.

The compressive strength of concrete is an important property because it determines how much load the concrete can support. Concrete with a higher compressive strength can support more load, so it is used in applications where high strength is required, such as foundations, columns, and beams.

Here is a table of the different grades of concrete and their characteristic compressive strengths after 28 days:

Grade	Characteristic Compressive Strength (MPa)
M10	10
M15	15
M20	20
M25	25
M30	30
M35	35
M40	40
M45	45