What is Grades of Concrete ?

As an Civil Engineer you could have come across the mentions of grades of concrete such as :

• M25 concrete for the RCC work in a foundation.
• M20 concrete for the roof slab.
• M15 concrete for PCC works etc.

Have you ever wondered what do these grades of concrete M25, M20, M15 etc really represents ?

These names represents the grade of concrete. In this the grade of concrete is represented by prefixing ‘M’ followed by the number where M stands for mix and number denote the minimum compressive strength of concrete of 15 centimeters cube at 28 days and expressed in Newton per millimeter square(N/mm²). These grade of concrete also represents various mix ratio of cement: fine aggregates: coarse aggregates.

For example : M20 concrete represents mix ratio of 1: 1.5: 3, that is for every one part of cement we should add 1.5 part of sand and 3 part of coarse aggregates is mixed as per Indian Standard Code. There are three major groups of concrete such as ordinary concrete, standard concrete and high strength concrete and there are total of 15 grades of concrete. Different grade of concrete have different compressive strength.

Each grade of concrete represents some mix ratio. In general there are two types of concrete mixes such as nominal mix and design mix. The nominal mixes are those whose mix ratio is defined which includes grades of concrete up to M25. Below table shows the different grades of concrete falling under nominal mix.

The nominal mix grades of concrete are generally used for small-scale construction where concrete consumption is not so high.

Besides the design mix concrete are those whose mix ratio proportions are obtained from various lab tests by considering the various process in concreting properties of concrete and quality of material used for the preparation of concrete. The grade of concrete such as M30 and above come under design mix. Design mixes are generally used for the construction of large structures, where high strength of concrete is required.

Also Read : Cement Concrete Specification for Design Mix 1:2:4