Concrete Mix Ratio – Types, Grades & Designs

What Is Concrete Mix Ratio?

Concrete Mix Ratio is the process of finding out the exact proportion of each ingredient of concrete to achieve the desired quality & property of concrete.

As we all know, concrete is a mixture of basic materials like cement, sand, aggregates, and water. Besides these materials, chemical admixtures are also added when there is a requirement for special properties in concrete.

Additional admixtures are always optional, but they do play an important role in enhancing the properties of concrete as per the requirements.

All of the above mention ingredients are mixed in a definite proportion to form the final product, which is fresh concrete. Basically, these proportions are selected in such a way that each set of proportions of materials in concrete determines a specific grade of concrete.

A specific grade of concrete represents a numeric value, which denotes the compressive strength of concrete, achieved after 28 days of construction of a structure from that concrete.

Let us be clearer with an example of an M25 grade concrete mix ratio.

The proportions of M25 grade concrete are as follows:-

• 1:1:2

1 part of cement, 1 part of sand or fine aggregates, 2 parts of coarse aggregates, and the Required quantity of water. Mixing the cement, sand & aggregates in the following proportions will result in M25 grade concrete. But what do you mean by M25?

• M25 represents the grade of concrete where M = mix

• 25 = compressive strength of concrete, achieved after 28 days, which is measured in MPa.

• MPa= Mega Pascal, which is a unit of measurement of compressive strength of concrete in SI units.

Types Of Concrete Mix Ratio

As per IS code 456 – 2000, there are three different types of concrete mix ratios. They are as follows:-

• Nominal concrete mix ratio.
• Standard concrete mix ratio, and
• Design mix ratio.

Let’s discuss each one of them in detail below.

1. Nominal Concrete Mix Ratio

Nominal concrete mix ratios are the proportions of lower-grade concrete. These mixtures are generally used for small & unimportant works which do not require very high strength.

In nominal concrete mix ratios, the quantity of fine aggregates, i.e. the sand, is fixed and the quantities of other materials like cement & coarse aggregate are not fixed.

Due to this reason, the quantity of concrete is not fixed as well as required strength may or may not be acquired. Also, the water-cement ratio is not specified. The grades below M20 are prepared by the nominal mix design method.

Type of concrete	Grade of concrete	Mix ratio	Compressive strength of concrete after 28 days, in MPa.
Ordinary concrete	M5	1:5:10	5 MPa
Ordinary concrete	M7.5	1:4:8	7.5 MPa
Ordinary concrete	M10	1:3:6	10 MPa
Ordinary concrete	M15	1:2:4	15 MPa
Ordinary concrete	M20	1:1.5:3	20 MPa

2. Standard Concrete Mix Ratio

The nominal concrete mix ratios do not have a fixed proportion of materials. So due to that the quality & performance have a variation every time.

For this reason, the minimum compressive strength has been included in many of the specifications. So these types of mixes are known as standard mixes.

Type of concrete	Grade of concrete	Mix ratio	Compressive strength of concrete after 28 days, in MPa.
Standard concrete	M25	1:1:2	25 MPa
Standard concrete	M30	Design mix	30 MPa
Standard concrete	M35	Design mix	35 MPa
Standard concrete	M40	Design mix	40 MPa
Standard concrete	M45	Design mix	45 MPa

3. Design Mix Ratio For Concrete

Designed mix ratios for concrete do not have a fixed proportion of quantity for any of the materials. The materials are taken in a ratio according to the requirements of the quality & and strength of concrete. Any desirable strength of concrete can be achieved using this method.

Also, it is possible to achieve the properties like setting time, workability & desired compressive strength of concrete by adding various additives & admixtures as per the requirements.

Usually, the concrete grades above M45 are prepared using the designed mix & they are also known as high-strength concrete mixes.

The high-strength concrete is used for heavy & important works like the construction of large slabs, piers in bridges, etc. The design mix ratio for concrete is given in the below table.

Type of concrete	Grade of concrete	Mix ratio	Compressive strength of concrete after 28 days, in MPa.
High strength concrete	M50	Design mix	50 MPa
High strength concrete	M55	Design mix	55 MPa
High strength concrete	M60	Design mix	60 MPa
High strength concrete	M65	Design mix	65 MPa
High strength concrete	M70	Design mix	70 MPa

Importance Of A Good Concrete Mix Design

A good mix design creates the formation of a sound structure. So, designing the concrete mix design plays are vital role in defining the quality of concrete manufactured. The strength & the properties are based on the concrete mix design.

So, if the concrete mix is not designed properly, it may lead to the failure of the structure. A good mix design assures that the structure built will be strong enough & will prevent failure.

Factors Affecting The Concrete Mix Design

There are a few factors that affect the strength & durability of the concrete mix design ratio. They are as follows:-

1. Selection Of Cement

There are various types and brands of cement available in the market. It is important to select a quality of cement that best suits for the required grade of concrete; hence does not affect the quality of concrete.

2. Selection Of Aggregates

Different mix does have different properties. These properties are due to the types of materials used in it. So the selection of aggregates of different types depends upon the physical property required for the concrete mix design.

3. Types Of Water Used

The types of water used for mixing the material to form concrete should not be contaminated. It should be clean & free from all the impurities that harm the concrete.

4. Water–Cement Ratio

The water-cement ratio is specified for a particular grade of concrete. If that ratio is not maintained accordingly, then the quality of concrete may get affected in terms of workability, slump & compaction factor.

5.  Workability Of Concrete

The workability of concrete defines the consistency of concrete. The workability of concrete is due to the amount of water added to it.

Approximately 2-3% of the variation in water quantity can cause a variation of 20mm in a slump, which would affect the strength of concrete by 2n/mm^2.

6. Durability Of Concrete

Durability is defined as the ability to resist deterioration due to an aggressive environment. The proportion of each material is responsible for the durability of concrete.

Advantages Of Concrete Mix Design

i) Good Quality: The quality of concrete obtained is better than the nominal mix as the ratio of the quantity of materials is accurate & hence the required strength of concrete can be achieved.

ii) Economical: The nominal mix having no fixed amount of ratio for material may sometimes suggest more cement. On the other hand, the design mix gives a fixed quantity of cement & other materials. So that difference. So that difference helps to save as much as 15 to 20% of the cost.

iii) Using the mix design, one can achieve the desirable properties of concrete, such as workability, strength, durability, and setting time.

Disadvantages Of Concrete Mix Design

i) It requires a set of skilled workers for its manufacturing as accuracy is needed while the concrete is made.

ii) It needs specific attention while it is being prepared. If the desired properties are not achieved, then it may result in the adversity of the structure.

iii) The initial cost of mix design is higher.

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