What Is Mix Design of Concrete?
Concrete mix design involves a process of preparation in which a mix of ingredients creates the required strength and durability for the concrete structure.
The nominal mix specifies the fixed proportion of the cement, sand, and aggregates. Ingredients of concrete are mixed on the basis of volume.
It is a site-level mixing of ingredients to prepare a concrete mix. Such What Is Concrete | 31 Plush Different Types of Concrete mix is generally used in small quantities or where the load is not high.
Nominal Mix Concrete
Nominal mixes offer simplicity and under normal circumstances, have a margin of strength above that specified.
However, due to the variability of mixed ingredients the nominal concrete for given workability varies widely in strength. Nominal mix ratios for concrete are 1:2:4 for M15, 1:1.5:3 for M20 etc.
Design mix is a process to prepare the concrete by testing all necessary properties (like properties of cement, fine aggregate, and coarse aggregate) of concrete ingredients.
Ingredients of concrete are mixed on the basis of weight. It is generally designed from ready Mix Concrete (RMC) plant.
Nominal Mix Ratio and Design Mix Ratio
|M5||Nominal Mix||1:05:10||5 MPa||725 psi|
|M7.5||Nominal Mix||1:04:08||7.5 MPa||1087 psi|
|M10||Nominal Mix||1:03:06||10 MPa||1450 psi|
|M15||Nominal Mix||1:02:04||15 MPa||2175 psi|
|M20||Nominal Mix||1:1.5:3||20 MPa||2900 psi|
|M25||Nominal Mix||1:01:02||25 MPa||3625 psi|
|M30||Design Mix||NA||30 MPa||4350 psi|
|M35||Design Mix||NA||35 MPa||5075 psi|
|M40||Design Mix||NA||40 MPa||5800 psi|
|M45||Design Mix||NA||45 MPa||6525 psi|
|M50||Design Mix||NA||50 MPa||7250 psi|
|M55||Design Mix||NA||55 MPa||7975 psi|
|M60||Design Mix||NA||60 MPa||8700 psi|
|M65||Design Mix||NA||65 MPa||9425 psi|
|M70||Design Mix||NA||70 MPa||10150 psi|
Difference Between Nominal Mix and Design Mix
1. Nominal Mix and Design Mix: Mixing
Nominal Mix: The nominal mix is site-level mixing small concrete mixer can be used to mix the ingredients.
Design Mix: The design mix is designed from a ready-mix concrete plant which is the RMC plant.
2. Nominal Mix and Design Mix: Mix Design
Nominal Mix: There are many grades of nominal mix concrete like M-5, M-7.5, M-10, M-15, and M-20.
Design Mix: A design mix is a process to prepare the concrete by testing all necessary properties (like properties of cement, fine aggregate, and coarse aggregate) of concrete ingredients.
3. Nominal Mix and Design Mix: Tests
Nominal Mix: For a nominal mix, no laboratory tests are conducted.
Design Mix: The design mix is based on the laboratory trial-and-error experiment method.
4. Nominal Mix and Design Mix: Time
Nominal Mix: The nominal mix is easy to make at the construction site. It does not take more time to decide the proportion because proportions are already given in IS456:2000.
Design Mix: Whereas the design mix is very difficult and its process takes more than 30 days, time to find out the most suitable mix for the project for design mix IS-20262 shall be followed.
5. Nominal Mix and Design Mix: Skilled Persons
Nominal Mix: For a nominal mix, there is no need for skilled persons.
Design Mix: Whereas for design mix skilled person shall be required to prepare the mix design.
6. Nominal Mix and Design Mix: Basis
Nominal Mix: The nominal mix is based on past experience and has no scientific approach.
Design Mix: The design mix is more scientific than the nominal mix.
7. Nominal Mix and Design Mix: Strength
Nominal Mix: The nominal mix may or may not give exactly design strength unless all other factors like compaction and water-cement ratio curing of concrete are strictly followed.
Design Mix: Design mix not only makes concrete of design strength but also makes it economical too.
8. Nominal Mix and Design Mix: Accuracy
Nominal Mix: In the case of nominal mix water-cement ratio is considered by the assumption so if we do not take care of it sometimes it leads to bleeding segregation and may make concrete of poor strength and durability.
Design Mix: Whereas in the case of design mix, there is no such problem slump and strength can be related that is for strength. We can use different slumps by changing the water-cement ratio with or without admixtures.
9. Nominal Mix and Design Mix: Use
Nominal Mix: The nominal mix is preferred for simpler relatively unimportant and small concrete works, in other words, the nominal mixes adopted for ordinary concrete work nominal mix may be used for concrete of M 20 grade or lower grade.
Design Mix: Whereas design mixed is used for more extensive and important concrete works design mix can be used for all the grades but it is generally used for M 25 and above grades.