Nominal Mix Concrete Vs Design Mix Concrete
Whereas for design mix skilled person shall be required to prepare the mix design.
Whereas the design mix is more scientific than the nominal mix.
Concrete is made up of mixing cement, sand, aggregate, admixtures and water. The strength, workability and durability of concrete
depend on mixing proportions of its ingredients.
Normally there are two types
of methods which are used for proportioning different ingredients
 Nominal Mix
 Design Mix
Selection of type of concrete
mix depends on the requirement of strength and nature of work. So in this article, we will discuss the differences between nominal mix and design mix of concrete
so let us start
Concept
The nominal mix is the process in which all the ingredients
are prescribed as per specifications and their proportions are specified in the ratio of cement to aggregates for the certain strength achievement.
The proportions
of ingredients in the nominal mix are the same for all the projects. To simplify this
statement let us take an example of M 20 grade concrete.
Its nominal mix
proportion is 1 :1.5:3 it means we have to weight them to 1 kg of cement 1.5 kg
of fine aggregate that is sand and 3 kg of coarse aggregates.
But we normally
take them on a volume basis and multiply them with 1.5 by constant to get the
bulk volume of the material so to conclude this we can say nominal mix
generally contains volumetric batching.
On the other, hand concrete shall be called design mix
concrete when the proportion of its ingredients are decided after trial and
error of various options in the laboratory.
After carrying out tests on
individual ingredients with the object of producing concrete of certain minimum
strength and durability as economically as possible. The proportions of
ingredients in the design mix differ from project to project.
Designation

Concrete
grade

Cement
Kg/m^{3}

C.A.
Kg/m^{3}

F.A.
Kg/m^{3}

Flyash
Kg/m^{3}

Glass
Fibre
Kg/m^{3}

Water
Litre

S.P.
Litre

VMA
Litre

SSC1

365

781

964

156

0

182

13.00

0.46


SSC2

365

781

964

162

0.25

182

13.80

0.46


SSC3

M40

365

781

964

169

0.50

182

14.70

0.47

SSC4

365

781

964

175

0.75

182

15.50

0.47


SSC5

365

781

964

182

1.00

182

16.40

0.48


SSC6

365

781

964

188

1.20

182

17.20

0.48

For example, this is the mix design for M 40 grade concrete
here you can see the quantity of cement, coarse aggregate, fine aggregate and
water is constant but the quantity of fly ash and two admixtures (S.P. & VMA) has
changed in each proportion.
Please note it is not necessary that the quantity
of cement, sand aggregate and water should be constant it can change in each means.
I am showing this picture just for your reference so accordingly the strength
of the concrete cube in 7 days, 14 days and 28 days changes.
Other concrete
properties like durability, workability, surface finish etc also change so as
per strength and project requirements the correct design mix shall be selected
also, you can see here all the ingredients are on a weight basis.
Also, read  What Is Workability of Concrete?
Also, read  What Is Workability of Concrete?
Mixing
The nominal mix is sitelevel mixing small concrete mixer can be
used to mix the ingredients.
whereas the design mix is designed from ready mix concrete
plant that is RMC plant
Tests
For a nominal mix, no laboratory tests are conducted.
whereas the design mix is based on laboratory trialanderror
experiment method.
Attributes of Ingredients
The nominal mix does not consider and check the specific properties
of individual ingredients that are the properties of cement sand and aggregates.
In the nominal mix, we don't actually find the specific gravity of cement, silt content of sand and weight proportions etc.
Whereas in the case of design mix we need to check every property of ingredients and after that, the mix design shall be started.
Properties of ingredients such as in case of cement, cement grade, consistency,
initial setting time, final setting time, specific gravity etc.
In the case of sand
and aggregates density, bulking of sand, specific gravity, grading of aggregate, fineness modulus, particle size, silt content, water absorption, unit weight etc.
Based on
above properties of ingredients, we will establish the Mix design according to
our needs and then check them with trial mix.
Once the trial mix has been tested
and passed on 7th and 28days for compressive strength then it will be approved for
batching and execution at the site level.
Time
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.
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 IS20262 shall be followed.
Skilled persons
For a nominal mix, there is no need of skilled persons.
Whereas for design mix skilled person shall be required to prepare the mix design.
Basis
The nominal mix is based on past experience and has no scientific
approach.
Whereas the design mix is more scientific than the nominal mix.
Strength
The nominal mix may or may not give exactly design strength
unless all other factors like compaction watercement ratio curing of concrete
are strictly followed.
Whereas design mix not only makes concrete of design
strength but also makes it economical too.
Accuracy
In the case of nominal mix watercement 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.
Whereas in the case of design mix, there is no such problem slump
and strength can be related that is for the strength. We can use different slump by
changing the watercement ratio with or without admixtures.
So as to suit concreting of different elements that are for footing, it may have less slump that is less watercement ratio but for thin elements like chajja or thin walls it may need a larger slump that is the higher watercement ratio or more quantity of admixtures this is not possible in the nominal mix.
So as to suit concreting of different elements that are for footing, it may have less slump that is less watercement ratio but for thin elements like chajja or thin walls it may need a larger slump that is the higher watercement ratio or more quantity of admixtures this is not possible in the nominal mix.
Use
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.
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 25and above grades.
Also, read
So, friends, I hope I have covered all the differences
between nominal mix concrete and design mix concrete in this article. If you learn something please
be sure to share it with someone who might benefit from it. If you want to add
any information which has missed in this article you can mention it in the
comment section. Finally, thanks for reading this article.
Also, read
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