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In this article, we will discuss the difference between nominal mix and design mix.
Concrete is the composite material that is composed of a mixture of fine and coarse aggregates bonded together with biding material which hardens over time. The binding material mostly includes fluid cement paste, lime putty, lime, etc. In simple language, Concrete is a mixture of cement, sand, aggregates, and water.
1. Nominal Mix
In the nominal mix concrete, cement, sand, and aggregates are utilized in the required ratio or conditions. For the needed strength to attain, these ratios are defined in the ratio of cement to aggregate.
In a nominal mix, a ratio of all the ingredients of concrete-like cement, and aggregates are kept fixed. The ratio of water to cement in the nominal mix is taken by need. So, if the w/c ratio is not considered with care then it may result in segregation or bleeding of concrete which eventually affects the strength and durability of the concrete.
Nominal mix concrete is utilized for concrete of M20 grade or lower grade that can be M15, M10, M5, etc. They are utilized or acquired for lower grade concrete or if we wish to construct structures of comparatively less essential or have a very low load. The ratio of different grades of cement is provided on a table.
Where ‘M’ denotes Mix whereas the number (20,15,10,7.5, 5) shows the compressive strength of the concrete after 28 days of curing in N/mm2.
For M15, the ratio of ingredients is: 1(cement) : 2(fine aggregate or sand) : 4(coarse aggregate).
2. Design Mix
Design mix may be defined as the method of making the concrete mix in which concrete of needed strength is acquired by calculating the proportion of ingredients correctly with their relative ratio. Before acquiring a design mix of concrete, testing of all the ingredients like cement, and fine and coarse aggregate is compulsory.
For example, if we want to get a concrete grade of M30, then we will prepare at least 4 trial mixes of various ratios of all the ingredients in the lab based on computation or theoretical ideas. After 28 days, all the mixes are noticed and their strength and a grade are calculated.
The near result is taken and the same ratio of ingredients is utilized to prepare the concrete mix throughout the full project. In the design mix, slump and strength can be associated i.e. for the strength we can utilize various slumps by switching the water-cement ratio with or without admixtures to match the concreting of various elements.
For example: for thin walls like chajja, a bigger slump is needed i.e. higher water-cement ratio. For structures like footing, it needs less slump i.e. lower water-cement ratio. There are various grades of design mix concrete such as M25, M30, M35, M40, etc. They are utilized to make high-grade concrete.
Where ‘M’ denotes Mix whereas the number with M (40,35,30,25) shows the compressive strength of the concrete after 28 days of curing in N/mm2.
For M25, the ratio of ingredients is: 1(cement) : 1(fine aggregate or sand) : 2(coarse aggregate).
3. Difference Between Nominal Mix and Design mix
The difference between nominal mix and design mix is as follows:
|S.No||Nominal mix||Design mix|
|1.||For the nominal mix, specific features of individual ingredients are not taken or examined.||For the design mix, all features, and characteristics of materials should be taken and examined.|
|2.||All the materials of concrete are blended depending on volume.||All the materials of concrete are blended based on weight.|
|3.||It is utilized for normal concrete works or in minor areas.||They are utilized for fixed or specific areas based on the desire.|
|4.||They are utilized for concrete of M-20 grade or less than M-20 grade||They are utilized for concrete more than M-25 grade like M-40, M-35, M-30, M-25, etc.|
|5.||They are site-level mixing. A minor concrete mixture can be utilized to blend the ingredients.||They are calculated from a ready mix concrete plant.|
|6.||They are not scientific, as they are based on depending upon past experiences and past observed studies.||They are more scientific than that the nominal mix.|
|7.||For the nominal mix, no laboratory tests are carried out.||Laboratory tests are performed as they are depending on the laboratory trial and error test method.|
|8.||They are uncomplicated to prepare and are not time-consuming.||They are hard to prepare and take more than 30 days to calculate the best mix for the project.|
|9.||The ratio of water to cement is taken by considering experience.||Water is utilized in the actual amount according to the strength needed for the project or the grade of concrete needed.|
|10.||A skilled person is not needed to make a nominal mix.||A skilled person is important to make a design mix.|
|11.||They are utilized in less amount or where the load is not very large.||They are utilized in heavy structures or where the load is very large.|
|12.||They possess less strength and are not long-lasting.||They satisfy high durability and strength.|
This was the major difference between nominal mix and design mix of concrete.
|Read Also: Cement Plaster|
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