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[ Ссылка ] In this tutorial i have discussed briefly the different grades of concrete and their uses in which I have included concrete cube test, groups of concrete grades and uses of concrete grades. After watching the complete lecture, you will know the use of M19,M15,M20,M25 grades in construction work
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The grade of concrete is defined as the minimum strength achieved by concrete after 28 days of construction with proper quality control. The grade of concrete is the designation of concrete according to its compressive strength. According to Indian standards, Concrete grade is generally represented by the letter "M" which is followed by a number (e.g., M20).
The "M" represents the mix design of concrete and the number represents its characteristic compressive strength in N/mm2 at 28 days which is obtained from the concrete cube test.
What is a concrete cube test?
The concrete cube test is performed to determine the compressive strength of a concrete element. The cubes used for this test have a dimension of 150 x 150 x 150 mm.
As per IS 456 2000, Concrete grades are categorized as per their compressive strength based on cube test.
Generally, there are 3 groups of concrete grades.
1) Ordinary concrete:
Which is represented by M10 M15 & M20
2)Standard concrete:
Which is represented by M25, M30, M35, M40, M45, M50 & M55
3) High strength concrete:
which includes M60, M65, M70 & M80
Types of concrete grades and their ratio:
M10:
The M10 grade of concrete includes a mix ratio of 1:3:6 in which 1 part of cement is mixed with 3 parts of fine aggregates or sand and 6 parts of coarse aggregate with an adequate quantity of water having a compressive strength of 10N/mm2 at 28days after mixing.
M15:
This grade of concrete includes a mix ratio of 1:2:4 in which 1 part of cement is mixed with 2 parts of sand and 4 parts of coarse aggregate with a 15N/mm2 compressive strength at 28 days.
M20:
M20 grade contains a mix ratio of 1:1.5:3 in which 1part of cement is mixed with 1.5 parts of fine aggregates/sand and 3 parts of coarse aggregate with compressive strength 20N/mm2 at 28days.
M25:
The mix ratio of M25 grade is 1:1:2 in which 1 part of cement is mixed with 1 part of fine aggregates/sand and 2 parts of coarse aggregates with a compressive 25N/mm2 at 28 days.
The mix ratio for concrete grades above M25 is not specified in the code. Hence, we need to design the proportion of ingredients for such grades of concrete keeping in mind the economy in proportion, strength, and durability based on the construction site.
The proportions resulting from the mix design are tested for their strength with the help of a compressive strength test on concrete cubes.
E.g. for the M30 grade of concrete we need to prepare a design mix ratio and make calculations after performing tests on casted cubes from this mix. If the result exceeds 30N/mm2 then we can adopt such a ratio.
Uses of different grades of concrete:
M10 and M15 are used for PCC (Plain Cement concrete) works such as bedding for footing, leveling course, etc
M20 is used for RCC (Reinforced Cement Concrete) works such as slabs, beams, columns, footings, etc under mild exposure conditions.
M25, M30, M35 grades are used for RCC works like foundations, footings, columns, beams, slabs, etc.
M40 grade is used for prestressed concrete works in slabs, beams, columns, footings, etc.
M45 and M50 grades are used for RCC works in Runways, Concrete roads, prestressed beams, etc
M55 is Used in Pressurised concrete Girders and Piers
M60 & M80 grades are used where there is a need for high compressive strength. Such as in high-rise buildings, long-span bridges, etc. These are used when the constructions are to be done in aggressive environments. These are also used in spillways of dams and in the coastal construction of a passage for surplus water from a dam.
