British Standard (BS) provides specifications for various concrete grades. Common grades include C15, C20, C25, C30, C35, C40, C45, etc. The numbers represent the compressive strength of the concrete in megapascals (MPa) at 28 days.
For example:
1. C15 has a characteristic compressive strength of 15 MPa.
2. C20 has a characteristic compressive strength of 20 MPa.
The mix ratios vary based on the grade, and a common mix might include cement, water, coarse aggregates, and fine aggregates.
According to British standard BS, as per BS 8500-2 concrete grade concrete represented as C10, C15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65 and C70. For example, C20, It is indicated as C, which C is stand for concrete mix followed by a numerical figure 20, which is compressive strength of concrete as 20 MPa after 28 days of mixing on axial compression test on cubic concrete block of cube size 15cm × 15cm × 15cm.
Characteristic strength of concrete is their compressive strength which can be determined by axial compression test on cubic concrete block or cylinder shape. If Compression test is carried on cubic concrete block, when tested with cube size 15cm × 15cm × 15cm, that’s known as Cubic test and their strength is called cubic strength. And compression test is carried on cylinder shaped concrete block, when tested with 15cm dia and 30cm length of cylinder, that is known as cylinder test and their strength is called cylinder strength.
Value of cube strength and cylinder strength are different for same mix. Value of cube strength is higher than cylinder strength. Using Thumb Rule, value of cube strength is is 1.25 times higher than cylinder strength.
Cube strength = 1.25 × cylinder strength
British Standard (BS) codes concrete grade generally refers cube test, for finding out compressive strength of different mix of concrete at 28 days after mixing. In this article we read about types of concrete grade and their ratio as per British Standard.
Types of concrete grade and their ratio as per British Standard (BS)
According to British standard (BS), concrete grade is indicated as C20, which C is stand for concrete mix followed by a numerical figure 20, which is compressive strength of concrete as 20 MPa after 28 days of mixing on axial compression test on cubic concrete block of 15cm × 15cm × 15cm.
What are the grades of concrete
As we know that concrete are made of mixing of cement sand and aggregate in required proportion. What are the grades of concrete, according to BS (British standard), the grades of concrete represented as C10, C15 & C20 is known as normal grade of concrete, C25, C30, C35, C40 & C45 is known as standard grade of concrete and C50, C55, C60, C65, & C70 is known as high strength concrete grade.
How many types of concrete grade are there
According to British standard, concrete grade is categorised according to their compressive strength based on cube test and cube strength, generally, there are 3 types of concrete grade -1) normal grade of concrete, which is represented by nominal mix of concrete grade like C10, C15 & C20, C25, (2) standard grade of concrete, which is represented by design mix of concrete grade like C30, C35, C40, C45 and (3) high strength concrete grade, which is represented by design mix of concrete grade like C50, C55, C60, C65, & C70.
Types of concrete grade and their ratio
As per British standard, different types of concrete grade are normal grade of concrete like C10, C15 & C20 and C25 are prepared according to their nominal mix ratio and standard grade of concrete and higher strength concrete grade like C30, C35, C40, C45, C50, C55, C60, C65, & C70 are prepared according to their design mix.
C10 concrete grade mix ratio
For nominal mix, ratio of C10 concrete grade is 1:3:6 by volume, in which one part of Portland stone cement mixed with 3 part of fine aggregate/sand and 6 part of coarse aggregate with required quantity of water to reach compressive strength 10 Newton per square millimetre (N/mm2) or 10MPa at 28 days curing of a concrete cube size 15cm×15cm×15cm.
C15 concrete grade mix ratio
For nominal mix, ratio of C15 concrete grade is 1:2:4 by volume, in which one part is portland stone cement mixed with 2 part of fine aggregate/sand and 4 part of coarse aggregate with required quantity of water to reach compressive strength 15 Newton per square millimetre (N/mm2) or 15 MPa at 28 days curing of a concrete cube size 15cm×15cm×15cm.
C20 concrete grade mix ratio
For nominal mix, ratio of C20 concrete grade is 1:1.5:3, in which one part is Portland stone cement mixed with 1.5 part of fine aggregate/sand and 3 part of coarse aggregate with required quantity of water to reach compressive strength 20 Newton per square millimetre (N/mm2) or 20 MPa at 28 days curing of a concrete cube size 15cm×15cm×15cm.
C25 concrete grade mix ratio
In United kingdom, for nominal mix, ratio of C25 concrete grade is 1:1:2, in which one part is Portland cement mixed with 1 part of fine aggregate/ sand and 2 part of coarse aggregate with required quantity of water to reach compressive strength 25 Newton per square millimetre (N/mm2) or 25MPa at 28 days curing of a concrete cube size 15cm×15cm×15cm.
Different types of concrete grade and their uses
There is three types of concrete grade, normal grade of concrete, standard grade of concrete and high strength concrete grade. Concrete grade is represented as C10, C15 & C20 are normal grade of concrete, C25, C30, C35, C40 & C45 are standard grade of concrete and C50, C55, C60, C65, & C70 are higher strength concrete grade.
C10 concrete grade is used for PCC flooring, patio making, slab and Pathways. Not used for structural work, used for filling, slab for garage, parking, temporary structure, etc.
C15 grade of concrete is used for pavement making, PCC flooring, PCC for garage. C20, C25 and C30 grade of concrete used in all structural work of building construction in RCC beam, column, Foundation,slab and in other RCC structure.
C35, C40 and C45 standard grade of concrete for basement making septic tank, water tank, and it is used in extreme environment condition also. C50, C60 so on concrete are higher strength concrete grade are used in lower floor of high rise building where maximum load is applied and used in extreme environment condition.
Meaning of C16/20 grade of concrete
In C16/20 concrete grade, C refers to concrete strength class, 16 number indicates its characteristics of compressive strength (fck) @28 Days that is 16MPa when tested with 15cm dia & 30cm Length cylinder and numerical figure 20 represents its characteristics of compressive strength (fck) @28 Days curing that is 20MPa when tested with 15cm × 15cm × 15cm cube.
C16/20 concrete mix ratio
C16/20 concrete grade has mix ratio of 1:1.5:3 (1 cement : 1.5 Sand : 3 Stone). This means, 1 bucket of Portland cement mixed with 1 1/2 buckets of Sand and 3 buckets of Stone. In C16/20 grade of concrete, cube’s compressive strength is 20MPa, while cylinder compressive strength is 16MPa.
C16/20 concrete composition for 1 cubic metre
To prepare one cubic meter of C16/20 concrete at 1:1.5:3 volumetric ratio, you would need to mix 8 50kg (403kg) bags of cement with 706kg of Sand, 1302kg of Stone and approximately 200- 220 litres of water.
Meaning of C12/15 grade of concrete
In C12/15 concrete grade, C refers to concrete strength class, 12 number indicates its characteristics of compressive strength (fck) @28 Days that is 12MPa when tested with 15cm dia & 30cm Length cylinder and numerical figure 15 represents its characteristics of compressive strength (fck) @28 Days curing that is 15MPa when tested with 15cm × 15cm × 15cm cube.
C12/15 concrete mix ratio
C12/15 concrete grade has mix ratio of 1:2:4 (1 cement : 2 Sand : 4 Stone). This means, 1 bucket of Portland cement mixed with 2 buckets of Sand and 4 buckets of Stone. In C12/15 grade of concrete, cube’s compressive strength is 15MPa, while cylinder compressive strength is 12MPa.
C12/15 concrete composition for 1 cubic metre
To prepare one cubic meter of C12/15 concrete at 1:2:4 volumetric ratio, you would need to mix 6 1/2 50kg (320kg) bags of cement with 704kg of Sand, 1276kg of Stone and approximately 175- 190 litres of water.
Meaning of C20/25 grade of concrete
In C20/25 concrete grade, C refers to concrete strength class, 20 number indicates its characteristics of compressive strength (fck) @28 Days that is 20MPa when tested with 15cm dia & 30cm Length cylinder and numerical figure 25 represents its characteristics of compressive strength (fck) @28 Days curing that is 25MPa when tested with 15cm × 15cm × 15cm cube.
C20/25 concrete mix ratio
C20/25 concrete grade has mix ratio of 1:1:2 (1 cement : 1 Sand : 2 Stone). This means, 1 bucket of Portland cement mixed with 1 buckets of Sand and 2 buckets of Stone. In C20/25 grade of concrete, cube’s compressive strength is 25MPa, while cylinder compressive strength is 20MPa.
C20/25 concrete composition for 1 cubic metre
To prepare one cubic meter of C20/25 concrete at 1:1:2 volumetric ratio, you would need to mix 11 50kg bags of cement with 624kg of Sand, 1194kg of Stone and approximately 240 litres of water.