# Compressive strength of M20 concrete -cube Test procedure

The compressive strength of M20 concrete after 7 days is typically around 65% of its 28-day strength. For M20 grade concrete, the target compressive strength at 28 days is approximately 20 megapascals (MPa). Therefore, you can expect the compressive strength after 7 days to be around 13 MPa

Compressive strength of M20 concrete -cube Test, procedure & result, hi guys in this article we know about compressive strength of M20 concrete cube Test, procedure and result.

As we know compressive strength is measured by compressive strength test machine (CTM). Compressive strength is defined as ratio of load applied by CTM machine on concrete cube or cylinder to surface area of concrete cube. Compressive strength is represented by F which is equal to F = P/A, where F = compressive strength,P= total load applied by CTM machine & A = cross sectional surface area.

Generally strength of concrete measured in psi (pound force per square inch in USA) & MPa (mega pascal) in India and other country. MPa in another terms represented as N/mm2. And 1MPa = 145.038 psi. In this topic we have to find compressive strength of M20 concrete, if it achieve strength 20MPa or 2900 Psi by cube test buy CTM machine, other than it rejected, so compressive strength of M20 concrete is 20MPa or 2900 Psi.

Overall Strength of a concrete structure such as flexural resistance and abrasion directly depends upon the compressive strength of concrete.

## Compressive strength of M20 grade of concrete

This strength is measured by CTM testing Standard 15cm larger & 10cm smaller cubes in India and standard cylinder specimens dai 15cm & height 30cm in USA and a few other countries.

● ALSO READ: COMPRESSIVE STRENGTH OF CEMENT

The grade of M20 concrete is denoted by the letter M or C (Europe) stand for mix & followed by numerical figure is compressive strength. Thus compressive strength of M20 concrete is 20N/mm2 (20 MPa) or 2900 Psi.

### Compressive strength of M20 concrete at 7 days, 14 days and 28 days

The compressive strength of M20 concrete is approximately 8 MPa (1160 psi) at 3 days, approximately 13 MPa (1900 psi) at 7 days, approximately 18 MPa (2600 psi) at 14 days, and approximately 20 MPa (2900 psi) at 28 days.

As per IS code the cube strength achieved by the M20 concrete in 7 days is about 13 MPa, in 1 day is about 3.2 MPa, in 3 days is about 8 MPa, in 14 days is about 18 MPa, in 21 days is about 18.8 MPa and in 28 days is approximately 20 MPa.

### Compressive strength of M20 concrete at 7 days

Making of at least 3 concrete cube size each 150mm×150mm×150mm in mould by cement sand and aggregate ratio 1:1.5:3, use tamping rod for levelling the surface of mould, it is kept for 24 hours setting after water mix in concrete, after 24 hours it is kept in water for curing for 7 days. And taken out just before test 7 days to find out compressive strength of M20 concrete at 7 days.

Calculation: Now concrete cube test by CTM machine,assuming 304 kN load is applied on concrete cube till the cube collapse. The maximum load at which the specimen breaks is taken as a compressive load.

Compressive load = 304 kN, cross sectional surface area A = 150mm ×150mm = 22500mm2 or 225cm2, then compressive strength F = P/A = 304 kN/22500mm2 = 13.5 N/mm2.

Now question is what is compressive strength of M20 concrete at 7 days of curing? Their answer will be following:

The compressive strength of M20 concrete is approximately 13.5 MPa (1958 psi) at 7 days. To calculate the compressive strength of M20 concrete used the formula:- F = P/A, compressive load = 304 kN, cross sectional area A = 150mm ×150mm = 22,500 mm^2, then compressive strength = 304 /22,500 = 13.5 N/mm^2.

### Compressive strength of M20 concrete at 14 days

Making of at least 3 concrete cube size each 150mm×150mm×150mm in mould by cement sand and aggregate ratio 1:1.5:3, use tamping rod for levelling the surface of mould, it is kept for 24 hours setting after water mix in concrete, after 24 hours it is kept in water for curing for 14 days. And taken out just before test 14 days to find out compressive strength of M20 concrete at 14 days.

● Calculation: Now concrete cube test by CTM machine,assuming 405 kN load is applied on concrete cube till the cube collapse. The maximum load at which the specimen breaks is taken as a compressive load.

Compressive load = 405 kN, cross sectional surface area A = 150mm ×150mm = 22500mm2 or 225cm2, then compressive strength F = P/A = 405 kN/22500mm2 = 18 N/mm2.

Now question is what is compressive strength of M20 concrete at 14 days of curing? Their answer will be following:

The compressive strength of M20 concrete is approximately 18 MPa (2611 psi) at 14 days. To calculate the compressive strength of M20 concrete used the formula:- F = P/A, compressive load = 405 kN, cross sectional area A = 150mm ×150mm = 22,500 mm^2, then compressive strength = 405 /22,500 = 18 N/mm^2.

### Compressive strength of M20 concrete at 28 days

Making of at least 3 concrete cube size each 150mm×150mm×150mm in mould by cement sand and aggregate ratio 1:1.5:3, use tamping rod for levelling the surface of mould, it is kept for 24 hours setting after water mix in concrete, after 24 hours it is kept in water for curing for 28 days. And taken out just before test 28 days to find out compressive strength of M20 concrete at 28 days.

Calculation: Now concrete cube test by CTM machine,assuming 450 kN load is applied on concrete cube till the cube collapse. The maximum load at which the specimen breaks is taken as a compressive load.

Compressive load = 450 kN, cross sectional surface area A = 150mm ×150mm = 22500mm2 or 225cm2, then compressive strength F = P/A = 450 kN/22500mm2 = 20N/mm2.

Now question is what is compressive strength of M20 concrete at 28 days of curing? Their answer will be following:

The compressive strength of M20 concrete is approximately 20 MPa (2900 psi) at 28 days. To calculate the compressive strength of M20 concrete used the formula:- F = P/A, compressive load = 450 kN, cross sectional area A = 150mm ×150mm = 22,500 mm^2, then compressive strength = 450 /22,500 = 20 N/mm^2.

● ALSO READ: COMPRESSIVE STRENGTH OF BRICK

●M20 concrete strength over time: Relationship between M20 concrete strength according to time is not linear, it means increasing strength is not increases according to applied load as time increases,it will increase in nonlinear.

Concrete is a macro content with Sand, Cement, & Coarse aggregate as its micro-ingredient (Mix Ratio) and gains its 100% strength over time at the hardened state.

Take a look at the below table. M20 Concrete Strength Overtime

Days after Casting Strength Gain
Day 1 ____ 16%  ___  3.2MPa
Day 3 ____ 40% ____ 8MPa
Day 7 ____ 65% ___ 13.5MPa
Day 14 ___ 90% ____ 18MPa
Day 28 ____ 99% ____ 20MPa

As you can see the m20 concrete gains its strength rapidly till 7th & 14th Days upto 90% after curing, then gradually increases from there. So we can’t predict the strength until the concrete comes to that stable state.

Once it attains certain strength at 7 days, then we know (according to the table) only 9% of strength going to increase. So at sites, we do normally test concrete at this interval. If the concrete fails at 14 days, then we will reject that batching.

## Compressive strength of M20 concrete cube test

Concrete cube test Apparatus for procedure and result completed in following steps:

● 1) IS code:- this concrete cube test it is completed according to IS code 516

● 2) Required Equipment & Apparatus:

a) Tamping rod:- tamping rod is used for levelling the surface of concrete cube mould, it is 16mm Dia and 60cm in length.

b) CTM machine : CTM machine is required for load applying on concrete cube mould, it should be apply minimum load of 14N/mm2/minute.

c) THREE type of mould: there is two size of concrete cube mould is used for test, first is larger size of 150mm or 15cm have specific dimension (l×b×h) is 150mm×150mm×150mm with aggregate size is 38 mm and second smaller size concrete cube mould size is 100mm×100mm×100mm with aggregate size 19mm used in India.

In USA and other country cylindrical concrete mould is also used have dia 150mm, height 300mm & aggregate size is 38mm.

d) other Apparatus is G.I Sheet (For Making Concrete),Vibrating Needle, tray & other tools.

● 3) Environmental factors:- for standard calculation of compressive strength of concrete environmental factors should be optimum, minimum number of test specimen should be 3, temperature should be 27± 2℃ and humidity is 90%

### M20 Concrete cube Test procedure

a) Measure the dry proportion of ingredients (Cement, Sand & Coarse Aggregate) in ratio 1:1.5:3 as per the M20 concrete. The Ingredients should be sufficient enough to cast test cubes.

b) first mix cement and sand till it got uniform colour then added aggregate in it, thoroughly mix the dry ingredients to obtain the uniform colour of mixture and Add design quantity of water to the dry proportion (water-cement ratio) and mix well to obtain uniform texture

c) Fill the concrete to the mould with the help of vibrator and used tamping rod for thorough compaction and levelling the surface of concrete cube mould,Finish the top of the concrete by trowel & tapped well till the cement slurry comes to the top of the cubes.

d) After some time the mould should be covered with red gunny bag and put undisturbed for 24 hours at a temperature of 27± 2℃,After 24 hours remove the specimen from the mould.

e) Keep the specimen submerged under fresh water at 27± 2℃ for curing, the specimen should be kept for 7,14 or 28 days. Every 7 days the water should be renewed. The specimen should be removed from the water 30 minutes prior to the testing and the specimen should be in dry condition before conducting the testing. The Cube weight should not be less than 8.1 Kgs.

● 5) Testing of concrete cube: Now place the concrete cubes into the (CTM) testing machine at centre. The cubes should be placed correctly on the machine plate (check the circle marks on the machine). Carefully align the specimen with the spherically seated plate. The load will be applied to the specimen axially.

Now slowly apply the load at the rate of 14N/mm2/minute till the cube collapse.
The maximum load at which the specimen breaks is taken as a compressive load.

● 6) Calculation:
Compressive Strength of concrete = Maximum compressive load / Cross Sectional Area

Cross sectional Area = 150mm X 150mm = 22500mm2 or 225 cm2

Assume the compression load is 450 KN,

Compressive Strength = (450N/22500mm2= 20N/mm2 (20MPa) or 2900 Psi.

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