**Compressive strength of M25 concrete after 7 days & 28 days of curing**, hi guys in this article we know about compressive strength of M25 concrete after 7 days, 14 days and 28days of curing.

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 M25 concrete, if it achieve strength 25MPa or 3626 Psi by cube test buy CTM machine, other than it rejected, so compressive strength of M25 concrete is 25MPa or 3626 Psi.

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

**Compressive strength of M25 grade of concrete after 7,14 & 28 days**

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 M25 concrete is denoted by the letter M or C (Europe) stand for mix & followed by numerical figure is compressive strength. Thus compressive strength of M25 concrete is 25N/mm2 (25MPa) or 3626Psi.

**Compressive strength of M25 concrete after 7 days**

Making of at least 3 concrete cube size each 150mm×150mm×150mm in mould by cement sand and aggregate ratio 1:1:2, 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 M25 concrete after 7 days of curing

● **Calculation:** Now concrete cube test by CTM machine,assuming 366 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.

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Compressive load = 366 kN, cross sectional surface area A = 150mm ×150mm = 22500mm2 or 225cm2, then compressive strength F = P/A = 366 kN/22500mm2 = 16.25 N/mm2.

● **Ans**. 16.25 N/mm2 (MPa) or 2357 Psi is compressive strength of M25 concrete after 7 days

**Compressive strength of M25 concrete after 14 days**

Making of at least 3 concrete cube size each 150mm×150mm×150mm in mould by cement sand and aggregate ratio 1:1:2, 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 M25 concrete after 14 days of curing

● Calculation: Now concrete cube test by CTM machine,assuming 506 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 = 506 kN, cross sectional surface area A = 150mm ×150mm = 22500mm2 or 225cm2, then compressive strength F = P/A = 506 kN/22500mm2 = 22.5 N/mm2.

● **Ans**. 22.5 N/mm2 (MPa) or 3263 Psi is compressive strength of M25 concrete after 14 days

**Compressive strength of M25 concrete after 28 days**

Making of at least 3 concrete cube size each 150mm×150mm×150mm in mould by cement sand and aggregate ratio 1:1:2, 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 M25 concrete after 28 days.

● Calculation: Now concrete cube test by CTM machine,assuming 563 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 = 563 kN, cross sectional surface area A = 150mm ×150mm = 22500mm2 or 225cm2, then compressive strength F = P/A = 563 kN/22500mm2 = 25N/mm2.

● **Ans**. 25N/mm2 (MPa) or 3626 Psi is compressive strength of M25 concrete after 28 days

**M25 concrete strength over time: **Relationship between M25 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. M25Concrete Strength Overtime

Days after Casting Strength Gain

Day 1 ____ 16% __ 4MPa

Day 3 ____ 40% __ 10MPa

Day 7 ____ 65% __ 16.25MPa

Day 14 ___ 90% __ 22.5MPa

Day 28 ____ 99% __ 25MPa

As you can see the m25 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 M25 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%

**Concrete cube Test procedure**

a) Measure the dry proportion of ingredients (Cement, Sand & Coarse Aggregate) in ratio 1:1:2 as per the M25 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.

**● 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 563 KN, then Compressive Strength of M25 concrete after 28 days = (563N/22500mm2= 25N/mm2 (20MPa) or 3626 Psi.

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