First ofall we make the concrete cube at some mix
proposition as M15,M20.Then after one day the curing on
concrete cube @7days or 28days.then we findout the
compressive strength of concrete.The formula for
compressive strength is breaking load/area of cube.

Cast the cube moulds of size of (150mmx150mmx150mm)
after curing period of 3,7,28 days test under compressive
testing machine.then caclculate result by using formula

Compressive strength =load in newton/Area of cube in mm2
(150x150)

generally compressive testing machine shows load in
Kilonewton so we required Kilonewton convert in to the
Newton.by multiplying kN X 1000 (1N = 1000 kN)

Sample taken from the Concrete mix is First made into
required number of Cubes of nominal dimension (150 mm x 150
mm)and allowed to set for one day. The after removing the
sett cubes from the mould -after attaining final setting,
the cubes are then named with - Grade, Date of casting and
date of testing to be done and then put in curing tank.
Then required number of cubes are taken out on Seventh day
and tested in Compression testing Machine. and the same
process repeated after 28 days.
The Strength achieved is calculated as The Load at
Breakage/The Surface Area of the Cube.
For 7th day test the Strength achieved should be above 70%
of the Grade Strength of the Concrete and 28 th day should
be 120% of the Grade Strength.

Depending upon the quantity of concrete ,the nos of cube
mould is decided .first you finalised the set of cubes the
standard size of ( 150x150mm). after pouring the cubes
moulds , every cubes moulds is filled in required layer by
layer and every layer is tamping by 10 strokes.after
compacted the cubes moulds the following information is
noted on cubes / to maintain the site register for testing
data such as
1. Name of the structure were the cubes will be taken
2. Nos of sets
3. Date of casting
4. Time of casting
5. Grade of concrete
6. 7 days result
7. 28 days result
Then all the cubes moulds shall be pouring into the water
tank for 28 days curing.to calculate the 7 days result
required nos. of cubes mould are taken out and tested in
the COMPRESSION TESTING MACHINE.the same process are
carried out for 28 days.
Compressive strength of concrete = LOAD AT BREAKAGE ON DIAL
GAUGE

SURFACE AREA OF THE CUBES MOULDS

For 7 days test result the strength to be gain by
approximately about 70% of the grade strength of the
concrete and For 28 days test result the strength to be
gain by approximately 100 % of the grade strength of the
concrete. Normally the unit of compressive strength as
KG/SQMM , N/SQMM.
As per thumb rule , at the time of weighing the cubes the
minimum weight of cubes are 8.6 kg .

we can also calculate the Compresive strength of concrete
by using rebound hammer test.this is an one of the NDT test
use at various sites.
in this process top end of rebound hammer kept on the
surface of concrete then giving stroke on surface of
concrete we can get the perticuler reading on bar. same as
above taking no of reading on same concrete surface and by
taking the average of reading we get the compresive
strength of concrete.

as per IS 456 3 cubes are mini req for testing the cubes.
prepare the std size 150x150x150 and mix ratio like
1:1:2.make 3 cubes in same ratio and leave 1 day for setting
after 1 day put on curing.if you need 7 days strength after
7 days test the specimen by using comp machine.in 7 days
specimen attain 65% of the target mean strength.in 28 days
specimen attain 90% of the target mean strength.the unit is
commonly used N/mm^2
1N = 1000 kN
Compressive strength =load in newton/Area of cube in mm2
As per thumb rule , at the time of weighing the cubes the
minimum weight of cubes are 8.1 kg

depending upon quality of concrete,the nos of cube mold are decide.the cube set are stander size 150mm*150mm after pouring the cube mould.every cube mould is filled in required 3 layer&every layer 35 storks given.
the testing data such as:
1.name of the structure were the cube will be taken.
2.date of casting.
3.time of casting.
4.grade of concrete.
5.7 days result.
6.28 days result.
compressive strength= load in newton/area of cube mould(cm2)

Concrete specimens are tested using the ASTM39 Test Standard
Test Method for Compressive Strength of Cylindrical Concrete
Specimens by using two samples made from the same test at
the same age, usually at strength of 28 days old.

For cube test two types of specimens either cubes of 15 cm X 15 cm X 15 cm or 10cm X 10 cm x 10 cm depending upon the size of aggregate are used. For most of the works cubical moulds of size 15 cm x 15cm x 15 cm are commonly used. This concrete is poured in the mould and tempered properly so as not to have any voids. After 24 hours these moulds are removed and test specimens are put in water for curing. The top surface of these specimen should be made even and smooth. This is done by putting cement paste and spreading smoothly on whole area of specimen.

These specimens are tested by compression testing machine after 7 days curing or 28 days curing. Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens fails. Load at the failure divided by area of specimen gives the compressive strength of concrete.

after 28 days we can test the cube if compressive machine show
1000kN on 7.09x7.09cm cube thus t he compressive strenth of cube is calculeted by = load/area
e.g 10000/50 = 20

Is This Answer Correct ?

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Abhinav Gupta

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