Kathmandu University Civil Labs
COMPRESSIVE STRENGTH OF CONCRETE BY CUBE TEST
OBJECTIVE:
To determine the compressive strength of concrete specimens prepared and to verify the strength
requirements as desired in the mix design.
APPARATUS REQUIRED:
1. Compression testing machine.
2. Cube moulds
3. Tamping rod
4. Mixing mould
5. Trowel
THEORY:
The maximum compressive stress that the concrete can resist before failure is called as its compressive
strength. It is many times greater than other stresses in concrete.
It can be easily checked by a standard uni-axial compression test and it is a general index of concrete
strength worldwide.
In order to determine the compressive strength of concrete 3 types of the specimen can be used.
1. Cubes
2. Cylinders
3. Prisms
SPECIMEN
6 cubes of 15 cm size Mix. M15 or above
MIXING
Mix the concrete either by hand or in a laboratory batch mixer
HAND MIXING
(i) Mix the cement and fine aggregate on a watertight none-absorbent platform until the mixture is
thoroughly blended and is of uniform colour
(ii)Add the coarse aggregate and mix with cement and fine aggregate until the coarse aggregate is
uniformly distributed throughout the batch
(iii)Add water and mix it until the concrete appears to be homogeneous and of the desired consistency
PROCEDURE:
(i) Clean the moulds and apply oil
(ii) Fill the concrete in the moulds in layers approximately 5cm thick
(iii) Compact each layer with not less than 35strokes per layer using a tamping rod (steel bar 16mm
diameter and 60cm long, bullet-pointed at the lower end)
(iv) Level the top surface and smoothen it with a trowel
(v)The test specimens are stored in moist air for 24 hours and after this period the specimens are marked
and removed from the moulds and kept submerged in clear freshwater until taken out prior to the test. The
water for curing should be tested every 7 days and the temperature of the water must be at 27 ± 2
oC.
(vi) Remove the specimen from the water after specified curing time and wipe out excess water from the
surface.
(vii) Clean the bearing surface of the testing machine
(viii) Place the specimen in the machine in such a manner that the load shall be applied
to the opposite sides of the cube cast.
(ix) Align the specimen centrally on the base plate of the machine.
(x) Rotate the movable portion gently by hand so that it touches the top surface of the
specimen.
(xi) Apply the load gradually without shock and continuously at the rate of 140kg/cm2
/minute till the
specimen fails
(xii) Record the maximum load and note any unusual features in the type of failure.
NOTE
A minimum of 3 cubes should be tested.
OBSERVATIONS AND CALCULATIONS:
Size of the cube =150mm x 150mm x 150mm
Area of the specimen =225000mm2
For 7 day compressive strength,
specimen Maximum load applied, N Average load, N
1.
2.
3.
Characteristic compressive strength (f ck) at 7 days =
For 28 day compressive strength,
specimen Maximum load applied, N Average load, N
1.
2.
3.
Characteristic compressive strength (f ck) at 28 days =
RESULT:
Average compressive strength of the concrete cube = ............ N/ mm2
(at 7 days)
Average compressive strength of the concrete cube =............. N/mm2
(at 28 days)
CONCLUSION:
Go through above-mentioned drive link for more clarity.
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