COMPRESSIVE STRENGTH OF CONCRETE CUBES
AIM
To determine the compressive strength of concrete specimens prepared and to verify the strength requirements as desired in the mix design and stipulated in the IS code.
APPARATUS
Compression testing machine
PREPARATION OF CUBE SPECIMENS
Quantity of materials required are calculated as per 6.3
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 water tight none-absorbent platform until the mixture is thoroughly blended and is of uniform color
(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
SAMPLING
(i) Clean the mounds and apply oil
(ii) Fill the concrete in the molds 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 lower end)
(iv) Level the top surface and smoothen it with a trowel
CURING
The test specimens are stored in moist air for 24hours and after this period the specimens are marked and removed from the molds and kept submerged in clear fresh water until taken out prior to test.
PRECAUTIONS
The water for curing should be tested every 7days and the temperature of water must be at 27+-2oC.
PROCEDURE
(I) Remove the specimen from water after specified curing time and wipe out excess water from the surface.
(II) Take the dimension of the specimen to the nearest 0.2m
(III) Clean the bearing surface of the testing machine
(IV) Place the specimen in the machine in such a manner that the load shall be applied
to the opposite sides of the cube cast.
(V) Align the specimen centrally on the base plate of the machine.
(VI) Rotate the movable portion gently by hand so that it touches the top surface of the
specimen.
(VII) Apply the load gradually without shock and continuously at the rate of 140kg/cm2/minute till the specimen fails
(VIII) Record the maximum load and note any unusual features in the type of failure.
NOTE
A minimum of 3 cubes should be tested.
CALCULATIONS
Size of the cube =15cm x15cm x15cm
Area of the specimen (calculated from the mean size of the specimen )=225cm2
Characteristic compressive strength(f ck)at 7 days =
Expected maximum load =fck x area x f.s
Range to be selected is …………………..
Similar calculation should be done for 28 day compressive strength
Maximum load applied =……….tones = ………….N
Compressive strength = (Load in N/ Area in mm2)=……………N/mm2
=……………………….N/mm2
REPORT
a) Identification mark
b) Date of test
c) Age of specimen
d) Curing conditions, including date of manufacture of specimen
f) Appearance of fractured faces of concrete and the type of fracture if they are unusual
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)
Related Posts
COMPRESSIVE STRENGTH TEST ON CONCRETE CYLINDERS
AIM To determine the compressive strength of concrete cylinders. APPARATUS Compression testing...
COMPRESSIVE STRENGTH OF MORTAR CUBES
Take 200gm of cement and 600gm of standard sand in the proportion...
SPLITTING TENSILE STRENGTH TEST ON CONCRETE CYLENDERS
AIM To determine the splitting tensile of concrete. APPARATUS Compression testing machine,...
DETERMINATION OF MODULUS OF ELASTICITY OF CONCRETE
AIM To determine the modulus of elasticity of concrete. SPECIMEN Concrete calender...
SLUMP TEST
To study the workability (determine the consistency) of prepared concrete either in...
