17-01-2014, 02:59 PM
COMPRESSION TEST
AIM
To determine the compressive strength of concrete specimens
as per IS: 516 - 1959.
AGE AT TEST
Tests should be done at recognized ages of the test specimens,
usually being 7 and 28 days. The ages should be calculated
from the time of the addition of water to the drying of
ingredients.
NUMBER OF SPECIMENS
At least three specimens, preferably from different batches,
should be taken for testing at each selected age.
PROCEDURE
i) The specimens, prepared according to IS: 516 - 1959 and
stored in water, should be tested immediately on removal
from the water and while still in wet condition. Specimens
when received dry should be kept in water for
24hrs. before they are taken for testing. The dimensions of
the specimens, to the nearest 0.2mm and their weight
should be noted before testing.
ii) The bearing surfaces of the compression testing machine
should be wiped clean and any loose sand or other material
removed from the surfaces of the specimen, which would be
in contact with the compression platens.
iii) In the case a of cubical specimen, the specimen should be
placed in the machine in such a manner that the load could
be applied to the opposite sides of the cubes, not to the
top and the bottom. The axis of the specimen should be
carefully aligned with the centre of thrust of the spherically
seated platen. No packing should be used between the
faces of the test specimen and the steel platen of the
testing machine. As the spherically seated block is brought
to rest on the specimen, the movable portion should be
rotated gently by hand so that uniform seating is obtained.
iv) The load should be applied without shock and increased
continuosly at a rate of approximately 140kg/sq.cm/minute
until the resistance of the specimen to the increasing load
breaks down and no greater load can be sustained. The
maximum load applied to the specimen should then be
recorded and the appearance of the concrete and any
unusual features in the type of failure should be noted.
CALCULATION
The measured compressive strength of the specimen should be
calculated by dividing the maximum load applied to the
specimen during the test by the cross - sectional area,