COMPRESSION TEST

Updated: May 1, 2020

AIM

To determine the compressive strength of concrete specimens

as per IS: 516 - 1959.

APPARATUS



COMPRESSION TESTING MACHINE

i) Compression testing machine conforming to 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,

calculated from the mean dimensions of the section and should

be expressed to the nearest kg/sq.cm. An average of three

values should be taken as the representative of the batch,

provided the individual variation is not more than ±15% of the

average. Otherwise repeat tests should be done.

A correction factor according to the height/diameter ratio of the

specimen after capping should be obtained from the curve given

below:-



The product of this correction factor and the measured

compressive strength is known as the corrected compressive

strength, this being the equivalent strength of a cylinder having a

height/diameter ratio of two. The equivalent cube strength of the

concrete should be determined by multiplying the corrected

cylinder strength by 1.25.

REPORTING OF RESULTS

The following information should be included in the report on

each test specimen:

i) identification mark

ii) date of test

iii) age of specimen

iv) curing conditions, including date of manufacture of

specimen

v) weight of specimen

vi) dimensions of specimen

vii) cross-sectional area

viii) maximum load

ix) compressive strength

x) appearance of fractured faces of concrete and type of

fracture, if unusual.

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