Compressive strength test of concrete -step by step procedure 

Apparatus

the compressive testing machine should be reliable, of sufficient capacity and able to apply the load at approx 140 kg/ SQ cm per minute. The permitted error should be limited to maximum +/- 2 % of maximum load.

Age at test

compressive strength testing shall be done at definite age the most common being 7,15 and 28 days. In case of urgency to calculate strength, the test may be done after 24 hours (+ / – 1/2 hours) and 72 hours ( + / – 2 hours). It is to be noted that the age of the specimen is calculated from the time of adding water to concrete ingredient.

Number of Specimens — At least three specimens, preferably from different batches, shall be made for testing for each selected age.

procedure for determining compressive strength test of concrete

1.The test specimen shall be immediately removed and tested while it is in wet condition. Excess water shall be wiped off. If test specimen is received in dry condition from outside, it shall be immersed in water for 24 hours before testing. The dimension with accuracy nearest to 0.2 mm and weight shall be noted.

2. Wipe clean both the bearing plates of the machine and place the test specimen at the centre such a manner that load shall be applied to the face opposite to top face while casting of the test specimen.

3.The load shall be applied gradually at a rate of approximately 140 kg/SQ cm per minute. When test specimen fails, maximum load applied shall be noted.

4. Calculate compressive strength of concert as per following

compressive strength = load applied / cross sectional area

5.Average of three samples are taken as the compressive strength for particular batch If variation with individual test result with average strength is more than 15 %, the whole test shall be repeated.

6.Compressive test report shall be prepared which shall include following data

a) identification mark,

b) date of test,

c) age of specimen,

d) curing conditions, including date of manufacture of the specimen in the field,

e) weight of the specimen,

f) dimensions of the specimen,

g) cross-sectional area,

h) maximum load,

j) compressive strength, and

k) appearance of fractured faces of concrete and type of fracture if these are unusual.