Compressive Strength Test of Concrete (Cube)

These steps will be followed for the experiment

Preparation of specimens:

  1. Specimens when received dry shall be kept in water for 24 hours before they are taken for testing. Specimen shall be tested immediately on removal from the water whilst they are still wet. Surface water and grit shall be wiped off the specimens and any projecting fins removed from the surfaces which are to be in contact with the packing strips.

Measurement

  1. The mass and dimensions of the specimen shall be noted before testing.

  2. The length of the specimen shall be taken to the nearest 0.2 mm.

Positioning

  1. The bearing surfaces of the testing machine and of the loading strips shall be wiped clean before positioning the specimen.

  2. Place the specimen in the CTM. Cube specimens shall be compressed perpendicularly to the direction of casting.

Rate of Loading

  1. The load shall be applied without shock and increased continuously at a nominal rate of 14 MPa/min.

Failure load

  1. The maximum load applied shall then be recorded. The appearance of concrete and any unusual features in the type of failure shall also be noted.

Assessment of type of failure

If the failure for cube/cylinder specimens is satisfactory or unsatisfactory as shown in the following figures, this fact shall be recorded.

If the failure pattern is unsatisfactory, then the type of failure recorded using the pattern number as shown in the following figures closest to that observed shall be indicated.

Figure. Satisfactory failure of cube specimen


Figure. Unsatisfactory failure of cube specimen

Observations and Calculation:

Average of three values shall be taken as the representative of the batch provided the individual variation is not more than ± 15 percent of the average.
Otherwise repeat test shall be made, however if there is no further sample then the average of two closest values may be taken as the average result.
The compressive strength shall be expressed to the nearest 0.5 MPa.

For _____________-day strength:
Shape of specimen: ______________

No. Length (mm), L. Breadth/Diameter (mm), B/D Cross section area (mm2), Ac Failure (Satisfactory / unsatisfactory) Load at Failure (N), Fu Compressive Strength(N/mm2) fc = Fu/Ac Check 0.85 fca≤fc≤1.15fca
1
2
3
Average: fca
*Corrected Average, fca (if there is no further sample)

Results:

Date of test: ____________________

Shape and size of the specimen in mm: ____________________

Age of specimen at date of test: ____________________

Weight of specimen in Newtons: ____________________

Average Compressive strength: ____________________

Type of failure (satisfactory or unsatisfactory): ____________________

Precautions

  1. Damaged specimens shall not be tested.
  2. The time between the extraction of the specimen from the curing tank until the test shall be as short as possible or not more than 2 hours.
  3. Cube specimens shall be compressed perpendicularly to the direction of casting.