Compressive strength of Concrete Cube

Aim
To determine compressive strength of concrete cube specimen.

Apparatus:
Testing Machine The testing machine may be of any reliable type, of sufficient capacity for the tests and capable of applying the load.Cube Moulds The mould shall be of 150 mm size conforming to IS:10086-1982. Cylinders The cylindrical mould shall be of 150 mm diameter and 300 mm height conforming to IS: 10086-1982. Weights and weighing device, Tools and containers for mixing, Tamper (square in cross section).


Theory
Age at Test - Tests shall be made at recognized ages of the test specimens, the most usual being 7 and 28 days. Where it may be necessary to obtain the early strengths, tests may be made at the ages of 24hours ± ½ hour and 72 hours ± 2 hours. The ages shall be calculated from the time of the addition of water to the 63 dry ingredients.
Number of Specimens - At least three specimens, preferably from different batches, shall be made for testing at each selected age.

Procedure :

1. Sampling of Materials - Samples of aggregates for each batch of concrete shall be of the desired grading and shall be in an air-dried condition. The cement samples, on arrival at the laboratory, shall be thoroughly mixed dry either by hand or in a suitable mixer in such a manner as to ensure the greatest possible blending and uniformity in the material.

2. Proportioning - The proportions of the materials, including water, in concrete mixes used for determining the suitability of the materials available, shall be similar in all respects to those to be employed in the work.

3. Weighing - The quantities of cement, each size of aggregate, and water for each batch shall be determined by weight, to an accuracy of 0.1 percent of the total weight of the batch.


4. Mixing Concrete - The concrete shall be mixed by hand, or preferably, in a laboratory batch mixer, in such a manner as to avoid loss of water or other materials. Each batch of concrete shall be of such a size as to leave about 10 percent excess after moulding the desired number of test specimens.

5. Mould - Test specimens cubical in shape shall be 15 × 15 × 15 cm. If the largest nominal size of the aggregate does not exceed 2 cm, 10 cm cubes may be used as an alternative. Cylindrical test specimens shall have a length equal to twice the diameter.

6. Compacting - The test specimens shall be made as soon as practicable after mixing, and in such a way as to produce full compaction of the concrete with neither segregation nor excessive laitance.

7. Curing - The test specimens shall be stored in a place, free from vibration, in moist air of at least 90 percent relative humidity and at a temperature of 27° ± 2°C for 24 hours ± ½ hour from the time of addition of water to the dry ingredients.

Placing the Specimen in the Testing Machine - The bearing surfaces of the testing machine shall be wiped clean and any loose sand or other material removed from the surfaces of the specimen which are to be in contact with the compression plates.

Observations

Sl.
No.

Age
of
Cube

Weight
of
Cement Cube
(gms)

Cross
Sectiona
l area
(mm2)

Load
(N)

Compressive
strength
(N/mm2)

Average
Compressive
strength
(MPa)

1

7 Days

2

3

4

28 Days

 

Result
i) The average 7 Days Compressive Strength of concrete sample is found to be …..…..
ii) The average 28 Days Compressive Strength of concrete sample is found to be …..…..

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