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Compressive strength of concrete cube.

Theory and Computations: This page exhibits online editable lab manual for compression testing of concrete cube. The dimensions like length and breadth of cube are noted down in millimetre. The compression strength of concrete cube is evaluated by dividing failure load to loaded area of cube. The result will be exhibited in MPa.

Calculator tab: The calculator tab consists of editable page and online calculator for compressive strength of concrete cube. In this concrete cube data can be entered for 7, 14, 21, and 28 days, This page calculates average compressive strength from the provided input values. A graph of compression strength vs curing days will be plotted for better understanding of quality of concrete.

Determination of compressive strength of cube concrete Specimens

Aim:

To determine the cube compressive strength of the specified concrete mix proportion.

Reference Indian standard codes:

• IS: 516-1959.
• IS: 1199-1959.
• SP: 23-1982.
• IS: 10086-1982.

Equipment's Required:

• Compression testing Machine: The testing machine may be of any reliable type, of sufficient capacity for the tests and capable of applying the load at the rate of 14 N/mm² per minute. The permissible error shall be not greater than ± 2 percent of the maximum load.
• Cube moulds:The mould shall be of 150 mm size conforming to IS: 10086-1982.
• Weighing balance.
• Tamping rod.
• Rubber gloves.
• Metallic sheet.
• Demoulding oil.

Theory:

One of the important properties of concrete is its strength in compression. The strength in compression has a definite relationship with all other properties of concrete i.e. these properties improved with the improvement in compressive strength. With this test we can estimate concrete quality. The cubical moulds of size 15cm x 15cmx 15 cm are used for finding compresion strength. The concrete is prepared with definite proportion is poured in the mould and tempered with tamping rod to minimize air voids. After 24 hours these moulds are removed and test specimens are put in water for curing. The top surface of this specimen should be made even and smooth. This is done by putting cement paste and spreading smoothly on whole area of specimen. These specimens are tested by compression testing machine after 7 ,14 21 and 28 days curing. Load should be applied gradually at the rate of 14 N/mm² per minute till the Specimens fails. Load at the failure divided by area of specimen gives the compressive strength of concrete. At least three specimens are tested at each selected age. Equation for compressive strength of cube, σ_cube is

\[\mathop \sigma \nolimits_{cube} = \frac{F}{A}\]

Where,

• σ_cube = Compressive strength of cube (N/mm² Or MPa).
• F = Failure load (N).
• A = Loaded area of cube (mm²).

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 15x15x15 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.
8. 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 platens.
9. In the case of cubes, the specimen shall be placed in the machine in such a manner that the load shall be applied to opposite sides of the cubes as cast, that is, not to the top and bottom.
10. The axis of the specimen shall be carefully aligned with the center of thrust of the spherically seated platen. No packing shall be used between the faces of the test specimen and the steel platen of the testing machine.
11. The load shall be applied without shock and increased continuously at a rate of approximately 140 kg/cm²/min until the resistance of the specimen to the increasing load breaks down and no greater load can be sustained.
12. The maximum load applied to the specimen shall then be recorded and the appearance of the concrete and any unusual features in the type of failure shall be noted.

Observations:

Sl.No.	Description.	Particulars.
1.	Type of cement.
2.	Specific gravity of cement.
3.	Type of sand.
4.	Specific gravity of sand.
5.	Fineness modulus of sand.
6.	Type of coarse aggregates.

Concrete mix proportions:

Sl.No.	Description.	Proportion for 1m3.	Proportion for batch mixing.
1.	Cement (Kg).
2.	Coarse aggregates (Kg).
3.	Fine aggregates (Kg).
4.	water (Kg).
5.	Aggregate/Binder ratio.
6.	Water/Cement ratio.
7.	Admixture.

Compression test data sheet:

Specimen No.	Days Cured.	Length of cube mm.	Breadth of cube mm.	Area mm2.	Load kg.	Load N.	Stress MPa.
1.	7
2.	7
3.	7
Average :
4.	14
5.	14
6.	14
Average :
7.	21
8.	21
9.	21
Average :
10.	28
11.	28
12.	28
Average :

Conclusion:

1. The average 7 Days Compressive Strength of concrete = ____________.
2. The average 14 Days Compressive Strength of concrete = ____________.
3. The average 21 Days Compressive Strength of concrete = ____________.
4. The average 28 Days Compressive Strength of concrete = ____________.

Viva Questions:

1. What is the effect of W/C ratio on compressive strength of concrete ?
2. Mention the factors affecting the compressive strength of concrete ?
3. What is the effect of increasing rate of loading on cube ?
4. How does workability of concrete affects strength of concrete ?
5. What is the relation between compresive strength and flexural strength oncrete ?

Determination of compressive strength of cube concrete Specimens

Aim:

To determine the cube compressive strength of the specified concrete mix proportion.

Reference Indian standard codes:

• IS: 516-1959.
• IS: 1199-1959.
• SP: 23-1982.
• IS: 10086-1982.

Equipment's Required:

• Compression testing Machine: The testing machine may be of any reliable type, of sufficient capacity for the tests and capable of applying the load
  at the rate of 14 N/mm² per minute. The permissible error shall be not greater than ± 2 percent of the maximum load.
• Cube moulds:The mould shall be of 150 mm size conforming to IS: 10086-1982.
• Weighing balance.
• Tamping rod.
• Rubber gloves.
• Metallic sheet.
• Demoulding oil.

Theory:

One of the important properties of concrete is its strength in compression. The strength in compression has a definite relationship with all other properties of concrete i.e. these properties improved with the improvement in compressive strength. With this test we can estimate concrete quality. The cubical moulds of size 15cm x 15cmx 15 cm are used for finding compresion strength. The concrete is prepared with definite proportion is poured in the mould and tempered with tamping rod to minimize air voids. After 24 hours these moulds are removed and test specimens are put in water for curing. The top surface of this specimen should be made even and smooth. This is done by putting cement paste and spreading smoothly on whole area of specimen. These specimens are tested by compression testing machine after 7 ,14 21 and 28 days curing. Load should be applied gradually at the rate of 14 N/mm² per minute till the Specimens fails. Load at the failure divided by area of specimen gives the compressive strength of concrete. At least three specimens are tested at each selected age. Equation for compressive strength of cube, σ_cube is

\[\mathop \sigma \nolimits_{cube} = \frac{F}{A}\]

Where,

• σ_cube = Compressive strength of cube (N/mm² Or MPa).
• F = Failure load (N).
• A = Loaded area of cube (mm²).

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 15x15x15 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.
8. 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 platens.
9. In the case of cubes, the specimen shall be placed in the machine in such a manner that the load shall be applied to opposite sides of the cubes as cast, that is, not to the top and bottom.
10. The axis of the specimen shall be carefully aligned with the center of thrust of the spherically seated platen. No packing shall be used between the faces of the test specimen and the steel platen of the testing machine.
11. The load shall be applied without shock and increased continuously at a rate of approximately 140 kg/cm²/min until the resistance of the specimen to the increasing load breaks down and no greater load can be sustained.
12. The maximum load applied to the specimen shall then be recorded and the appearance of the concrete and any unusual features in the type of failure shall be noted.

Observations:

Sl.No.	Description.	Particulars.
1.	Type of cement.
2.	Specific gravity of cement.
3.	Type of sand.
4.	Specific gravity of sand.
5.	Fineness modulus of sand.
6.	Type of coarse aggregates.

Concrete mix proportions:

Sl.No.	Description.	Proportion for 1m3.	Proportion for batch mixing.
1.	Cement (Kg).
2.	Coarse aggregates (Kg).
3.	Fine aggregates (Kg).
4.	water (Kg).
5.	Aggregate/Binder ratio.
6.	Water/Cement ratio.
7.	Admixture.

Compression test data sheet:

Specimen No.	Days Cured.	Length of cube mm.	Breadth of cube mm.	Area mm2.	Load kg.	Load N.	Stress MPa.
1.	7	150.2	150		11100
2.	7	150.1	150.3		11000
3.	7	150.0	150.1		11200
Average :
4.	14	150.1	150.2		12100
5.	14	150	150		12200
6.	14	150.1	149.9		12300
Average :
7.	21	150.1	150.2		13100
8.	21	150	150.1		13250
9.	21	150.1	150		13210
Average :
10.	28	150.3	150.2		14100
11.	28	150.1	150.0		14200
12.	28	150	149.9		14300
Average :

Graph:

Conclusion:

1. The average 7 Days Compressive Strength of concrete = MPa.
2. The average 14 Days Compressive Strength of concrete = MPa.
3. The average 21 Days Compressive Strength of concrete = MPa.
4. The average 28 Days Compressive Strength of concrete = MPa.

1. First video

2. Second video

3. Third video

Refrence

1. Brooks, J.J & Neville A. M. (2019). Concrete Technology (2^nd ed.). Pearson Publishers Pvt Ltd.

2. Shetty, M. S & Jain, A. K. (2018). Concrete Technology: Theory And Practice (8^thed.).S Chand Publishers Pvt Ltd.

3. Irving, K. (2009). Engineered Concrete, Mix design and test methods (2^nd ed.). CRC press, Taylor & Francis group.