COMPRESSIVE STRENGTH OF CONCRETE WITH ADMIXTURES, HOW TO INCREASE STRENGTH OF CONCRETE (IS:516- 1959)


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Admixtures are natural or manufactured chemicals other than water, aggregates, or cement which are added to the concrete or mortar before or during mixing to control setting, early hardening, workability and to provide qualities to concrete.
Admixtures are classified according to function. There are five distinct classes of chemical admixtures: air-entraining, water reducing, retarding, accelerating and plasticizers (superplasticizer).


Penetration of Concrete:-
  1. Prepare the concrete mix both with and without admixture except in the case of air-entraining admixture.
  2. The air-entraining admixtures are used as the reference or control concrete mixture.
  3. The admixture shall be used in accordance with the recommendation of the manufactures.
  4. When an admixture is to be tested specifically for air-entraining admixtures it shall be used in control concrete, such as a quantity that it produces air content in the range of 3.5 to 7 percent.
  5. The concrete mix shall be proportioned to have the cement content specified for the work and to meet the stipulated workability and strength requirements.
  6. In case of air entrained concrete. The air content specified for the work shall be used.
  7. If the maximum size of coarse aggregate is greater than 20 mm. The concrete mix shall be wet- screened over 20 mm IS sieve before test.
  8. The concrete mix may be designed according to any accepted method of mix design to meet the following requirement.
(a). The cement content of the mix shall be (304 to 307)kg/m³
(b). The concrete mix shall have a slump of 40 mm to 60 mm or a compaction factor of 0.85 to 0.90 facilitate compaction by hand rodding.


  • IS: 516- 1959

APPARATUS REQUIRED FOR THE TEST:-


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Concrete Mixer Machine


Compression Testing Machine

No. of Specimens:-   
Take at least 3 specimens, preferably from different batch, for testing at each selected age.


PROCEDURE OF THE TEST:- 
  1. At first, store the test specimens in water at a temperature of 24°C to 30°C for 24 hours before testing.
  2. Surface water and grit shall be wiped off the specimens and any projecting fins removed specimens.
  3. Test the specimens immediately on removal from the water while they are still in a wet condition. The dimension of the specimens to the nearest 0.2 mm.
  4. Note down the dimension of each specimens before testing.
  5. Wipe cleanly the bearing surfaces of the supporting and loading rollers. Also remove any loose sand or other material from the surface of the specimen which are in contact with the compression platens.
  6. In the case of cube place the specimens in the testing machine in such a manner that the load shall be applied to opposite sides of the cube as cast, that is not the top and bottom.
  7. Align carefully the axis of the specimen with the centre of the thrust of the spherically seated platen.
  8. No packing should be used between the faces to the test specimen and the steel platen of the testing machine as the spherically seated block is brought to bear on the specimen, the movable portion shall be rotated gently by hand so that uniform seating may be obtained.
  9. Apply the load with ought shock and increase it continuously at a rate of approximately 140 kg/cm²/min.

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Report:-
Average of 3 specimens value shall be reported.