Sampling of Concrete Cubes for Test -As per IS 516-1959

 Blog By Er. Navneet Kumar

Sampling of Concrete Cubes for Test -As per IS 516-1959

Size of Test Specimens -
  •  Test specimen cubical in shape shall be 15 X 15 X 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. They shall be 15 Cm in diameter and 30 cm long.


Cube Moulds-
  1. The cube mould shall be of  metal, preferably steel or cast iron, and stout enough to prevent distortion. 
  2. The height of the mould and the distance between opposite faces shall be the specified  size + 0·2 mm. 
  3. The angle between adjacent internal face and between internal faces and top and bottom planes of the mould shall be 90° + 0.5°.
  4. The interior faces of the mould shall be plane surfaces with a permissible variation of 0·03 mm.
  5.  The base plate shall be of such dimensions as to support the mould during the filling without leakage and it shall be preferably attached to the mould by springs or screws.
  6. The interior surfaces of the assembled mould shall be thinly coated with mould oil to prevent adhesion of the concrete and to ensure that no water escapes during the filling.

Cylinders Moulds-
  1. The cylindrical mould shall be of metal which shall be not less than 3 mm thick.
  2. When assembled ready for use, the mean internal diameter of the mould shall be 15·0 cm ± 0·2 mm and in no direction shall the internal diameter be less than 14·95 cm or more than 15·05 cm.
  3.  The height shall be 30·0 cm ± 0·1 cm.
  4. The base plate and the capping plate shall be at least 6·5 mm thick, and such that they do not depart from a plane surface by more than 0·02 mm.
  5. The mould and base plate shall be coated with a thin film of mould oil before use, in order to prevent adhesion of the concrete. 
Tamping Rod-
  1. The tamping bar shall be a steel bar 16 mm in diameter, 0·6 m long and bullet pointed at the lower end.
Compacting-
  1. The concrete shall be filled into the mould in layers approximately 5 cm deep.
  2. Each layer shall be compacted either by hand or by vibration.
  3. When compacting by hand, the standard tamping bar shall be used and the strokes of the bar shall he distributed in a uniform manner over the cross-section of the mould.
  4. For cubical specimens, in no case shall the concrete be subjected to less than 35 strokes per layer for 15 cm cubes or 25 strokes per layer for 10 cm cubes.
  5.  For cylindrical specimens, the number of strokes shall not be less than thirty per layer.
  6. The stroke shall penetrate into the underlying layer and the bottom layer shall be rodded throughout its depth. 
  7. Where voids are left by  by the tamping bar, the sides of the mould shall be tapped to close the voids.
  8. When compacting by vibration, each layer shall be vibrated by means of an electric or pneumatic hammer or vibrator or by means of a suitable vibrating table until the specified condition is attained.
  9. After the top layer has been compacted, the surface of the concrete shall be finished level with the top of the mould, using a trowel, and covered with a glass or metal plate to prevent evaporation.
Curing-
  1. The test specimen 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 ± 1/2 hour from the time of addition of water to the dry ingredients. 
  2. After this period, the specimens shall be marked and removed from the moulds and kept submerged in clean fresh water until taken out just prior to test.
  3. The water or solution in which the specimens are submerged shall be renewed every seven days and shall be maintained at a temperature of 27° ± 2°C. 
  4. The specimens shall not be allowed to become dry at any time until they have been tested. 
Notes - Precaution to be taken at site during curing
  1. The test specimens shall be stored on the site at a place free from vibration under damp matting sacks or other similar material for 24 hours ± 1/2 hour from the time of adding the water to the other ingredients.
  2. The temperature of the place of storage shall be within the range of 22° to 32°C.
  3. After the period of 24 hours, they shall be marked for later identification, removed from the moulds and stored in clean water at a temperature of 24° to 30°C until they are transported to the testing laboratory.
  4. They shall be sent to the testing laboratory well packed in damp sand, damp sacks or other suitable material so as to arrive there in a damp condition not less than 24 hours before the time of test.







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