Methodology : Compressive Strength Test Of Concrete

The compressive strength test is a crucial procedure in assessing the ability of a material to withstand axial loads. In the context of construction materials like concrete, the compressive strength is a key parameter. The Indian Standard (IS) code that provides guidelines for the compressive strength test of concrete is IS 516:1959 – “Method of Tests for Strength of Concrete.”

Here is a basic methodology for conducting the compressive strength test according to IS 516:1959:

Apparatus Required:

  1. Compression Testing Machine:
  • The compression testing machine should conform to the requirements of IS 14858:2000.
  1. Cubical or Cylindrical Molds:
  • The molds should conform to the requirements of IS 10086.
  1. Weighing Balance:
  • Capable of weighing up to 10 kg and accurate to 1 gram.
  1. Tamping Rod:
  • A steel rod 16 mm in diameter and 600 mm long.
  1. Mallet:
  • A mallet weighing 0.59 kg.
  1. Steel Trowel:
  • A steel trowel about 150 mm long and 100 mm wide.
  1. Measuring Cylinder:
  • A graduated cylinder for measuring water.

Procedure:

  1. Sample Collection:
  • Collect samples of concrete in accordance with the relevant standard.
  1. Preparation of Test Specimens:
  • Prepare test specimens either in the form of cubes (150 mm x 150 mm x 150 mm) or cylinders (150 mm diameter x 300 mm height).
  1. Mixing of Concrete:
  • Prepare concrete mixtures in accordance with the mix design and standard procedures.
  1. Filling the Molds:
  • Fill the molds with the freshly mixed concrete in layers approximately 5 cm deep. Compact each layer with 25 strokes of the tamping rod.
  1. Finishing the Surface:
  • After filling the mold, strike off the excess concrete using the trowel so that the surface of the concrete is level.
  1. Curing:
  • Cure the specimens in a curing tank or by covering them with wet hessian cloth for a specified period (typically 7 or 28 days).
  1. Testing:
  • After the curing period, remove the specimens from the molds and wipe off any water from the surface. Place the specimen on the compression testing machine and align it properly.
  1. Loading:
  • Apply a load gradually without shock, at the rate of 140 kg/cm² per minute until the specimen fails. Note the maximum load sustained by the specimen.
  1. Calculations:
  • Calculate the compressive strength using the formula:
    [ f_c = \frac{P}{A} ]
    where ( f_c ) is the compressive strength, ( P ) is the maximum load, and ( A ) is the cross-sectional area of the specimen.
  1. Reporting:
    • Report the compressive strength of the specimen in megapascals (MPa).

Precautions:

  1. Ensure that the testing machine is calibrated.
  2. The testing environment and curing conditions should comply with the standard specifications.
  3. Handle specimens carefully to prevent damage.

Always refer to the latest version of the relevant IS code for the most accurate and up-to-date procedures and requirements.

The compressive strength test is a crucial procedure in assessing the ability of a material to withstand axial loads. In the context of construction materials like concrete, the compressive strength is a key parameter. The Indian Standard (IS) code that provides guidelines for the compressive strength test of concrete is IS 516:1959 – “Method of Tests for Strength of Concrete.”

Here is a basic methodology for conducting the compressive strength test according to IS 516:1959:

Apparatus Required:

  1. Compression Testing Machine:
  • The compression testing machine should conform to the requirements of IS 14858:2000.
  1. Cubical or Cylindrical Molds:
  • The molds should conform to the requirements of IS 10086.
  1. Weighing Balance:
  • Capable of weighing up to 10 kg and accurate to 1 gram.
  1. Tamping Rod:
  • A steel rod 16 mm in diameter and 600 mm long.
  1. Mallet:
  • A mallet weighing 0.59 kg.
  1. Steel Trowel:
  • A steel trowel about 150 mm long and 100 mm wide.
  1. Measuring Cylinder:
  • A graduated cylinder for measuring water.

Procedure:

  1. Sample Collection:
  • Collect samples of concrete in accordance with the relevant standard.
  1. Preparation of Test Specimens:
  • Prepare test specimens either in the form of cubes (150 mm x 150 mm x 150 mm) or cylinders (150 mm diameter x 300 mm height).
  1. Mixing of Concrete:
  • Prepare concrete mixtures in accordance with the mix design and standard procedures.
  1. Filling the Molds:
  • Fill the molds with the freshly mixed concrete in layers approximately 5 cm deep. Compact each layer with 25 strokes of the tamping rod.
  1. Finishing the Surface:
  • After filling the mold, strike off the excess concrete using the trowel so that the surface of the concrete is level.
  1. Curing:
  • Cure the specimens in a curing tank or by covering them with wet hessian cloth for a specified period (typically 7 or 28 days).
  1. Testing:
  • After the curing period, remove the specimens from the molds and wipe off any water from the surface. Place the specimen on the compression testing machine and align it properly.
  1. Loading:
  • Apply a load gradually without shock, at the rate of 140 kg/cm² per minute until the specimen fails. Note the maximum load sustained by the specimen.
  1. Calculations:
  • Calculate the compressive strength using the formula:
    [ f_c = \frac{P}{A} ]
    where ( f_c ) is the compressive strength, ( P ) is the maximum load, and ( A ) is the cross-sectional area of the specimen.
  1. Reporting:
    • Report the compressive strength of the specimen in megapascals (MPa).

Precautions:

  1. Ensure that the testing machine is calibrated.
  2. The testing environment and curing conditions should comply with the standard specifications.
  3. Handle specimens carefully to prevent damage.

Always refer to the latest version of the relevant IS code for the most accurate and up-to-date procedures and requirements.

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