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The test measures the force required to pull out a previously cast in steel insert with an embedded enlarged end in the concrete. In this operation, a cone of concrete is pulled out and the force required is related to the compressive strength of concrete.
Principle

This test is based on the principle that the force required to pull out a cone of steel embedded in concrete is proportional to the strength of concrete.

Test Procedure

Pull out insert (shown in fig) is embedded in plain concrete during pouring. When the strength is required to be determined, the force is applied at the embedded end. The force required to pull out the assembly is measured.
Pull out test of concrete
Limitations
  • Steel rod assembly has to be embedded in concrete during pouring and hence test cannot be undertaken at later ages.
  • Repair of damaged concrete is required.

Evaluation 
  • The pull out assembly is pulled with a lump of concrete, which is subjected to tension and shear and the force required to pull out is related to shearing strength of concrete and not to the compressive strength.
  • Ratio of pull out force to compressive strength decreases slightly with increase in the level of strength.
  • Pull out may not be carried out till completion. It my be sufficient to apply a predetermined force to the embedded rod and if it is not pulled out, a given strength is assumed to exist.
  • According to Malhotra, the pull out test is superior to Schmidt hammer and penetration resistance test because larger volume and greater depth of concrete are involved in the test. Repair of concrete after test is also required. Relation between compressive strength and pull out force is shown in figure below.