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  • Destructive test on concrete specimen in the lab don’t necessarily give direct information about the concrete in the actual structure, yet it does matter. Test specimens are not true representative of the concrete in the structure due to a number of reasons. Non Destructive Tests (NDT) are easy and quick to perform and saves labour time and materials.
  • Field cured specimens and core cut from the structure and subsequently tested in the lab provide some what better information than destructive tests. 
  • To get around these problems a wide range of tests known as in situ tests have been developed. These tests are traditionally known as non destructive tests (NDT). The test may cause minor damage to the structure but don’t impair their performance and appearance.
  • An important feature of NDT is that they permit retesting at the same or nearly the same location so that changes with time can be monitored.
  • NDT can broadly be classified into two categories:
  1. Test which assess the strength in situ and
  2. Tests which determine other characteristics of concrete such as voids, flaws, cracks, concrete cover, rebar size, rebar spacing etc.
  • In NDT, the strength of concrete is assessed and not measured. An experimental relation between the property being measured and compressive strength of concrete is determined in the lab and then used to convert NDT into strength values. 
  • An understanding of the physical relation between the given NDT and compressive strength is essential and engineering judgment should be exercised in interpreting the test results.








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