Non destructive test is a method of testing existing concrete structures to assess the strength and durability of concrete structure. In the non destructive method of testing, without loading the specimen to failure (i.e. without destructing the concrete) we can measure strength of concrete. Now days this method has become a part of quality control process. This method of testing also helps us to investigate crack depth, micro cracks and deterioration of concrete.
Non destructive testing of concrete is a very simple method of testing but it requires skilled and experienced persons having some special knowledge to interpret and analyze test results.
Methods of Non-Destructive Testing of Concrete
1. Surface Hardness Test
These are of indentation type, include the Williams testing pistol and impact hammers, and are used only for estimation of concrete strength.
2. Rebound Hammer Test
3. Penetration and Pullout Techniques
These include the use of the simbi hammer, spit pins, the Windsor probe, and the pullout test. These measure the penetration and pullout resistance of concrete and are used for strength estimation, but they can also be used for comparative studies.
4. Dynamic or Vibration Tests
These include resonant frequency and mechanical sonic and ultrasonic pulse velocity methods. These are used to evaluate durability and uniformity of concrete and to estimate its strength and elastic properties.
5. Combined Methods
The combined methods involving ultrasonic pulse velocity and rebound hammer have been used to estimate strength of concrete.
6. Radioactive and Nuclear Methods
These include the X-ray and Gamma ray penetration tests for measurement of density and thickness of concrete. Also, the neutron scattering and neutron activation methods are used for moisture and cement content determination.
7. Magnetic and Electrical Methods
The magnetic methods are primarily concerned with determining cover of reinforcement in concrete, whereas the electrical methods, including microwave absorption techniques, have been used to measure moisture content and thickness of concrete.
8. Acoustic Emission Techniques
These have been used to study the initiation and growth of cracks in concrete.