Non-destructive testing of concrete (NDT on concrete)
Non-destructive testing is a method of testing existing concrete structures to assess the strength and durability of a concrete structure. In the non-destructive method of testing, we can measure the strength of concrete without loading the sample to failure (i.e. without destroying the concrete). Nowadays this method has become part of the quality control process. This method of testing also helps us to check the depth of the crack, micro cracks and deterioration of the concrete.
Non-destructive testing of concrete is a very simple method of testing, but it requires skilled and experienced persons with some specialized knowledge to interpret and analyze test results.
Various methods of non-destructive testing of concrete
Various non-destructive methods of testing concrete have been developed to analyze the properties of hardened concrete, which are given below.
1. Surface Hardness Test
These are of the indentation type, include the Williams Testing Pistol and the Impact Hammer, and are used only for estimating concrete strength.
2. Rebound Hammer Test
The Rebound Hammer Test measures the elastic rebound of concrete and is primarily used for strength estimation and comparative testing of concrete.
3. Entry and Pullout Techniques
These include the use of the symbi hammer, spit pin, windsor probe and pullout test. These measure the penetration and pullout resistance of concrete and are used for strength estimation, but can also be used for comparative studies.
4. Dynamic or Vibration Testing
These include the resonant frequency and mechanical sonic and ultrasonic pulse velocity methods. These are used to evaluate the durability and homogeneity of concrete and to estimate its strength and elastic properties.
5. Combined Methods
Combined methods involving ultrasonic pulse velocity and rebound hammer have been used to estimate the strength of concrete.
6. Radioactive and Nuclear Methods
These include X-ray and gamma ray penetration tests to measure the density and thickness of concrete. In addition, neutron scattering and neutron activation methods are used for moisture and cement content determination.
7. Magnetic and Electrical Methods
Magnetic methods are mainly concerned with determining the cover of reinforcement in concrete, whereas 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.