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THE NEED FOR NON DESTRUCTIVE TEST ON CONCRETE

October 7, 2016

 

A variety  of  Non  Destructive Testing  (NDT)   methods  have  been  developed  or  are  under  development  for investigating  and  evaluating concrete  structures. These methods are aimed at estimation  of   strength  and other  properties;  monitoring  and  assessing  corrosion;  measuring  crack  size  and  cover;  assessing  grout quality; detecting defects and identifying relatively more vulnerable areas in concrete structures.

 

Many  of   NDT  methods  used  for  concrete  testing  have  their  origin  to  the  testing  of  more  homogeneous, metallic system.  These  methods  have  a  sound  scientific  basis,  but  heterogeneity  of   concrete  makes interpretation of   results  somewhat  difficult.  There  could  be  many  parameters  such  as  materials,  mix, workmanship and  environment,  which  influence  the  results  of   measurements.  Moreover, these tests measure  some  other  property  of  concrete  (e.g. hardness)  and  the  results  are  interpreted  to  assess  a different property  of   concrete  e.g. strength,  which  is  of  primary  interest.

 

Thus, interpretation of   results is very important and difficult job where generalization is not possible.

 

As such, operators can carry out tests but interpretation of   results must be left to experts having experience and knowledge of application of such non-destructive tests.

 

Non-Destructive Testing of Concrete (NDT on Concrete)

 

 

What is Non Destructive Test?

 

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.

 

 

Purpose of Non-destructive Tests:

 

The non-destructive evaluation techniques are being increasingly adopted in concrete structures for the following purposes:

 

(i)  Estimating the in-situ compressive strength

 

(ii)  Estimating the uniformity and homogeneity

 

(iii)  Estimating the quality in relation to standard requirement

 

(iv) Identifying areas of lower integrity in comparison to other parts

 

(v)  Detection of presence of cracks, voids and other imperfections

 

(vi) Monitoring changes in the structure of the concrete which may occur with time

 

(vii)  Identification of reinforcement profile and measurement of cover, bar diameter, etc.

 

(viii)  Condition of prestressing/reinforcement steel with respect to corrosion

 

(ix)  Chloride, sulphate, alkali contents or degree of carbonation

 

(x)  Measurement of Elastic Modulus

 

(xi)  Condition of grouting in prestressing cable

 

 

 

Different Methods of Non-Destructive Testing of Concrete

 

Various non-destructive methods of testing concrete have been developed to analyze properties of hardened concrete, which are given below.

 

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

 

The rebound hammer test measures the elastic rebound of concrete and is primarily used for estimation of concrete strength hand for comparative investigation.

 

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.

 

 

 

 

Types of Non Destructive Tests: 

 

According to their use, non-destructive equipment  can  be grouped as under:

 

i)  Strength estimation of concrete

 

ii)  Corrosion assessment and monitoring

 

iii)  Detecting defects in concrete structure

 

iv)  Laboratory tests

 

 

 

RECOMMENDATION

 

 It is of outmost importance to ensure the structural integrity of the concrete structures of buildings are assessed for safety and structural competence.

 

 

 

REFERENCES

 

  1. Handbook on Non Destructive testing of concrete

  2. Handbook of Concrete Engineering

  3. Guide on NDT on Concrete structures

  4. Evaluation of Compressive strength using Non Destructive test methods

  5. www.theconstructor.org/practical-guide/purpose-of-non-destructive-tests-on-concrete-structures/7688/

  6. www.civilblog.org/2015/03/27/what-is-non-destructive-testing-of-concrete-various-ndt-test-methods/

     

     

     

     

     

     

     

     

     

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