PURPOSE OF NON-DESTRUCTIVE TESTS ON CONCRETE STRUCTURES
NON DESTRUCTIVE EVALUATION OF CONCRETE STRUCTURES
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 test s 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.
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 ducts
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
