WHAT IS NDT FULL FORM?
NDT is Non Destructive Test which can be performed on any material to determine the strength or capacity of it, without destructing it.
NON DESTRUCTIVE TESTING OF CONCRETE
Non-destructive evaluation is widely employed for inspecting the strength of structures. Non destructive techniques, which are less time consuming and relatively inexpensive, can be used for the following purposes:
- Test on actual structures.
- Test at several locations.
- Test at various stages.
- Assess the quality control of actual structures.
- Assess the uniformity of the concrete.
- Assess the materials used and workmanship with specification.
- Assess the poor construction practices.
- Assessment of the extent of cracks, voids, honeycombs.
- Confirmation of suspected distress due to poor design
- Assessment of partial durability
- Integrity testing of piles
- Monitoring of progressive changes in structure
The results of non-destructive tests are most useful when supplemented by a limited number of destructive test procedures. There are more testing techniques with different principles and applications are available to evaluate the properties of concrete. The concrete material is so complicated that the efficiency and quality cannot be established just by one single test. Most of the tests, which are used, for estimating the parameters of concrete provide an excellent means of establishing and evaluating the uniformity of concrete.
Semi destructive test - Core Cutting Test for Concrete - pdf
Non destructive testing methods - Surface hardness test or Rebound Hammer test
 |
| non destructive testing of concrete |
The surface hardness method consists of impacting the concrete surface in a standard manner. Activating a mass by a given energy and measuring the indentation or rebound achieve this. The most commonly and widely used instrument is a "Rebound Hammer". There are several types of hammers having varying impact energy from 0.07 kg m to 3 kg m. the high impact energy is used for mass concrete, road pavements and airport runways. The low impact energy hammers (0.07 to 0.09 kg m) are used for small and low strength materials.
Test procedure:
The test procedure consists of applying the hammer on the concrete surface and observing the rebound reading indicated by a rider over a scale. Before applying the hammer, the surface of the concrete is cleaned and smoothened. A minimum of 10 readings is compared and each reading should not differ by more than 7 units. The average of remaining readings is determined for evaluating the strength. If more than two reading differ from the average by 7 units, than the entire set of readings are taken afresh. The testing procedure in hammer is as shown.
The procedure for determining the rebound values has been specified in ASTM C 805-85, BIS-13311 Part 2 and also in the latest ASTM specification. Estimation of concrete compressive strength from rebound number is determined from standard calibration curve based on the laboratory results. The calibration curve should be established for each type of concrete. A typical calibration curve is shown in The main factors that affect the readings are:
- Size and age of concrete
- Surface texture
- Concrete mix characteristics
- Stress state & temperature
- Carbonation level in concrete &
- Moisture content
 |
| rebound hammer test is code |
Rebound hammer test IS code Download
It should be noted that the rebound values reflect the concrete quality up to a depth of 50 mm in the member. In practical situation, the strength prediction can be made to an accuracy of 25%. The application of surface hardness measurements can be used for:
- Checking the uniformity of concrete
- Comparing a given concrete with a specified requirement
- Approximate estimation of strength by using laboratory calibrated graphs
- Abrasion resistance classification
 |
| non destructive testing typical calibration curves |
 |
| non destructive testing types |
QUALITY OF CONCRETE USING NON DESTRUCTIVE TEST REBOUND HAMMER TEST
Average Rebound number | Quality of concrete |
| GREATER THAN 40 | VERY GOOD HARD LAYER |
| 30 TO 40 | GOOD LAYER |
| 20 TO 30 | FAIR |
| LESS THAN 20 | POOR CONCRETE |
0 Comments