NDT techniques can evaluate concrete structures in a non-destructive manner by assessing strength, quality, and durability without damaging the concrete. Some key NDT tests described in the document include rebound hammer testing to estimate concrete strength, UPV testing to evaluate homogeneity and detect cracks or voids, half-cell potential testing to assess corrosion risk, and cover meter testing to determine reinforcement location and concrete cover thickness. NDT allows for more extensive evaluation than destructive testing methods at a lower cost. Test results are influenced by factors like moisture, temperature, reinforcement properties, and concrete composition.

1. Abhishek gupta
Vikas Dubey

2. NDT
• Powerful technique for evaluating exiting concrete structures with
regard to their strength and durability apart from assessment and
control of quality of hardened concrete without or partial damage
to the concrete.
• Concrete is not loaded to the failure, therefore, the strength inferred
or estimated can not be expected to yield absolute value of strength.

3. • Destructive testing
– Huge Cost initially has to put in for taking sample and
then to test it.
• NDT
– Its very easy and simple process and a lot many tests can
be performed on concrete less than single amount
require for sampling of concrete
Cost Effectiveness

4. Deliverables of NDT

5. • Rebound Hammer Test: To estimate strength and hardness of the concrete in
the cover region (IS: 13311 Part II)
• UPV Test: To measure homogeneity, uniformity, compactibility and presence
of crack or void, thus representing durability of concrete (IS: 13311 Part I).
• Core Test: To evaluate in situ compressive strength of concrete (IS 516 &
ASTM C42/41)
• Corrosion Assessment: Half Cell Potential (ASTM C876-9), Resistivity and
RCPT (ASTM C1202), to know about extent and rate of ongoing corrosion
activity.
• Bar Locater and Cover Meter: To know the structural strength and protection
to the reinforcement by cover concrete.
• Carbonation: To evaluate extent of carbonation for strength and corrosion
estimation.
HOW NDT INVESTIGATION HELPS IN
ASSESSMENT?

6. OBJECTIVES
• To assess quality of the concrete in relation to the standard
requirements
• To estimate compressive strength of concrete with the help of
suitable correlations between rebound index & compressive
strength
• To delineate regions of poor quality or deteriorated concrete in a
structure
• To assess quality of one element of the concrete in relation to
another
REBOUND HAMMER

7. Rebound hammer

8. FACTORS AFFECTING THE TEST RESULTS

9. Mechanism of Rebound Hammer

10. Average Rebound Number Quality of Concrete
more than 40 Very good hard layer
30 to 40 Good layer
20 to 30 Fair
less than 20 Poor concrete
0 Delaminated
INTERPRETATION OF THE TEST RESULTS

11. OBJECTIVES
• To assess uniformity and homogeneity of concrete
• To assess quality of concrete in relation to standard requirements
• Detection of the presence & approximate extent of cracks, voids & other
imperfection in concrete
• Measurement of changes occurring with time in the properties of the
concrete
• Correlation of pulse velocity & strength as a measure of concrete quality
ULTRASONIC PULSE VELOCITY

12. 1. Smoothness of contact surface under test
2. Influence of path length on pulse velocity
3. Temperature of concrete
50 – 300 Ideal
300 – 600 (Reduction in UPV up to 5%)
Below 50 (Increase up to 7.5%)
4. Moisture condition of concrete (pulse velocity is
proportional to moisture content)
5. Presence of reinforcing steel (UPV of R/f is 1.2 to 1.9 times
than normal concrete)
6. Stress Level in concrete
FACTORS AFFECTING TEST RESULTS

13. • Ultra sonic pulse velocity meter

14. Techniques measuring for pulse Velocity Test

15. Velocity criteria for concrete quality grading
INTERPRETATION OF THE TEST RESULTS

16. OBJECTIVES
• To evaluate potential of concrete in promoting corrosion activity
of reinforcement by Half Cell Potential test
• To evaluate reinforcing steel in concrete that has carbonated to the
level of the embedded steel
• To compare corrosion activity in outdoor reinforced concretes of
highly variable moisture or oxygen content, or both, at the
embedded steel
Half Cell Potential

17. • Moisture
• Temperature
• Concrete Cover Thickness
• Oxygen content of the reinforcement
Half cell potentiometer
FACTORS AFFECTING TEST RESULTS

18. Potential over an area Most likely outcome
more positive than -0.20 V CSE 90% probability that no
reinforcing steel is
corroded
(at the time of test)
-0.20 to -0.35 V CSE corrosion activity of the
reinforcing steel
more negative than -0.35 V CSE 90 % probability that
reinforcing steel is
corroded
Interpretation of Test results

19. OBJECTIVES:
To assess
1. pH of the concrete
2. corrosion
Chemical used: Phenolthalein solution (colour less below a
pH of 8.2 and is pink/purple at a pH greater than 10.0)
commercially available indicator measures pH from 1 to 14
with a rainbow spectrum
Carbonation Test

20. • Dark concrete
• Saturation
• Extent of drilling
Factors affecting test results

21. Carbonated concrete

22. OBJECTIVES
To assess
1. diameter
2. location of the R/F
3. cover
profometer
Cover meter test

23. • cover measurement maybe affected by neighbouring bars
parallel to the bar being measured
• Magnetic effects from the aggregate or matrix of the
concrete
• variations in the properties of the steel
• cross-sectional shape of bars
• roughness of the surface
Factors affecting test results

24. THANK YOU!