Concrete NDT ( Non destructive testing of concrete ) . Rebound hammer & UPV ultra pulse velosity

1. Non-Destructive Tests of concrete
(REBOUND HAMMER AND ULTRA PULSE VELOCITY TEST)

2. Source of Defects in concrete
Construction Phase :
Improper detailing
disregard for quality control
Cost control at expense of durability
Post construction Phase :
Enviromental changes due to increased pollution
Industrialization
Vehicular traffic
And so on..

3. Preliminary Knowledge of Building
building drawings
layout plan
construction specifications (type of structure, material used, interconnection elements)
Building age, purpose
previous investigation reports
previous repair work details
adjacent structure
nearby locations like industries, presence of saline enviroment, sea etc.
climatic conditions

4. Properties from test reults
Strength
Density
Elastic modulus
Homogeneity
Absorption and permeability
Resistivity
De laminations
Chemical composition
Crack width measurement
Surface pressure
Steel corrosion
Reinforcement Location/cover

5. Resistance
Factor
Should be always greater than ONE.

6. Assessment flow diagram
- Concrete Technology – A.R.Santhakumar

7. Types of Test

8. REBOUND HAMMER

9. Uses
Assessing the….
……likely probable compressive strength of concrete
……uniformity of concrete.
……quality of the concrete in relation to standard requirements
……quality of one element of concrete in relation to another.

10. -Mehta & Monteiro

11. •Calibration against steel anvil having Brinell hardness number of about 5000 N/mm2.
•Even and smooth surface
•Dry & free of moisture
•Perpendicular to surface
•Test point at least 20mm away from the edge
•At least 9 to 12 readings generally taken
Types of Hammers
Preparation for test
Type
M heavy structures and mass concrete
N impact energy of 2.2 N-m and is suitable for grades of concrete
from M-15 to M-45
L lightweight concrete or small and impact sensitive part of the
structure
P below M15 grade

12. ‘Global’ graph

13. Factors affecting the Rebound Number
Aggregates
Age of concrete
Surface smoothness
Type of curing
Moisture
Surface carbonation
Stiffness of member
Compaction

14. BENEFITS
Portable
Ease of use
Instantaneous results
No particular skill required
Inexpensice

15. Discussions
Surface properties reflected up to around 30mm
Graph not accurate
Correlation between rebound number & strength to be done.
Structure large as possible at least 150mm thick.
Dissipation of impact energy
Wet surface gives a lower rebound number
Variation in reading about +/-25%
Specimen to be rigid
Variation is values from person to person

16. Rebound Number vs. Strength
Paper by - Dr. Andrzej Moczko, Dept of Civil Engineering, Weoclaw Technical University Poland
Compressive test results from cores, capo-test and schimdt hammer
Structur
e No.
CTM -Core from
structure
Rebound hammer
on structure
Rebound hammer
on core
1 19.6 36.9 28.4
2 24.7 37.4 28.4
3 29.7 49.5 38.2
4 34.2 56.8 43.1
5 33.3 61.6 49.3
6 34.2 56.5 36.5
7 35.4 66.3 57
8 37.1 56.9 46.1
9 37.5 70.9 61
10 42 68.4 57.4
Avg - 32.77 56.12 44.54
0
20
40
60
80
0 10 20 30 40 50
CTM
Rebound Number
Core specimen - Rebound number
vs. CTM

17. Experiment conduction in SEMT lab on 30.08.16
Grade of concrete : M30
OPC 53 : 375 kg/m3 Correction for water : 20mm passing =0.84% ; 10mm passing=1.62% ; sand=2.88%
Coarse : Fine Aggregate = 60:40 Sp gravity: 20mm=2.75 ; 10mm = 2.74 ; sand=2.75
Coarse- 20mm passing:10mm passing= 70:30 Temperature - 28.2 degree celcius
Relative Humidity – 79 Age of samples- 7 days and 14 days.
Rebound hammer vs. CTM
NDT (MPa) CTM (MPa) % diff.
10.5 21.9 52.05
14 33.54 58.26
21 33.92 38.09
22 35.11 37.34
25 35.51 29.60
0
10
20
30
40
0 5 10 15 20 25 30
CTM(MPa)
Rebound Hammer (MPa)
Compressive strength- Rebound
hammer vs. CTM

19. ULTRASONIC PULSE VELOCITY TEST
Homogeneity
Presence of voids, cracks, honeycombs and other deformation
Changes in the structure of the concrete with time
Quality of the concrete in relation to standard requirements
Elastic modulus of concrete
Quality comparison between specimen

20. • Transducer--one emitting
and other receiving
• Electrical pulse generator
• Amplifier
• Electronic timing device

21. Based on the propagation of Ultrasonic Pulse waves through the
concrete
Pulse produced by one trasducer
Pulse propagates through path length (L)
Other transducer receives the pulse of vibrations and converts
into electronic signal
Electronic timing circuit gives the transit Time (T)
Wave Velocity --- V = L/T

22. longitudinal waves
Transverse waves
love waves
Rayleigh waves
Travel fastest
Near the surface

23. Propagation of waves
Path Length (mm) Natural Frequency of transducer
(kHz)
Minimum Transverse Dimensions
of Members (mm)
Upto 500 150 25
500-70 >60 70
700-1500 >40 150
Above 1500 >20 300
As per IS-13311.1.1992
• Denser the medium higher the velocity and vice versa
• Independent of geometry of material.
• Depends on the elastic property of the material
• Transducer operating with frequency range of 20 kHz to 150
kHz generally used

24. Methods of probing
Good quality concrete has a difference less
than 0.5km/sec between direct and indirect methods.

25. Pulse Velocity by cross probing (direct method)- km/s Concrete Quality Grading
Above 4.5 Excellent
3.5 to 4.5 Good
3.0 to 3.5 Medium
Below 3.0 Doubtful*
IS-13311(Part-1) gives a velocity criteria for grading quality of concrete
*Incase of doubtfull quality further tests may be required
The Young’s modulus of elasticity (E)
E= 𝑝(1 + 𝑢)(1 − 2𝑢)𝑉𝑥𝑉 / (1 − 𝑢)
Where;
E = dynamic Young’s Modulus of elasticity
𝑝= density in kg/ms,
𝑉 = pulse velocity in m/second
𝑢 = Poissons ratio

26. Factors affective UPV
Age of concrete – Velocity increases with age
Moisture of concrete – More moisture leads to higher velocity
Amount and type of aggregate- Type and Size
Micro cracking- Cracks reduce elastic modulus .Wave velocity reduces
Presence of reinforcement- Velocity in RCC is 1.2 to 1.9 times more than that of plain cement comncrete of same
mix
minimum path length Nominal size of agg.
100 mm </= 20 mm
150 mm 20 to 40 mm

27. Strength vs. Ultrasonic pulse velocity
No direct correlation exists
Self generated equation can be obtained by relating the wave velocity with strength results
provided concrete should have --
-Similiar mix
-Method of compaction
-Exposure conditions
-Curing methods etc.,

28. In a paper by Cengiz Kurtulus and Ali Bozkurt-
“Determination of concrete compressive strength of the structures in Istanbul and
Izmit Cities (Turkey) by combination of destructive and non-destructive Methods”,
Linear equation was generated by relating the-
UPV of different structures Compressive test on the same core drilled
A total of 200 readings were taken.

29. Combined method using UPV & Rebound
hammer
Better accuracy
Better correlation
Compensates limitation of each method
Correlation valid for specimen with same mix, exposure etc.
However variability of one property may have opposite effect for the other method
Eg. – rise in moisture increase the pulse velocity but reduces the rebound number
When the UPV gives higher result only then the Rebound value on surface can be assumed to
reflect the properties of bulk
If very low UPV obtained Rebound value cannot be used to get the properties of concrete as a
whole.

30. SONREB
A very useful tool to determine probable strength of concrete using both UPV & Rebound
hammer
Developed with help of RILEM technical committee- 7 NDT and TC-43 CND .Originated in
Romania and developed further in Australia and Europe
IN SONREB the in situ compressive strength of a structure can be found by the following expression
---(I)
a, b, c are constants
V - Ultrasonic Pulse Velocity
R - Rebound Number
From microsoft excel Linest Function valus of a,b,c can be obtained from UPV and Rebound number

31. Researchpaper-
Useofcombineddestructivetestingintheconcretestrengthassessmentfromlaboratoryspecimenandexistingbuilding
By-MulikNikhil,BalkiMinal,ChhabriaDeep,GhareVijay,TeleVishal,
Mrs.Patil Shweta-Asst.Prof.inCivilEngineering
DepartmentOfCivilEngineering,GenbaSopanraoMozeCollegeofEngineering,UniversityOfPune,India
60 cube specimen were prepared using various mixes from M15 to M40 and cured for 28 days
The UPV, Rebound hammer and compressive testing of each was done .
For above values--
a=1.64111E-09
b=2.293662304
c=1.30768373