Measurement of Concrete Damage Mechanics by Internal Friction and Laser Shearography Richard A. Livingston Materials Science & Engineering Dept University of Maryland 12 th Int. Symposium on Nondestructive Characterization of Materials Blacksburg, VA June 23, 2011
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Measurement of Concrete Damage Mechanics by Internal
Friction and Laser Shearography
Richard A. LivingstonMaterials Science & Engineering Dept
University of Maryland
12th
Int. Symposium on Nondestructive Characterization of Materials
Blacksburg, VA June 23, 2011
Co‐Authors, Civil Engineering Dept.
•
Nicolas McMorris
•
Cintia
Lijeron
•
Amde
M. Amde
•
Jorgemai
Ceesay
•
Hung Khong
Outline
•
Introduction
•
Experimental Approach
•
Q‐factor Analysis
•
Shearography
Analysis
•
Conclusions
Distributed Damage in Concrete•
Characteristic of:–
Alkali Silica Reaction (ASR)
–
Delayed Ettringite
Formation (DEF)
–
Freeze‐thaw Damage (F‐T)
•
Mechanism is the formation of expansive phases:‐
Ettringite
‐
ASR gel
‐
Ice
•
Results in multiple subvisible
microcracks
•
Damage is usually measured on laboratory specimens by
reduction in strength or stiffness
•
Therefore an NDT method is needed to measure distributed
damage in the field
Damped Free Oscillator( ) exp( ) cos ou t A t t
where :
u(t) = displacementA
= amplitude
α
= damping factor or internal friction
ωo
= fundamental frequency in radians per secondt
= time.
2o Q
Q‐factor
2 1
o
Q
Experimental Approach
•
Standard 3”
x 3”
x 11”
concrete prisms
•
Two types of accelerated damage–
Freeze‐thaw cycles ASTM C 666
–
Duggan expansion test
•
Two potassium levels–
Control = 0.56 % K2
O
–
High Potassium =2.06% K2
O
Duggan Test Water Storage
Test Methods
•
Ultrasound : ASTM C 215: Fundamental Transverse Frequency and Quality Factor
•
Expansion: ASTM C 490
•
Weight change
•
Compressive strength
•
Fracture surface Scanning Electron Microscopy
•
Laser shearography
ASTM C 215
Q‐factor for F‐T samples
Q‐factor for DEF samples
All Q vs
Normalized Damage
Q‐factor
2 1
o
Q
Q 2o
12
2
114o Q
Resonant Frequency Dependence on Q
For Q
≥
5, ω
≈
ωo
DEF Specimens, Damping
DEF Specimens, Frequency
ASTM C‐215 Equation for Resonant Frequency
3
3
* **0.9464* *
E b tfM L c
where: f = resonant frequency, HzE = Dynamic elastic modulusM
= mass of prism, KgL = Length of prism, mb
= Width of prism, mt = Depth of prism, mc = Correction factor, depends on radius of gyration
and Poisson’s ratio
F‐T Specimens, Damping
F‐T Specimens, Frequency
Schematic Diagram of Laser Shearography
Presenter
Presentation Notes
It is important to detect very fine cracks in concrete as early as possible. An NDT method that is being applied to this problem is laser shearography, presented in this slide. Unlike conventional holography which requires two beams of light, shearography employs a single beam of laser light which is reflected off the specimen as shown in this slide. The camera then produces a pair of laterally sheared images in the image plane and hence the method is called shearography. The effect of shearing is to map a point on the image into two points in the image. Conversely, this is equivalent to bringing two separate points on the object surface to meet in the image plane. The two overlapped portions of the sheared images interfere and produce a speckle pattern. When the object is deformed, the speckle pattern is slightly modified. Comparing the two speckle patterns (stressed and unstressed) produces a fringe pattern which depicts the relative displacement of two neighboring points. Since the magnitude of shearing is small, the fringe pattern approximately represents the derivative of displacement with respect to the shearing direction. This differs from holography which depicts displacement rather than its derivative. This difference from holography results in shearography being much less sensitive to external vibration interference and hence much more suitable for production and field environments.
Shearogram
Crack Image Analysis, F-T Control, 100 Days
Crack Detection Segmented Image
Crack Density, Control Crack Density, Hi-K
DEF
Freeze-Thaw
DEF
Freeze-Thaw
Summary,DEF•
DEF does not significantly change internal
friction
•
Resonant frequency increases over time because elastic modulus increases due to continued concrete curing
•
Therefore linear resonance spectroscopy is not feasible as an NDT method for DEF.
•
Higher potassium levels systematically reduce elastic modulus
Summary, Freeze‐Thaw•
F‐T damage only weakly increases internal
friction
•
F‐T damage significantly affects resonant frequency
•
Therefore, resonant frequency rather than Q‐ factor would be an effective basis for NDT
Comparative Damage Mechanics•
F‐T distributed damage develops through
microcracking
•
DEF damage involve crystallization of ettringite which fills cracks
•
Conventional mechanism for distributed damage of expansive pressure does not explain DEF damage
2nd
Order Harmonic Ratio2 2
2
22 21 2 ...o
u u uc
t x x
.
co
= constant β2
= second‐order nonlinear coefficient
β2
= A2
/(A1
)2
A1
= Amplitude of fundamental peakA2
= Amplitude of second harmonic peak
Duggan Test Thermal Cycling
Mas
s Lo
ss %
Cycles
Mass Loss for F-T Specimens
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