Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
Venu Gopal Madhav ANNAMDAS University of Pittsburgh, PA
Co-Authors:
SPIE 2009 San Diego
RADHIKA Madhav Annamdas, JNTU, India Chee Kiong SOH, NTU, Singapore
March/11/2009
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
Outline • • • • • • • •
Introduction : Background of EMI Technique Experimental Setup PZT Epoxy Wrapped PZT Steps to Fabricate Robust Embeddable PZT Curing monitoring Damage assessment RMSD Analysis Conclusions Q&A
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
PZT based Electromechanical Impedance (EMI) principle PZT: surface bonded or embedded + Electric field along direction 3 Structure
PZT
2 3 1
Zďƒ 1 / Admittance (Y)
{Y = Conductance + j (Susceptance)}
ďƒ&#x;Finally obtain it
PZT: measures resistance of structure to vibrations
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
Experimental Setup
PZT embedded inside the concrete mould
Multiplexer Specimen
Impedance Analyzer
PZT 4
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
Epoxy Wrapped PZT • Thin layer of the epoxy adhesive mix (consisting of equal proportions of hardener and resin). • Nominal pressure was applied over the wrapped PZT to ensure a thin uniform thickness of epoxy layer. • Sealing provides protection against chemical, mechanical and electrical effects. • Allowed to cure under room temperature for 24 hours and irregular shape of epoxy wrap was later trimmed.
It provides First protection
The admittance signatures of ‘free’ PZT along with epoxy wrapped PZT was compared
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
Initial Comparison
Admittance signatures of ‘Free’ and epoxy wrapped PZT transducers
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model Steps to fabricate embedded PZT
Robust Embeddable PZT Layering sequence
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model Steps to fabricate embedded PZT • Card-board mould (40 x 40 x 15 mm3) was prepared • Portland cement paste of 1:2 cement to sand ratio was then poured into the card-board mould in three layers •The epoxy wrapped PZT was positioned after the first layer, followed by wire mesh positioning after the second layer. Finally, the third layer was poured •The mould was then left to cure for 24 hours under room temperature. • The admittance signatures were again recorded to determine if there was any damage (like crack or breaking in the PZT, etc) incurred during this step.
Robust Embeddable PZT Layering sequence
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model The admittance signature was recorded form the embedded PZT transducer and compared with epoxy wrapped PZT
Real admittance signatures of epoxy wrapped and robust patch PZT transducers
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
•The ready to use embedded PZTs, located at central position inside the moulds of dimensions 150 x 150 x150 mm3 [cube] and 500 x 100 x 100 mm3 [beam] • Filled with concrete. •The specimens were then allowed to cure for 24 hours under room temperature
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model The admittance signatures were recorded to check the functionality of the embedded PZT and to obtain the required pristine state (undamaged) signatures of the concrete specimens.
Effect of robust PZT type transducers in concrete cube
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model SURFACE BONDED PZT Protected and un protected PZTs was surface bonded on concrete cube (150 x 150x150 mm3) using a thin epoxy adhesive.
EFFICIENCY OF EMBEDDED ZPT The experimental admittance signatures were recorded for the following two purposes. 1. Comparison between surface bonded PZT and embedded PZT 2. Monitoring of concrete cube
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
• Similar up to frequency of 300 kHz and some differences were observed later after 500 kHz. • The large variation at frequency above 500 kHz due to the extreme localized sensing area. • Embedded PZT has slightly shorter peaks than the surface bonded PZT due to greater damping effect inside the concrete. •Taller and sharper peaks imply that there is greater dynamic interaction over that frequency range. • However, the embedded transducer is still very sensitive to minor cracks on the surfaces, as described in the later slides for frequencies less than 500 kHz
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model MONITORING OF CONCRETE CURING The peak shifted rightwards and became progressively sharper with time. The shifting of the peaks suggested that the stiffness was increasing with the gain in concrete strength.
(a)
(b)
Monitoring of concrete curing for (a) cube, (b) beam
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model DAMAGES
Two types of damages were induced in the concrete specimens to study the changes in admittance signatures. Type 1 damage: Four edges of the concrete cube were chipped off one after another using hammer to create loss of mass (disturbance to structure integrity)
For Cube
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model
For beam
Type 2 damage: Inducing four cuts (line damages) of 5 mm deep with a spacing of 50 mm on the upper surface of a concrete beam. The locations of 1, 2, 3 and 4 crack lines were 200 mm, 150 mm, 100 mm and 50 mm respectively from the embedded transducer at the centre of the beam.
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model Results and Discussions on Damage Assessment The most widely used root mean square deviation (RMSD) index was used to evaluate the deviations in admittance signatures during the damaged states.
i=N
RMSD(%) =
∑ (w i =1
i
i= N
2
− ui )
2 u ∑ i i =1
x100
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model The figure depicts the RMSD values for the damaged state signatures in Concrete CUBE obtained at a frequency range of 80-100 kHz. The lowest RMSD value was 1.7% for the first damage and the largest RMSD value was 3.5% for the fourth damage.
RMSD vs. Damaged state for concrete cube
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model For BEAM : The lowest RMSD value was 1.0% for the first crack line (200 mm away from the PZT) and the largest RMSD value was 1.5% for the fourth crack line (50 mm away from the PZT). The trend of upward slope and a linear relationship between the RMSD value and the damage was observed. The upward trend in RMSD was because of the increase in overall damage, and also the damages were approaching the PZT transducers
RMSD vs. Damaged state for concrete beam
Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model CONCLUSIONS • Step by step building of robust embeddable PZT was successfully presented. • Embedded PZT- concrete model is presented, and its implementation in monitoring of concrete curing and damage analysis was also shown. •Successfully demonstrated the monitoring of strength gain of concrete during curing using embedded PZT •Comparisons were made with surface bonded PZTs. It was observed that up to 500 kHz there was not much deviation in the EM admittance signatures of surface bonded and embedded PZTs •The slope of the RMSD trend lines indicates that in both the cube and beam specimens, the damage index increased with increase in damaged state i.e. severity of damage. •Embedded PZT was able to detect the damage as far as 200 mm. •The maximum RMSD value of the cube and beam specimens are about 7.4% and 7.0% respectively in the frequency range of 80-100 kHz. • Study shows that rugged embedded PZT is efficient in damage detection and moreover, durability and protection from surface finish, vandalism and environment are the important features of embeddable of PZT patches
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