Fiber Optic Sensors for Real-time Monitoring of Civil Infrastructure

Transcription

1 Fiber Optic Sensors for Real-time Monitoring of Civil Infrastructure Yi Bao, Ph.D. Assistant Professor in Civil Engineering Advanced Structure and Process Innovation Research (ASPIRE) Laboratory Department of Civil, Environmental and Ocean Engineering Stevens Institute of Technology Phone: (201) Webpage:

2 Goal My research aims to advance condition monitoring technologies for civil infrastructure through innovations of fiber optic sensors. 2

3 Objectives This research addresses the following challenges: To develop a high-resolution (centimeter order) condition monitoring technique using fiber optic sensors; To detect, locate and quantify shrinkage cracks in concrete; To detect, quantify and predict delamination in layered concrete; To develop novel corrosion sensors for reinforced concrete. 3

4 Optical Fiber Telecommunication-grade single-mode optical fiber: Core: high-purity fused silica, doped with germanium Cladding: high-purity fused silica, doped with germanium Coatings: mechanical protection Light wave is guided through total internal reflection at the corecladding interface Cladding Core n 2 =1.463 n 1 =

5 Sensing Technology Pulse pre-pump Brillouin Optical Time Domain Analysis (PPP- BOTDA): Pulse pre-pump Strain/temperature change Laser diode Incident laser Backscattering Optical fiber Probe laser Receiver z ε 1 Strain/temperature change ε 2 Intensity Brillouin frequency shift ( v B =v B2 -v B1 ) ε 1 Fiber Strain ε 1 Strain ε 2 Distance Frequency v B1 v B2 Freq. Brillouin frequency shift: v B = C ε ε + C T T 5

6 Application 1: Measure autogenous shrinkage of ultra-high performance concrete (UHPC) Non-uniform shrinkage strain was measured for the 1st time Specimen (unit in mm) Non-uniform shrinkage strain Test set-up for average shrinkage strain Bao, Y., Meng, W., Chen, Y., Chen, G., Khayat, K.H. (2015). Measuring mortar shrinkage and cracking by pulse prepump Brillouin optical time domain analysis with a single optical fiber. Materials Letters, 145,

7 Application 2: Cracks / Debonding in Concrete Pavement Overlays Shrinkage of UHPC produces stresses in bonded overlay Delamination Bonded overlay Concrete substrate Overlay specimen (unit in mm) Bao, Y., Valipour, M., Meng, W., Khayat, K.H., Chen, G. (2017). Distributed fiber optic sensor-enhanced detection and prediction of shrinkageinduced delamination of ultra-high-performance concrete bonded over an existing concrete substrate. Smart Materials and Structures, 26(8),

8 The increase of the peak s magnitude represents the development of delamination. Re-plot Strain (με) d 3 d 7 d P1 P2 P3 P4 P5 P6 P7 P8 P Distance along the optical fiber (m) P10 P11 (P12) P13 P14 P15 P16 Delamination (μm) Delamination at the interface Dye penetrant test 8

9 Distributed sensors are embedded in concrete: Monitor strain, temperature, and cracks Understand degradation mechanisms of concrete pavement overlay in cold weather Improve the design and management of the pavement Sensor Field test in Minnesota Crack Crack Strain distribution Bao, Y., Tang, F., Chen, Y., Meng, W., Huang, Y, Chen, G. (2016). Concrete pavement monitoring with PPP-BOTDA distributed strain and crack sensors. Smart Structures and Systems, 18(3), 19p. 9

10 Application 3: Monitoring Corrosion in RC Distributed fiber optic corrosion sensor Load (kn) Ref S10 S5 S Slip (mm) Beam specimen Strain (µm/m) h 48 h 58 h 68 h 74 h 78 h 88 h 98 h 108 h 118 h 130 h Distance (m) V CL (cm 3 ) VV CCLL-3 =20.1Δm-7.23 RR 2 =0.98 VV CCLL-2 =3.23Δm-0.84 RR 2 = Mass loss (g) Fan, L., Bao, Y.*, Chen, G. Feasibility of distributed fiber optic sensor for corrosion monitoring of steel bars embedded in concrete, Sensors. 10

11 Discrete fiber optic corrosion sensor Sensor fabrication: Fused silica fiber Inscribe gratings using CO 2 laser Thin-film deposition 20 μm Fe-C 800 nm silver Fe-C film Silver film 200 nm 200 nm Sensor application: 11 Chen, Y., Tang, F., Bao, Y., Chen, G., Tang, Y. (2016) Fe-C coated long period fiber grating sensors for steel corrosion monitoring. Optics Letters, 41(13),

12 Application 4: Digital Construction Install fiber optic sensors via construction robotic system monitor and control the concrete 3D printing process monitor structural health condition for long-term durability Concrete ingredients Extruder Concrete mixer Concrete pump Robotic arm 3D printed structure 12

13 Conclusions Distributed fiber optic sensors based on PPP-BOTDA can be used to measure detailed strain distributions with adequate accuracy and long measurement distance (20-50 miles). Non-uniform autogenous shrinkage of UHPC and cracks were monitored using the distributed sensor. Delamination occurred at the substrate/overlay interface due to early age shrinkage of UHPC, and was detected, located and quantified using the distributed fiber optic sensor. The presented fiber optic sensors can be used to detect, locate and quantify corrosion in reinforced concrete. Fiber optic sensors become more promising and practical in digital construction. 13

14 Acknowledgement The research was funded by: US Department of Transportation through the University Transportation Centers (UTC) Program and PHMSA Program Minnesota Department of Transportation National Institute of Standards and Technology (NIST) National Science Foundation (NSF) University of Michigan Ann Arbor 14