Unbonded Portland Cement Concrete/Pavement Monitoring with Integrated Grating (Local) and Scattering (Global) Optical Fiber Sensors

MnDOT, NDSU, and Neubrex Co. Ltd.

Genda Chen
Professor
Missouri University of Science and Technology
328 Butler-Carlton Hall, 1401 N. Pine Street
Rolla, MO 65409-0710
(573) 341-4462
gchen@mst.edu

One graduate student

The main objectives of this study are (a) to extend structural applications and document the performance of the recently-developed FBG-BOTDA sensing technology in pavement applications, (b) compare the performances of FBG-BOTDA and PPP-BOTDA/TW-COTDR in field condition, and (c) to develop a database of concrete pavement performance with a benchmark roadway to be built by MnDOT engineers. In addition, one full-scale pavement specimen may be designed and fabricated as needed for laboratory tests at Missouri S&T in collaboration with Dr. Khazanovich and MnDOT engineers so that the specimen is comparable with the benchmark pavement. To achieve the main objectives, the scope of work includes, but is not limited to,

• Design and calibrate an integrated grating and Brillouin scattering optical fiber sensing system for concrete pavement monitoring at Missouri S&T, including both tension and shear effects among different pavement layers as well as temperature compensation between the grating and Brillouin scattering optical technologies.
• Validate the sensing system with full-scale pavement tests under a full design load simulated by driving a dump truck across the pavement specimen at Missouri S&T.
• Apply the validated sensing system into the laboratory and/or field testing of concrete pavements at the project site.
• Compare the FBG-BOTDA and PPP-BOTDA/TW-COTDR measurements and evaluate their accuracy with the laboratory and/or field testing of concrete pavement.

Unbonded Portland cement concrete overlays have recently received increasing attention in new highway constructions and existing pavement rehabilitations. The AASHTO Mechanistic-empirical Pavement Design Guide (MEPDG) provides an analysis and evaluation methodology for such multilayer systems. However, interaction between the overlays and the underlying layers cannot be fully taken into account in the current design methodology, which was the motivation for the on-going NCHRP 01-51 study led by Dr. Lev Khazanovich from the University of Minnesota (UMN). For example, the time-varying friction or bonding between the new and existing layers, and its dependence on the underlying base material were not considered in the AASHTO Guide. The influences of construction practices and bonding behaviors on pavement performances were not sufficiently accounted for. For the same reason, Minnesota Deparmtent of Transportation (MnDOT) is currently leading a multi-state pool funded study with Dr. Lev Khazanovich as Project Director to understand and quantify the above-mentioned factors on pavement performance tailored into the state specific applications in field condition.

Missouri University of Science and Technology (Missouri S&T or formerly University of Missouri-Rolla) recently developed a cost-effective, integrated global-local monitoring system with optical fiber sensors for large-scale transportation infrastructure. In the compact instrumentation system, the grating technology (e.g. fiber Bragg grating for local strain and temperature measurement) was integrated with the Brillouin scattering technology (e.g. single mode optical fiber for global strain and temperature measurement). One of the original developers of the monitoring system is Dr. Ying Huang, an assistant professor from North Dakota State University (NDSU) and a former Ph.D. student from Missouri S&T under the supervision of Dr. Genda Chen.

More recently, NeubreScope NBX-7020 model was manufactured by Neubrex Co. Ltd., Japan. NBX-7020 represents the state-of-the-art, long-distance optical measurement technology, combining advantages of both Brillouin and Rayleigh backscattering phenomena. The Brillouin sub-system employs the latest optical measurement breakthrough technology with Pulse Pre-Pump Brillouin Optical Time Domain Analysis (PPP-BOTDA) while the Rayleigh sub-system uses the Tunable Wavelength Coherent Optical Time Domain Reflectometry (TW-COTDR). With a single-mode optical fiber, the hybrid measurement system provides non-proportional frequency shifts for Brillouin and Rayleigh scatterings and, as such, allows a separation of the measured strain and temperature at every point of the optical fiber. The strain and temperature accuracies can be as low as 10 με and 0.5 ºC, respectively, over a length of as short as 2 cm.

Relationship to other Research/Projects

This is a stand alone project.

Transportation-Related Keywords

Technology Transfer Activities

A technology transfer presentation will be prepared and presented at the CIES/NUTC annual conference. A short article will also be prepared for the NUTC Newsletter. In addition, at least one technical paper will be prepared and published at archival journals or technical conferences such as the annual Transportation Research Board meeting.

Project Deliverables

The deliverables from this project mainly include a final technical report, a technology transfer presentation, and a short article that summarizes the laboratory and field performances of FBG-BOTDA and PPP-BOTDA/CW-COTDR technologies in pavement applications. In addition, results and findings related to the use of the acquired equipment in other structures applications as listed in the equipment purchase justification section will be summarized in a few technical papers and submitted for possible publications.

Anticipated Benefits

For new highway constructions, jointed plain concrete pavements and continuously reinforced concrete pavements are applied with concrete slabs placed on a base that is made of various layers and materials. The base may be densely graded or permeable drainage layers. For highway rehabilitations, concrete overlays may be placed over existing pavements. The contact force and slide friction between concrete pavements/overlays and their underlying substrates are critical in the pavement design and analysis with MEPDG procedures but appear to be inadequately taken into account in the current AASHTO Manual.

Once available, an inventory database of contact force and slide friction at the interface between concrete slabs/overlays and their substrates as well as temporal and spatial strain distribution in the complete pavement system can not only verify the assumptions made in the AASHTO Manual, but also reduce the potentially underdesigned and overdesigned pavements, thus improving the associated safety and cost effectiveness in pavement construction and operation. The data and analysis results are more valuable when collected from actual highway pavements. Therefore, a benchmark pavement will be constructed and tested in this study under the technical and financial support of MnDOT engineers.

The proposed project represents the first case study of an integrated grating and Brillouin scattering optical sensing technology and a hybrid Brillouin/Rayleigh scattering sensing technology in the U.S. As such, it will enable future cost-effective implementations of the innovative technologies in large-scale civil infrastructure since both FBG-BOTDA and PPP-BOTDA/TW-COTDR can be used with a single optical fiber over a distance in the order of kilometer.

Milestones