Detection of Flaws in Asphalt Overlaid Concrete Decks Using Ultrasonic Guided Waves

Background The research proposed here builds on the achievements of a previous NOOT project. The novel, nondestructive ultrasonic guided wave leakage (UGWL) based testing method we developed recently promises to be able to detect the onset of corrosion and delamination in reinforced concrete bridge decks earlier than any other nondestructive testing (NDT) method (Garcia, Erdogmus, et al. 2017 and 2019); however, the effects of asphalt overlay on the method's effectiveness remains unclear. With this project, we aim to investigate the effect of asphalt overlays on the feasibility of the recently developed UGWL method. In this section, the background and the motivation for the proposed work are summarized. Reinforced concrete bridge decks are highly susceptible to deterioration, mainly due to corrosion of the rebars and the subsequent propagation of issues, such as delamination, cracking, and spalling. According to the Federal Highway Administration (FHWA 2014), 145,890 out of the 610,749 highway bridges (24%) in the U.S. are structurally deficient. Yunovich et al. (2001) state that corrosion and delamination problems account for approximately 40% of all bridge deck repair costs; and Arndt et al. (2011) identify the highway bridge corrosion related repair costs to be around $8.3 billion, with $2 billion of this just for the repair of bridge decks. There are several NDT methods gaining more popularity to help with these issues, but most of these methods can only detect flaws after they reach a certain size, at which point, structural behavior may already be compromised and the deck has to be replaced. In the past few years, in collaboration with NDOT, we have developed a novel NDT method that is capable of detecting the onset of rebar-concrete separation (mechanical delamination) and rebar corrosion (chemical delamination). This method utilizes a commercially available ultrasonic testing system; however, we developed innovative techniques for placing the transmitters and receivers, as well as for the analysis of the data. Due to the unique placement of sensors, instead of measuring the ultrasonic waves directly (the sensors on two ends of a steel pipe or both sensors on the concrete are common placements); we measure the leaked energy. The transmitter (T) is placed at the end of the steel rebar using the rebar as a waveguide. This allows the ultrasonic waves to propagate for longer distances within the boundaries of a linear element. The receiver (R) on the other hand is placed on the concrete's surface. As a result of this arrangement, the leaked energy from the ultrasonic guided waves propagating through the rebar are measured from the surface of the concrete. Using this technique, which we refer to as "ultrasonic guided wave leakage (UGWL) method", we were able to detect delaminations as small as 0.008" and record signals up to 10 and 14 feet away from the transmitter on a lab specimen and on an actual bridge deck, respectively. For the analysis/post-processing, we utilize the energy or the amplitude, instead of the typically measured velocity. This allows smaller changes in condition to be detected more clearly. Thus far, we have tested this method only on reinforced concrete lab specimens and a bridge deck without any membrane or asphalt overlay.To make sure the idea is adequately tested with reinforced concrete decks first, we have intentionally kept asphalt out of the scope thus far, per mutual agreement between the Pl and the NDOT. Meanwhile, given the high cost of bridge deck failures, NDOT's philosophy is to add an asphalt overlay to bridge decks based on age (i.e. when they are 10 years old) as a precaution. As a result, there is an urgent need to study the feasibility of the UGWL method with the inclusion of an asphalt overlay, to ensure it remains feasible and applicable to Nebraska's infrastructure. It is also further identified through discussions with NDOT that, given the complex and multi­ layered construction of asphalt-overlaid reinforced concrete bridge decks, currently there are no effective NDT methods to detect issues underneath the asphalt and membrane layers. If our method proves successful, it will provide a highly valuable tool to NDOT's capabilities for inspection and maintenance. There are a few studies on the ultrasonic testing of asphalt based on our preliminary review. Tigdemir et al. (2004) have demonstrated the possibilities of applying ultrasonic methods on asphalt-concrete specimens to estimate fatigue life. Khazanovich et al. (2005) have shown that ultrasonic testing techniques can provide a simple, quick, and objective procedure for evaluation of surface distresses in asphalt concrete pavements. Hoegh et al. (2012) demonstrated that ultrasonic tomography could detect delamination between new and old asphalt layers, as well as delamination of lifts within new asphalt pavements. Pahlavan et al. (2016) investigated the influence of asphalt on fatigue crack monitoring in steel bridge decks using guided waves; however, they concluded that the type of asphalt greatly affects the extent of propagation of guided waves. Haser et al. (2015) monitored the viscosity of asphalt binders, while Zargar et al. (2017) evaluated the air voids in asphalt. Finally, a very recent study by McGovern et al. (2018) evaluated the life expectancy of asphalt pavements. These studies render the use of ultrasonic testing on asphalt more promising, while in the past, the high attenuation of ultrasonic waves in asphalt has been stated as a concern. It should be noted that none of these studies attempted the exact procedure we aim to investigate; therefore, our proposed work remains novel. A more in-depth literature review regarding the characteristics of asphalt and their effects with respect to our method and objectives is included in the proposed scope of work. Objectives The ultimate goal of the project is to expand the capabilities of the recently developed novel UGWL testing method to detect flaws in asphalt overlaid reinforced concrete bridge decks. Two objectives will help achieve this goal: 1. To determine the effects of the asphalt overlay on the testing method 2. To understand to what extent we can detect the flaws in reinforced concrete decks when there is an asphalt overlay 2. To determine if we can use the "asphalt" as a waveguide in addition to or instead of the rebar.

    Language

    • English

    Project

    • Status: Active
    • Funding: $ $52,957.00
    • Sponsor Organizations:

      Nebraska Department of Transportation

      1500 Nebraska 2
      Lincoln, Nebraska  United States  68502
    • Project Managers:

      Halsey, Lieska

    • Performing Organizations:

      University of Nebraska, Lincoln

      1400 R Street
      Lincoln, NE  United States  68588
    • Start Date: 20190701
    • Expected Completion Date: 20201231
    • Actual Completion Date: 0
    • USDOT Program: Transportation, Planning, Research, and Development

    Subject/Index Terms

    Filing Info

    • Accession Number: 01705869
    • Record Type: Research project
    • Source Agency: Nebraska Department of Transportation
    • Files: RiP, STATEDOT
    • Created Date: May 24 2019 2:30PM