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Detecting Hidden Damage

This article describes an effort to develop low-cost, wireless sensors for detecting corrosion in reinforced concrete bridges. This sensor enhances the type and quality of information that can be obtained during a periodic inspection of a bridge. To minimize life-cycle costs and to maximize service life, the sensors do not include onboard processing capabilities or batteries. An external reader is used to interrogate and power the sensors in a wireless manner using inductively coupled magnetic fields. The sensors are designed to be embedded in the concrete during construction and interrogated using a reader coil on the surface of the concrete. The prototype corrosion sensor may be idealized as two resonant circuits. The frequencies of the two circuits are easily identified by measuring the phase of the impedance across the terminals of the reader coil. The lower frequency resonant circuit includes a sacrificial steel wire, which extends into the concrete and is exposed to the same levels of oxygen, moisture, and chlorides as the nearby reinforcement. As corrosion develops on the surface of the steel sensing wire, the resonant frequency of this circuit is lost, and only one resonant frequency is detected when the sensor is interrogated. If two resonant frequencies are detected when the sensor is interrogated, the likelihood of corrosion at that location is low. However, if one resonant frequency is detected, the likelihood that corrosion has initiated is high. The results of accelerated corrosion tests demonstrated that the prototype sensors provided valuable information about the condition of the embedded reinforcement before evidence of corrosion was visible. The prototype sensors also demonstrated that wireless transmission of data through reinforced concrete structural elements is possible. The initial expenditure associated with installing this type of wireless sensor is expected to be low, with the cost of materials needed to fabricate a single sensor being less than $2.

Language

  • English

Media Info

  • Media Type: Print
  • Features: Figures;
  • Pagination: pp 12-13
  • Serial:
    • Bridges
    • Volume: 10
    • Issue Number: 6
    • Publisher: ZweigWhite

Subject/Index Terms

Filing Info

  • Accession Number: 01100290
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jun 3 2008 7:22AM