State-of-the-Art Radar Tomography for Concrete Structure Assessment

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Title: State-of-the-Art Radar Tomography for Concrete Structure Assessment

Author(s): B. Giroux, P. Rivard, E. Gloaguen, and M.C. Chouteau

Publication: Special Publication

Volume: 235

Issue:

Appears on pages(s): 31-50

Keywords: alkali-aggregate reaction; attenuation; radar tomography; structure assessment; velocity; water content

Date: 3/22/2006

Abstract:
The knowledge of the concrete condition and monitoring of on-going deterioration processes are key factors for the management of concrete structures. Traditional assessment often remains limited and qualitative. This paper presents a new methodology based on radar tomography to estimate the water distribution in concrete, and therefore to assess indirectly the concrete condition. It aims at providing effective nondestructive procedures for engineers and structure managers. Work was conducted on a hydraulic structure suffering from alkali-aggregate reaction. Six boreholes were drilled to allow for core recovery and radar downhole measurements. Borehole radar antennas of 100 MHz central frequency were used for crosshole tomography. Radar data pointed out a high attenuation (high electrical conductivity), corroborated with the core testing. Both travel time and amplitude tomography needed to be carried out for an accurate determination of the dielectric permittivity. The Complex Refractive Index Model (CRIM) was used to relate the permittivity to the volumetric water content. The tomographic calculations were done using an algorithm based on geostatistical methods and stochastic simulations, allowing to draw probability maps of the volumetric water content. Results indicate that the overall volumetric water content is moderately high (0.15), and that some zones have high water content (above 0.2). These results will be used in the maintenance program of the structure.