NDT Corporation uses an automated sonic/ultrasonic bridge deck testing system for evaluating the condition of bridge decks with and without wearing surfaces. This system makes nondestructive measurements to determine the mechanical properties of concrete by measuring (at the surface) the compressional and shear wave velocities of a transmitted stress wave generated by a projectile impact energy source. The deck slab in the thickness direction is evaluated using continuous reflected (resonant frequency) compressional waves. These measurements determine the presence of vertical cracking as well as major and minor delamination. In addition, the seriousness of deck cracking is evaluated by measuring the average deck concrete strengths through a developed empirical relationship between the measured stress wave compressional and shear wave velocity values and the concrete unconfined compressive strength. In addition to the empirical strengths, the velocity values can be used to calculate the moduli values, Young's, bulk and shear as well as Poisson's Ratio. Bridge deck testing projects where the sonic/ultrasonic testing system was used and the results were successfully compared with known flaws, post survey repairs are presented. The comparison indicates that the sonic/ultrasonic testing will detect cracking, vertical or horizontal (partial or full deck) and delamination that are not visible and detected by traditional inspection methods.
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