This project developed a vehicle-mounted scanner system based on non-destructive evaluation methods, including impact echo (IE), slab impulse response (SIR), spectral analysis of surface waves (SASW) and acoustic sounding for condition evaluation of concrete bridge decks. Several non-contact transducers were evaluated that included non-contact microphones, a microwave transducer and a laser vibrometer along with traditionally used ground-contact transducers for comparison. All these devices except microphones showed limitations for use on the mobile bridge deck scanner system. Consequently, efforts were directed at rolling ground contact transducers that could be connected to the hitch of a survey vehicle and the microphones that showed promise for impact echo, acoustic sounding and surface waves (“leaky” Lamb waves). Work was completed on the hardware design and building of the bridge deck scanner prototype. The system comprises of four major subassemblies: the sensor wheel, the bearing box, the universal link, and the tow bar. The prototype was built in August, 2009 and was used on Douglas Bridge in Douglas, WY and the bridge on 1st Street in Casper, WY to determine bridge deck conditions along with other traditional evaluation methods such as ground penetrating radar, impact echo (point by point) and infrared thermography for comparison. The tests showed excellent results from the rolling Impact Echo component (the sensor and impactor wheel).The delamination map of the bridge deck obtained from the Impact Echo wheels and the chain drag results showed good agreement. The design of the prototype was revised to make it more robust based on feedback from field experiments. The final system comprises of two sensor wheels. These two wheels will be used for the Impact Echo test simultaneously with the Spectral Analysis of Surface Wave tests. Each sensor wheel, machined from a solid piece of Delrin plastic, is 11.46” in diameter and 2.5” wide and has a 0.063” thick polyurethane band (tire) stretched over its rolling surface. This replaceable wearing surface acts as an acoustic couplant to pick up the compression and surface wave energy. Embedded within the wheel perimeter are six displacement transducers, equally spaced around the 36” circumference, that are spring loaded to help ensure positive contact for good acoustic coupling. Mounted to the side of the wheel, in line with each transducer, is an electrically powered impact solenoid that impacts the test surface thereby providing both compression and surface wave energy. The timing of the impact that should occur precisely when the sensor tip is in contact with the surface to maximize the signal is accomplished using a single, fixed, infrared LED, and six phototransistors positioned in the hub of the wheel. For the slab impulse response component, a 1-3 lb impulse force transducer with hard plastic head is raised and dropped periodically (at least every 3 feet). The response of the bridge deck is monitored with a vertical, fixed velocity transducer (geophone) on the axle. The contractor's final report is available.
