NDT Corporation’s Automated Sonic/Ultrasonic Nondestructive System Tests Over 12,000 Square Feet Of Bridge Deck Per Day

An automated nondestructive sonic/ultrasonic bridge deck testing system (Pictured below)designed and built by NDT Corporation provides bridge engineers with a foot by foot measurement of deck concrete strength and the specific location of delaminations, weakened partial thickness (to the top rebar layer) and full thickness deck concrete, and debonded patches and wearing surfaces. This data provides bridge engineers with high resolution data necessary to design an affective repair program.

During the summer of 2008, NDT Corporation used this system to test the east bound and westbound 2,000 foot long 2 lane wide Chain of Rocks Bridges in Madison County Illinois and I-95 Bridges in Connecticut. The Chain of Rocks Bridges have a micro silica wearing surface and the I-95 Bridges have an asphalt wearing surface. Over 12,000 square feet of deck was tested each day. GPR data were acquired simultaneously to determine rebar spacing and depth of cover and to evaluate for moisture infiltration.

The sonic/ultrasonic measurements determine the characteristics of concrete by measurements of compressional and shear wave transmission velocities as well as the reflected compressional waves (pulse-echoes). The transmission velocity values determine the elastic deformational characteristics of the concrete, including Young's, Bulk, and shear moduli, as well as Poisson's ratio, and calculated strength values, which are principally controlled by the amount of cracking. The reflected (impact-echo) signals resonate at a frequency that is related to the thickness of the concrete and wearing surface and compressional velocity. For depth of deterioration determinations, an array of sensors is used to distinguish between direct (near surface) and refracted (deeper) wave velocity data. The combination of velocity and resonant frequency data are used to determine if wearing surfaces or patches are bonded to deck concrete. Continuous GPR measurements are made with high frequency ground contacting antennas to identify individual reinforcing bars and water infiltration into the deck concrete. Reinforcing data are used to determine rebar spacing and depth of cover. Water infiltration data can be used to evaluate the affectedness of water proofing membranes’ and to determine if there is delamination associated with the reinforcing steel (indication of reinforcing corrosion).

In addition to sonic/ultrasonic and radar data, detailed field descriptions of visual deck conditions are recorded. Available coring results and field observations are correlated with the sonic/ultrasonic and radar data resulting in a comprehensive high resolution multi method assessment of the deck concrete. These results are correlated and presented on deck plans (see below) with highway stationing and specific location, description and severity of weakened areas of deck concrete.

For additional information call NDT Corporation at 508-754-0417 or check our web site www.ndtcorporation.com.