NONDESTRUCTIVE TESTING BRIDGE INSPECTIONS

Recent bridge failures remind us of the importance of documented bridge inspections. Nondestructive testing techniques, if used, are a valuable resource to assist the bridge engineer and enhance inspection accuracy and results. These methods identify, locate, quantify and document flaws and weakness that in most cases are not visually detectable or audible to the human ear when hammer sounded.

NDT Corporation has successfully used sonic/ultrasonic testing to: determine the condition of bridge deck concrete; identify voids in post tensioning ducts; identify areas of broken pre-stressing in beams; assess epoxy repairs; and to evaluate the integrity of abutments and piers. Our projects include new bridges (under construction) as well as bridges that are over 70 years old.

The primary benefit of the sonic/ultrasonic testing is its ability to identify and quantify micro cracking. The initial phase of cracking is at the micro level well below what is visible to the naked eye. With continued use, vibration, loading and unloading or freeze thaw cycles, these micro-cracks coalesce and become larger reducing the concrete strength.

At each sonic/ultrasonic test point, the compressional and shear wave velocity values as well as the thickness resonant frequency are measured, providing a 3-D assessment of cracking and concrete strength. This data becomes a bench mark for future measurements to identify changes in concrete conditions. Sonic/ultrasonic measure the mechanical properties; Young’s and shear modulus and Poisson’s Ratio of the concrete.

The sonic/ultrasonic system used by NDT Corporation is very efficient. Typically, several thousand bridge deck measurements can be completed in a day and several hundred measurements in difficult to access areas like bridge beams.

Shown above are the results of a sonic/ultrasonic bridge deck inspection. The bridge deck results identify specific areas of weak concrete; differentiate areas of partial and full deck weakness/ repair.

Shown below are the results from a sonic/ultrasonic investigation of pre-stressed beams. These results identified locations where the beam concrete is low velocity/strength, no longer in compression and indicative of broken pre-stressing.

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