The project refined and field-tested a prototype nondestructive evaluation system previously developed in an FHWA-sponsored project. The system utilizes the Shadow Moiré interferometry method and measures both vertical surface displacement and changes in slope of surface distress. The IDEA research focused on improving the Shadow Moiré inspection technology and completing a comprehensive user-friendly software package to assess road surface distress. Improvements involved an increase of maximum vehicle acquisition speed of 22%, new light emitters with special horizontal condensers to improve interference fringe pattern contrast, lightweight grating as opposed to two smaller gratings for greater road coverage, and a more accurate distance measuring system. Refinements in post-processing included rewriting C-based image analysis algorithms so that they run under the Pentium personal computer (PC) processor rather than slow video processors. Improvements in image digitization were also realized, such as improved image data integrity and large increases in throughput, allowing for faster post-processing of videotape images.
The prototype road inspection vehicle (Figure 1) was an enclosed uni-axle trailer and was available from the National Technical Information Service (NTIS # PB97-151617).The final report is capable of acquiring road surface distress information at velocities up to about 55 mph, allowing users to categorize, rate, and determine roadway locations of all out-of-plane surface deformations along a particular roadway. The cost of the road inspection system is estimated to be about $60,000.
Ford Motor Company has donated a full-size field vehicle to replace the trailer system for performing field tests. The system is ready for field validation under operational conditions. State agencies and private consulting companies have shown interest in using the system in the field.
A special two-page IDEA product report, Surface Condition Assessment and Profiler System for Pavements Using Shadow Moiré Interferometry,was released in June, 1995.
The final report for this IDEA project can be found at:
https://www.trb.org/studies/idea/finalreports/highway/NCHRP012_Final_Report.pdf
