Low-Speed vs. High-Speed Infrared Bridge Deck Scanning: The Pros and Cons

Why?

  • IR camera's "integration time" (typically >10 ms).
  • The faster the speed, the more the image is blurred (a vehicle at 60 mph moves almost 0.9 ft. in 10ms).

But...

  • Low speed method requires a rolling lane closure
  • Higher speed would have some advantages
  1. No closures (safer)
  2. Lower cost
  3. Higher production rate

As a result, several agencies have specified high-speed IR and a number of high-speed projects have been carried out by Infrasense and others. 

  • Michigan DOT (11 decks, 2015)
  • Wyoming DOT (32 decks, 2015)
  • Nevado DOT (Las Vegas viaduct, 2015)
  • Colorado DOT (15 decks, 2014)

How good are the results? When is it appropriate to do high-speed vs. low speed?

Infrasense has tested the effects of speed on the quality of the IR data

Typical Corresponding Visual and IR Data Frames at Low Speed

visual vs IR.jpg

IR Images vs Speed - Patches under an AC Overlay

IR Images vs. Speed - Deck Delaminations

Images get blurrier at higher speed, but there is still information. 

Images get blurrier at higher speed, but there is still information. 

 

Summary of findings:

  • Low speed provides more detailed delineation of delaminations
  • When delaminations are clear in the IR data, high speed and low speed results match reasonably well
  • When delaminations are not as clear (as occurs with overlays), high speed data is harder to interpret (based on project experience)
  • High speed does not allow for confirmation sounding

Conclusions - Low-Speed vs. High-Speed

  • Low-Speed is a preferred option for:
  1. Project level evaluations and mapping of repairs
  2. Low-speed, low-volume roads
  3. Decks with concrete overlays
  • High-Speed is a viable option for:
  1. Network level evaluations
  2. High-speed, high-volume roads (no closures)
  3. Decks without overlays