Infrared Testing System to Identify Delamination Between HMA Layers
I. Information
Infrared Cameras Inc. (ICI)
2105 West Cardinal Drive
Beaumont, Texas 77705
garys@infraredcamerasinc.com
409-861-0788 Office
713-859-3599 Cell
409-866-7227 Fax
II. Description of Proposed Thermal Imaging Technique
Thermal imaging is a high speed non-contact technique that can detect delaminations, voids, and other discontinuities in asphalt and concrete roadways and bridge structures. Because of the decrease in cost of hand held thermal imaging cameras they are used by many state highway department inspectors to identify cool spots or discontinuities when the asphalt is being placed. Non-contact point radiometers have been utilized to measure asphalt temperatures for years, but thermal imaging cameras allow you to visually see problem areas and some hand held cameras now allow you to measure as few as 256 points or as many as 307,200 points in a single image. The thermal imaging inspection used to identify delaminations or discontinuities does not require a radiometric thermal camera, but most inspectors using these systems prefer using cameras that measure temperature rather than qualitative imagers. The thermal imaging technique is based on sensing, visually seeing, and digitally capturing an image via a computer integrated in the camera or via a computer located in the inspection vehicle. Thermal cameras sense the difference in emitted radiation from the surface of the road. Delaminations and other discontinuities typically appear as mottled darker or lighter areas on the surface of the road and various color palettes in light hot or inverted dark hot can be used by simply choosing the best color palette for the environment and application. Other than for aerospace applications and what we call active thermography where a portable external heat source is used I am not aware of any developed thermal imaging system that can measure the depth of a discontinuity in the field.
I would also like SHRP and NCAT to know I, Gary Strahan am an (ASNT) American Society of Non-Destructive Testing Level III. I am certified in or have experience with Liquid Penetrant Testing, Magnetic Particle Testing, Ultrasonic Testing, Radiographic Testing, Leak Testing, Acoustic Emission Testing, Laser Testing, Infrared Thermal Testing, Ultra Violet (UV) Corona Testing.
ASNT Certification # MM 1383 in several Non-Destructive testing methods and have been involved with the ASNT and numerous NDT projects and testing development since 1979. I have attended Lamar University, Wellington University, U.S. Navy HTA School, Don Boscoe Technical Institute, UCSD, College of Oceaneering (Under Water Welding, Saturation Diving and Underwater Non-destructive testing) now California Polytechnic. I was a commercial diver and have been down 640 feet breathing a helium oxygen mix. I owned West Coast Welding and Diving (San Diego), International NDT Services, and managed a PSI Civil and NDT Testing Laboratory in Beaumont, Texas. My studies have included but are not limited to Marine Biology, Materials Science, Corrosion Engineering (NACE), Civil testing (cylinder, Troxler, slump, etc.) ASME Pressure Vessel and Piping system Design.
I was a Manager of the Inspection Engineering Department at the Mobil Oil Refinery in Beaumont, Texas and Senior NDT Level III for Mobil Oil Corporation and am now President of the Infrared Training Institute, Texas Infrared, and CEO of Infrared Cameras Inc., Certified as an AI Authorized Inspector for the National Board of Boiler and Pressure Vessel Inspectors, API 510, 653, and 570 Certified.
III. Proposed System, Technique, and Basic Physics
The proposed thermal imaging technique is used and utilized almost daily by several U.S based companies as well as companies located abroad. The thermal imaging system is typically elevated approximately 12 to 15 feet above the road surface and utilizes a wide field of view (FOV) lens to insure coverage of the complete road or multi lane surface, within the thermal cameras FOV. Several issues must be considered when choosing the correct thermal system for Non-destructive testing of road and or bridge deck surfaces. The physics and specifications of the thermal systems should be understood in order to make the correct choice. Many types and various wavelength thermal cameras are available today. The two primary thermal camera systems considered for this application are a (VaOx) or Vanadium Oxide microbolometer based camera and an InSb or Indium Antimonide (photon counter) type of sensor. There are two types of microbolometers the first is an Amorphous silica (As) and the seconds is VaOx. Amorphous silica is less sensitive but has a higher thermal time constant and can operate at higher speeds. Example: Amorphous silica microbolometer electronics have been designed to image at frame rates up to one hundred frames per second and VaOx up to sixty frames per second. The VaOx sensor has outstanding sensitivity (as low as .027 degrees Celsius) and will work adequately at the forty five miles per hour speed which was mentioned at our meeting in Atlanta. The As sensor has a best typical sensitivity of .070 Celsius. The InSb sensor with the proper electronics can image a bullet (twenty two thousand frames per second) in flight and has the best sensitivity, but an InSb camera utilizes a cryogenic cooler and costs 5 to 25 times that of a VaOx microbolometer based camera. Our InSb camera sensor has a thermal sensitivity of < .014 degrees Celsius. The ICI 7320 is the most sensitive microbolometer based thermal imaging radiometer in the world today. This product was recognized by NASA Tech Briefs as “Product of the Month” in February 2009 and is in the running now for product of the year. ICI also manufactures several lower cost options like the Centurion, but thermal sensitivity is not as good as the ICI 7320.
IV. System Accuracy, Repeatability, and Cost
Unlike NDT methods such as Ground Penetrating Radar and Moisture Analysis Typical industrial thermal imaging systems are accurate in temperature measurement to plus or minus two degrees Celsius at thirty degrees Celsius. This is a typical industry standard. Because ICI manufactures system used for Non-destructive testing and medical applications we have reduced that calibration accuracy to less than one tenth of one degree Celsius. These measurements are repeatable even during environmental conditions change. The thermal imaging systems are actually calibrated in environmental chambers for this reason and continually cycled during the more than six hour calibration process.
Thermal Imaging is affected by environmental conditions. Solar loading caused by radiation from the sun versus night time conditions can create totally different results. Although this is an issue it is not insurmountable, but does need consideration when conceptually designing a system that will possibly integrate four or more technologies. I have personally used the systems to look at asphalt roadways at sun up, early morning, mid day, early afternoon, sunset, directly proceeding sunset and night time. Because asphalt is such a great emitter of thermal radiation it is a fantastic test specimen. Finding delaminations and various other types of discontinuities in asphalt surfaces is very repeatable. The sun and water located between layers of an asphalt covered concrete surface actually are friends to the technology and the inspector. Areas where water is present typically look quite different than areas of complete homogeneity. I have attached a link to an article I wrote on bridge deck inspection that was published in June of 2008.
I believe this article will give SHRP an idea of my experience in this particular secular field of NDT.
Please click on the following link:
Concrete and Asphalt Bridge deck delamination
With the cost of hand held systems decreasing annually I envision a day when every highway inspector and even construction crews will own and use these systems. In 2008 the Texas Highway Department purchased approximately twenty hand held systems from ICI. These systems provide good images and lots of data in each stored picture as measurement can be accomplished on each of the more than nineteen thousand two hundred pixels with these 160 x 12o microbolometer based imagers. The cost of one of these hand held cameras is $4995.00.
There are several reasons ICI has chosen the 7320 and or the Centurion to possibly be used for testing for his application and the primary reasons are sensitivity and cost. The secondary reasons are accuracy and reliability. The frame rate of each of these systems is 60 Hz and the frame rate our 640 x 480 systems are 30 Hz so using the 320 x 240 microbolometer gives you the road speed ability you need as well as sensitivity and image quality. This frame rate is the same for all 640 x 480 camera manufacturers. The ICI 7320 sensitivity as stated earlier is unsurpassed. The cost of an ICI Centurion is $5500.00 and the cost of the ICI 7320 is $9995.00. As always cost is a huge part of the end product and we are offering these options with this as a primary consideration. Prices could come down some in quantity.
V. Time for Development and Proposal
ICI has off the shelf systems that could be utilized for preliminary Phase One testing available today. We would propose using both the Centurion and the ICI 7320 for initial testing for a proof in concept and do determine the need for sensitivity. We also believe we could meet the current time lines required by SHRP.
I believe we could and should work together with the other parties interested in devoting time, manpower, and dollars to the development of this application with an understanding that end product would include an ICI system and be a product ICI and partners could offer commercially. ICI would appreciate any financial help from funding available, but would be committed in investing our own time, experience, and resources in helping develop a usable HMA inspection.
Thank you,Gary Strahan
CEO
Infrared Cameras Inc.
