There has been a lot of discussion about non-destructive tools for examining asphalt pavement—the Dielectric Profiling System being one of them—but what do we have for concrete? The Ultrasonic Shear-wave Tomography technique called “MIRA” is a tool that answers that question in a number of ways.
A 2011 paper titled “Ultrasonic Tomography Technique for Evaluation of Concrete Pavements” was written by Kyle Hoegh, Office of Materials and Road Research-MnDOT and 2011 Student and Research Assistant-Department of Civil Engineering-University of Minnesota; Lev Khazanovich, Ph.D., Adjunct Professor-Department of Civil, Environmental, and Geo-Engineering-University of Minnesota and 2011 Associate Professor-Department of Civil Engineering-University of Minnesota; and H.Thomas Yu, Office of Asset Management, Pavement, and Construction-Federal Highway Administration and 2011 Pavement Rehabilitation Engineer Federal Highway Administration.
Tom Burnham, Senior Road Research Engineer-MnDOT, has been running the latest version of the MIRA device through its paces for several weeks. This is what he’s found:
The MIRA uses ultrasonic waves to build a 3D image of the features within a concrete pavement. It can be used to detect:
• Thickness: Concrete thickness estimation up to 3 feet deep with high accuracy
• Voids
• Delamination: Detection of cracking in the PCC layer or de-bonding between PCC layers
• Reinforcement/Dowel bars: Accurate estimation of reinforcement depth
• Joint diagnostics: Detection of concrete deterioration, dowel position, spalling, etc. at PCC joints.
Burnham has been using the MIRA recently to detect joint activation and he says the device makes it very easy to detect whether a joint has deployed or not. Just place the device over the sawn joint and in 2 seconds it displays the ultrasonic image on the screen and saves the data internally for later processing on a laptop.
In the case of delamination, the MIRA provides a few advantages over traditional methods. The current method for detecting delamination involves dragging a chain over the surface of the concrete and “listen” for hollow spots. That worked well, to some extent. With the MIRA however, the image generated can tell you exact depth, location and size of the delamination. Having that information about delamination, below the surface, can be very helpful.
Burnham said, “You can evaluate ahead of time if you think you are going to do just a partial depth repair, half way down, or are you going to have to do a full depth repair.”
In a recent test, Burnham discovered a delamination at a dowel bar, which was later verified by a core sample. He says he can do about 50 MIRA images in the time it takes to drill one core. The software stitches all the images together into a grid and allows the user to manipulate the image so you can look at the 3D rendering from every side.
Finally, the MIRA detects cracks in a concrete pavement that cannot be seen with the naked eye. Burnham will continue to test its capabilities through summer 2019. For example, he wants to see how soon after sawing a joint in a fresh concrete panel can the device be used to detect crack development within the joint. A recent report that included use of the MIRA to determine joint deployment was part of a conducted by a National Road Research Alliance (NRRA) member of the National Concrete Pavement Technology Center (CP Tech Center) at Iowa State University titled “Optimized Joint Spacing for Concrete Overlays with and without Structural Fiber Reinforcement”.
For the MnDOT article, please go to: http://www.dot.state.mn.us/mnroad/nrra/newsletter/currentissue.html?utm_content=&utm_medium=email&utm_name=&utm_source=govdelivery&utm_term=#mira
For the CP Tech Center Study titled “Optimized Joint Spacing for Concrete Overlays with and without Structural Fiber Reinforcement”, please go to: https://intrans.iastate.edu/app/uploads/2019/06/optimized_joint_spacing_for_overlays_t2.pdf
For the 2011 Paper titled “Ultrasonic Tomography Technique for Evaluation of Concrete Pavements”, please click on image above or go to: http://www.germann.org/TestSystems/MIRA%20Tomographer/TRB_2011_MIRA.pdf
2011 PAPER ABSTRACT: Ultrasonic tomography is an emerging technology that shows promise for quality assurance/quality control (QA/QC) during construction, or for making rehabilitation decisions in concrete pavements. However, the benefits of this emerging technology have not yet been fully captured for widespread use in highway infrastructure management. Verification of a state-of-the-art ultrasonic tomography device (MIRA) is presented through multiple field trials involving typical pavement constructability and rehabilitation issues. Field trials indicate that, while the device is a useful portable pavement diagnostic alternative capable of consistent thickness measurement, reinforcement location, and distress evaluation, significant efforts and user expertise are required for measurement and data interpretation of large scale application. Thus, software was developed for a more productive, objective signal interpretation method with automated analysis of reinforcement location in continuously reinforced concrete pavement. This type of automation for multiple applications shows promise for the use of ultrasonic tomography to improve large scale pavement QA/QC and rehabilitation projects in the future. Nevertheless, the research in the paper shows ultrasonic tomography to be an accurate, reliable, and convenient alternative or supplement to traditional techniques that can be utilized for a wide variety of small scale pavement diagnostics applications.
HOME PAGE PHOTO: From CPTech Center Study:
Joint activation data being collected on an existing
overlay in Worth County, Iowa using
a MIRA device placed over the sawcuts.