Investigate feasibility of using ground penetrating radar in QC/QA of rubblization projects

This study investigated if Ground Penetrating Radar can offer a suitable technology for mapping the physical condition of fractured slab rapidly, particularly under the steel reinforcement, without disturbing the fractured layer. A 4000" long composite pavement section was selected on BUT/WAR 75 in Ohio. The asphalt concrete layer was milled and the jointed reinforce concrete pavement was exposed. A thorough GPR assessment of the pavement prior to rubblization was performed, allowing a "baseline" condition assessment. Three passes were made to collect data along two wheel paths and the center of the lane. Following this, the exposed concrete pavement was rubblized in accordance with ODOT's rubblization specification using a resonant type pavement breaker and three multi head type pavement breakers. GPR tests were conducted on the rubblized layer at the same locations. Soon after completing GPR studies, several test pits were made using a backhoe. Physical measurements of the particle sizes were made through the depth of concrete pavement. This information, ground truth, was used to verify the information obtained from GPR signals. The data was analyzed to investigate any evidence leading to determination of fragments exceeding the size specification. Analysis of the data collected on the exposed concrete pavement, prior to rubblization, showed no significant peak in reflection of signals between the top and bottom of the slab. Analysis of the data on rubblized layer showed some peaks. However, the strength of the signals (reflections) was not strong enough to detect significant peaks. This analysis revealed the sensitivity of the data was not adequate enough to distinguish two layers within the concrete slab. In other words, the data did not indicate significant peak at the interface of rubblized and partially rubblized layers within the concrete slab. It became apparent that by increasing the signal-to-noise ratio, it may become possible to differentiate and distinguish the two internal layers. In summary, the study provided insight into additional data needed to establish GPR as a potential device in the future for evaluating the size fragments in R/R project. Lessons learned lead to a conclusion that, further work is needed to establish GPR as a rational, non-destructive and quick procedure to estimate the particle sizes in a rubblization project.