Challenge – Measuring Asphalt Thickness and Uncovering the PCC Layer
multiVIEW was retained by Applied Research Associates (ARA) Inc. to perform a two phase Ground Penetrating Radar (GPR) survey for a 1.12 km section of Spragues Road in the Regional Municipality of Waterloo. The survey was targeted towards finding the asphalt thickness layer along with the thickness and extent of the concrete (PCC) layer underneath the road asphalt.
The first phase of the survey involved identifying the longitudinal extent of PCC sections within the pavement structure. This data was required to inform the second phase of the project which would focus on identifying and marking the lateral extent of PCC pavement structures. Once captured, cross sections of the GPR images would need to be processed and analyzed to define profiles of the pavement interface depths.
Solution
GPR was leveraged to conduct a high-speed longitudinal survey on both the north and southbound lanes of Spragues Road. Where possible, the bottom of the granular and PCC layers were identified, based on embedded reinforcement and slab joints. The second phase of the survey was performed along grid lines with 10 metre spacing and the identifiable PCC extents were marked on asphalt using fluorescent paint.
Data was viewed in real-time so information could be interpreted onsite. Post processing of the GPR data was then performed using proprietary RoadMap analysis software, a data processing package that makes it possible to view GPR cross section images and define profiles of pavement interface depths.
This information was then used to generate overall statistics for asphalt thickness along with PCC across the vast area. It was also leveraged to record variations in thickness across both the north and southbound lanes.
“Common field investigations often rely on discrete, widely spaced sampling and it is assumed that the data residing between discrete points is consistent, but this is not always the case. GPR allows more data to be captured with less drilling. Subsurface conditions can be thoroughly checked every metre along the road.”
Lori Schaus, P.Eng., Senior Engineer, Applied Research Assoicates Inc.