"Coring with Your Eyes Open" (GPR and coring)

Using GPR to better understand pavement construction prior to Coring

The "Coring with your eyes open" technique is a method for combining GPR with coring. For project level rehabilitation coring is still an important method, but GPR will never replace coring. GPR will never have the clarity of digging up the road and physically measuring that material, while it excels at scanning large areas to produce a simple large scale view.

With "coring with your eyes open", we recommend that before any digging is done, each potential core location is marked on the surface, or has it's GPS location collected.

Normally coring is done at regular intervals (e.g. every 50-100 meters) for a section of road. When analyzing, the cores are then combined with road plans to understand the pavement condition and outline any issues. The problem with this approach is when there are differences between the road plans and reality, significant subsurface patching, a localized repair work, areas of local moisture ingress or other localized defects. When this occurs, often a percentage of the cores taken do not make sense. The typical result is that these cores are not considered as part of the analysis: only using the cores that match up to road plans are used. This can lead to an incorrect understanding of the subsurface.

The GPR data is then collected for the road. RPS analyzes the data, and provides to the customer a quick "changes of construction" view of the pavement. In this view it becomes clear where the subsurface differences are. If a region is consistent, only one or two cores will be required in that zone. Areas of higher moisture ingress can be detected and coring then used to investigate further. Also areas of significant subsurface patching or localized anomalous asphalt depth changes can be avoided, as coring in these locations may not to be representative of the remainder of the section.

Core samples

HRA wearing course, HRA base course with gravel aggregate, up base a DBM with gravel aggregate, and a lean concrete lower road base. Bituminous mixtures with gravel require 2% hydrated lime added.

As a result of using this method, most customers can more than halve the number of cores taken, while still getting a better understanding of the pavement construction. Normally the saving in the number of cores pays for the GPR, so the end result is a better understanding of the pavement condition at a lower total cost. Once RPS obtains the core data, further refinements in the accuracy of the GPR layering can be made and delivered to the customer.

Another alternative is thatGPR can be collected after coring. This allows for a better understanding of existing core data. While this is very effective it may not have as many cost benefits as a full "coring with your eyes open" technique as you are not reducing the number of cores taken.

Return to top