Concrete Reinforcement Cover Survey on a Bridge

Xradar conducted a survey on a set of bridges in southwestern British Columbia in order to gain information about how much cover the reinforcing bars (rebar) had.

Situation

The main objective was to identify any areas with severe corrosion and accurately map out the concrete cover of the rebar within selected areas.

There are a wide range of factors that can lead to the corrosion of steel within concrete and bridges are especially susceptible. Environmental factors such as wind, water, temperature changes and rivers all contribute to the corrosion of the rebar within the concrete.

Due to the risk associated it is important to carry out regular corrosion mapping and rebar cover surveys on at risk areas in order to ensure public safety.

Solution

Xradar was hired to scan the bridges, with an area of 40,000 square meters needing to be surveyed. In order to avoid lane closures and disruptions data was collected using our specialized towed array, which performed scans on the bridges at 19km/h.

A typical slab section from the radar dataset

60 lineal kilometres of data was collected over the survey area using the towed array along with GPS and local coordinates to accurately map the positioning of the grid.

No concrete corrosion was detected in the survey area, so the survey results consisted of heat maps highlighting the concrete cover using AutoCAD and overlays on satellite imagery. This would allow the client to accurately estimate the remaining life and at risk areas of the concrete.

Conducting the same survey in a couple of years will allow for comparisons utilizing a four dimensional data set.

Xradar used a high frequency GPR survey to achieve the required accuracy and a mid-range frequency GPR to reveal information about the structural details underpinning the area. Several grids with evenly spaced lines were laid out resulting an approximately 350 sqm of total coverage.

The Xradar systems used were carefully calibrated onsite to ensure accurate depth measurements. Data was processed and compiled to produce contoured heatmap style results. Results were presented in a CAD workspace and digital reports delivered.

The Xradar survey was complimented with Vuit 3D laser scanning to achieve accurate, scaled georeferencing of our survey grids, and a convenient way to view and present the asphalt thickness results.

The survey revealed a distinct change in the asphalt thickness due to the structural change to the subsurface that was confirmed with the survey results from the mid-range frequency GPR. The data uncovered not only the asphalt thickness but also the nature and location of the subsurface features such as: beams, voids and structural slab changes.

3D Laser Scan, with Xradar results overlaid
Asphalt Thickness Map