Overview
Swiss federal laboratories for material science and technology already examined numerous bridges with the mobile geo-radar system. It mostly focused on the detection of the lining thickness and the depth of the top reinforcing layer in the foreground. Most of these studies could be clearly seen as a success, but the success of control was limited to a comparison between results and individual radar soundings.
Should be carried out and evaluated a radar investigation from demolition along the intended cut lines, this would offer a rare opportunity for a one to one comparison between radar results and reality.
Evaluation of the accuracy and benefits of radar results (ground penetrating radar) by a one-to-one comparison with reality.
Field tests on total of 6 bridges.
Bridges designated for demolition were inspected with ground penetrating radar and the results were laid open. During and after demolition radar results are verified through a comparison with actual bridge parts.
In a laboratory experiment the interior of a bridge girder was mapped in three dimensions
and in great detail.
Funding
Results
The mean difference between radar results and reality was 9mm. The suitability of the radar method for the detection of pavement damage was not evaluated conclusively during this project.
The concrete cover of the top layer of re-bar was determined on 77% of the inspected
sections. The mean difference between radar results and reality was 10mm. In addition, the spacing between single bars was determined in many places.
The position of tendon-ducts in a bridge deck was determined with errors of less than 50mm.
The percentage of ducts that can be localized depends on the amount of effort and on the
object under inspection.
Technical Implications
A pilot study suggested that the method is suitable for the detection of zones of increased
chloride content within the concrete (for example on bridge decks beneath pavement and
sealing). Further work on this subject is advisable.
Other results
J. Hugenschmidt: A one-to-one comparison between radar results and reality on a concrete bridge, Proc. 9th International Conference on Ground Penetrating Radar April 29-May 2, 2002, Santa Barbara, California, USA;
J. Hugenschmidt: Accuracy and reliability of radar results on bridge decks, Proc. 10th International Conference on Ground Penetrating Radar, June 21-24 2004 Delft/NL;