For the first time in Germany, CRC has been used to strengthen a highway bridge. The structure is a three-span, approximately 70 m long bridge, part of the federal highway A648 in Frankfurt (Main), which crosses over the river Nidda and two cycle paths. It was built in 1971 using the KA 141/40 prestressing system from the company Philipp Holzmann AG. The embedded "Sigma Oval" pre-stressed steel bars were considered to be at risk of stress corrosion cracking. The calculative assessment showed that a large proportion of the pre-stressed steel could fail unnoticed under normal traffic conditions, so that the structural safety of the superstructure would no longer be guaranteed under full load. In this case, one speaks about a structure without sufficient warning behaviour - an unacceptable condition. Due to the importance of the bridge in relation to the transport network, it was not feasible to rebuild it in the short term. Strengthening of the entire structure was therefore necessary to extend the remaining lifetime of the bridge. Conventional strengthening methods, or even shoring, would have significantly shrinked the clearance under the structure for the cycle paths, caused massive encroachment into the nature conservation area, and severely and permanently reduced the flow cross-section of the Nidda. Alternative solutions were needed!

Thanks to purposeful strengthening, the deficit in load-bearing capacity is now compensated for by just a few centimetres of CRC. On the upper side, the strengthening layer is fully integrated into the roadway without the need to increase the bridge's gradient. On the lower side, the strengthening layer applied under the edge girder is only 3 cm thick, causing minimal impact on the undercrossing cycle paths. The sensitive natural area of the riverbank below the main span remains completely unaffected by the strengthening work!