Carbon reinforced concrete - An alternative method for strengthening Concrete Bridges; Part 2: Strengthening of concrete bridges with carbon reinforced concrete - pilot project "federal highway bridges (A 648) across the river Nidda

In 2020 two of three bridges, which are part of the german highway road A 648, were strengthened with carbon reinforced concrete for the first time in Germany. The two superstructures were erected in the 1970s as a pre-stressed beam. As tendons a so called -sigma-oval-steel was used, which is sensitive for stress corrosion cracking. According to German guidelines and to exclude a sudden failure, it has to be verified if a damage of the tendons can be seen at the surface of the cross section via cracks along the superstructure. This -crack before failure- criteria was not fulfil for the described superstructures. With reference to the relevance of the bridges in the local infrastructure around Frankfurt a. M., a strengthening concept was necessary. Due to that fact, a strengthening with carbon reinforced concrete was identified as an economic and minimal invasive method. The report on that forerunner project is spread into three parts. The first part gives an overview about the bridges and the background on stress corrosion cracking, added with explanations about the planning steps. The following second part describes the strengthening with carbon reinforced concrete with focus on bridges. The third part goes further into detail, regarding the construction and the design of a carbon reinforced strengthening.