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 following first part gives an overview about the
bridges and the background on stress corrosion cracking,
added with explanations about the planning steps. The second
part describes the strengthening with carbon reinforced concrete
with a focus on bridges. The third part goes further into
detail, regarding the construction and the design of a carbon
reinforced strengthening for the superstructure.