The Zwingli above-ground bunker in Bremen was built at the end of the Second World War to protect the population. Because of the massive reinforced concrete shell and the security it provides, the building is now used as a data centre. However, the load-bearing capacity of the ceilings needs to be increased to allow for greater loads in future use. Furthermore, the use of the building also places demands on the temperature resistance of the strengthening solution. During normal operation, a temperature of 55 °C is expected and in the event of a cooling failure, temperatures of up to 80 °C are possible for short periods. In this context, the CARBOCON GMBH developed a detailed design together with the concept of strengthening with CRC. With this solution, the load-bearing capacity can be increased with a thin layer of CRC, a reduction in interior ceiling height can be avoided and an economical implementation can be achieved.