Renovation of the Rhine Tower in Düsseldorf with CFRP reinforcing bars

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A special attraction of the Rhine Tower is the restaurant, which rotates around its own axis once an hour. From the closed platform below, panoramic windows allow visitors to enjoy a sweeping view over Düsseldorf all the way to Cologne. Another special feature, unique in the world, are the luminous portholes arranged around the tower. Coordinated with each other, they form a decimal clock. The tower stands on a cone-shaped support element, which transfers the total load of the tower to the ring foundation. Here is the access to the technical level and the tower entrance level.

Damage assessment

Meanwhile, there is damage to the tower, which was examined by the surveyor's office Exponent Industrial Structures. Here, it was found that in the area of the coated shaft substructure, there was rebar corrosion and concrete spalling in places, which extended in a ring around the shaft substructure. The coating, which had been applied during a previous rehabilitation, was detaching from the substructure in these areas. The damage revealed had to be rehabilitated in a targeted manner, taking into account the component edge conditions. However, the stability of the Rhine Tower was not at risk.

Remediation measures with carbon fiber composite

The objective of the refurbishment was to replace the corroded reinforcement and to create a permanent surface protection system to slow down the carbonation progress and to regulate the moisture in the concrete. The existing cone appearance was not to be altered by the measures. The requirements for the repair material were accordingly specified. A concrete replacement system with high ductility, a fine centric corrosion-free reinforcement of the concrete replacement system and a high crack bridging capacity of the surface protection were required. For the renovation of the Rhine Tower, the expert office Exponent chose Sto S&P CFRP round bars (3 mm and 5 mm) from StoCretec GmbH for the reinforcement. The round bars made of carbon fiber composite material are corrosion-free. To achieve a secure bond with the concrete replacement system, the CFRP bars had to be pretreated by applying an epoxy resin and then sprinkling with quartz sand. The laminating resin StoPox LH was used for the epoxy resin application and sprinkled with quartz sand with a grain size of 0.1-0.5 mm when fresh. The interlocking of the quartz grain bonded to the CFRP bars with the sprayed mortar enabled an optimum bond to be achieved. Anchors made of stainless steel threaded rods were inserted into the substrate and the CFRP rods were crimped with stainless steel wire. The sprayed mortar StoCrete TS 100 was applied to the reinforcement in two layers. An elastic surface protection system was applied to the finished sprayed mortar surface using StoCryl GQ and StoCryl RB. With the OS buildup, it was also possible to visually emphasize the edges in the polygonal structure of the cone.

Construction panel Rheinturm in Düsseldorf