Carbon for the Marienturm
The RWTH Institute of Structural Concrete has restored the window of the Marienturm or St. Mary's Tower of Aachen City Hall with a carbon-based textile concrete, while adhering to the strict monument protection requirements.Copyright: © Institute of Structural Concrete
The Marienturm was destroyed during World War II. During reconstruction of the tower, 19 different glass concrete windows were constructed on the western side based on the old masonry of the rubble. In accordance with the technical standards of the time, the thick glass panes were imbedded into the concrete, the gaps were filled with steel-reinforced concrete, and affixed to the wall with a bordering steel frame.
Keeping in mind that 2014 was the Year of Charlemagne, these windows were to be restored, since they were badly affected by corrosion. However a prerequisite to this was that the look of the exterior could not changed. "After we removed the windows and brought them to our workshop, we numbered all of the glass pieces," says Dipl.-Ing. Sergej Rempel, a scientist at the RWTH Institute for Structural Concrete. "This allowed us to put them back exactly where they belonged."
They first carefully separated the glass from the windows they had removed and free it from any old concrete. In order to meet today's static demands regarding wind strain and to do so without increasing the thickness of the concrete layer, they resorted to a epoxy resin soaked carbon textile. "This can increase the test load to an ultimate moment of 2.5 kilonewton meters per meter," explains Remptel. "This corresponds to a wind strain of about 14 kilonewtons per square meter." In comparison, the exposure measures a maximum of two kilonewtons per square meter, proving that the windows' strain capacity is more than sufficient.
After work was completed, all of the windows were fitted to the old openings in the wall down to the last millimeter and then grouted.
Source: Press and Public Relations