The discus-shaped, translucent roof of the BayArena, with a diameter of 217 meters is a new and spectacular showpiece project for the application of Makrolon® high-tech sheeting.

After a complete overhaul, the BayArena, the home of Bundesliga soccer team Bayer 04 Leverkusen, re-opened its gates in time for the start of the new season, and now complies with the very latest international standards. Bayer MaterialScience played a significant role in this. The discus-shaped, translucent roof with a diameter of 217 meters is a new and spectacular showpiece project for the application of Makrolon® high-tech sheeting. To ensure durability, the steel support structure, weighing around 3,000 metric tons, has been provided with a special anti-corrosion coating based on polyaspartic raw materials that has both economic and ecological advantages. Both applications underline Bayer MaterialScience's many years of expertise in these fields and highlight the intensive cooperation with customers along the value chain.

The World's Largest Makrolon Frisbee

With a total area of 28,000 square meters, the roof spans the stadium's entire extended stand area. Its construction is based on the spoked wheel principle. The triple-wall sheets of Makrolon Multi UV 3X/25-25ES white S 146 were supplied by Bayer Sheet Europe GmbH, a subsidiary of Bayer MaterialScience that specializes in the development, production and marketing of high-quality polycarbonate and polyester sheet for a wide variety of applications. Polycarbonate is noted above all for its high break resistance, impact strength, high- and low-temperature resistance, and light weight. "This material is brilliant. I can't imagine anything better for designing a large roof like this without any additional supports," says Hans Dannenberg, who headed the stadium redevelopment project. "What we have here is the world's largest Makrolon Frisbee".

The design and subsequent assembly of the sheets presented a major challenge, because the roof’s circular external contours gradually change to a rectangular shape towards the inside. This means, simply because of the very large area involved, that enormous forces act on the roof. Another handicap was that very little time was available for actually putting up the roof. But Makrolon has two great advantages: its outstanding machinability and the very low weight of the individual plastic sheets. After preliminary assembly, the sheets were hoisted up by cranes to a height of 30 meters, where they were mounted on the unsupported steel cable structure by specially trained industrial climbers.

Makrolon sheets have, in fact, been doing an outstanding job in the BayArena since the 1990s. In the meantime, the product's properties have been further optimized: for example, the light transmission of the sheets is better suited to the requirements of a stadium. While they protect the spectators from too much sunshine, they also allow enough light through to encourage the grass to grow.

Decision makers in the building sector also value the versatility and attractiveness of polycarbonate, as is shown by other large-scale projects that are currently being planned, for example in China. "The models we have demonstrate once again how adaptable polycarbonate sheeting is in use," says Thomas Kastner, head of the semi-finished products segment. Other spectacular stadiums were also projected – for the next European Football Championship in Poland in 2012 and the Football World Cup in Brazil in 2014, for example. Says Kastner: "I am delighted with the continually increasing popularity of polycarbonate and the status it enjoys as the material of choice in modern architecture. We intend to continue expanding  our sheet business, both in horizontal and in vertical applications."

Economical, Ecologically Effective Corrosion Protection

With large structures such as bridges and power plants, a three-coat paint system is normally used to provide the corrosion protection needed to withstand the ravages of wind and weather. To protect the steel girders of the BayArena, however, a different concept was chosen. With the innovative topcoat used here, which is based on polyaspartic binders from Bayer MaterialScience, two coats were sufficient, because a much higher film thickness can be obtained with one application than is possible with conventional topcoats.

"It would never have been possible to keep to the tight schedule for the BayArena without this new topcoat," explains Karl-Heinz Birk, head of the coating shop at Max Bögl Bauservice GmbH & Co. KG, one of the two general contractors responsible for the rebuilding of the BayArena. "Thanks to its rapid drying, we were able to significantly increase the throughput in the workshop compared with the conventional system. Furthermore, we were able to reduce solvent emissions very considerably due to its low VOC content."

Whereas a normal three-coat system takes about 24 hours to apply and dry, the complete application of the new two-coat system takes only six to eight hours. This saves time and money and is also good for the environment. If the topcoat is based on raw materials from the Desmophen® NH and Desmodur® N ranges, it will contain some 40 percent less VOCs than a conventional three-coat system. An ultra-high-solids coating such as this more than meets the present statutory requirements. "A further bonus with this topcoat is its excellent adhesion to metal. I see enormous potential for one-coat application directly to such surfaces," says Dr. Markus Mechtel, a corrosion protection expert at Bayer MaterialScience.

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