An impressive office and commercial building of Swiss Life AG is under construction in Zurich. The three-piece building complex with different dimensions and number of stories was given the name Tic, Tric and Trac in reference to Walt Disney. Despite the distinctions, it was possible to provide the complex with a uniform, but nevertheless striking appearance by means of a curtain façade consisting of precast elements made of architectural concrete.
Nägele, the precast concrete and ready-mixed concrete factory based in Austria and Switzerland, was awarded a contract for these precast elements; the company is running one of Europe‘s most modern production facilities.
According to the specification of the project tender, a total of more than 1000 precast elements were needed in four different designs. The quantities were too small for steel formwork and rather too large for conventional wooden formwork, as stated by the manufacturer. In search of a cost-effective alternative corresponding to the requirements, they came across the Alkus solid plastic panel, which was shortlisted owing to the advantages provided and the high number of repeat uses expected. For testing the practical feasibility, full-size mock-ups were made of the formwork using Alkus panels; this led to a good result and the decision to use the solid plastic panel.
Alkus panels allow for precast elements without visible joints
The solid plastic panel was already easy to use when manufacturing the sample formwork. The panels are available in any length that can be transported because Alkus panels are manufactured in a continuous production process; moreover, the panels can be welded together to produce any width without joints. Therefore, maximum dimensions of the elements, in this case 8.05 m x 1.24 m, just play a minor role.
The project required the production of façade elements with straight parts on the longitudinal sides and bent parts on the corners. As the Alkus solid plastic panel can be bent and shaped easily, it was possible to manufacture the curves and corners without any loss of quality.
The detailed production planning was made in close cooperation with Alkus engineers, thus optimizing the number of formwork units needed. Eventually, the 1150 precast elements were manufactured with 13 formwork units, corresponding to 88 precast elements per formwork, in theory. Depending on the shape, the number of parts varied: Hence, for example, 130 high-quality elements were produced with the circular formwork. Such high quantities were manufactured with a consistently excellent surface quality, from the first concrete placing process up to the last. Further advantages prove true during production: The Alkus solid plastic panel is non-sucking, thus requiring relatively little formwork oil. Moreover, the cleaning times are reduced owing to less concrete residues.
Consequently, the statement made by production manager Markus Achtelik was quite positive: “We are glad that we have decided to use the solid plastic panels of Alkus. All advantages referred to, as long service life, consistently high surface quality from the first up to the last element and the high degree of dimensional accuracy have proven to be true. I also appreciated that the workers of Alkus took part in formwork construction and that they shared their experience with our workers.”