Construction of the first of 28 chalice-shaped concrete pillars that will be the eye-catching feature of the 400m long and 80m wide train station concourse in Stuttgart begins. The pillars will support the roof of the underground station and serve as “light eyes”, allowing daylight to enter the hall below.
What began with extensive testing in 2015 can now finally continue: The construction of the spectacular and complicated pillars for the underground through station in Stuttgart. The finished pillars will weigh over 1,000 tons and be of up to 13m in height. Building one pillar takes approximately five months; two pillars can be built simultaneously in each construction stage.
The requirements for the concrete used for the design are equally demanding. Christoph Ingenhoven, architect of the Global LafargeHolcim Awards Gold 2006 prize-winning project, requested that the surface of the concrete has to be white and smooth; the imprint of the wooden molds not visible on the finished pillar. To achieve this non-porous surface, a special resin has to be used to coat the molds.
When the first molds were taken off, a perfectly even surface appeared that was slightly turquoise. This effect called “greening” was expected and happens because of metal sulfides contained in the special concrete mix that makes the pillars extra durable. Once the molds are taken off and the concrete gets in touch with oxygen, it gradually turns a perfect white. To protect the foot of the chalice of the pillar from rain and wind, it is covered in plastic until construction of the upper part continues.
A mammoth project
The pillars are only a small part of the extensive project Stuttgart 21. The project includes the rearrangement of the Stuttgart rail hub with four new stations and 57km of new track, of which roughly 30km are in tunnels. The aims of the project are to transform the station quarter in Stuttgart, improve the rail network for high-speed trains around the city and thus reducing journey times. Due to many delays, protests, and debates about funding, the project is expected to finish in 2024, three years later than planned.