Liège [satellite]
Rudy Ricciotti 🔗, Bandol
refurbishment, precast concrete, glass
BFT 08/2016
38 - 42
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Museum-extension "La Boverie" in Liege

Concrete trees

The historic La Boverie Museum in Liege has been expanded. The loadbearing support structure consists of precast exposed concrete components made from SCC and brightened with limestone powder from local quarries.
At first glance, one does not expect that this historic building, which is vaguely reminiscent of the Sanssouci Palace in Potsdam when seen from the park, is actually a monument to modern construction technology. In fact, it is the world's first building to have a foundation of driven concrete piles extending to depths of about 10 m. The subsoil consists of alluvial deposits, which is hardly surprising in an island set in a river: the Meuse, in this case. The building was erected as an exhibition pavilion for the first Belgian world fair in 1905. (The second - known for the Atomium - took place in Brussels in 1958). Liege was originally selected because in those days this Belgian city was a leading industrial metropolis and famous for its steel. Today's art museum is the only building from the fair that has been preserved.
Transparent "nothingness"
Today the building is positioned off-center in a small park at the upstream tip of the island. The rear of the building is very close to the bank of the narrower Meuse channel. French architect Rudy Ricciotti, who also designed the MUCem Museum in Marseille, placed a 1,000 m² extension between the pavilion and the river. His concept was to enlarge the building with a transparent "nothingness" and draw the surrounding landscape into the building, making it part of the exhibition.
Specifically, it involves an avenue of trees on the island that runs along the bank of the Meuse and the trees that had to give way to the addition where the avenue meets the museum. The architect placed concrete tree columns on the alignment of the avenue. They now support the extension's flat roof and are enclosed by areas of vertical glass. The row of trees appears to pass through the structure, which consists of a single, 6-m high hall, and continue on the far side.
The extension floats between 3 and 5 m above the ground. A footpath and a delivery road run beneath it, parallel to the river. This location is characterized by 34 cylindrical piers, some of which act as supports for the above-mentioned tree columns in the hall. The architect also understands them as a reference to the concrete pile foundations that were required for the extension.
The Liege architectural order
As in the classical period, the viewer encounters an abstract architectural order in the Liege museum. With the ancient Greeks, it was the famous triad of Doric, Ionic and Corinthian. In Liege, it is a formally reduced dyad, consisting of a simple, remarkably smooth pier, surmounted by a very complex cruciform column.
The lower piers were cast in place using a cylindrical steel form. One story higher, the columns inside the hall were produced using precast concrete methods. The latter stand plumb on the former, separated only by the ground floor slab. With their heads widening across the diagonal and enlarged footings, these columns look like trees carrying the roof load. They are cruciform in plan with regular legs. This shape provides additional cross bracing for the hall. It is an elegant physical solution that meets the legal requirement for increased structural stability, since Liege is threatened by earthquakes.
The 21 interior columns were made in the Netherlands by Hurks prefabbeton, using self-compacting concrete (SCC). (See pages 28/29). The SCC was produced by the company, which specializes in architectural concrete. They used CEM 1 cement obtained from HeidelbergCement AG's Elsa grinding plant in Gesecke, Germany. The result was a concrete in strength class C 50 with a standardised grey color that consistently matches RAL color 9009. "The architect really wanted the columns to be produced in UHPC, which would certainly have resulted in an even more attractive surface, but that was too expensive for the owner", says Rik Weyns, the Hurks group's project manager in charge.
At the architect's request, the precast components were mixed with local limestone powder, brightening them slightly to achieve a color identical to the exposed concrete ceiling, which did not use SCC. Tilman Reichert, lead architect at Rudy Ricciotti Architecte, points out that, in his experience, it is easier to achieve a color match by lightning, rather than darkening. Because with the latter - recalling paint boxes from school days - an additive comparative color adjustment would usually become darker than actually anticipated. Ultimately, the proportion of limestone powder in the columns amounted to 3 % of the cement mix. The cruciform columns were produced in an upright matrix form in rapid succession to avoid color variations resulting from different material batches.
Prestressed ceiling grid
The color of the prestressed exposed concrete ceiling elements provided the reference for the shade of grey. They represented the most complex components in construction technology terms. Each of these 3 m wide and 11 cm thick filigree ceiling elements stretched across the entire 15 m width of the hall. A 30 cm thick concrete grid with compartments consisting of polystyrene blocks containing channels for tension cables was superimposed. Concreted on site, the polystyrene was left in place, allowing it to serve efficiently as interior insulation. The prestressing cables are connected to the columns and set under tension. They ensure the load bearing function of the roof and, like the cruciform columns, serve in cross bracing the building, especially in the event of an earthquake. The underside of the filigree ceiling elements remained completely untreated.
"Concrete is sustainable"
In his buildings, which are consistently composed of concrete, Rudy Ricciotti strives to display the construc¬tion material as naturally as possible. For him the material, which was already known in ancient times, is "by far the most natural! " In addition, steel was out of the question for him in this project, because Liege was once a leader in steel. However, no steel is produced nowadays.
Belgium's third largest city has undergone radical structural change since the decline of heavy industry many years ago. The architect approached the pressing social questions architecturally: For him, concrete is a key and an indication of redistribution of regional wealth. That is why he considered the admixture of local limestone powder so important. He wanted to send a positive signal, with this museum, this public building: For him, the texture and shape of the construction ma¬terial embodies a visible commemoration of the work that went into its creation.
Robert Mehl, Aachen