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Beton Doux: Concrete Silos in Paris by Vialet Ballus

On the edge of Paris, a utilitarian complex of cement silos is elevated into a sculptural composition that animates a dreary and dislocated urban enclave

Officially launched in 1991, the 130-hectare Paris-Rive Gauche redevelopment plan is the city’s biggest single urban operation since Haussmannian times. Located in the 13th arrondissement, it runs alongside the Seine all the way down to the city limits (where Paris meets the neighbouring municipality of Ivry) and concerns former railway land behind the Gare d’Austerlitz. Because of the SNCF’s refusal to move the station out to the periphery, the operation has proved fantastically complex, requiring the construction of a 32-hectare concrete platform over those railway tracks that are still in operation, a huge infrastructural investment that has created a giant artificial hill on this flat riverside site.

The operation is now entering its final and perhaps most complicated phase, on the border with Ivry, where a spaghetti jumble of roads and railways − both Paris’s ring of outer boulevards and its six-lane orbital motorway cross the tracks at this point − makes for a very noisy and convoluted environment.

SiloSitePlan

Site plan

This is also the most controversial phase, since veteran architect and urbanist Yves Lion, called in to draw up the masterplan for this sector of Paris-Rive Gauche, insisted that the only building type that could work in this difficult context was the tower block, thereby precipitating the end of a 33-year moratorium on tower building in Paris. After impassioned debate, the municipality voted in 2010 to raise the general building height in this area from 37 to 50 metres, as well as approving the construction of stand-alone towers, the tallest of which (to be built by Jean Nouvel) will rise to 175 metres on completion in 2018.

Among the redevelopment casualties in this sector are the elegant Calcia cement silos (built by the Arsène-Henry brothers in 1968) that currently occupy a prime riverside site earmarked for housing. But since neither the municipality nor Calcia wanted the silos to leave the sector, a new location was proposed 300 metres away, allowing Paris to keep the business tax generated by the facility and Calcia to keep their competitive edge, since very few of their rivals are so centrally sited. The new location, on the other side of the orbital motorway, comprises a small, irregular plot of land, part of which actually sits under the motorway viaduct, with one side bordered by railway tracks. Indeed it is by train that the cement arrives, from Couvrot, 200 kilometres to the east, before being pumped into the top of the new silos, from which it can be distributed to lorries that pass underneath them.

SiloFormwork

The concrete sections were prefabricated off-site and assembled by crane

Architects have long been sensitive to the sculptural qualities of silos − Le Corbusier famously included photographs of North American examples in his 1923 Vers une architecture − and here was a chance for an architect to shape the plastic potential of this utilitarian facility. Initially Franck Vialet, the partner in charge, imagined a pair of rather slender cylindrical silos rising to the new 50-metre height limit, but planning permission was refused, on the grounds that it was not for this kind of thing that the regulations had been relaxed.

Asked to bring the silos down to 37 metres, the architects were forced to widen them to maintain capacity (11,000 cubic metres in total), meaning that, at 20 metres’ diameter each, they now filled a sizeable portion of the site. It is for this reason that the ancillary spaces required by the brief − administrative offices and a testing centre for Calcia’s subsidiary Unibéton − have been raised up on pilotis (so that vehicles can pass underneath) on the one hand, and slid under the motorway viaduct on the other. Linking them is a slender circular tower that acts as the linchpin of the ensemble: equipped with a central lift (capable of carrying heavy loads) and a peripheral spiral stair, it provides access from the exterior and the testing centre to both the offices and to the silos’ rooftop equipment.

SiloPlanPreview

Floor plans - click to expand

SectionPreview

Sections - click to expand

Vialet has rather a penchant for concrete and, since one if its principal ingredients is cement, it seemed only appropriate to use it to build the Calcia silos. In fact, as he likes to point out, the whole site is realised in concrete, from the grade platform, to the offices and testing centre, to the silos themselves. All the cement used in the mix came, of course, from Couvrot, but the techniques employed to construct the different elements varied. The platform was poured in situ using traditional formwork, and while the silos and the linchpin tower were also poured in situ, sliding formwork was used since the calendar was very tight and no overrun could be tolerated. Rising at a rate of 12 centimetres an hour 24 hours a day, each was completed in around two weeks, the first requiring, moreover, a special concrete mix so that it could be built during the winter months in sub-zero temperatures. Meanwhile, the oval-sectioned offices and testing centre, which Vialet likens to horizontal silos, were prefabricated in pieces offsite and assembled by crane. Since concrete is permeable when used horizontally, a polyurethane resin, tinted the same colour as the untreated concrete, was applied to their upper surfaces, while elsewhere the concrete has been left brut de décoffrage − streaked, stained, smooth and steely grey.

While the silos are by necessity entirely blind, the offices, testing centre and linchpin tower are each pierced with openings, all of which take the form of irregular polygons of different proportions and dimensions. On the linchpin tower the openings get bigger the higher they go, the idea being to express a progressive dematerialisation as the tower rises to the sky. On the offices and testing centre, on the other hand, they are scattered randomly, and fitted with glass that is held in place by beautifully detailed metal frames painted in Calcia orange. For Vialet, these irregular polygons are an evocation of the aggregate used in concrete, ‘a mineral expression of smashed rock’. Certainly, when viewed from a distance, they give the impression that the structures have been pockmarked by heavy-artillery shelling. The octagons are also expressed in the railings separating the site from the street, a subtle, ghostly presence visible only from an oblique angle.

SiloImagepreview

The oval-sectioned testing centre is like a horizontal silo - click to expand

ConstructionSectionPreview

Construction section - click to expand

It is in this, the handling of this project’s dichotomy of scale, where the massing of enormous pure forms brought together in light has been realised with an attention to surface and detail worthy of the most intimate domestic interior, that this utilitarian facility has been elevated to the level of architecture. Whether seen close to or from afar, it looks just as good. At the time of writing, the silos dominate their surroundings, appearing especially dramatic when viewed from the orbital motorway, the linchpin tower having been sited so as to create maximum billboard impact on passing drivers.

Soon, however, the facility will be dwarfed by attention-seeking mastodons almost five times taller, but will surely hold its plucky little own against these architectural Goliaths.

Concrete Silos

Architect: vialet.ballus

Photographs: Daniel Moulinet (Interiors), Stéphane Chalmeau (Exteriors)

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