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Precast parts becoming accepted
Homage to the continuity
In the vicinity of Reims in France a school has been opened recently, the eye-catcher of which is an exposed corner of the building. Seen from a certain angle, the upper story appears to look like a huge two-dimensional setting for a film because of this corner of the construction. This impression is enhanced by the shear magnitude of the sturdy façade on the ground floor. The structure has been realized using precast concrete parts.
It is rare that architects appreciate the aesthetic value of precast parts in the restoration of an old structure. This was not however the case in Saint Thierry, a hamlet at the top of the Mont d´Hor to the northwest of Reims: The project here was for both extensions to and renovation of the existing school complex from the late sixties. Instead of as is so often the case, simply hiding the old precast units behind a metal façade, the washed-concrete surfaces were cleaned and existing corridors no longer used and now superfluous by the new organization for the building were closed by attaching yellow sheet panels. The decision was made to take an even more radical step for the area inside the old building: The original suspended unplastered gypsum plasterboard was taken out and the old cavity floor units exposed. The coarse butt joints of these, the bulky precast joints and as well the patina easily 40 years old now, are in a harsh yet not unattractive contrast to the paneled wall areas in shining-white or clad in blue timber, and the light gray of the linoleum floor.
Whereas enhancing the aesthetics of the construction stood foremost in restoring the old building, honor to the historic core was still to be realized in the new building construction: Modularity and precast parts was the concept here.
The new construction is based on the same grid as for the supports in the old building. Also taken from the original building are the opening dimensions and the pane size for the windows on the upper floors. These have been arranged directly above the floor and below the intermediate floor. The goal of the architects was to suggest the existence of a second upper floor that is not in fact there: The building should be higher and more imposing looking over the street. The irony of this trick is at the north of this “apparent façade”: It simply ends here in a pointed spur. Only a thin shear wall here indicates the building’s height in the upper floor region. The case on the ground floor below is a completely different one: The façade here is made from massive concrete ballast and the areas for the windows have been set back quite far. Both the vertical as well as the horizontal units for these niches have been realized by the prefabricated method of construction. Made from self-compacting concrete, the surface was polished immediately after being stripped so as to retain the natural-stone characteristics.
The architects are wanting the use of precasting concrete to be understood as a homage to the old building. In particular they see in the ground surface a further development of the established washing-concrete technique.
Also, the some 30 m-wide, slightly downward, path from the expressive school gates to the new main entrance is over prefabricated concrete. A dozen precast parts, perhaps 20 centimeters in thickness, lie on the terrain, raised, without touching one another: the some 2 cm-wide butt joints between the
2.5 m x 5 m large elements are exposed. To prevent these paving units from settling, the substrate underneath had to be prepared beforehand, like a roadway.
All precast parts were produced from mobile equipment at the site. Besides the formal references to the continued existence, the technique used had another clear advantage and this is particularly apparent for the façade elements because of the requirement for the constancy of parts. With the path there was also the requirement that the flags be of equal thickness: Since these simply rest on the ground they are completely visible. As the ground falls however by a 2.5 % towards the building, it was more straightforward to the cast these parts in the horizontal position to let these cure, and then to place them in the slightly inclined position.
Robert Mehl, Aachen