Interview with Mouloud Behloul, Lafarge concrete engineer, Romain Ricciotti, structural engineer, and Rudy Ricciotti, architect of the Villa Navarra.

Villa Navarras roof in Ductal® concrete is a world first, the hybrid fruit of the boldness and expertise of Rudy Ricciotti, architect and laureate of the National Architecture Grand Prix 2006, Romain Ricciotti, structural engineer, and Mouloud Behloul, Lafarge concrete engineer. They meet up for a round table to talk about this building.

An exceptional work, both aesthetically and for its technical complexity, Villa Navarra looks like a long, furtive silhouette set on the very rock, simply laid bare. And it is around this notion of "minimal aesthetics", so dear to Rudy Ricciotti, that the discussion begins.

 

Rudy Ricciotti : Our intention was to limit the villa's impact on the site by blending it into the slope, without backfill, following a logic of unobtrusiveness. The outcome of this logic is its ultra-thin Ductal® roof. Can you remind us of its size, Romain?

Romain Ricciotti : 40 meters long, with a 7.86-meter cantilever and edges 3 centimeters thick.

Mouloud Behloul : In terms of concrete, that's a sheet of paper! Ductal® is an ultra-high performance fiber concrete, which allows us to break away from passive structures. It opens the way to a huge reduction in material and great creative freedom in forms, which, in this case, are curved, feminine.

Romain Ricciotti : These forms were dictated by external restrictions, such as the width of the trucks used to transport materials. But also by the resolute demand for optimum mechanical yield, similar to that of steel structures. This structural roof only Works in flexion, with a warp of 4 millimeters as a result of temperature variations, which is completely new. It has no incorporated waterproofing or insulation.

 

Is all about a choreography of efforts: an exceptional material [...] employed with the traditional, even archaic, skills of craftsmen.

Rudy Ricciotti
 

Mouloud Behloul: Here, the material is used in its purest expression. Its specific nature - neither metal, nor wood, nor glass, and not really concrete - forced us to re-ask all those questions that "reinforced concrete" engineers hardly ever ask these days and to re-invent design and manufacturing methods. So, at the pouring stage, we had to calculate and check the direction of the fibers, because these change the mechanical properties of the concrete.

Rudy Ricciotti: What we are talking about here is the very core of our work, which, in my opinion, is all about a choreography of efforts: an exceptional material, used in nuclear power stations, poured in aluminum moulds similar to the moulds used in the aeronautics industry, but employed with the traditional, even archaic, skills of craftsmen.

Romain Ricciotti: You mention a "choreography of efforts"... It's Worth pointing out that the successive révolutions initiated by concrete have always come about through "committed" collaboration between architects and engineers.

Mouloud Behloul: As I see it, the Navarra project is the fruit of reflection on the structural properties of Ductal® concrete. It probably marks the beginning of new beliefs and new practices concerning structures.

Rudy Ricciotti: And I'm fairly optimistic about the chances of seeing the use of this exceptional material becoming very widespread.

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