Diabolo is a major infrastructure project that includes both a rail link between Brussels Zaventem Airport and Antwerp via the 25N railway line, and also a connection on the same 25N line from Schaerbeek out to the airport. AM Valens - AB is constructing the 1.5 km long route, an 810m long section of which includes the so-called Iris Viaduct with its 34 pillars. The TUC-Rail planners based the design of the viaduct pillar heads on the iris flower, the symbol of the Brussels-Capital Region. Due to the complexity of the design, AM Valens - AB drafted Construx into the project to develop the formwork systems required.