Since its opening in May 2010, a record number of people visited the World Expo in Shanghai, China. One of the most striking buildings on the 5.3 km2 site is the national pavilion of Luxembourg. Designed by architect Francois Valentiny, the pavilion utilises weathering steel to create a dramatic dialogue between the Expo visitor and nature.

Weathering steel, marketed by ArcelorMittal in Europe as Indaten®, was first developed in the United States in the late 1930s. Since then it has been used in many buildings, bridges and sculptures where a natural and long-wearing finish are required. Pablo Picasso famously used the material for his 1967 sculpture known as the Chicago Picasso which still stands in the city’s Daley Plaza.

The latest creation in weathering steel is Luxembourg’s national pavilion at the Shanghai Expo. Designed by Francois Valentiny, a native Luxembourger, the pavilion takes the form of an enlarged single-family house surrounded by a fortress-like wall. The hardness of the weathering steel is softened by trees planted on top of the enclosure, a hanging garden along the inner core, and a pond covered by giant steel lily-pads. “I planted trees and vegetation so the central building looks like a castle,” explains Valentiny. “In Chinese, Luxembourg means fortress and forest, so I am playing with images, signs and forms.”

A magical product

Valentiny chose weathering steel from ArcelorMittal after having worked with the material on a number of projects. His choice was influenced by the purpose of the building as well as a consideration for its lifespan. “For a pavilion with a life of six months steel or wood are ideal because they are easy to construct and recycle.”

The 5.6 by 1.5 metre sheets of weathering steel were milled at ArcelorMittal’s Fos-sur- Mer plant in France and shipped to Shanghai where the pavilion was assembled by local engineers.

Initially the choice of material was unfamiliar to the Chinese team and the build was delayed for three weeks. “For the Chinese engineers, weathering steel is a magical product,” explains Valentiny. “It is something high-level, and they believed that it should be respected.” After reassurances that they could work with the material in the same way as other types of steel, the engineers began construction, finishing the pavilion well in time for the opening of Expo.

Steel, spruce and glass

Weathering steel is used for the exterior, floor and roof of the pavilion. This is a signature of Valentiny’s design philosophy: “Three materials are enough!” he explains. “I like to use the same surfaces on the walls, the roof and the ground, and there are a limited number of materials you can do that with.” The interior ceiling is lined with spruce timber from the forests ofLuxembourg, which is set into steel frames.

The third and final material is glass which is used in the openings of the pavilion. Standing on a three-metre steel column at the entrance to the pavilion is the statue of Gëlle Fra (the Golden Lady). Designed in 1923, the statue normally stands in Luxembourg City’s Constitution Square but was donated to the pavilion for the duration of Expo. “The contrast between the oxidised steel and the golden surface of Gëlle Fra produces a strange feeling,” says Valentiny. “When you look at it at night, the steel also looks like gold.”

Millions of visitors

The reaction from Expo visitors to the pavilion was positive. “Chinese people were very curious and they showed great interest in this material,” said Valentiny. “In the first weeks they touched the façade because they thought it was impossible to construct with rusted steel.”

More than six million people passed through the pavilion during the half-year that Expo was open. Although weathering steel formed both the internal and external flooring, no coating was needed to protect it from the elements or wear and tear from the visitors. While Gëlle Fra returned to Luxembourg City, the pavilion will find his new home in China:  It was donated to  ValinLianyuan Iron and Steel Co.,Ltd. and will be errected again in the city Loudi (Hunan Province) as part of a new siderurgical complex. It will house an exposition of the Hunan Valin Group's products. As we can see, the weathering steel will persist - just like Gëlle Fra.

About weathering steel

Marketed by Flat Carbon Europe as Indaten®, weathering steel develops its patina following exposure to the atmosphere. The first oxide layer appears within a few weeks with the final colour being achieved within one to two years. The fi nish can last, without maintenance, for at least 80 years. The steel can also be pre-oxidised. The primary alloying material in the weathering steel is copper at concentrations up to 0.55%. The copper produces a homogenous and regenerating protective layer over the surface which retards corrosion and ensures the integrity of the underlying steel.

Today, weathering steel is more fashionable than ever. It fits with modern ideas that architecture and infrastructure should blend in with the natural and built environment. Using our decades of experience with corrosion resistance mechanisms, ArcelorMittal has developed its own brands of weathering steels: Indaten® for flat products, and Arcorox® for sections and published a new dedicated brochure.

This publication aims to provide you with a good understanding of ArcelorMittal’s weathering steels and how they can be used. The document also included several examples of successful projects realised in weathering steels to inspire your future projects.

Like a fine wine, weathering steel is enriched by air and enhanced with age. When exposed to the natural environment, this magical steel develops a beautiful patina which serves as protective armour and is the basis for the steel’s trademark purplish brown colouring. The marvellous paradox of weathering steels is that rust protects the steel from rust!

Discover it now…