Text:
Constructalia

Images:
©Darby Sawchuk (Parkway Gate)
©Dekmetal (Hala Nebovidy)
©ArcelorMittal

When designing a building envelope with steel, the end product for roofing or cladding is usually at the centre of attention - aesthetically as well as functionally speaking. Profiled sheets of different shapes, sandwich panels with steel shells in diverse surface structures, architectural siding systems, or tailor-made solutions are all aimed at providing the final aesthetics for our buildings. However, the selection of facade and roofing products involves the choice of the material itself, which is often defined in the design phase. Pre-painted steel is a choice option.

Pre-painted steels: endless aesthetic possibilities combined with durable and sustainable properties

Pre-painted steel is a material that not only meets a wide range of technical requirements but offers an infinite number of colour shades, different surface appearances, and printed effects, thus providing endless aesthetic possibilities.

The visual qualities of organic coated steels go hand in hand with the functional properties of their paint systems and steel substrates: very long corrosion and UV resistance; colour stability to maximise durability; scratch and abrasion resistance in fabrication, erection, and use phases; flexibility to withstand forming operations; or optimised low carbon footprint per m². These are just a few characteristics of the material that makes up the vast majority of facade and roofing products and are key criteria to consider when choosing the right steel for your facade or roofing product, taking into account the environmental conditions it will be used in.

The material of choice: ArcelorMittal’s Granite® range of organic coated steels

With its Granite® range of organic coated steels developed for the construction industry, ArcelorMittal Europe - Flat Products offers pre-painted steels with paint coating systems from 25 to 70-75 μm on galvanised steel or ZnAlMg alloy substrates, guaranteeing durability and corrosion resistance in environments up to categories RC5+ and RUV5 as classified in the newly revised EN10169 standard. The choice of paint system to ensure long term durability depends on the environmental conditions to which the product will be exposed.

Aesthetically, Granite® leaves no desire unfulfilled: apart from the sheer endless chart of solid, metallic, and pearlescent colours, Granite® is available in a vast selection of surface patterns including smooth, grained, embossed, textured, or orange-peel effect - with surface finishes ranging from matt to high gloss and metallic sparkles.

In addition to the numerous economic and sustainability factors, the main advantage of organic coated steel is its consistent quality. Paint film thickness, colour matching, and surface appearance are reproducible within narrow tolerances from batch to batch.

A responsible choice

Granite® coated steel forms part of ArcelorMittal's range of organic coated steel building solutions and, as such, is free from heavy metals and chromates. With this product range, ArcelorMittal is offering a responsible option - a sustainable advantage for your projects.

Sustainability: greener steels with XCarb® Recycled and renewably produced

Making its steel products more sustainable is at the heart of ArcelorMittal's objectives, and decarbonisation is an important part of the process. With XCarb®, the company’s global programme of steelmaking innovation, the aim is to achieve carbon-neutral steel by 2050.

In 2023, ArcelorMittal Europe - Flat Products will offer organic coated steels with the label ‘XCarb® Recycled and renewably produced’, meaning that they will be produced from recycled steel in an electric arc furnace using 100% renewable electricity. This will be a real breakthrough in CO2 footprint reduction per m² of organic coated steel for the construction industry.

There will be a new dedicated Environmental Product Declaration (EPD) for the Granite® and Estetic® product ranges, in which ArcelorMittal Europe - Flat Products will provide extensive information about the environmental impacts of this new organic coated steel offer.

Choose the right organic coated steel to maximise protection and durability

There is a wide range of characteristics that can be built into organic coated products, and this explains the diversity of the solutions proposed by ArcelorMittal. It is therefore essential to define precise prior specifications, so that the optimum solution in terms of technical and economic requirements can be determined.

EN 10169, the standard that specifies the appropriate technical and performance criteria for continuously organic coated (coil coated) flat steel products, defines corrosion resistance categories from RC2 to RC5+ (in its new published version).  ArcelorMittal’s Granite® organic coated steel offers a safe solution for all of these environments with guaranteed performance and without sacrificing aesthetic freedom.

Coastal and industrial environments with high pollution (RC5/RC5+)

ArcelorMittal’s new building for industrial digitalisation (INDI) is located on the ArcelorMittal Gent site, close to the industrial environment of the mill and the sea. The newest organic coated steel in the product family, Granite® HDXtreme, was the intelligent choice for its facades as it offers best in class resistance to corrosion thanks to its coating system.

Marine and industrial environments (RC4)

Due to its marine environment in Toulon, France, the Sittomat waste incineration and energy plant’s original zinc envelope had aged rapidly, creating the need for a renovation of its roofing and facades. Its double-sided 35-micron organic coating made Granite® HDS the perfect solution for this industrial site close to the sea.

Rural, urban, and in between (RC3)

The 55µm coating system of Granite® HDX steel provides the necessary aesthetics, durability, and protection for the perforated facade elements of the Stoas Vilentum University building in the Netherlands. Although not the initial material selected for this project, Granite® HDX turned out to be the more sustainable solution. A special concern were the perforations: In order to avoid compromising the integrity of the substrate over time, ArcelorMittal’s R&D team calculated different options before specifying a 350 g/m² (Z350) zinc substrate that will prevent the cut edges from corroding for many decades.

Granite® Impression Cloudy organic coated steel with its 35µm thick paint coating system was chosen for the front facade of the Distrifill company headquarters in the Netherlands thanks to its lively bicolour effect. The copper and brown merging in Granite® Impression Cloudy make the facade look warmer and give the building that includes offices and a warehouse a more human feel.

Blending into the surrounding landscape aesthetically while providing a viable solution to make the construction earthquake resistant were the reasons why Granite® Deep Mat was used for the sandwich panels that make up the facade of the Bottovini wine centre in Northern Italy’s Piemonte region. And – the beauty lies in the detail: The textured surface coating reinforces the natural feel.

Apart from durability, the requirements for the material to be used for the envelope of the stadium in the Polish town of Tychy were light weight and good formability. The solution? ArcelorMittal’s Granite® HD, characterised by excellent resistance to atmospheric agents as it is coated on both sides with a 25μm polyester coating.

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Steel roofing and cladding materials are among the most cost-efficient solutions available on the construction market today. As well as being light and easy to handle, these products are quick to assemble, and they are available in a wide range of shapes and colours to suit almost any built environment. Due to the updated Euronorm (EN 508-1) for self-supporting roofing and cladding sheets that came into force in October 2021, ArcelorMittal Europe – Flat Products has been helping the makers of profiling machines ensure their systems meet the new standard.

Successful co-engineering

DACHPOLL, a leading manufacturer of profiling machines, has collaborated with ArcelorMittal to ensure the roofing tiles produced on their machines meet the new standard, particularly in regard to the minimum bending radius.

DACHPOLL has been active in the profiling market for over three decades. Around 12 years ago, the company began to produce its own profiling machines for roofing tiles, trapezoidal sheets, and roof accessories at its facility in Poland.

Updated Euronorm and new bending requirements

The publication of the updated Euronorm for roofing and cladding products introduced a new mandatory requirement on bending. Steel roofing and cladding materials must now observe a minimum internal forming radius that is at least twice the thickness of the material. If this minimum is not respected, the paint and metallic coating layers of roofing and cladding products can crack, reducing the lifetime of the application.

“In 2019, DACHPOLL started working with ArcelorMittal to ensure our profiling machines use the appropriate radii during profiling and stamping operations,” says Michał Brewka, DACHPOLL’s Commercial Director. “It is particularly important that the minimum radius is not exceeded on the ridge of the tiles. Otherwise, the paint layer can crack during the forming operation. This weakens the integrity of a roof as it allows humidity to penetrate and corrode the metallic coating – and then the steel core. In extreme cases, this can lead to premature perforation of the roof.”

Tiny adjustments invisible to end users make a big difference

During the co-engineering project, ArcelorMittal tested roofing tiles where rust had appeared prematurely. “ArcelorMittal’s R&D team found that many profiling machine customers were exceeding the minimum bend radius specified in our documentation,” says Daniel Drozdowski. “Tiny adjustments to the design of the final product can make a big difference, and they are not noticeable to the end user.”

“Thanks to the cooperation between ArcelorMittal and DACHPOLL, we can assure customers that they can profile strips correctly for roofing and cladding applications,” says Michał Brewka. “DACHPOLL has also gained additional experience which allowed us to find a compromise between the expectations of roofing tile consumers for aesthetic shapes and designs and the processability of materials such as ArcelorMittal’s Granite® Ultramat and Granite® Storm organic coated steels. We expect that the changes will dramatically reduce the number of complaints we receive.”

“It may seem unusual for a steelmaker such as ArcelorMittal to take on a project like this,” notes Paweł Patyk, Head of ArcelorMittal’s Technical Client Team for Region East. “But we believe that we must take responsibility for ensuring consumers can enjoy undisturbed use of their new roof for the long-term.”

About DACHPOLL

DACHPOLL began as a sheet metal profiling business in the late 1970s. As well as producing roofing and cladding systems, the company began to make sheet metal profiling machines. Today, DACHPOLL makes a range of innovative profiling machines with highly advanced electronics and control systems. The company’s experienced and creative team of specialists are continuing to modernise this product range.

More info: dachpoll.pl

Text:
ArcelorMittal Europe Communications
Constructalia

Images:
DACHPOLL
ArcelorMittal

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Text:
Jerome Guth, ArcelorMittal Europe - Flat Products - Product Marketing
Georges Axmann, ArcelorMittal Europe - Long Products - Sales & Marketing

Images:
©ArcelorMittal Europe
©Gilles Martin, Courtesy of Infosteel
©Paul Kozlowski/ACAUM - Atelier BETTINGER DESPLANQUES Architectes Associés

Since the 1970s, the use of weathering steels, also known as corten or COR-TEN steels (for corrosion resistance and tensile strength), has spread through Europe. Engineers appreciate its corrosion resistance in combination with high strength steels. Weathering steels help reduce maintenance costs while lightening structures - especially useful for bridges. Architects like the expressiveness of this material (often used for facades) and its ability to fit into urban landscapes and natural environments. Additionally, the environmental footprint is greatly improved with the use of weathering steels due to the absence of coating. This article will describe the processes leading to the self-protecting behaviour of weathering steels.

Why are weathering steels corrosion resistant?

When weathering steel is exposed to the ambient atmosphere it develops an initial layer of iron oxide in the same way as carbon steel. The rate of oxidisation depends on how much oxygen, moisture, and atmospheric contaminants can access the surface of the metal. In the initial stages, a complex mix of iron oxides covers the surface to create a layer of rust. As the process progresses, the rust layer forms a barrier against the corrosive agents and the rate of corrosion slows. On a standard low alloy carbon steel, this iron oxide layer is porous. Over time, the layer detaches from the surface of the metal and the corrosion process starts again. The oxidation rate progresses in increments that depend on weather conditions and the chemical and mechanical aggressiveness of the environment. It can end with the complete destruction of the metal.

To increase the resistance of weathering steels to corrosion, alloying elements such as copper, phosphorous, nickel, or chromium are incorporated into the steel. These alloys lead to the formation of an oxide layer which remains stable and adheres to the metal's surface. A so-called 'patina' thus develops as the weathering steel is exposed to alternate wetting and drying cycles. As well as being aesthetically pleasing, the patina creates a protective barrier which impedes the further access of oxygen, moisture, and pollutants into the steel. This results in a much lower corrosion rate than that of unalloyed steels.

Conditions for long lasting protection

No constant humidity
If it is left in permanently wet or damp conditions, weathering steel will oxidise like any other unprotected carbon steel. A succession of wet and dry phases is mandatory to form a stable oxide layer on the surface. Weathering steels should not be used in:

• Sheltered locations with damp conditions
• Permanent contact with water. Welded structures require special attention to avoid the retention of water.
• Soil or covered by vegetation

Weathering steels used in these locations should be protected with paint. The paint must extend above the level of the water, soil, or vegetation.

No aggressive atmosphere
High concentrations of chloride ions negatively affect patina adherence. According to EN ISO 9223, weathering steels should not be used within two kilometres of coastal waters unless airborne chloride levels do not exceed the salinity classification S2 (Cl < 300mg/m 2/day). Direct contact between weathering steels and de-icing salts used on roads should be avoided.

No atmospheric pollution
Air-borne pollutants and industrial fumes can affect patina development. Corrosion is much higher if the metal surface is covered by solid particles such as dust or dirt. These particles can retain moisture and salts. In an industrial atmosphere, large amounts of sulphur dioxide (SO2) are detrimental to the compactness of the patina. EN ISO 9223 advises that weathering steels should not be used without protection in environments above P3 (SO2 > 200mg/m 2/day).

ArcelorMittal's weathing steel

ArcelorMittal has more than 80 years of experience in producing weathering steels. It started in the 1930s when the company Denain-Anzin created ‘InDA steel,’ the first copper-phosphorous steel. ArcelorMittal has continued the production of this type of steel, now called lndaten®. Its chemical composition has been improved to achieve better strength and corrosion resistance. lndaten® is supplied in flat formats such as heavy plates or steel coils. They are used to create facade elements, flat panels, blades, solar shading elements, profiled sheets, framing, or containers. In the 1970s, ArcelorMittal began to produce Arcorox® branded weathering steel for long products such as hot-rolled I and H sections, channels, and angles. Its use spread rapidly as the European infrastructure market began to grow.

The branded weathering steels grades produced by ArcelorMittal meet the requirements of EN 10025-5 and are CE marked.

Multiple uses and unique aesthetics

The first major work using weathering steels was realised by Eero Saarinen who designed the John Deere World Headquarters in Moline, USA in 1960. Since then, weathering steel has been used in various outdoor steel applications: bridges, buildings, railway cars, and even works of art! Today, this material continues to create enthusiasm among designers thanks to its unique aesthetic and technical benefits.

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