Durable steel sheet piles from scrap metal

Traditional steel sheet piles often have a lesser reputation from an environmental point of view, due to the fact that the steel is produced in blast furnaces from ore. This is not the most environmentally friendly method of production. ArcelorMittal, on the other hand, takes a different approach. At its plant in Luxembourg, sheet piles are produced from scrap in an electric arc furnace. This leads to an environmental impact that is lower by a factor of 4 to 5. This is also one of the reasons why these sheet pile walls are being used on a large scale in the dike reinforcement at Wolferen-Sprok. Against the failure mechanism macro-instability, ArcelorMittal steel sheet piles are unmatched. 

"Because of the substantial share of steel sheet piles, we determined the frameworks together with combination De Betuwse Waard right at the beginning of the project," begins Roel Bijlard, Technical Sales Engineer at ArcelorMittal Projects. "A total of 11,500 tons of steel sheet piles will be processed over a three-year period. Part of it, about 4,500 tons of sheet piles were delivered last year, the remaining 7,000 tons are stored at a temporary storage site near the project and will be delivered on demand."

Low environmental impact with production in electric arc furnace

The project mainly incorporates sheet piles from ArcelorMittal's AZ18-700 series with a smaller proportion from the AZ24-700 and AZ28-700 collections in addition. "All these sheet piles are 1,400 mm wide and the majority are between 9 and 16 meters long," says Bijlard. "Because we use 100 percent scrap as input instead of ore and thus use secondary material, the environmental impact is many times lower. The CO₂-footprint of our sheet piles is about 47 kg/m2, a fraction of steel obtained through the blast furnace process. On top of that, our plant is located in Luxembourg, so transport distances are extremely limited. The sheet piles for Wolferen-Sprok were transported to the temporary storage site via barges. It is then rolled out in phases for the combination by axle to the dike."

Reduce, re-use, recycle

Environmental impact is an increasingly important issue on projects, Bijlard also knows. "In recent years, both as a company and as an industry, we have invested heavily in reducing the environmental impact under the guise of reduce, re-use and recycle. The biggest environmental gain has been achieved with a reduction in the number of pounds of steel going into the ground through innovations to the sheet piling itself and the steel quality. By comparison, 30 years ago a sheet pile was on average 30 percent heavier. ArcelorMittal is the only sheet pile supplier with the 800 mm wide Z-Series that achieves a unique weight-strength ratio. We were also closely involved in the sheet pile test in Eemdijk, a dike reinforcement study into macro stability. The test showed that the calculation rules for steel sheet piles were too conservative and that they could be made up to 30 percent lighter. Based on this, the calculation rules were adjusted and Wolferen-Sprok also benefits from this by applying lighter sheet pile walls compared to the old calculation rules."

For dike reinforcement Wolferen-Sprok, the Rivierenland Water Board, in close cooperation with the construction consortium, has determined that of the thirteen kilometers of new sheet piling to be installed, half should be made of plastic in order to advance this innovation as well. Bijlard can understand this and says, "For the application in which it is being used on this project, exclusively as a piping screen, it is a possible alternative. In situations where there is both the failure mechanism of piping and macro-instability, the steel sheet pile wall remains the only correct solution to eliminate both failure mechanisms with one product. In that application, steel sheet piles are a reliable and proven technique and can be removed from the ground at the end of their service life and used as scrap for a new sheet piling product. That's how we complete the circle."