Reinforcement and renewal of Afsluitdijk

The reinforcement and renewal of the 92-year-old Afsluitdijk are subject to high sustainability requirements. The Levvel construction consortium (BAM Infra, Van Oord, Rebel and Invesis), which began work in 2019, has signed a DBFM contract with client Rijkswaterstaat and will be responsible for maintenance for 25 years. Then you choose the best solutions, also because there is a very high corrosion class here. For example, all the anchors and guides of the pump and sluice gates, among others, are made of Duplex steel. "For the contract period, this was the qualitatively best and cheapest solution. More importantly, it gives longer-term assurance that the sliding properties of the guides remain intact, thus ensuring an essential requirement, namely the self-closing capability of the gates."

The project includes the raising and strengthening of the Afsluitdijk along its entire length, complete renewal and modification of the road surface, a completely new floodgate both at Den Oever and Kornwerderzand, additional sluices and a new pumping station at Den Oever to drain more water from the IJsselmeer. But also the construction of the fish passage Vismigratierivier at Kornwerderzand, which will make fish migration between the Wadden Sea and IJsselmeer possible again.

Levvel asked Dion Papen of Partner in Protection to advise on corrosion and corrosion prevention. "Conservation is very important for this project. You want to do everything rock solid and keep corrosion out for as long as possible, and in this case that applies even more strongly. After all, you are charged based on availability. If a rolling door does not function and shipping cannot get through, the costs quickly mount up. So just painting to get rid of corrosion becomes a very expensive task during the maintenance period. You don't want that."

The very small tolerances on the sliders in particular also played a role. At the sluice gates, the tolerances are only 3 mm. "That's due to the requirement that a lock door can only let through one cubic meter of water per meter of door," Papen explains. "When you consider that the door rebates are nine to 15 meters high and there are guides running on three sides in the rebate, it demands a lot from the corrosion resistance and sliding properties of the material. Preserved carbon steel, for example, will corrode in no time, rendering the guides ineffective. This is why it was decided at the design stage to use DIN 1.4462 Duplex steel for both all anchors and guides. This also prevents crevice cracking corrosion, or crevice corrosion, which can occur in this brackish water at temperatures as low as 21 degrees. Even the widely used stainless steel 316 is thus dropped as a material, and so you end up with DIN 1.4462 material, for example." In addition, the material of the anchors and guides must be of the same material to prevent galvanic corrosion. "If hot-dip galvanized anchors were used, they would start to act as anode and sacrifice themselves to protect duplex 1.4462 material."

Dozens of guides made of Duplex steel were used in the various subprojects. These are composed of strips 350 mm wide, 45 mm thick and up to 3,000 mm long. "Smooth and the same thickness everywhere," Papen said. "And smooth they remain over time, which is why slides with Duplex guides basically always close. In addition, many thousands of Duplex anchors have been used. A deliberate investment in quality. It's about longevity in a very aggressive environment, and then you choose the highest quality. An additional reason for choosing Duplex is the detachability of the connections. Connections that rust solid and are therefore poorly or only destructively removable are not desirable."

The Duplex anchors (including nuts, threaded ends and coupling tubes) were supplied by Schroeder Ankers of Wehl, Gelderland, which also advised in the process. The strips and anchors were provided with material certificates by Schroeder.