Strong example of sea lock technology: concrete reinforcement

News item

The new sea lock has to withstand enormous forces. To achieve this, hundreds of thousands of steel concrete reinforcement bars are installed. Gerrit van Hak, Project Manager with concrete reinforcement company Van Noordenne Wapeningsstaal, explained how this important process works. “We made three test set-ups of the concrete reinforcement mesh in advance.

A great deal of strength is required to carry the gigantic walls and lock gates of the new sea lock. These walls and lock gates must also be able to withstand the large force and pressure of the water. To make the concrete strong enough, hundreds of thousands of steel bars of reinforcement steel are installed first.

Extensively tested

A lot of preparation went into this, Gerrit van Hak explained. “We started preparing the concrete reinforcement mesh as early as 2016. We did this together with people from building contractor OpenIJ and with designers and draughtsmen. We made three test setups beforehand. We carried out tests on the production of ready-made prefabricated steel reinforcement mesh for the walls in Almere. Prefabricated steel reinforcement mesh units can be assembled in their entirety. We also made a test floor in Lelystad to see if the liquid concrete would pour well around and between the steel reinforcement bars. At the OpenIJ site, finally, we tested if a piece of floor would be strong enough to be handled by telescopic handlers. Telescopic handlers are small cranes used for installing steel reinforcement bars”.

Extra steel power

As steel reinforcement bars are 14 metres long and weigh as much as 140 kilogrammes, we definitely need these telescopic handlers. Van Hak added, “Many T-heads are used in the walls and floors. T-heads or T-headed bars are steel bars fitted with top plates to withstand even stronger forces. T-heads are specially made and supplied for us. The steel itself is not special, but to protect it from being damaged by salt seawater, it must be covered with a 7 centimetres thick layer of concrete”.

Transported by pontoon to the lock gate chamber

“Most of the reinforcement steel is loaded directly onto flatrack containers at our logistics centre in Amsterdam. A flatrack is comparable to the chassis of a trailer. Flatracks can be loaded onto a pontoon in their entirety without having to be transferred later. The flatracks are then transported by water from our logistics centre to the IJmuiden lock complex. After their arrival at the lock, the flatracks are transported to the lock gate chamber where the reinforcement steel will then be installed”.


Concrete reinforcement company Van Noordenne Wapeningsstaal is working in partnership with two other Dutch concrete reinforcement companies, Diepstraten, and BBC (Wapeningscombinatie P.E.C.). Diepstraten and BBC provide concrete reinforcement for the flood defence structures and for the walls of the lock chamber of the new sea lock. They also supply reinforcement cages for the diaphragm walls. Van Noordenne Wapeningsstaal is responsible for the outer and inner lock head, the concrete structures that will house the lock gates. Van Hak's team is working on the large inner lock head that will also house the second - spare - lock gate. Van Hak enthusiastically explained what it all involves.

Layer by layer

“Early in 2017, we started installing reinforcement steel for the cutting edge under the caisson of the inner lock head. The cutting edge plays a role in the caisson sinking operation. On top of the cutting edge we built a four metre thick floor. At one point we were working there with as many as four telescopic handlers across the full width of the floor. The completed floor had starter bars sticking out of it. Starter bars are lengths of reinforcement steel bars to which the concrete walls of the lock gate chamber will be attached. The construction of the walls is done layer for layer. We will build six layers of concrete with a height of 3.60 metres each. So in total we will build up the walls to a height of more than 20 meters. Once the sinking operation has been completed, we will add a seventh layer onto the walls. That will mark the completion of the lock gate chamber for the inner head”.

Every day I am proud

“It is very hectic here”, Van Hak remarked. “We work in shifts and make long days and very often we also work on Saturdays. Just try to imagine more than 50 people and a number of cranes working here all at the same time. The workers are divided into teams, each team with a crane. Without cranes you can't do anything here. Cooperation with OpenIJ is very good and everyone pays close attention to safety. This really is a great project. I would say, a once in a lifetime project. I take much pride in working here!”

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