Geopolymer concrete fits sustainability ambitions Amsterdam

The use of cementless concrete is common in several countries. The Netherlands is somewhat out of step in this respect, but the turnaround is coming. If no hydration is involved in the production of concrete, you may not call it concrete according to the current NEN standard. For many clients, this stands in the way of the application of cementless concrete. This is unfortunate, because the CO2 footprint of geopolymer concrete, for example, can be about 50 to as much as 75% lower than that of traditional Portland cement-based concrete. Gebr. De Koning, contractor in civil engineering, road construction and hydraulic engineering, and manufacturer Van Dijk Beton, do not want to wait on the sidelines for a change in standards. They have joined forces to realize projects with geopolymer concrete wherever possible. A good example is the new quay wall of the former Coffee Factory in Amsterdam.

Commissioned by the City of Amsterdam, two hundred meters of quay wall were recently replaced as part of the redevelopment of the site on the Duivendrechtsevaart near Overamstel subway station. Gebr. De Koning renewed the quay up to the Van der Valk Hotel Amsterdam-Amstel, prepared the coffee factory site for the construction of an apartment building and made new mooring facilities for a number of houseboats. Precast concrete suspension aprons were used for the quay, partly with the application of geopolymer concrete. 

The City of Amsterdam, with a strong ambition in the field of sustainability, put the project on the market based on a UAV-GC contract with EMVI, in which Sustainability and BLVC (Accessibility, Livability, Safety and Communication) were the main pillars. A challenging project for Gebr. De Koning, in addition to the shared ambition for sustainability, to successfully deploy its knowledge and skills in the field of quay walls. At the same time, Van Dijk Beton participated in an Innovation Partnership with ProRail to develop a sustainable platform wall. Van Dijk Beton participated in the innovation program based on a geopolymer concrete element with application of secondary aggregates and partial (basalt) fiber reinforcement. At TU-Delft, Noah Wols had started his graduation (fiber-reinforced geopolymer concrete) and he approached Gebr. De koning to see if there were opportunities to do that with her. Matthias Mast, project manager for Gebr. De Koning: "Sometimes puzzle pieces fall nicely into place. We had good contacts with Van Dijk beton before and then Noah and the Koffiefabriek project came along. Noah looked into the proverbial kitchen at Van Dijk Beton during the Innovation Partnership for sustainable retaining walls, successfully graduated in fiber-reinforced geopolymer concrete and is now working at Gebr. De Koning as a planner/constructor."

Gebr. De Koning eventually won the tender in Amsterdam with its own design and EMVI elaboration in which concrete suspended aprons would be used. Paul de Vries, Manager of Strategic Development and Sustainability for Van Dijk Beton, wants to put sustainability and sustainable concrete further on the map. "The Concrete Agreement states that the industry will take measures to improve the environmental profile of concrete. In 2021, Van Dijk Beton qualified for ProRail's Innovation Partnership and started developing sustainable retaining walls made of geopolymer concrete. That was an excellent opportunity to gain experience with the material and to explore the possibility of certification." You could think of a hanging apron as an inverted retaining wall, smiles De Vries, with product properties largely similar. "Gebr. De Koning had emphasized in the EMVI that they wanted to capitalize on opportunities during the project to become more sustainable. We then jointly set the goal of executing part of the quay wall with suspended aprons of cementless concrete. The municipality of Amsterdam agreed to this application."

The environmental benefits of geopolymer concrete are great. Wols: "Traditional concrete production with cement has a double CO2 burden because of cement production. In geopolymer concrete, the cement is replaced by other binders. Alkaline activation therein provides polymerization and long chains that turn the mixture into a stony material with the same properties as concrete. The Romans used volcanic ash to make concrete thousands of years ago in this way. In Australia, the UK and Eastern Europe, this building material has long been common and certified. However, in the other Western countries, the concrete industry has been based on cement for almost 100 years and all standards are based on that. For example, hydration must take place. This doesn't happen with geopolymer concrete so you can't call it concrete and that keeps many clients from applying it. Fortunately, more and more clients, such as ProRail and municipalities, are actually picking up this gauntlet. With sustainability becoming increasingly important, I expect the opportunities to start turning around. We still have to test the product ourselves for each project because there is no certification yet."

This is why contractor Gebr. De Koning is pleased to have a client like the City of Amsterdam. Mast: "If we want to move forward with this, we need ambitious parties. The municipality of Amsterdam is strict, careful and wants everything to run smoothly, but at the same time is ambitious when it comes to sustainability. That is why the preliminary process at the municipality and the Omgevingsdienst went very smoothly. With other large municipalities like Rotterdam and Utrecht, which have a lot of knowledge about sustainable developments in-house, we also experience this room for innovation, supported with additional resources to investigate."

Project the Coffee Factory was completed last June after 10 months of work. This began with the preparation of the future building lot and the demolition and construction of 80 meters of that lot's quay wall. Mast: "The Coffee Factory had been demolished down to the floor much earlier. That floor, including the old pile foundation up to four meters below ground level, also had to disappear because it was anchored to the quay wall. A silent piler was used to create a temporary construction pit in the water in front of the quay, which could be electrified at the end. Next, the existing quay wall was demolished and, again, rebar and concrete were disposed of separately. A steel sheet pile was then inserted in front of the new quay wall and secured with tension anchors. The AZ18 profiled sheets for the sheet piling were taken from other projects and checked for condition and thus given a second life at the Coffee Factory. Constructively, this structure can last a hundred years. The second phase of the quay construction, about 120 meters, was carried out in a similar way. This section extends to near the Van der Valk Hotel." 

For the completion of the quay, the sheet piling was fitted with a steel cover plate. Wols: "The 1.20-meter-high suspended aprons were laid on top of this with dummy joints. A casting mortar provides the filling and bonding of the suspended aprons to the foundation. The precast suspension aprons were bricked off on site with real brick in blended colors. That's the only drawback of this type of project: the precast elements of polymer concrete are invisible, all you see is a beautiful masonry quay 200 meters long." Meanwhile, all the houseboats have been made accessible again at their old spots with stairs or a footbridge between the new mooring posts. De Vries is positive about the application of polymer concrete. "In Amsterdam there are hundreds of kilometers of quays waiting to be renovated. In these quay projects, geopolymer concrete can be excellently applied. A product with a substantially lower CO2 profile, which fits in with the sustainability ambitions of the City of Amsterdam. Gebr. De Koning and Van Dijk Beton do want to move forward with this."