Master test with geopolymer concrete at railroad underpass in Heiloo

At a railroad underpass under construction in Heiloo, intermediate walls in reinforced geopolymer concrete were constructed for the first time in Western Europe. One of the major advantages of this concrete is that the CO₂-footprint is considerably lower than with traditional cement concrete. In the Heiloo project, a fifty percent reduction is achieved.

This makes Mobilis the first civil contractor in the Netherlands to build a section of a railroad underpass in reinforced geopolymer concrete. "The intermediate wall in Heiloo is our first 'master test', to show the world that Geo-beton™ is just perfectly manufacturable, perfectly transportable and perfectly processable up to 3 hours after fabrication at a concrete mortar plant," states Mobilis initiator Herman van den Noort.

After a slight adjustment in the recipe, six sections, each about 20 meters long, of the partition wall have now been poured.

Completely equivalent

Traditional concrete based on cement, sand, gravel and water accounts for at least 8 percent of all man-made CO₂-emissions. Those emissions occur mainly in the production of the binder cement, which requires a lot of energy for the kilns. Van den Noort: "In geopolymer concrete there is no cement at all, but a combination of cement-substituting mineral substances derived from known industrial residues such as blast furnace slag and fly ash and from natural sources such as biomass ashes or sediments such as river sludge. These substances are 'alkaline activated' using substances such as water glass and caustic soda."

The type of geopolymer concrete developed by Mobilis in collaboration with Delta Concrete Consult is completely equivalent to traditional concrete, according to Van den Noort. "We do not have to use any primary raw materials from a far-off foreign country and the hardened concrete remains circularly deployable and recyclable - and all at comparable production and realization costs." Mobilis was one of the three finalists for the 2018 TBI Innovation Award with this new type of concrete.

Successful field tests

Mobilis first conducted successful field tests with its proprietary Geo concrete™ in reinforced structural components. On its own initiative, it was then shortlisted for government projects and contacted Rijkswaterstaat and ProRail. Van den Noort: "Large public clients like Rijkswaterstaat and ProRail are very interested in Mobilis' initiative. In the Netherlands, following the signing of the international Environmental Agreement in Paris and the national Concrete Agreement - also signed by Mobilis - large market parties are increasingly explicitly looking for sustainable alternatives to common raw materials and products."

One section of the track underpass will be built with reinforced geopolymer concrete

A trial pour of a wall in reinforced Geo-beton™ was done in Heiloo in October 2019 for the railroad underpass in Vennewatersweg. Van den Noort: "This is a new product and that requires getting used to it by everyone involved at all stages." After a minor adjustment in the recipe, six sections, each about 20 meters long, of the partition wall have now been poured. In this tunnel project, the partition wall is a component with a reduced risk profile; the sections are, in principle, easy to replace if necessary. Thanks to sensors installed in two sections, it will be possible to monitor how the geopolymer concrete behaves over the next ten years.

Validated product

Mobilis is now in talks with several clients about a project. Van den Noort: "The structural safety of Geo concrete™ is guaranteed; it is a validated product. We will continue to develop and test it in full, but we now want to put our shoulders to the wheel and accelerate the application of geopolymer concrete."