'Geopolymer concrete could be a real game changer'

The reinforced geopolymer concrete used in Heiloo for the first time in the Netherlands in a railroad underpass is a distant descendant of a "forgotten" binder concept established as early as 1908. It was translated by the specialists at Delta Concrete Consult into contemporary raw materials with the aim of delivering modern performance, at a halved carbon footprint compared to traditional blast-furnace cement that would otherwise have been used.

Railroad underpass in Heiloo.

Delta Concrete Consult from Vianen is an independent engineering and consultancy firm specializing in concrete and cementitious composites. ''We build a bridge between the disciplines of design and execution because it turns out that they do not always speak each other's language and are also not always well informed about new material technology. We translate everything into performance specifications recognizable for the target group,'' says director Jos Kronemeijer.

Kamel Arbi (chemist) and Jos Kronemeijer (director).

That was also the challenge in applying geopolymer concrete in Heiloo. Part of the challenge was to develop a formulation that matched what stakeholders in the production chain are used to with traditional cement concrete. A transport time of 1 hour, adequate fluidity and maintaining it for an hour and a half after receipt at the construction site, usual pouring and compaction techniques; the whole pallet had to be close to traditional cement concrete. Based on preliminary research and the transparent sharing of insights, ProRail, Rijkswaterstaat and infrastructure main contractor Mobilis gradually grew more confident about the feasibility of technically equivalent, safe and reliable performance, but with a significantly lower environmental profile.''

Determination of air content by Mathijs de Vaam.

The geopolymer concrete used in Heiloo includes the well-known blast furnace slag as a raw material. ''The advantage of this is availability and familiar recognition with the concrete producer. A strength of the cementless binder system is that there is a much wider acreage of raw materials than many suspect; more than 18 different raw materials can be found in the Netherlands alone. This enables us to work with the raw materials closer  to be able to sit at work, and that makes a big difference in CO₂-emissions from transportation.''

Director Jos Kronemeijer.

However, the new concrete cannot be simply prescribed everywhere and applied indiscriminately in everyday practice. Kronemeijer: ''We need to (re)gain the trust of all stakeholders in the construction process; new production routines need to be developed against the background of a sector where concrete knowledge needs to be improved and therefore the introduction of a new type represents both an opportunity and a threat. In addition, there is logically the necessary skepticism from the cement lobby because this concept does not use their primary product and a multi-year track record of this alternative is not yet available, but at the same time this also applies to the types that are now being developed by them on an accelerated basis. That each stakeholder in the concrete construction process seeks its "leeway" is logical; you must and can still "turn the knobs" during production to control properties. The concrete used in Heiloo had a deliberately extended formwork period, but was at design strength earlier despite the cold weather, meaning the structure could be put into service 'net' earlier. Independent laboratory tests determined that properties are fully comparable to traditional concrete and, in the longer term, for performance aspects such as resistance to chemical attack and thermal stability, may even set a new standard for structural concrete. With that, geopolymer concrete can become a real game changer.''    

Partition wall of reinforced geopolymer concrete.