Press release Cement-free concrete in ILVO bunker silos can reduce CO₂ footprint by up to 70%
First large-scale construction project with geopolymer-bonded concrete in agricultural sector
For the first time, the use of innovative geopolymer-bonded (cementless) concrete was applied in a demanding practical environment such as agriculture. This reduces the climate impact by about 70% compared to the same structure in ordinary "standardized" concrete. In the construction of the new trench silo complex at ILVO in Merelbeke-Melle, recycled concrete is also being used, with significant environmental gains as a bonus.
After a series of laboratory and pilot tests by the construction industry's innovation center, Buildwise, the innovative concrete types appear to be at least as strong and wear-resistant, and considerably more durable than cement-based concrete. The construction project with innovation support from VLAIO will have a long-term technical follow-up. Its figures will promote the sustainability transition of concrete construction.
Climate and nature impacts of concrete
Concrete is the most widely used building material in the world. It is loved for its strength, longevity and local availability. About 14 million m³ of concrete is produced annually in Belgium, for housing, roads, industrial construction including agricultural infrastructure. But there are two downsides.
First, concrete producers use large quantities of natural raw materials such as sand and gravel. This raises sustainability questions as these natural materials become scarcer.Second, the production process of the cement fraction (the binder of concrete with the technical name Portland clinker) causes high carbon emissions.The carbon footprint of one m³ of traditional concrete averages 300-360 kg of CO₂ equivalents. In Europe, concrete construction causes 4-5% of total greenhouse gas emissions. Globally, that percentage is running towards 10%. About 85% of the climate impact of concrete comes from the production of cement.
The manufacturing process of cement
Limestone is extracted from limestone quarries, which is homogenized after crushing, screening and purification. This raw material is heated in a rotary kiln, adding silicon, iron and aluminum oxides to obtain the desired mineralogical composition. The flame temperature in the furnace can reach about 2000°C, while the actual sintering process ("calcination") takes place at about 1450°C. During this process, calcium carbonate (CaCO₃) decomposes into calcium oxide (CaO), releasing significant amounts of CO₂. After cooling, the semi-finished product "clinker" is formed. To produce cement, this clinker is finely ground, often together with calcium sulfate (gypsum) and with limestone or blast furnace slag to obtain specific properties.
When cement comes into contact with water, it hydrates and forms a hardening matrix that binds sand and coarse aggregates to form concrete. The cement industry accounts for about 8-10% of global man-made CO₂ emissions. Of this, about 60% comes from the decomposition process of calcium carbonate and about 40% from the use of fossil fuels to heat the kilns.
Two promising solutions
To address both challenges, the construction industry has been studying and testing alternative binders and more sustainable bulk raw materials for some time.
RECYCLED CONCRETE
The primarily mined raw materials for concrete, namely sand and coarse aggregates, are not inexhaustible and are often imported. The pressure on natural raw materials is increasing worldwide. To this environmental impact of concrete, circularity is a viable answer. Specifically, waste streams such as stone and concrete rubble can be converted into reusable raw materials. Urban mining (read: recovering materials from a built environment) requires careful selection, specific processing (sorting and crushing machines) and recipe development. Through research and validation tests, Buildwise has demonstrated that circular concrete compositions provide equivalent performance in terms of strength and durability, compared to concrete made from primarily mined raw materials. The construction industry's self-imposed regulations do not yet incorporate this innovation: for example, for the construction of trench silos, "standardized" concrete allows 0% recycling.
Stijn Quintelier, Oosterzeel Crushing and Concrete Plant OBBC: "In the trench silo construction project, we make concrete for our building plot with 30% recycled sands and 88% recycled coarse aggregates from locally crushed concrete rubble. We see the advantages: we save raw materials and reduce transport distances because our region is certainly self-sufficient in terms of reusable concrete rubble. We reduce the environmental impact and offer a high-quality alternative. We hope that the long-term follow-up with sensors and the example of the building owner ILVO will provide an additional argument to go for recycled concrete."
GEOPOLYMERS as a substitute for CEMENT
Geopolymer concrete is concrete in which the binder is a geopolymer, rather than cement. Geopolymers are made via a chemical combination of an aluminosilicate (such as fly ash or blast furnace slag) and an alkaline (i.e., non-acidic) activator. The alkali-activated binders can then combine with conventional aggregates to produce a hard concrete-like end product.
Geopolymers: technical details
The principle is quite simple: by bringing together aluminosilicate-containing residual streams such as fly ash (powdery material left over from coal combustion in power plants) or slag (residual streams from the metal industry) with an alkaline solution such as sodium hydroxide and sodium silicate, the desired polymerization occurs. The cured geopolymer acquires a three-dimensional molecular structure, a so-called "aluminosilicate network. Through the chemical bonding with a base, the in itself non-reactive metal slag or fly ash becomes a potentially robust matrix. This provides the strong adhesion and curing in a concrete mix. The effective implementation of geopolymers as concrete binders requires continued development work. Precise recipe development is required for each desired concrete application. In a lab, one can match the composition of the binder to the variable chemistry of the raw materials to achieve the appropriate workability, compressive strength and durability.
The Belgian construction industry's innovation center Buildwise concludes, based on a lot of study and test work on polymer concrete, that there are objective added values:
- Climate impact: CO₂ emissions from geopolymer concrete can be 40-70% lower than those from conventional cement concrete. The main difference comes from the fact that there is no need to produce Portland clinker (the process that normally accounts for most of the emissions). The net environmental impact of geopolymer binders is determined by the primary raw materials chosen (e.g., blast furnace slag, fly ash, metakaolin) and the alkaline activators used (such as sodium silicate and sodium hydroxide). Although these activators themselves can be energy intensive, life cycle analyses show that overall greenhouse gas emissions typically remain substantially lower than for Portland cement. Moreover, climate gains can further increase when secondary raw materials and residual streams are available locally, reducing transportation emissions and promoting circularity.
- Circularity: Geopolymer production makes it possible to convert industrial waste streams that were previously difficult to valorize into high-quality building materials.
- Technical performance: In terms of mechanical strength and structural properties, geopolymer concrete is similar to traditional concrete. In addition, it exhibits higher resistance to chemically aggressive environments, such as acidic or sulfate-rich environments. This makes it particularly suitable for applications where conventional concrete degrades rapidly, such as in trench silos. The lower porosity additionally contributes to a longer service life.
A reinvention?
The very first experiments with geopolymer concrete were already there at the beginning of the 20th century, both in the then Soviet Union and in Western Europe. There were even first industrial applications in the 1940s and 1950s, e.g. in and around Marioepol (Ukraine). Belgium was also a pioneer country back then (now again). English chemist Arthur Purdon, who studied and worked here, discovered and patented a binder based on activated blast furnace slag. He ran a startup PurdoCement for 3 years, but did not get his product PurdoCement to be profitable, due to opposition from Portland cement companies, among others. In Brussels, you can still find realizations with PurdoCement concrete from the 1950s: Parking 58, parts of the Royal Building and houses on the Koning Overwinnaarsplein.
Lukas Arnout, CEO van ResourceFull in Eke: "Our company has fine-tuned the geopolymer for the trench silo concrete. With knowledge of chemistry, rheology and hydration kinetics, and with adapted production logistics, we can stably and reproducibly control the chemical activations of the geopolymers. Our goal is to advocate harmonized European standards for these binders in this construction consortium. Today, the absence of a BENOR label is a bottleneck for the smooth rollout in the concrete world."
First large-scale construction project: 12 trench silos at ILVO
The innovative concrete construction project involves 12 trench silos, requiring over 5,000 m2 of concrete.
Dr. Leen Vandaele, scientific director & bovine research expert at ILVO: "Due to the acidic silage juices released during the fermentation process, trench silos pose a particular challenge to the quality of concrete. We know from experience that in some existing trench silos on field farms, the concrete has corroded after only 10 years. The measurements of the biopolymer concrete in this practical environment will undoubtedly be of interest to the construction industry, but also to the agricultural sector."
ILVO, as building owner, made the bold but reasoned decision to go to work with innovative, expectedly much more durable, but also slightly more expensive concrete. In construction projects, clients tend to be risk averse. They stick to safe standards such as BENOR-certified construction products and processes.
ILVO had clear drivers for preferring the as-yet non-BENOR-certified concretes.Evy De Vlieghere - Infrastructure and Construction Projects Coordinator ILVO: "We had learned about the promising possibilities of both geopolymer concrete and recycled concrete at study days. Especially the excellent chemical resistance, the high compressive strengths as well as the sustainability performance attracted our attention, besides of course the responsible use of raw materials."
PIO (Program Innovative Public Procurement at VLAIO), in addition to financial support (almost €400,000), provided the practical guidance and partnership with Buildwise (role of control agency, as no BENOR standardization yet). PIO helps governments and public organizations with the tendering process, the search for the right suppliers and developers, and also takes on part of the financing (up to 50%).
Mark Andries, Administrator-General, VLAIO: "This project shows how the pursuit of sustainability and circularity goes hand in hand with innovation and leads to future-proof solutions. I am pleased that we were able to contribute to this state-of-the-art concrete technology and hope that - once realized and successfully validated - it will act as an example for the entire Flemish construction sector."
Sensors in three types of concrete, years of monitoring
Three different types of concrete are placed side by side at the new trench silos and compared:
- The best available "classic" concrete, namely the most durable BENOR concrete. This constitutes the reference, against which the quality and durability of the other, innovative concrete types will be measured.
- A series of trench silos will receive recycled concrete aggregates. Here cement is added as a binding agent, but the traditionally used raw materials (crushed stone and sand) are replaced by circular materials such as crushed concrete rubble and crushed sand. The modification reduces the use of primary raw materials by 60% and also reduces transport costs.
- The trench silos made of cementless concrete with alkali-activated materials are cast by STRABAG Belgium, part of the international construction group STRABAG SE (headquartered in Austria, 86,000 employees, active in various construction sectors), in cooperation with AC Materials and ResourceFull.
Sensors are placed in each of the three concrete types that transmit real-time data over several years to an online dashboard at Buildwise. The continuously monitored parameters are temperature, moisture content, electrical conductivity and reinforcement potential. They provide a picture of the degradation processes. There will also be classic sampling and additional analysis in the lab. This is how Buildwise validates the use of geopolymer concrete for this construction application. The data collected feed the dossier to obtain a product standard for innovative binders such as alkali-activated binders. A BENOR quality label, for example.
Conclusion
The two construction consortia involved (STRABAG Belgium/ ResourceFull/ AC Materials and O.B.B.C/ De Clercq Aannemingen) make the case that the innovative concrete compositions could cause a major sustainability leap in the industry. After this challenging agricultural application, others may follow. In terms of price, recycled concrete is already comparable to BENOR concrete. Alkali-activated concrete is still 30% more expensive for now due to low volumes. As sales and long-life increases, the additional price may come down.
Joren Bracke, chief project officer at STRABAG Belgium: "For STRABAG, this construction project is a strategic participation. We may be able to use this experience with climate-friendly concrete in subsequent projects. In our opinion, there is already a win for the agricultural sector in these innovations."
Joris Relaes, Administrator-General, ILVO: "Agriculture is a highly innovative sector, in all areas. ILVO, with this pioneer construction decision, and thanks to PIO, is giving a push to the further breakthrough of a perhaps important innovation. The use of innovative and circular concrete technologies for the construction of these trench silos seems at first glance a purely technical optimization, but one that can contribute to the transition to a more sustainable and climate-resilient agricultural and construction sector."
Niels Hulsbosch, research expert at Buildwise: "The new technology is close to market introduction. The PIO project at ILVO accelerates knowledge building of technical feasibility and long-term performance, and scaling up. If in the future we can build in a different way, with lower environmental impact as well as with more recycled raw materials, that will be a huge gamechanger."
More info
Contact
Greet Riebbels, Head of Communications at ILVO: Greet.riebbels@ilvo.vlaanderen.be M. +32 486 260014
Hanna van Renterghem, ILVO Communications: Hanna.vanrenterghem@ilvo.vlaanderen.be M. +32 472 642937
