- 07/06/2025
- Article
- Sustainability & carbon-neutrality
Building materials in transition: Four approaches to climate-friendly construction
The building sector is responsible for a significant proportion of CO2 emissions. Reducing these emissions requires more than one solution. Four companies demonstrate the diversity of approaches that can be taken – from innovative binders and CO2 storage to data-based process optimization. Their common goal is to significantly reduce the carbon footprint of building materials and buildings.
Written by Marius Schaub
When it comes to the impact of the construction industry on climate change, several alarm bells are ringing at once: the building sector regularly fails to meet its climate targets – and not just in Germany. Globally, cement production accounts for almost a tenth of man-made CO2 emissions. These are good reasons to start thinking as soon as possible about how the industry can reduce its carbon footprint.
Fortunately, there are numerous players who are fully committed to the goal of not only reducing operational emissions, but also lowering the gray energy of buildings – that is, the energy required for the production, transport, and installation of building materials. Here is an overview of large and small companies whose mission is to decarbonize the building sector.
A new binder for CO2-reduced concrete
Concrete is one of the most widely used building materials in the world – and one of the most CO2-intensive. This is mainly due to the cement content, which typically accounts for around 90 percent of concrete's greenhouse gas emissions. This is where Celitement comes in: The Karlsruhe-based company has developed an alternative binder that is comparable to conventional cement but releases significantly less CO2.
The key lies in the mechanochemical production of a binder based on calcium silicate hydrate (C-S-H) – the solid phase that also provides strength in Portland cement. Instead of burning limestone at 1,450°C, which causes significant emissions, Celitement mixes only a small amount of hydrated lime with quartz sand and converts it into a solid C-S-H stone at a moderate temperature in an autoclave. This is then mechanically activated – a step that can be carried out purely electrically and is therefore potentially CO2-free if green electricity is used.
The advantage for users: Celitement can be processed like conventional cement. It is hydraulic, reacts with water, achieves comparable early and final strengths, and is also suitable for unreinforced and reinforced concrete. In addition, the resulting cement stone has a particularly dense structure that prevents the penetration of harmful substances such as chloride ions – a plus for durability and corrosion protection.
The approach is also promising from an ecological point of view. Compared to conventional gray cement, Celitement saves around 40 percent CO2, and up to 50 percent compared to white cement. The only raw materials used are lime and silicon – in the form of sand, for example – which secures the material base in the long term. Even desert sand could be used, as the smoothness of the sand grains is irrelevant here.
Building materials such as Celitement could make a significant contribution to the decarbonization of construction in the long term – not as a niche product, but as a mass-market binder with clear technical and ecological advantages.
Recycling instead of landfill: recycled concrete saves CO2 and resources
Recycled concrete has been around for a long time – and suppliers have been struggling with image problems for just as long. Inferior formulations with mixed batches, unclear properties, and low demand have long made life difficult for manufacturers of high-quality secondary building materials. But the market and demand are gradually changing. This is also thanks to suppliers such as Zirkulit: the Swiss brand is fully committed to recyclable construction. It not only recycles concrete, but also upgrades its quality to such an extent that it can compete with primary concrete.
The focus is on RC concrete, which is based exclusively on single-type concrete demolition waste – i.e., without masonry or other admixtures. This improves the strength properties, reduces water requirements, and ensures a stable grading curve of the aggregate. This is made possible by modern processing technology with finely graded fractions, separation of heavy minerals and light fractions, and defined grain distribution.
But Zirkulit goes further: the light fraction of the mixed demolition waste is used to develop a mineral foam concrete as an insulating material, which serves as a fully recyclable substitute for polystyrene or rock wool. This creates a holistic approach: insulation, masonry, prefabricated parts, and concrete components—all made from mineral demolition material.
The products meet strict environmental requirements and are certified. Particular attention is paid to equivalence with primary building materials: compressive strength, consistency, durability, and workability correspond to conventional concrete formulations. That is why Zirkulit does not refer to “RC concrete” but deliberately to “circular concrete.” The company shows that high-quality recycling does not have to be a compromise but can be a driver of innovation. With precise processing, industrial scalability, and a clear strategy for the circular economy, concrete can become part of the solution instead of the problem.
Negative emissions with a system: recycled concrete as a CO2 storage medium
Neustark's goal is not only to avoid CO2, but also to actively remove it from the atmosphere. The Swiss company permanently stores the greenhouse gas in recycled concrete, thereby contributing to so-called negative emissions. This is made possible by an innovative process that is installed directly at concrete recyclers.
At the heart of the process is a simple chemical reaction: the phases adhering to cement residues in concrete rubble react with CO2 to form stable limestone. This process of natural carbonation usually takes place slowly, but Neustark greatly accelerates it. In a reaction chamber, the material is fumigated with pure CO2 from biogas plants. The advantages for recycling companies are manifold: the treated material has higher strength, better technical properties, and can be reused as high-quality RC material, for example for recycled concrete. In addition, CO2 certificates are generated that can be sold on the market. The income contributes to the amortization of the plants supplied by Neustark as a technology provider.
The storage is permanent: the CO2 remains bound for thousands of years unless it is thermally decomposed, which is impossible under normal operating conditions. This distinguishes the process from many CO2 offsets based on short-lived sinks such as trees.
The process is particularly useful where recycled concrete is already established. In combination with other measures, it could be possible in the future to construct buildings with a significantly reduced or even neutral carbon footprint. Neustark demonstrates that circular economy and climate protection can go hand in hand, even with mineral building materials.
Sustainable concrete through real-time optimization
Concrete production has traditionally been considered a black box: while cement plants are relatively easy to control, there is often a lack of oversight when it comes to concrete ex works, especially between the mixing plant and the construction site. Alcemy wants to ensure transparency and thus also reduce CO2 emissions. The Berlin-based company has developed a software platform that uses machine learning to monitor and predict the quality of concrete in real time. This allows the concrete properties to be predicted for each individual delivery vehicle – from the mixing plant to unloading at the construction site. The software takes into account both the recipe and real process conditions such as transport time, weather, and water additions.
The goal: less cement, more safety. Until now, many concrete plants have worked with generous safety margins in the cement content to compensate for fluctuations. With Alcemy, these buffers can be reduced in a targeted manner without compromising product quality. This saves costs and reduces the carbon footprint. This is particularly relevant when using clinker-reduced cements. Such cements are promising in the laboratory, but difficult to control in practice. Alcemy enables their use because the software provides precise predictions at low water-cement ratios – a prerequisite for predictable strength. In addition to the concrete solution, Alcemy also offers an AI tool for cement manufacturers that helps predict the strength of the cement while it is still in the mill – also with the aim of saving energy and clinker.
The ecological advantages are obvious: Less cement means fewer emissions. In addition, precise control also means that RC aggregates, recycled water, and other alternative raw materials can be used more safely. For many customers, the investment in the software pays for itself after just two years – not only because of the CO2 savings, but also through reduced cement consumption, assured quality, and better planning of laboratory and personnel resources.
Conclusion: Many paths lead to the goal
After water, concrete is the most widely used material in the world. That is why even small improvements in concrete and cement have a major impact on a global scale. This is where the decarbonization of construction comes in—in a variety of ways. Alternative binders, CO2 storage, recycled materials, and digital optimization of manufacturing processes can massively reduce the ecological footprint of the building sector.
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