Concrete as a CO₂ sink

Concrete is considered a climate-damaging building material. The main reason for this is the cement it contains, which ensures that the building material holds together. The production of cement clinker, a raw material for cement, accounts for around 8% of global CO₂ emissions.

„These high emissions are caused by the energy used in production, but above all by the chemically induced deacidification of limestone in the manufacture of Portland cement clinker, the most commonly used binder for concrete,“ explains Professor Frank Dehn, head of the Institute for Solid Construction and Building Materials Technology and the Materials Testing and Research Institute Karlsruhe at KIT.

There are cement substitutes, such as fly ash from coal-fired power generation or granulated blast furnace slag. However, these will become scarcer in the foreseeable future due to the phase-out of coal and the industrial transformation of the steel industry. The development of a sustainable alternative to such cement substitutes is the goal of the EU-funded C-SINC project, which involves researchers from Germany, the Netherlands, Belgium, and Spain. Dehn‘s working group is testing the practical suitability of the new concretes that can be produced with these substitutes.

CO₂ remains permanently bound

The focus is on magnesium-containing silicates, which react with CO₂ to form magnesium carbonate in a targeted, accelerated mineralization process. As a so-called secondary cementitious additive, this should be able to replace part of the clinker. „By specifically separating the CO₂ used in this process from industrial waste gases, i.e., removing it from the atmosphere, concrete can not only become lower in emissions in the future, but also actively act as a CO₂ sink,“ says Dehn. „The CO₂ is not simply stored, it is chemically incorporated into a mineral. It remains firmly bound and cannot escape again over very long periods of time.“

The goal is rapid applicability

Coordinated by an industrial partner, the research teams are not only developing new materials in the laboratory. The central goal is to ensure that the concrete bound with these materials can be used as an actual building material in the near future. KIT plays an important role in this: „We use machine learning strategies and structural mechanical models to investigate how the binder behaves in concrete, how we can optimally compose the concrete, and how it performs in practice,“ says Dehn. „We do this on a small scale, but also in real, large components.“

A particular strength here is the close integration of simulation, experimental research, and large-scale, realistic testing at the Materials Testing Institute in Karlsruhe. „We can use simulations and machine learning to predict which concrete formulations will work. We then use experiments in a targeted manner to verify these predictions. In this way, we want to develop reliable characteristic values that show that concrete with the new binder is climate-friendly and meets the requirements for load-bearing capacity, durability, and safety,“ says Dehn.

Multiple project partners and sponsors

The project is funded by the European Innovation Council (EIC) as part of the Pathfinder program „Towards cement and concrete as a carbon sink.“ The total funding amounts to around €4 million over a period of four years. Around €1 million of this will go to KIT – the only German partner in the project consortium and also the only German university funded by the EIC in the Pathfinder program. In addition to KIT and the coordinating PAEBBL AB (Sweden), the partners are Delft University of Technology (Netherlands), Katholieke Universiteit Leuven (Belgium), Agencia Estatal Consejo Superior de Investigaciones Científicas and Prefabicados Tecnyconta S.L. (both Spain), as well as Holcim Technology Ltd. (Switzerland) in a supporting role.