The rule until now has been "no concrete without cement," but concrete's traditional binding agent has a high carbon footprint. In cooperation with partners from four European countries, researchers at the Karlsruhe Institute of Technology (KIT) are working in the EU-financed C-SINC project on a climate-friendly material that can partly replace cement. They are using magnesium silicates to permanently bind carbon dioxide in mineral form. Not only does concrete produced with this cement substitute cause significantly lower emissions, it actively stores carbon and removes it from the atmosphere.
Concrete is a climate-damaging construction material because of the cement it contains, which acts as its binding agent. The production of cement clinker, a key ingredient of cement, is responsible for about 8 percent of global CO₂ emissions.
"These high emissions result from the energy consumed during production, but especially from the deacidification of limestone during the production of Portland cement clinker, which is the most common binding agent for concrete," explained Professor Frank Dehn, who heads the Institute of Concrete Structures and Building Materials and the Materials Testing and Research Institute at KIT.
There are already substitute materials for cement, such as fly ash from coal combustion and ground blast-furnace slag. However, these materials will become scarce in the foreseeable future due to Germany's coal phase-out and the industrial transformation of the steel industry. Developing sustainable alternative cement substitutes is the goal of C-SINC, an EU-funded project involving researchers from Germany, the Netherlands, Belgium, and Spain. Dehn's working group tests the suitability of the new types of concrete that can be produced with these cement substitutes.
CO2 Bound Permanently
The focus is on magnesium silicates that react with CO₂ to form magnesium carbonate in a targeted and accelerated mineralization process. As a secondary cement additive, this material can be used to replace part of the clinker. "By using CO₂ that's extracted from industrial exhaust gases (in other words, removed from the atmosphere), not only can we lower emissions due to concrete, we can also make it work as a carbon sink," Dehn said. "The CO₂ isn't just stored, it's chemically bound in a mineral. It remains firmly bonded, so it can't escape over very long periods."
Putting the Material to Use Quickly
Under the direction of an industrial partner, the research teams are not only developing new materials in the lab. Their primary objective is to quickly put concrete with the new cement to use as an actual construction material. KIT is playing an important role in the efforts. "Using machine learning strategies and structural-mechanical modeling, we're investigating how the binding agent behaves in concrete, how to best mix the concrete, and how well it works in practice," Dehn said. "We're doing that on a small scale, and in real large-scale structural elements as well."
KIT's strength is its tight integration of simulation, experimental research, and large-scale, realistic testing at its materials testing facility in Karlsruhe. "With simulations and machine learning, we can predict which concrete formulations will work. Then we plan experiments to test our predictions. We want to work out reliable parameters that show that concrete with the new binding agent is climate-friendly and satisfies requirements for load-bearing capacity, durability, and safety," Dehn said.
About C-SINC
The project is funded by the European Innovation Council (EIC) within the framework of its Pathfinder Challenge entitled "Towards cement and concrete as a carbon sink." The funding amounts to about EUR 4 million over four years, of which about EUR 1 million will go to KIT, the only German partner in the project consortium as well as the only German university funded by the EIC in the Pathfinder program. Besides KIT and the coordinating company, PAEBBL AB (Sweden), other partners are Delft University of Technology (the Netherlands); Katholieke Universiteit Leuven (Belgium); the Spanish National Research Council and PREFABRICADOS TECNYCONTA S.L. (Spain); and, in a supporting capacity, Holcim Technology Ltd. (Switzerland).
