CO₂-reduced cement production: pilot plant for tempered clays starts operation

The new test facility rises 24 meters into the air. The raw material is stored in the silo tower in the foreground and the finished product in the silo at the back left.

Rohrdorf, July 9, 2025 – The new pilot plant for tempered clays at the Rohrdorf cement plant successfully went into operation at the beginning of July. In the plant, raw clay is activated (“tempered”) through thermal treatment. The aim of the plant is to research tempered clays, as these can be used as a lower-CO₂ alternative to clinker, the main component of cement. This makes them a milestone in Rohrdorfer’s decarbonization roadmap. The test plant was created as part of a pilot project funded by the German Federal Ministry for Economic Affairs and Energy and the European Union and is receiving funding of up to 8.65 million euros due to its innovation potential. The project was launched in October 2023 and will run until December 2026.

Low-energy and low-emission operation thanks to innovative plant concept

The pilot plant uses the existing waste heat from the clinker production line and was therefore built directly next to the rotary kiln. By using the waste heat from the kiln and the specially designed flash calciner, it is possible to temper the clays with very little primary energy. The waste gases produced during operation are fed into the existing waste gas purification system of the clinker production line after leaving the plant. This means that no additional emissions are produced.

The plant was planned and built by French plant manufacturer Fives FCB, in collaboration with the Rohrdorf Net Zero Emission team. The construction phase took around six months. The maximum production volume is 50 tons of tempered clay per day.

Sophisticated process engineering

By the end of 2026, the Net Zero Emission team will have investigated the ideal composition of the raw clays and optimized the processes for thermal treatment. Various grinding finenesses and the use of different aggregates are also being tested. As a result, the tempered clay should serve as a CO₂-saving replacement for clinker and meet all standards for cement production. “By systematically researching the technology of tempered clays in the production process at the Rohrdorf plant, we are doing pioneering work in the cement industry,” says Markus Judendorfer from the Net Zero Emission team. „A particular challenge is to optimize the product and at the same time further improve the energy efficiency of the plant. Our first results from the initial phase are very satisfactory.“

CO₂ avoidance through less clinker in the cement

Trials with various raw clays and process parameters are currently planned until mid-2026. Building on these trials, a large-scale plant is to be built in the future that will enable significant CO₂ savings. „The potential for CO₂ savings amounts to a total of 60 percent. Almost half of this can be avoided thanks to tempered clays. The new pilot plant is therefore an important step on our way to CO₂-neutral cement production, which we are aiming for by 2038,“ explains Dr. Christopher Ehrenberg, Technical Director of the Rohrdorf cement division.

Front view of the plant. On the left is the silo with the raw material. In the middle are the cyclones and the combustion chamber. On the right, the rotary kiln and the pipe for the clinker cooler exhaust air.
Rear view of the system. The exhaust air filter is in the foreground.
The plant viewed from the heat exchanger tower. On the left: The rotary kiln, whose waste heat is used to operate the plant.
Example of raw clay for use in the test plant.
Tempered and ground clay for the replacement of clinker in cement.

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