The production of cement accounts for around a tenth of the world’s total industrial CO2 emissions. It is estimated that the construction industry accounts for a third of Denmark’s total CO2 emissions – a very large proportion of this comes from cement production.
Lime is burned at a high temperature
The background is that a significant part of the cement manufacturing process consists of so-called calcination of limestone. In short, the calcining process involves burning the lime at very high temperatures. The very high temperatures naturally require very large amounts of energy. So much so that cement producer Aalborg Portland is Denmark’s biggest CO2 emitter.
Now a new research project at the Technical University of Denmark (DTU) is to investigate whether it is possible to replace the calcined limestone with low-quality ones, which is the type of clay that is most abundant in the subsoil. The project has just been awarded almost DKK 2.9 million from Denmark’s Independent Research Foundation.
Chemical reactions at room temperature
The new research project will develop a method for processing the clay so that it can be used in cement production. The process is called mechanochemical activation, and – if the method works – has the clear advantage that the process can take place at significantly lower temperatures than calcination. In fact, the definition of mechanochemistry is that by supplying mechanical energy, chemical reactions can be triggered at room temperature.
It is DTU senior researcher Navid Ranjbar who is behind the project, which has been aptly named “A novel ternary blended cement with low-grade clay”.
A further advantage of being able to use completely ordinary clay (low-quality clay) in the cement is that the clay can be practically dug up directly from the subsoil anywhere. This will also save on the transport of limestone to the cement factory.
Compared to benchmark cement
We monitor the chemical reaction involved in microstructure development and the curing process and compare the climate footprint with a benchmark low-carbon cement. The new approach can reduce the climate footprint compared to other cements, especially with a view to reducing demand for rarer high-quality clays and the energy savings from activating the clay, states the description of the project from Denmark’s Free Research Foundation.
Futurecem with clay
Aalborg Portland is already marketing the product Futurecem, where part of the clinker in the cement is replaced with clay, but that product still requires high temperatures and thus emits more CO2 than the mechanochemical activation clay.
