Support for the journey to CO2-negative cement

More than four billion tons worldwide each year, and rising: Cement is by far the most widely used building material and inevitably releases large quantities of the CO₂ "bound" in the limestone during its production from burnt lime. Although manufacturers around the world have already significantly reduced the amount of their greenhouse gas emissions - but the more global warming progresses, the more urgently alternatives are called for.

Cements based not on limestone, aka calcium carbonate (CaCO₃), but on magnesium carbonates are one source of hope. Empa experts have been investigating such binders for years on the basis of the mineral olivine, which is available in large quantities in Norway, for example. In simple terms, magnesium oxide obtained from this magnesium silicate can be processed with water and CO₂ to produce cement. The bottom line is that more carbon dioxide is bound than emitted – in other words: a carbon sink.

Generous support for important goals

But unlike conventional cements, whose hardening has been researched down to the tiniest detail, these materials still raise many questions. The research project "Low Carbon Magnesium-Based Binders" led by Empa expert Barbara Lothenbach should soon provide answers – thanks to an Advanced Grant from the Swiss National Science Foundation (SNSF; see info box) with funding of 2.2 million Swiss francs.

The effort is justified, because the task is tricky. In seven focal areas, Empa experts, together with partners from the University of Oulu, Finland, want to explore what is happening at the molecular level. How do such cements harden with which formulations? What is the effect of temperature, pH and other factors such as reaction accelerators? Does the volume of a "magnesium concrete" remain stable in the long term? And how resistant is it?

Basic research with a view to practical application, in which two production processes would be available: curing with CO₂ under increased gas pressure, a complex process that would be particularly useful for precast concrete parts. And hydration: curing with water under ambient conditions, which is also suitable for production on construction sites.

In the end, the findings from laboratory experiments and thermodynamic modeling should flow into a digital twin of magnesium carbonate cement. In other words, a simulation of the chemical and physical processes during hardening – and thus the basis, Empa experts hope, for formulations of robust concretes that bind as much CO₂ as possible.