CO2-neutral and -negative Mg-binders based on olivine

The production of ordinary portland cement releases large amounts of CO₂ by burning of fossil fuels and by decarbonation of limestone, in which CO₂ is chemically bound as CaCO₃. The burning process leads to decomposition of CaCO₃, where CO₂ is released and CaO is part of the clinker.

For this new building material, olivine is used as raw material instead. In this study, the Mg-end-member forsterite, Mg₂SiO₄, is used as model system to describe the hydration of olivine, which naturally occurs as a Mg-rich solid solution. Forsterite is able to react with water, forming serpentine, Mg₃Si₂O₅(OH)₄, and brucite, Mg(OH)₂. This reaction is known as serpentinization and lasts long time scales during geological processes, but can be accelerated by an activation process [1] for technical applications.

The activation process consists of two steps. First step is autoclavation of forsterite, which corresponds to serpentinization. Serpentine and brucite are thermally activated in second step. Annealing these hydrate phases leads to thermal decomposition, where H₂O is partially released and a reactive amorphous magnesium silicate phase is formed. The activation process is low in energy consumption and does not release chemically bound CO₂.

The activated magnesium silicate phase reacts with water forming a M-S-H phase. M-S-H has only low crystallinity [2]. Furthermore, this binder shows the possibility of CO₂ uptake by mineral carbonation, creating a CO₂-negative building material.

References:

[1] F. Bellmann, Method for producing a hydrated cement, WO2025/012209A1, 2025

[2] C. Roosz et al. (2015) Cement and Concrete Research 73, 228-237. doi: 10.1016/j.cemconres.2015.03.014