Conference Agenda

Magnesium silicate hydrate (M-S-H) type binders are being discussed as a CO₂-neutral alternative to ordinary Portland cement (OPC). A widespread replacement of OPC however requires a raw material with no embodied CO₂ that is also globally available in sufficient quantities.

Oliment^® is a binder produced by thermal treatment of serpentinite rock, a raw material that meets these criteria. The thermal treatment leads to an amorphization of the serpentine minerals. At temperatures between 600 °C and 800 °C the degree of amorphization is high while at the same time the formation rate of the unreactive magnesium silicates forsterite and enstatite is low. Upon contact with water the amorphous and highly reactive meta-serpentine dissolves and M-S-H phases are precipitated.

The nanoscale nature and morphology of these M-S-H phases is responsible for the strength buildup in concrete structures made with Oliment^® binder. A fast reaction progress during the first 24 hours of the hydration reaction leads to concrete with a high early strength.

A pilot scale Oliment^® production plant with an electrically heated rotary kiln demonstrates the technical feasibility of the thermal activation process with equipment known from ordinary Portland cement production. If renewable energy is used for thermal activation the process leads to a CO₂-neutral binder material that can be produced at scale and cost-competitive.

During Portland cement production about two-thirds of its total manufacturing-related CO₂ emissions are due to the decarbonation of its main raw material component CaCO₃. Materials that can capture these CO₂ emissions are a crucial part for the decarbonisation of the cement industry.

The activation of Mg-silicates produces an activated Mg-silicate material that contains X-ray amorphous magnesium silicate as reactive phase. The activation of the Mg-silicates releases no chemically bound CO₂ and thus can be considered as CO₂-neutral. Moreover, when using the activated Mg-silicate for CO₂ sequestration via mineral carbonation the material can be considered CO₂-negative.

In order to study the carbonation of the activated Mg-silicates wet carbonation experiments were conducted. Therefore, the material was mixed with CO₂ saturated deionized water and simultaneously 100 vol.-% CO₂ gas was continuously bubbled through the mixture. The experiments were carried out at room temperature and the setup was open to the laboratory atmosphere [1]. During the carbonation experiments the development of pH and electrical conductivity was measured constantly. After completion, the slurry was filtered and the solid residue was characterized using quantitative X-ray diffraction and thermogravimetric analysis. Two different activated Mg-silicates were investigated regarding their wet carbonation behaviour. As a result of the wet carbonation experiments, the carbonate phase that formed was Nesquehonite.

[1] S. Villmow, A. Mielkau, F. Goetz-Neunhoeffer, J. Neubauer, Wet carbonation of C3A and pre-hydrated C3A, Cement and Concrete Research. 173 (3023) 107259, https://doi.org/10.1016/j.cemconres.2023.107259.

Mg-based binders offer an opportunity for CO₂-neutral cements due to the absence of chemically bound CO₂ in the raw materials and the low energy requiring activation process. For a new Mg-binder [1,2] magnesium silicates such as olivine and serpentine are used. Hydrothermal and thermal activation lead to formation of an amorphous meta-serpentine that reacts with water by forming a M-S-H phase. Synthetic forsterite is used in our studies to investigate a simplified pure magnesium silicate system.

Three different compositions of “M-S-H”, which differ regarding their structural properties and composition, could be identified, differentiated according to their formation process. Autoclavation of forsterite, which is favoured by using KOH solution, a high surface area of forsterite and a duration of several weeks, leads to formation of lizardite, brucite, periclase and a M-S-H compound. Autoclaved autoM-S-H shows nanocrystalline and amorphous features and is a mixture of M-S-H compounds with variable chemical composition. Annealing of the hydrothermally formed hydrate phases at 600-750 °C leads to partial dehydroxylation and formation of periclase and a reactive amorphous activM-S-H compound with variable chemical composition. At 600 °C, residual lizardite is still present, while at 800-850°C forsterite and enstatite crystallize from this amorphous fraction. Thermally activated activM-S-H dissolves in water forming a hydrated nanocrystalline hydrM-S-H compound. Periclase dissolves as well due to its low crystallinity. The overall reaction is nearly completed after 48 h.

[1] F. Bellmann, Sequestration of CO2, WO2023/134849A1, 2023

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