Enhanced weathering in building materials: Capturing CO2 with olivine-based façade plaster

Carbon dioxide (CO₂) is the main greenhouse gas emitted by human activity, and reducing its presence in the atmosphere is one of the major challenges of the 21st century. The building and construction sector is responsible for a significant proportion of current anthropogenic CO₂ emissions. According to the “2022 Global Status Report for Building and Construction”, the sector accounted for approximately 37% of global CO₂ emissions in 2021.  Reducing the carbon footprint of building materials is a challenging task, as some process-related CO₂ emissions are unavoidable. The industry is currently developing methods to mitigate these emissions by capturing CO₂ from flue gas streams. In this study, we investigate an alternative approach to reducing the carbon footprint of building materials by incorporating olivine into building materials such as façade plaster.

In nature, CO₂ is removed from the atmosphere through silicate weathering and stored over geological time scales as carbonate minerals. Incorporating olivine powder into building materials exposes the mineral to increased weathering conditions, which is expected to accelerate the process of CO₂ sequestration. Façade plaster is advantageous because it covers large areas of building walls that are in direct contact with the atmosphere. The method is similar to the original idea of enhanced weathering, where crushed olivine is spread over large areas of land. However, the crucial distinction is that olivine-based façade plaster is a marketable product, making its implementation more appealing.

In collaboration with Knauf Gips KG, two test stands were constructed to expose olivine-containing façade plaster to natural and accelerated weathering conditions. Knauf Gips KG is a company that specialises in drywall and flooring systems, plaster, and facades, and produced the olivine-plaster used in the experiments. This plaster is exposed to ambient weathering conditions for 12 months at an outdoor test stand. Rainwater runoff is collected and analysed for dissolved species. The fluid analyses are used to identify potential ecological hazards resulting from olivine weathering, such as the release of heavy metals into the environment. In addition to the outdoor test stand, laboratory experiments are conducted to accelerate weathering by exposing the olivine-plaster to a constantly moist CO₂ atmosphere. The composition of the water and atmosphere is monitored throughout the experiment. Mineralogical and structural changes of the plaster samples are analysed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The extent of CO₂ mineralisation will be assessed based on mass balance calculations with the experimental reactants and their products. This contribution reports interim results from the outdoor test stand after a 6-month period and presents the results of laboratory experiments on olivine and plaster alteration.