Indoor CO₂ buffering potential of clay-based building materials

To mitigate the anthropogenic greenhouse gas emissions from the operational energy consumption in buildings, increasingly high-performance envelopes are developed. A reduction in indoor air renewal is observed that leads to a higher pollutant concentration in the built environment. Particular attention was given to CO₂, an anthropogenic gas that has consequences on the Indoor Air Quality (IAQ) and the health of occupants. Developing a passive regulation system appears to be a promising solution for improving IAQ and reducing the energy consumption of ventilation systems. For that purpose, earth-based materials present interesting characteristics through the presence of clay minerals and their microstructure. In this context, this paper aims at presenting a novel experimental method to assess the CO₂ retention potential of natural earth plasters. The method uses a thermogravimetric device (TGA/DSC) associated with a gas mixer and humid air generator. The mass variation resulting from the interaction of the increasing CO₂ content could thereby be measured and analysed. Results show the important role of reversibility in the phenomenon: the majority of the captured CO₂ being released when the CO₂ concentration drops. It also highlights the role of the relative humidity on the retention capacity. As the retention of CO₂ is lower when the material is wet, the water molecules may occupy part of the adsorption sites and react themselves with the CO₂. This experiment provides the first values and thus evidence of the CO₂ retention capacity and passive regulation potential of this material.