CO2 Foamed Concrete: An Innovative Approach to Combining Mechanical Strength and Carbon Storage

Carbon capture and utilization technologies, along with the use of lightweight concrete, offer promising solutions toward the decarbonization of cement industry. Combining both practices, this paper proposes an innovative type of foamed concrete produced with CO2 gas foam instead of common air foam. The objective is to demonstrate the viability of inducing the formation of porosity in the material, which is necessary for its optimal structure, while simultaneously enabling the permanent storage of carbon dioxide through the chemical reaction between the CO2 gas and the fresh cementitious paste. Samples were produced using the preformed foaming method, injecting CO2 gas instead of air, and mixing foam and cement paste prior to casting in prismatic molds. Common foamed concrete samples produced with air foam were considered as reference. Compressive tests were carried out to investigate the mechanical properties. X-ray diffractometry and scanning electron microscopy were conducted to investigate influence of CO2 gas on the microstructure of the foamed concrete. Thermogravimetry was adopted to quantify the stored CO2. The results obtained from this study are extremely encouraging. The use of CO2 foam was found to nearly double the CO2 uptake, without producing any significant change in the compressive strength to density ratio. Furthermore, the utilization of CO2 foam demonstrated a favorable influence on the microstructure of the material, resulting in the formation of smaller pores that exhibited a more uniform size distribution.