Microstructural and chemical effects of accelerated carbonation of high-volume fly ash binders in view of carbon sequestration

According to the Intergovernmental Panel on Climate Change (IPCC), global climate change induced temperature rise should remain below 1.5 °C by 2100 to guarantee the livability of our planet. This can only be achieved by immediate action by all sectors, including the cement and concrete industry. Carbonation of cementitious materials in presence of atmospheric CO2 can on the one hand hamper the durability when used in steel-reinforced applications prone to corrosion. On the other hand, the binding of CO2 through carbonation in non-steel reinforced applications could actually be of interest. When considering the worldwide application of cement-bound materials in construction along with their CO2 sequestration potential, CO2 emissions inherent to Portland cement production can partly be compensated for. Obviously, for such CO2 uptake estimations to be reliable, a thorough understanding of the carbonation behavior is imperative. In this paper, this was studied for high-volume fly ash (HVFA) binder systems with a low production related carbon footprint. HVFA mortar was subjected to accelerated carbonation experiments at 1% and 10% CO2. Carbonation-induced changes in microstructure were assessed using mercury intrusion porosimetry (MIP) while the changes in proportioning of CH and C–S–H carbonation reaction products were measured with thermogravimetric analysis (TGA). A carbonation-induced coarsening of the pore structure was observed which is more pronounced at 10% CO2 levels and attributable to more dominant C–S–H carbonation. Also the calcium carbonate content in the carbonated zone tends to significantly increase with the applied CO2%