CO2 sequestration potential of high-volume fly ash (HVFA) mortar when based on accelerated carbonation tests

The high carbonation susceptibility of binder systems with high volumes of supplementary cementitious materials (SCMs) makes them more prone to steel reinforcement corrosion than ordinary Portland cement (OPC) binder systems. However, in non-steel reinforced applications, the low carbonation resistance could be a major advantage from the environmental viewpoint since anthropogenic CO2 emissions are captured quite fast that way. This would be an additional benefit to the low production related CO2 emissions of these binders. If these materials would be applied on a sufficiently large scale this could reduce global warming. In this paper, this CO2 sequestration potential was specifically investigated for High-Volume Fly Ash (HVFA) mortar in which at least 50% of the binder consists of pozzolanic fly ash from coal-fired electricity production. Phenolphthalein based natural and accelerated carbonation data obtained at 0.04%, 1% and 10% CO2, as well as corresponding thermogravimetric analysis (TGA) results were used to try to estimate the expected carbonation rate and carbonation degree of HVFA mortar at the end of its service life and see what CO2 uptake capacity would be reached by then. It was found that depending on the CO2 concentration applied during accelerated tests to estimate field carbonation rates and carbonation degrees that are expected under realistic exposure conditions, the CO2 sequestration potential of HVFA binder systems within a timeframe of 100 years can vary significantly. Carbonation tests conducted at 10% CO2 for this purpose tend to underestimate the maximum CO2 uptake a lot more than carbonation tests at 1% CO2