## 3 Results
### Co\({}_{2}\) Sequestration Potential  
When assuming full carbonation (by assessment of the phenolphthalein color indicator) for the 1 m\({}^{3}\) mortar volume, the CO\({}_{2}\) sequestration potentials (CO\({}_{2}\)SP) of the HVFA mix, the CEM II/B-V 42.5 N mix and the CEM I 42.5 N mix amount to 72-91 kg/m\({}^{3}\), 123-138 kg/m\({}^{3}\) and 128-158 kg/m\({}^{3}\), respectively (Figure 2, grey bars). Despite their differences in the 14-day sample preconditioning and exposure period for the HVFA mix and the other two mixes, the observed increasing CO\({}_{2}\)SP values can most probably be associated with their decreasing fly ash content and thus increasing carbonatable material content. It should be noted though that the differences in CO\({}_{2}\)SP between the CEM II/B-V 42.5 N mix and the CEM I 42.5 N mix are not that large. A larger difference might perhaps be expected given the fact that the Portland clinker content of the composite cement CEM II/B-V 42.5 N is reduced with 21-35% in comparison with the Portland cement CEM I 42.5 N mix. Differences in potential carbon material and related CaO content (see Table 1) are a direct result of this. Another peculiar observation is that the highest CO\({}_{2}\)SP values for the CEM I 42.5 N mix are there despite the fact that this mortar mix showed the lowest carbonation degree of all three considered mixes (see Section 3.2). Apparently, the higher CaO content of the Portland cement (Table 1: 63.12% vs. 49.28%) compensated for this. Additionally, the somewhat higher binder content of the Portland cement mortar mix (Table 2: 490.36 kg/m\({}^{3}\) vs. 483.21 kg/m\({}^{3}\)) played a role in that. The underlying carbonation test method to determine the achievable carbonation degree for each binder system seriously affected the eventually obtained CO\({}_{2}\)SP value that is calculated from it. With an increasing CO\({}_{2}\) concentration applied during the carbonation experiment (from 0.04% CO\({}_{2}\) to 1% CO\({}_{2}\) and 10% CO\({}_{2}\)), the expected CO\({}_{2}\)SP value increases significantly. This is a serious matter of concern. Apparently, accelerated carbonation testing cannot be used for an adequate assessment of the expected CO\({}_{2}\) sequestration potential under natural exposure conditions. Even slightly accelerated carbonation at 1% CO\({}_{2}\) already gives this problem. The findings described above might be of limited use since the exposure periods needed to come to the earlier mentioned state of full carbonation varied considerably between the three mortar mix designs under investigation. From that point of view, it is more interesting to look at CO\({}_{2}\)SP values obtained for a dimensions specific 2.24 \(\times\) 2.24 \(\times\) 0.20 m\({}^{3}\) = 1 m\({}^{3}\) mortar volume after 100 years of exposure (Figure 2, white bars). As such, differences in progression of the carbonation front with time and related differences in carbonated mortar volume up to the point of the carbonation front after 100 years are accounted for. The resulting CO\({}_{2}\)SP values for the HVFA mix, the CEM II/B-V 42.5 N mix and the CEM I 42.5 N mix amount to 55-29 kg/m\({}^{3}\), 19-20 kg/m\({}^{3}\) and 15-17 kg/m\({}^{3}\), respectively. Contrarily to the previous calculation approach for a generic 1 m\({}^{3}\) mortar volume, the HVFA mix now seems the most beneficial one when it comes to potential CO\({}_{2}\) sequestration and related sustainability aspects. For a time and dimensions specific mortar volume, the effect of the applied CO\({}_{2}\) concentration during carbonation testing changes. For the HVFA mix, CO\({}_{2}\)SP values decrease with the applied CO\({}_{2}\) concentration. This mainly due to the important underestimation of natural carbonation rates when estimated from the outcome of accelerated carbonation experiments (see Section 3.1: 29-59%). The other two mortar mix designs still show a slight increase in CO\({}_{2}\)SP value when CO\({}_{2}\) concentration during carbonation testing shifts from 0.04% to 1%.