## 3 Results
### CO\({}_{2}\)-Sequestration-to-Emission Ratios  
An overall evaluation of sustainability performance in relation to global warming can only be made by considering the CO\({}_{2}\) sequestration potential and the greenhouse gases emitted during production together. To achieve this goal CO\({}_{2}\)SP/EM values were calculated. Figure 4 shows these values for the binder fraction of a generic 1 m\({}^{3}\) mortar volume of the HVFA mix (Figure 4a) and the CEM II/B-V 42.5 N mix (Figure 4b) while considering different options of assigning production-related environmental impact to the fly ash. Figure 4: CO\({}_{2}\)-sequestration-to-emission ratios for the binder fraction of 1 m\({}^{3}\) of the HVFA mortar (**a**) and CEM II/B-V 42.5 N mortar (**b**) in relation to the one of reference CEM I 42.5 N mortar, using various approaches for assigning impact for their fly ash content: No impact (No), impact of basic treatment (Tr), impact of basic treatment and economic allocation (Tr + Ce). An assigned impact consisting of both the impact of basic treatment (Tr) and the allocated impact of coal-fired electricity production by economic value (C\({}_{\rm e}\)), can result in a substantial decrease of the CO\({}_{2}\)SP/EM indicator when compared with corresponding values of scenarios considering no impact assignment or mere consideration of only the basic fly ash treatment. As soon as the economic allocation coefficient reaches 0.98% (cf. data of [PERSON] et al. for the US [9], see Table 3), this drop in CO\({}_{2}\)SP/EM value becomes quite substantial. An economic allocation coefficient of 4.30% cf. [PERSON] et al. [10] for Canadian fly ash causes a drop in CO\({}_{2}\)-SP/EM value of more than 50% for the HVFA mix. A similar trend was observed for the CEM II/B-V 42.5 N mix, yet be it to a lower extent given the lower fly ash content of the mix. When additionally looking at the effect of the underlying carbonation test conditions, it is clear that accelerated testing at elevated CO\({}_{2}\) levels significantly overestimates the CO\({}_{2}\)SP/EM indicator corresponding with the actual natural exposure conditions. However, it seems that the way of calculating production-related greenhouse gas emissions has a more dominant effect on the outcome of this indicator, than the way of quantifying the CO\({}_{2}\) sequestration potential. Comparison with the expected CO\({}_{2}\)SP/EM value for the Portland cement reference demonstrates that when based on natural carbonation tests (Figure 4, grey line, CO\({}_{2}\)SP/EM = 31%), the HVFA mix outperforms the CEM I 42.42.5 N mix, unless the economic allocation coefficient for the fly ash is 0.50% or more (i.e., scenarios Tr(DE)+Ce(DE), Tr(DE)+Ce(US) and Tr(DE)+Ce(CA)). In case of accelerated carbonation at 1% CO\({}_{2}\) as underlying test method (Figure 4, black line, CO\({}_{2}\)-SP/EM = 38%), the CEM I 42.5 N mix gets the benefit over the HVFA mix as soon as the economic allocation coefficient reaches 0.25% (i.e., scenario Tr(DE)+Ce(CN)). For the CEM II/B-V 42.5 N mix with a fly ash content of only 21-35%, a much higher economic allocation coefficient is required before it is outperformed by the Portland cement reference. This was only the case under the assumption of a C\({}_{\rm e}\) value of 4.30% (scenario Tr(DE)+Ce(CA)) and carbonation at 0.04% CO\({}_{2}\) as underlying test method. When based on slightly accelerated carbonation at 1% CO\({}_{2}\), a C\({}_{\rm e}\) value of 0.98% (scenario Tr(DE)+Ce(US)) seems to be sufficient already to have a CO\({}_{2}\)SP/EM value that is lower than the one of the Portland cement reference. When shifting from generic fully carbonated 1 m\({}^{3}\) mortar volumes to time and dimensions specific 1 m\({}^{3}\) mortar volumes with a varying carbonation status after 100 years, the CO\({}_{2}\)SP/EM results are quite different (Figure 5). First of all, CO\({}_{2}\)SP/EM indicators drop quite spectacularly in value.