## 2 Materials and Methods
### Calcium Carbonate Content, Carbonation Degree and CO2 sequestration Potential  
With the CaCO3 content known and some basic stoichiometry one can easily quantify the amount of CaO that reacted with the CO2 that penetrated during the natural, slightly accelerated and highly accelerated carbonation experiments (Equation (3)).  
\[\%\ \rm{m}/\rm{m}\ CaO_{\rm{ reacted}}=\%\ \rm{m}/\rm{m}\ CaCO_{3}\cdot\frac{MW_{CaO}}{MW_{CaCO_{3}}} \tag{3}\]  
with \(\%\ \rm{m}/\rm{m}\ CaCO_{3}\), the outcome of Equation (2), MWCaO, molecular weight of CaO (56 g/mol) and MWCaCO3, molecular weight of CaCO3 (100 g/mol). By dividing this value by the reactive CaO content that is initially available in the binder system (CaOreactive = CaO as specified in Table 1), an estimation of the carbonation degree \(\rm{a_{c}}\) (-) is obtained (Equation (4)). For the HVFA mortar this overall initially available reactive CaO content equals 0.5 x CaO\({}_{\rm{CEM}\ 152.5\ \rm{N}}+0.5\) CaO\({}_{\rm{Fly\ ash}}\) or 33.02\(\%\ \rm{m}/\rm{m}\). For the CEM II/B-V 42.5 N mix and the CEM I 42.5 N reference mix the CaO values of their cements amount to 49.28\(\%\ \rm{m}/\rm{m}\) and 63.12\(\%\ \rm{m}/\rm{m}\), respectively.  
\[\rm{a_{c}}=\frac{CaO_{\rm{reacted}}}{CaO_{\rm{reactive}}} \tag{4}\]  
Given the carbonation degree per carbonation condition (natural vs. slightly accelerated vs. highly accelerated) for each studied mortar mix, one can now determine a CO2 sequestration potential (CO2 SP, kg/m3) cf. Equation (5) as proposed by [27].  
\[\rm{CO_{2}SP}=\rm{a_{c}}\cdot B\cdot CaO_{\rm{reactive}}\cdot\frac{MW_{CO_{2}}}{MW_{CaO}} \tag{5}\]  
with \(\rm{a_{c}}\), the carbonation degree (-), B, the binder content of the mortar (Table 2: 473.28 kg/m3 (HVFA Mix), 483.21 kg/m3 (CEM II/B-V 42.5 N Mix), 490.36 kg/m3 (CEM I 42.5 N Mix), CaO\({}_{\rm{reactive}}\), the initially available reactive CaO content (33.02\(\%\ \rm{m}/\rm{m}\) (HVFA mix), 49.28\(\%\ \rm{m}/\rm{m}\) (CEM II/B-V 42.5 N Mix), 63.12\(\%\ \rm{m}/\rm{m}\) (CEM I 42.5 N Mix), MW\({}_{\rm{CO2}}\), molecular weight CO2 (44 g/mol) and MWCaO, molecular weight CaO (56 g/mol). Note that the as such calculated CO2 SP value assumes that the carbonation front traversed the entire mortar volume. In reality, the natural carbonation rates for each of the studied mortar compositions will be different. To enable comparisons, a reference timeframe during which carbonation can take place needs to be set. In this study, a time period of 100 years was considered in this regard. Moreover, the earlier mentioned generic mortar volume of 1 m3 should be specified more in terms of dimensions. For this study, a 1 m3 wall element measuring 2.24 \(\times\) 2.24 \(\times\) 0.20 m3 was considered with only one 2.24 \(\times\) 2.24 m2 side subject to CO2 exposure. As such, the carbonated mortar volume within a 100-year timeframe could be calculated using the actual natural carbonation rates and the ones estimated from the slightly and highly accelerated carbonation experiments. CO2 sequestration potentials were then calculated for only this mortar volume. Subsequent CO2 sequestration-to emission-ratios (CO2-SP/EM) of all three binder systems were determined using two approaches: (i) by dividing the CO2 sequestration potential of the full carbonated volume by the global warming potential of the binder fraction of the full generic 1 m3 mortar volume, and (ii) by dividing the CO2 sequestration potential of the carbonated volume within 100 years by the global warming potential of the binder fraction of the full 2.24 \(\times\) 2.24 \(\times\) 0.2 m3 mortar volume of the wall element.