## 2 Materials and Methods
### Life Cycle Assessment
#### 2.6.2 Inventory Analysis  
Life Cycle Inventories (LCIs) for the binder fractions per m\({}^{3}\) of each mortar were compiled in the LCA software SimaPro (Version 9.1.1.1) equipped with the ecoinvent database (Version 3.4) [28]. The following ecoinvent data sets were used to model the cements of three mortar mix designs:  
* CEM I 52.5 N: Cement, Portland {Europe without Switzerland} | production | Cutoff, U. * CEM II/B-V 42.5 N: Cement, pozzolana and fly ash 11-35% [Europe without Switzerland] | cement production, pozzolana and fly ash 11-35% | Cut-off, U. * CEM I 42.5 N: Cement, Portland {Europe without Switzerland} | production | Cutoff, U. It should be noted that the same LCI was assigned to CEM I 52.5 N and CEM I 42.5 N. Within ecoinvent, there is currently no possibility to differentiate within a certain cement type (i.e., Portland cement) when their strength class varies. A higher strength class of a cement normally requires more intensive milling of the Portland clinker and thus more milling related energy consumption. Therefore, one would expect a set of LCIs being available for Portland cement with an increasing energy input as the strength class goes up. It remains unclear at this point whether this anomaly is due to the fact that the extra milling does not cause significant extra impacts or that this issue has simply been overlooked until now. Either way, this specific aspect should definitely be subject of further research, but for now no differentiation was made between Portland cements with a strength class of 52.5 and 42.5. With regard to the composite cement CEM II/B-V 42.5 N, it must be mentioned that the selected ecoinvent data set for this cement corresponded best with this cement type in terms of clinker content. With a clinker content of 77%, this cement can be classified as a CEM II/B-V 42.5 N in accordance with NBN EN 197-1 [22]. Unfortunately, the actual clinker of the cement used was not known. Based on its compliance with NBN EN 197-1 [22], we could only conclude that it ranged between 65% and 79%. Yet, we do not know how exact the match in clinker content was. Further, note that the LCI does not include any processes that can be traced back to the fly ash. Environmental impacts calculated using this LCI will not reflect any fly ash related impact. This is questionable given the available literature on LCA of fly ash based cementitious materials. Therefore, this issue will be dealt with further on after having dealt with the inventory analysis of fly ash as separate mortar constituent in the HVFA mortar. Different approaches were followed based on the product status of fly ash. As pointed out by [PERSON] et al. [7], fly ash can no longer be seen as a mere waste product. In accordance with the applicable European Directive 2008/98/EC [29], it meets all the criteria of being a valuable industrial by-product. As a consequence, part of the life cycle inventory and resulting environmental impact of the main production process, i.e., coal-fired electricity production, should be assigned to it in a fair manner. Normally, the ISO standards on life cycle assessment (ISO 14040-14044 [30; 31]) point out that this is rather to be done using the subdivision method or the system expansion method, than via allocation. However, [PERSON] al. [10] explain that these methods are unfeasible when dealing with coal-fired electricity production and fly ash. Thus, only an allocation of impacts remain as valid options. Mass allocation imposes a huge environmental impact onto the fly ash as only a very little amount of fly ash (0.052 kg) is produced per kWh of electricity. It results in a carbon footprint of fly ash that is way higher than for cement. From an environmental viewpoint it would no longer be worthwhile to use the fly ash as partial cement replacement [6]. Apart from that, [PERSON] et al. [10] have more general concerns with mass allocation.