# Formulation of Alkali-Activated Slag Binder Destined for Use in Developing Countries
## 3 Results
### Economic and Environmental Aspects  
The use of chemical reagents to prepare AAM can be taken into account in economic and environmental terms. The selection of a given chemical reagent has repercussions on both the cost and CO\({}_{2}\) emissions associated with mortar or concrete preparation. Regarding economic savings, the selection of NaOH, Na\({}_{2}\)CO\({}_{3}\), or a mixture of both, influences the cost of chemical reagents. For this study, 712 \(\upepsilon\)/ton of NaOH and 556 \(\upepsilon\)/ton of Na\({}_{2}\)CO\({}_{3}\) were selected as the cost of reagents (these data were provided by a chemical company). Accordingly, the cost of \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Abbreviation** & **Name** & **Formula** & **PDF Card** \\ \hline A & Akermanite & Ca\({}_{2}\)MgSi\({}_{2}\)O\({}_{7}\) & 350592 \\ C & Calcite & CaCO\({}_{3}\) & 050586 \\ H & Hydrol calcite & Mg\({}_{6}\)Al\({}_{2}\)CO\({}_{3}\)(OH)\({}_{16}\) 4H\({}_{2}\)O & 140191 \\ K & Katoite & Ca\({}_{3}\)Al\({}_{2}\)(SiO\({}_{4}\))(OH)\({}_{8}\) & 380368 \\ M & Monticellite & CaMgSi\({}_{04}\) & 350590 \\ R & Rankinite & Ca\({}_{3}\)Si\({}_{2}\)O\({}_{7}\) & 220539 \\ S & Tobermorite-11A & Ca\({}_{9}\)(OH)\({}_{5}\)Si\({}_{6}\)O\({}_{16}\) 4H\({}_{2}\)O & 191364 \\ T & Thermonatrite & Na\({}_{2}\)CO\({}_{3}\).H\({}_{2}\)O & 080558 \\ V & Vaterite & CaCO\({}_{3}\) & 240030 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Assignment of the XRD peaks in pastes. Figure 9: XRD spectra of the pastes cured for (**a**) 28 days and (**b**) 90 days. the activator per ton of prepared mortar was calculated (Table 6). Obviously, when the amount of activator is increased, the cost per ton rises. For a given Na\({}_{2}\)O\(\%\), SC mixtures are the most costly because, although the cost of Na\({}_{2}\)CO\({}_{3}\) is lower, the quantity of Na\({}_{2}\)CO\({}_{3}\) is larger. All SHC mixtures contain Na\({}_{2}\)O\(\%\) at 4.96 in relation to the BFS content and 1.11 in relation to the prepared mortar. Hence the cost per ton of mortar increases when the Na\({}_{2}\)CO\({}_{3}\) proportion does. As the strength developed for the prepared mortars was different, the variable cost per ton of mortar and MPa was calculated by taking into account mechanical behavior after 90 curing days (Table 6). It was noticed that the mortars containing Na\({}_{2}\)CO\({}_{3}\) (SC and SHC series) were less costly (range: 0.19-0.34 \(\upxi\)/ton \(\times\) MPa) than the mortars containing NaOH (SH series, range: 0.33-0.49 \(\upxi\)/ton \(\times\) MPa). This means that selecting Na\({}_{2}\)CO\({}_{3}\) as an activator is preferable from an economic point of view. The best mixture in relative cost terms per MPa was SC 1.5, which had a value of 0.19 \(\upxi\)/ton \(\times\) MPa. This mortar presented an excellent mechanical performance at 90 curing days (41.4 MPa) for a mixture containing only a little Na\({}_{2}\)CO\({}_{3}\) (14.2 kg Na\({}_{2}\)CO\({}_{3}\)/ton of prepared mortar). Regarding CO\({}_{2}\) emissions, several data were taken from the bibliography and technical reports. The value of kgCO\({}_{2}\) emitted per ton of NaOH was 1.12, as reported by [PERSON] et al. [12]. Na\({}_{2}\)CO\({}_{3}\) synthesis is usually carried out by two methods: from natural carbonate ore (usually trona, Na\({}_{3}\)(HCO\({}_{3}\))(CO\({}_{3}\))\(\cdot\)2H\({}_{2}\)O) and by the Solvay process. In the first case, Na\({}_{2}\)CO\({}_{3}\) production is carried out by means of trona calcination [39]:  
\[2\ (\text{Na}_{2}\text{CO}_{3}\text{NaHCO}_{3}\text{.2H}_{2}\text{O})\to 3 \ \text{Na}_{2}\text{CO}_{3}+5\ \text{H}_{2}\text{O}+\text{CO}_{2}\]  
During this process, carried out at \(\approx\)160 \({}^{\circ}\)C, two moles of trona produced one mole of CO\({}_{2}\) and yielded 3 moles of Na\({}_{2}\)CO\({}_{3}\). From the stoichiometric calculations, 176.7 kg of CO\({}_{2}\) were emitted for each ton of synthesized Na\({}_{2}\)CO\({}_{3}\).