## 3 Results and Discussion
In addition, laminar forms of LDH were recognizable: stratlingite, monosulfoaluminate (Figure 4B) and tetracalctium in various sizes and intergrown with the gels, forming aggregates, indicating successive phases of growth (Figure 4E). For the APS/Ca(OH)\({}_{2}\) system, in the APS sample, crystalline compounds of calcite were identified by XRD as a stable mineral for both reaction times, at a quantity of 66%. The new compounds such as LDH (Figure 4C) had already appeared at two days of reaction time, at an amount of 2%, and were conserved after 28 days (Figure 2). Stratlingite, non-existent at an early age, appeared at 28 days with a concentration of 1%, and the majority components at both 2 and 28 days were the C-S-H gels (Figure 4C, whose value, 30%, was practically constant for both control points. The SEM technique permits the identification of amorphous phases such as C-S-H gels. An EDX analysis permits the calculation of the CaO/SiO\({}_{2}\) ratio in the compounds that varied between 1.60 and 1.63 [36] (Table 2). This interval corresponds to gel type II (Figure 4D), according to the Taylor classification, which is the principal compound of hydration. The structural order increases when the aforementioned relation grows, linked to the reaction time. Thus, in the short term (2 days) the C-S-H gels have a rounded appearance, while in the longer-term (28 days) they appear interspersed between the LDH structures and the stratlingite (Figure 4E), both similar to each other and with a hexagonal laminar appearance, and only identified by their chemical composition through EDX. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Orides (\%)**} & \multirow{2}{*}{ \begin{tabular}{c} **C-S-H Gels** \\ **(at 2 Days) in ACW** \\ \end{tabular}  } & \multirow{2}{*}{\ \begin{tabular}{c} **C-S-H Gels** \\ **(at 2 Days) in ACW** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **C-S-H Gels** \\ **(at 2 Days) in ACW** \\ \end{tabular}  } \\ \cline{1-1} Na\({}_{2}\)O & 0.22 \(\pm\) 0.10 & 0.78 \(\pm\) 0.12 & n.d. & n.d. \\ \hline MgO & 0.43 \(\pm\) 0.08 & 0.60 \(\pm\) 0.28 & n.d. & n.d. \\ \hline Al\({}_{2}\)O\({}_{3}\) & 19.49 \(\pm\) 1.32 & 22.91 \(\pm\) 0.42 & 21.87 \(\pm\)Table 3 shows the Si/Al, Ca/Si, and Ca/Al ratios, obtained by SEM/EDX of each one of the C-S-H gels at 2 and at 28 days of hydration. The Ca/Si ratio of the gel that formed is higher in the APS (with less Si and more Ca than ACW) than in the ACW, for both study ages. Initially, the ACW fixed more lime than the APS (Figure 3); however, calcium was not incorporated in the gel and it reacted to form calcite, as identified by XRD. The C-S-H gels formed via the APS in no way modified the Ca/Si ratio over the hydration time, while the gel formed with the ACW increased that ratio; and given that it increased the quantity of fixed lime to a lesser extent, we can assume that it produced changes in the structure of the C-S-H gels that were formed (Figure 5). Figure 4: (**A**) Gels of a spongy nature in ACW; (**B**) Monosulfoaluminate crystals with C-S-H gels in ACW; (**C**) LDH and C-S-H gels in APS; (**D**) Type II gels in APS; (**E**) Stratlingite in APS waste with aggregates (**F**) Mica in ACW waste. Thus, recent studies [37; 38] have indicated that the Ca/Si ratio of the C-S-H gels can provide information on their structure; with low Ca/Si ratios below 1.0, the gels present structures with a high percentage of Q2 units, while the upper Ca/Si ratios increase the number of Q1 units, therefore producing shorter chains. Therefore, they change from foil-like structures to fibrillary structures. Consequently, the gel obtained in the ACW sample may be considered to have shorter gel chains than the one obtained in the pozzolanic reaction of the APS. The Si/Al ratio was, nevertheless, modified in an opposing way in both gels, increasing over time in the APS samples and decreasing in the ACW samples. It may be observed from Table 2 that the quantity of Al decreases in the APS sample, while the concentrations of calcium and silicate increase.