## 3 Results and Discussion
The C-S-H gel that was formed therefore initially incorporated the entire Al, and with the hydration it modified the structure by breaking up the chains and decreasing the Ca/Si ratio. In the case of the gels generated in the ACW sample, the behavior was different. The gels increased the content of Al, increasing the polymerization of the chain, confirming the results obtained from the analysis of the Ca/Si ratios. It is interesting to note that the ACW sample initially contained a higher content of Al; however, the incorporation of Al in the gel was not initially present, which explains the decrease in the Si/Al ratio from 2 to 28 days. Having characterized the gels obtained in the lime/waste system, cement pastes were mixed with two proportions of waste (10 and 20%), to determine the influence of the waste on their physical and mineralogical characterizations. In the 10% ACW/cement system, the following hydrated crystalline phases were identified: portlandite (64%), ettringite (18%), and C4 AH13 (18%). At substitutions of 20%, the same mineralogical  
Figure 5: Si/Al, Ca/Si and Ca/Al ratios in the studied residues, standard cement and C-S-H gels at 2 (red) and 28 (yellow) days of reaction. \begin{table}
\begin{tabular}{c c c c c} \hline
**Ratio** & **APS Gels (2 Days)** & **APS Gels (28 Days)** & **ACW Gels (2 Days)** & **ACW Gels (28 Days)** \\ \hline Ca/Si & 1.60 & 1.63 & 1.05 & 1.27 \\ Si/Al & 1.37 & 1.71 & 1.97 & 1.35 \\ Al/Ca & 0.45 & 0.35 & 0.48 & 0.58 \\ \hline \end{tabular}
\end{table} 
Table 3: Si/Al, Ca/Si and Ca/Al ratios from the thermically activated wastes. phases were identified, but at different concentrations, some increasing and others decreasing; thus, the concentrations of portlandite and ettrineite decreased to 41% and to 13% respectively, while the concentration of C4 AH13 increased to 36%. This fact means that an increase in the substitution of cement for this thermally activated industrial waste favours the formation of aluminates and calcium carboaluminates to the detriment of portlandite and ettrineite. With respect to the APS, the crystalline phases were modified with respect to the earlier pozzolan, due to their different calcium nature. Thus, portlandite (45%) appeared at a substitution of 10%, calcite appeared from the original material (36%), as did C4 AH13 (19%). An increase from 10% to 20% APS when substituting with pozzolan caused the portlandite to decrease to 37%, the calcite to slightly increase to a concentration 40%, and the C4 AH13 to remain practically constant (18%); and for the first time an LDH neo-formation phase was identified (5%). Table 4 shows the analyses of the C-S-H gels and the Ca/Si, Si/Al and Al/Ca gels determined by SEM/EDX in the different cement paste matrices with substitutions of 0, 10 and 20%. The incorporation of the waste in the pastes decreased the Ca/Si ratio of the gel, initially caused by increased amounts of silica present in the waste. In the case of the samples that incorporated APS and as seen in the activated sludge by itself (Table 3), the reaction time hardly modified the Ca/Si ratio. Likewise, the presence of ACW generated an increase in that signal, because the higher content of Al produced more polymerized gels (Figure 6). Furthermore, the lower concentration of Al in the APS produced C-S-H gels with higher Si/Al ratios [39]. [PERSON] [40] suggested that C-A-S-H gels incorporate more aluminum as the Ca/Si ratio decreases, as is confirmed in the samples with APS. However, the presence of cement in the case of the ACW samples inhibited the incorporation of aluminum in the gel and favoured the formation of aluminate phases, as observed through XRD. Finally, the higher levels of Al in the C-S-H gels formed in the cement/APS mixtures meant a lower Ca/Si ratio [41].