## 3 Results and Discussion  
### Geopolymer Characterization  
The technological behavior of the geopolymer with EAFD has been studied based on its water absorption and flexural strength for the two studied curing temperatures of 75 \({}^{\circ}\)C and 225 \({}^{\circ}\)C. Table 2 shows the evolution of the two properties with the dosage of EAFD and the temperature.  
The water absorption values up to a 10% dosage of EAFD are approximately constant, and although at 75 \({}^{\circ}\)C is lower, the difference from 225 \({}^{\circ}\)C is not significant. From 15% of EAFD the tendency of the absorption at both temperatures is the opposite, at 75 \({}^{\circ}\)C it experiences a small decrease and at 225 \({}^{\circ}\)C it increases slightly, producing the greater difference between both, at the dosage of 20% of EAFD.  
EAFD favors the development of flexural strength of geopolymers [17], although the trend differs as a function of the curing temperature. At 75 \({}^{\circ}\)C the flexural strength is independent of the amount of added EAFD, whereas at 225 \({}^{\circ}\)C the increase is gradual, up to 15% of EAFD the value reached at 75 \({}^{\circ}\)C is equal, being greater for percentages of 20%.  
However, other authors [16; 17] reported a decrease in the compressive strength of the materials with introduction of EAFD in fly ash based geopolymers, respect a reference without EAFD, for curing temperature below 70 \({}^{\circ}\)C. This discrepancy in the trend may be due to the presence of clay, which has influence in the strength development.  
In relation to the effect of curing temperature, the samples cured at a higher temperature, show a slight increase of strength for 20% of EAFD. Therefore, a light influence of the curing temperature on the development of strength when EAFD is introduced into the clay-fly ash based geopolymer have been observed.  
As shown in the images taken by the SEM (Figure 2) geopolymers made from EAFD, clay and fly ash are heterogeneous materials. On the one hand, they present zones of high densification, consisting of the aluminosilicate gel formed by the reaction of the amorphous particles of the raw materials used with the activating solution. On the other hand, within these densified zones are unreacted spherical particles, which could be particles belonging to EAFD, fly ash, and clay [16]. Furthermore, as the addition of EAFD is higher it can be observed that the geopolymers are more porous. However, different authors have observed that aging influence the morphology of the material, which is considerably denser without particles [17; 48]. Regarding the effect of the curing temperature, in the SEM images, no significant differences are observed, except in the geopolymers with 20% EAFD, where a greater densification is observed at a temperature of 225 \({}^{\circ}\)C. This information confirms the result obtained from flexural strength.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**\% EAFD**} & \multicolumn{2}{c}{**Water Absorption (\%)**} & \multicolumn{2}{c}{**Flexural Strength (MPa)**} \\ \cline{2-5}  & **75 \({}^{\circ}\)C** & **225 \({}^{\circ}\)C** & **75 \({}^{\circ}\)C** & **225 \({}^{\circ}\)C** \\ \hline
0 & 5.41 \(\pm\) 0.15 & 5.89 \(\pm\)