## 3 Results and Discussion
### Hardened State Properties  
#### 3.4.1 Compressive Strength  
Figure 4a shows that the compressive strength in cubes increased. Table 4 contains the average values of the compressive strength as well as their standard deviations for cylindrical and cubic specimens. eased over time for all SCC and decreased with an increasing amount of cement replaced. Likewise, C10 FA20 BA, C20 FA10 BA, C20 FA40 BA and C40 FA20 BA reached 70%, 58%, 55% and 53% of the average strength of 91 days, at seven days, respectively. It can also be observed that the lower compressive strength values correspond to SCC with higher MIBA content. The same strength reduction trend was verified by [PERSON] et al. [43] with binary mixtures of MIBA and \(f_{\text{ad}}\) up to 30%. Moreover, for binary mixtures with \(f_{\text{ad}}\) up to 40%, [PERSON] et al. [44], [PERSON] [45] and [PERSON] [46], obtained a decrease in strength with the increase of MIBA in the mixture. [PERSON] et al. [47] studied ternary mixtures (MIBA and FA) obtaining the same behaviour, with an average decrease at 28 days of 25% and 34%, for \(f_{\text{ad}}\) = 30% and \(f_{\text{ad}}\) = 40%, respectively. However, all authors used as a basis of comparison a concrete with 100% cement. In Figure 4b, the trend lines of the direct comparison between the compressive strength of cylinders and cubes are presented for 28 and 91 days. The correlation between cylindrical and cubic specimens is high for both, 28 days (R\({}^{2}\) = 0.93) and 91 days (R\({}^{2}\) = 0.96). Figure 4: Compressive strength in cubes (\(f_{\text{cm,cube}}\)) at 7, 28 and 91 days (**a**); relationship between compressive strength in cubic (\(f_{\text{cm,cube}}\)) and cylindrical specimens (\(f_{\text{cm}}\)) at 28 and 91 days (**b**). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Mixture**} & \multicolumn{2}{c}{**Slump-Flow**} & \multicolumn{2}{c}{**Funnel V**} & \multicolumn{1}{c}{**L Box**} \\ \cline{2-5}  & **t\({}_{\text{500}}\)** & ***SF** & **t\({}_{\text{v}}\)** & ***PL** \\ \cline{2-5}  & **(s)** & **(mm)** & **(s)** & **(H\({}_{\text{2}}\)/H\({}_{\text{1}}\))** \\ \hline RC & 2.7 & 680 & 5.6 & 0.8 \\ C10 FA20 BA & 2.8 & 685 & 4.9 & 1.0 \\ C20 FA10 BA & 2.7 & 620 & 4.8 & 0.8 \\ C20 FA40 BA & 2.2 & 585 & 2.8 & 0.8 \\ C40 FA20 BA & 3.1 & 625 & 3.5 & 0.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Fresh concrete properties, slump-flow, funnel V and L box (*SF—spread classes and *PL— classes of the capacity of passage in the box L). The reduction of the compressive strength could be partially due to the notable amount of calcite present in the MIBA, as verified in the XRD analysis (Figure 1). The greater presence of calcite in detriment to other more reactive phases suggests that MIBA may present low pozzolanicity and thus more likely to lead to a decline in mechanical performance when used as partial cement replacement. Likewise, the relatively high content of metallic Al present in MIBA was the main cause for compressive strength loss [10]. Metallic Al in an alkaline medium reacts to produce gaseous H\({}_{2}\), which became trapped in the fresh mix thereby significantly increasing the porosity of the hardened concrete (Figure 5). The alkaline medium is generated when the tricalcium silicate (C\({}_{3}\)S) and the dicalcium silicate (C\({}_{2}\)S) present in the anhydrous cement are hydrated, producing portlandite (Ca(OH)\({}_{2}\)) and CaO-SiO\({}_{2}\)-H\({}_{2}\)O (C-S-H); the high solubility of portlandite increases the pH above 12.5, thus providing the alkaline medium required to react with the metallic Al present in MIBA (4.32 mg per kg of MIBA) acting as a reagent of the reaction to produce H\({}_{2}\)[48; 49]. The chemical reaction that takes place behind the corrosion of Al and the thermodynamics of it are presented in Equation (5), in which the OH\({}^{-}\) ion is supplied by the Ca(OH)\({}_{2}\)[50; 51].