## 3 Results and Discussion
### Mortar Characterization
This happens because the most degraded fibers, as is the case of the fiber treated with KOH, present higher surface roughness and, consequently, higher adhesion, resulting in lower porosity [49; 50]. However, the treatment not only degraded the fiber superficially, but also destroyed the fibrous structure, as shown in Figure 4. This compromised the mechanical behavior of the composite with fiber treated in KOH. In other words, even if there was a potential for better performance of mortars with fibers treated with KOH, this was not verified in this research. Therefore, it is not possible to directly relate the porosity with the mechanical strength in cementitious composites with natural fibers. Table 2 presents the ANOVA results (\(p\leq 0.05\)), for the compressive strength data at 28 days. Note that the \(\mathrm{F_{CALUATED}}\) is greater than the \(\mathrm{F_{TABulated}}\), which represents a statistically significant difference between the means studied [51; 52]. Because of this, it is possible to perform a contrast of means through Tukey's Test (\(p\leq 0.05\)), to analyze which is the strongest influencer of the treatments on the compressive strength. The results are presented in Table 3. The results of compressive strength testing are also presented in Figure 10.  
Figure 7: Density of mortars containing corn straw fibers. Figure 8: Water absorption of mortars containing corn straw fibers. Figure 9: Porosity of mortars containing corn straw fibers. Among the treatments, the one that presented the best result was the mortar with 2.5% fiber treated with NaOH (AB), being equivalent to the reference (A) and the 2.5% natural fiber (B). It can be observed that the treatments with Ca(OH)\({}_{2}\) and KOH obtained lower results in parameters (C) and (D) than the treatment with NaOH. This can be justified due to the low water absorption that these treatments presented, as shown in Figure 8, compromising the compressive strength of the mortar. In addition, there was a degradation in the fiber with KOH, as discussed earlier, which justifies the drop in strength observed for this composition. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source of Variation** & **DF** & **SQ** & **MS** & **F\({}_{\text{CALCULATED}}\)** & **F\({}_{\text{tabulated}}\)** \\ \hline Treatment & 8 & 34.680 & 4.334 & 5.279 & 2.510 \\ Residue & 18 & 14.780 & 0.821 & - & - \\ Total & 26 & 49.459 & - & - & - \\ \hline DF = degrees of freedom; SQ = sum of squares; MS = mean squares; F\({}_{\text{CALCULATED}}\) = F test value calculated by statistical analysis; F\({}_{\text{TABLE}}\) = F test value obtained through comparison tables in ANOVA. & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: ANOVA (\(p\leq 0.05\)) for compressive strength at 28 days. Figure 10: Compressive strength at 28 days of curing. For practical applications, it is important that the fiber used does not statistically change the mechanical behavior of the mortar and some property of interest, which in the case of this research was the reduction in water absorption and porosity of the mortars promoted by the use of treated fibers, as shown in Figures 8 and 9. Therefore, the statistical analysis presented in Tables 2 and 3 is important to identify which mortar composition presents statistical equivalence in relation to the reference composition and to define the selection of coherent materials for the proposed application. Based on this, it is observed that the 2.5% NaOH composition represents a mortar with physical-mechanical parameters compatible with the proposed application, defined according to the ANOVA and Tukey's Test. For mortars for coating and laying walls and ceilings, all treatments were between the minimum value of 2 MPa and the maximum value of 5 MPa for compressive strength, established by the Brazilian standard [53]. This maximum value is very important, since very rigid mortars can have their mechanical performance compromised.