## 4 Conclusions  
There was a large reduction in impurities in the natural fibers with the alkaline treatments, being 3.89% for Ca(OH)\({}_{2}\), 4.08% for KOH and 4.69% for NaOH, which is important for the indices of durability and mechanical strength of the fiber. This reduction is beneficial, because the presence of sugars in the fibers compromises the hydration of the cementitious mixture.  
The chemical characterization and the XRD test proved the increase in crystalline cellulose, from 59.03% to 63.50% (NaOH), 62.41% (KOH) and 60.40% (Ca(OH)\({}_{2}\)). Note that the largest increase was evidenced in the fiber treated with NaOH; the fiber strength was 522.4 MPa for the natural fiber and 728.5 MPa for the treated fiber. On the other hand, the treatment with KOH decreased this strength, which can be justified by the fiber degradation, because it is a more aggressive treatment.  
Regarding the compressive strength of the mortars, both treatments obtained values compatible with the limits imposed by the Brazilian standard, being between 2 and 5 MPa, which makes the mortar acceptable for use in coating and laying walls and ceilings. Thus, the importance of fiber treatments is emphasized because they favor the mechanical properties of the cementitious composite.  
The water absorption of the mortar containing natural fiber was higher when compared to the mortars with treated fibers. The high level of water absorption does not favor  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Composition**} & **Consistency** & **Density** & **Water** & **Porosity (\%)** & **Compressive** \\  & **(cm)** & **(g/cm\({}^{3}\))** & **Absorption (\%)** & **Porosity (\%)** & **Strength (MPa)** \\ \hline
0\%–Reference & 26.03 \(\pm\) 0.33 & 1.68 \(\pm\) 0.03 & 15.97 \(\pm\) 0.26 & 27.38 \(\pm\) 0.37 & 4.23 \(\pm\) 0.16 \\
2.5\% Natural & 25.05 \(\pm\) 0.24 & 1.68 \(\pm\) 0.04 & 15.92 \(\  
the mechanical strength; thus, the importance of fiber treatment is clear, since there was a reduction in this content with all treatments. The treatments containing 2.5% of fibers incorporated with the mortar obtained the following reductions in relation to the mortar with natural fiber: 0.46% (NaOH), 9.58% (KOH) and 8.33% (Ca(OH))\({}_{2}\)).  
Based on this, it is possible to include a practical recommendation that corn straw fiber treated with NaOH, especially the 2.5% NaOH composition, be used for mortars for coating and laying walls and ceilings.  
It is suggested that for future research, the following items should be addressed:  
1. Durability of mortars containing corn straw fibers;
2. Long-term durability under field conditions of mortars containing corn straw fibers;
3. Application of other alkaline treatments, such as magnesium hydroxide and tannic acid;
4. Study of the impact of superplasticizers on the workability and rheological characteristics of mortars with corn straw fibers;
5. Analysis of drying shrinkage or autogenous shrinkage of mortars with corn straw fibers.  
T.R.C.S.: Writing--review and editing, Methodology, Investigation. L.A.S.d.A.: Writing--original draft, Visualization, Methodology, Investigation. L.C.M.: Writing--review and editing, Visualization, Validation, Methodology, Investigation. M.G.M.: Writing--review and editing, Visualization, Validation, Methodology, Investigation. A.R.G.d.A.: Writing--review and editing, Visualization, Methodology, Investigation, Data curation. M.T.M.: Writing--review and editing, Project administration, Methodology, Funding acquisition, Conceptualization. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors would like to thank the Federal University of Vicosa, campus Rio Paranaiba, for their support in carrying out the research.  
The authors declare no conflicts of interest.