## 2 Materials and Methods  
The corn straw fiber used in the research was collected in the city of Rio Paranaiba, MG, Brazil. Located in the Alto Paranaiba region in Minas Gerais, the city in which the fiber was collected is a major reference in agribusiness. The fiber is extracted from corn straw, as illustrated in Figure 2. The fiber used was treated with NaOH, KOH and Ca(OH)\({}_{2}\), as illustrated in Figure 2, and also in its natural state. For the cement matrix, the materials were Ordinary Portland Cement (OPC), hydrated lime, quartz sand and water. The sand used went through a sieving process in which the maximum diameter was 2.4 mm and the fineness module was 2.97. The OPC used was CP II-E-32. The hydrated lime was type CH-III, providing better quality in the properties of the mortar in its fresh state.  
For the treatment of the fibers, the same process was followed for the three alkaline solutions, using the recommendations of other studies [19; 20]: (i) the fibers were dried in an oven at a temperature of 60 \({}^{\circ}\)C for 24 h; (ii) the fibers were removed from the oven and cooled to a room temperature of 25 \({}^{\circ}\)C; (iii) the fibers were immersed in a 2 L glass beaker, having dissolved 150 g of the alkaline solution in 1.5 L of water, using a solution with a 5% concentration of the alkaline product (NaOH, KOH or Ca(OH)\({}_{2}\)); (iv) the fibers were mixed until they became a homogeneous solution with the aid of a metal spatula for a period of 10 min; (v) finally, the fiber was washed in running water to remove excess activating solution until it was neutralized.  
Figure 1: Bibliometric analysis using the keywords “natural fiber”; “mortar”; “treatment”.  
The specimens were made according to NBR 7215 [21] following the proportion 1:1:6:1.55 (OPC/HL/sand/water), since this composition has already been used by other authors in scientific research [22]. A total of 9 specimens were made for each treatment in the proportions of 0, 2.5 and 5% of fiber in relation to cement. For the hardened state, 3 specimens were used to perform the diametral compressive strength and axial compressive strength testing, after moist curing with hydrated lime at 28 days, following the respective standards NBR 7215 [21] and NBR 7222 [23]. In this same state and curing process, the specific mass and water absorption of the mortar were evaluated according to NBR 9778 [24]. The workability of the mortars was evaluated in the fresh state, by means of NBR 7215 [21] by the slump test on a table.  
For a better interpretation of the compressive strength results, a statistical analysis by ANOVA (\(p\leq 0.05\)) was used, in which the statistical differences of the values found were verified. Then, Tukey's Test (\(p\leq 0.05\)) was applied for comparison of the means.  
A complementary analysis was performed through X-ray diffraction (Photo Manufacturing equipment) using, as test parameters, scanning (20) between 5 and 60\({}^{\circ}\) and 2 mA current generation. Another analysis carried out was the identification of the organic chemical components of the fiber, using Axios Max Malvern Panalytical equipment (Malvern Panalytical, Malvern, UK).  
With the XRD results, the Segal Crystallinity Index (CI) was used, following the recommendations of different authors [25; 26] to evaluate the crystallinity of cellulose present in the natural fibers, through the difference in intensity detected in the XRD results for amorphous cellulose (IAM--18.6\({}^{\circ}\)) and crystalline cellulose (I200--22.3\({}^{\circ}\), i.e., cellulose in the 200 crystallographic plane). The diffraction patterns for cellulose should have a peak height of an absolute minimum of 2000 counts for the highest cellulose peak. The CI calculation is performed following Equation (1).  
\[CI(\%)=\frac{I_{200}-I_{Am}}{I_{200}}\times 100 \tag{1}\]