## 3 Results and Discussion  
### Characterization of Corn Straw Fibers  
Figure 3 presents the results regarding the chemical composition of the natural and post-treated corn straw fibers. These indices are important because the chemical aspects directly affect the fiber behavior [27]. It can be seen that in all treatments, the cellulose content increased in relation to the natural fiber, with an emphasis on the treatment with NaOH, in which this variation was 4.47%. Based on the international literature, the greater presence of cellulose in the fiber directly influences the compressive strength in mortars with lime, due to carbon  
Figure 2: (**a**) Natural fiber; (**b**) fiber treated with NaOH; (**c**) fiber treated with KOH; (**d**) fiber treated with Ca(OH)\({}_{2}\). The lignin present in the fiber negatively influences the durability of the composites and, as can be seen in Figure 3, in the Ca(OH)\({}_{2}\) and KOH treatments, this content increased, while in the NaOH treatment, it decreased [7]. Another very important content is the wax, responsible for hindering the cement hydration reaction of the composite, and consequently reducing the strength of the material [29,30]. This is due to the fact that the fiber is an organic material rich in fructose. In both treatments, this content was reduced compared to the natural fiber, being 4.69, 4.08 and 3.89% for NaOH, KOH and Ca(OH)\({}_{2}\), respectively. Such a reduction is seen as a positive point in the literature, since durability and mechanical strength are favored [7]. Figure 4 presents the physical characteristics of fibers. One of the main physical aspects of the fiber is water absorption, as already cited by some authors [15]. This parameter is important because its excess generates a lack of water for hydration; on the other hand, the increase in this factor negatively influences the adhesion between the matrix and the reinforcement [31,32]. In Figure 4a, it can be observed that the values of water absorption of the treated fibers are lower than those of the untreated, staying between 115.3 and 128.6%, values that are close to those of the curaua fiber [7], which obtained 121.1% water absorption in the treated fibers. Typically, the water absorption values of lignocellulosic fibers are higher than 100% [33]. Therefore, the reduction in absorption content from 130.2% to values between 115 and 118% in the case of the NaOH and KOH treatments is beneficial information. In Figure 4b, it can be seen that the treatment increased the crystallinity index of the fibers in all treatments, including an increase in the NaOH treatment, which changed from 48.56% in the natural fiber to 66.21% in the NaOH-treated fiber. This variation is positive from the point of view of tensile strength and the XRD test, and Figure 4c validates this property [9,31]. On the other hand, in the KOH-treated fiber, there was a reduction in its tensile strength. It is known that mercization treatments with hydroxides attack the fiber surface and may damage the lignocellulosic structure of the fiber. This is probably what happened in the fiber treated with KOH, since this hydroxide is more alkaline than NaOH, affecting the structure of cellulose, which, as it is an organic material formed by carbon chains, undergoes chemical degradation in very alkaline environments, causing the molecular chains of the fiber to break and reducing tensile strength [34,35,36]. This behavior will probably affect the behavior of the cementitious composite produced with KOH-treated fibers, since, in composite materials, the behavior is defined based on the properties of three phases: matrix, reinforcement (fiber) and adhesion. Although the KOH treatment  
Figure 3: Chemical composition of natural and post-treated corn straw fibers. promotes greater adhesion, the reinforcement presents worst strength parameters than the untreated fiber, impairing the transfer of stresses [15]. Ductility is associated with the fiber's modulus of elasticity [7; 37; 38].