## 1 Introduction  
In the last decades, the use of natural fibers for application in cementitious matrices has intensified. This is because the cement production industry is one of the biggest polluters, due to the amount of pollutant gases that are released into the atmosphere during its manufacturing process. Because of this, research in the construction area evaluates the use of alternative materials, such as recycled aggregates [1], multimaterial 3D-printed geopolymers and ecological binders [2; 3]. Added to this, the use of synthetic fibers, such as steel fiber, is increasingly intense in the application of cement composites [4; 5], which makes the sustainable development of cement composites difficult, unlike natural fibers of animal or vegetable origin, which are renewable resources [6]. With this, the use of natural materials can be considered a means for the growth of the industry [7], resulting in several benefits, since it allows the reuse of agro-industrial waste, which consequently reduces the dumping of this waste in landfills and the emission of carbon dioxide gas (CO\({}_{2}\)) [8]. It is in this context that the analysis proposed in this research arises: to verify which chemical treatment is more efficient in the application of corn straw fibers in mortars. The lignocellulosic plant fibers present in their chemical composition impurities, sugars and waves that do not favor their use in their natural state. However, several studies have already been conducted aiming at a means of improving these characteristics by means of treatments in alkaline solutions. [PERSON] et al. [9] performed a study using corn straw fiber with treatment in sodium hydroxide (NaOH) and in natural form, concluding that by performing the treatment, there was a reduction in impurities by 4.8%, an increase in cellulose by 3.7% and an increase in fiber surface roughness, improving its adherence in the cementitious matrix. Other relevant work was carried out by [PERSON] et al. [7], who used NaOH treatment on curaua natural fiber in the proportions of 1, 2 and 3%; and by [PERSON] et al. [10], who used NaOH treatment on banana fiber in the proportions 1, 3, 5, 7 and 9%. One of the greatest difficulties in using natural fibers is due to their hydrophilic characteristic, making it difficult for them to adhere to the cementitious matrix [11; 12]. Several scholars have already used chemical treatments to obtain better results, aiming to change the physical characteristics of the natural fiber surface and improve the relationship between the fiber and the matrix [13]. One possibility is the use of products that promote greater interaction between the fiber and the matrix. It is known that the cementitious matrix, formed by concrete or mortar, is rich in calcium. Therefore, treatments with Ca(OH)\({}_{2}\) are interesting. [PERSON] et al. (2018) [14] analyzed the durability of curaua fiber, which was submitted to alkaline treatment with Ca(OH)\({}_{2}\), aiming to increase the fiber surface roughness and reduce the moisture absorption capacity. The authors concluded that the fiber was well adhered to the matrix, since Ca(OH)\({}_{2}\) allowed the mineralization of the fiber in the matrix, forming anchoring points and improving the behavior of the cementitious composite. It is worth pointing out the possibility of treatment with KOH. It is known that potassium belongs to the family of alkali metals like sodium. The bases formed by these two elements have similar properties, with one essential difference: KOH is more alkaline than NaOH, due to the larger atomic radius of potassium [15]. This promotes greater aggressiveness in the fiber, which can improve adhesion, but consequently can degrade the cellulosic structure. Some authors [16] studied different methods of treatment in natural acai fiber incorporated with specimens in the proportions of 2.5 and 5%, using three types of treatments, among them KOH, which led to a reduction in the capacity of water absorption by capillarity in the treated fibers.