Agro-industrial waste from corn straw fiber: Perspectives of application in mortars for coating and laying blocks based on Ordinary Portland cement and hydrated lime

The use of new natural fibers is considered a great advance in the science of cementitious materials to promote the use of natural resources in place of commonly used synthetic fibers. In this scenario, the objective of this research is to evaluate the incorporation of corn straw fiber in mixed cement and lime mortars for application in coating and laying blocks. Cylindrical specimens measuring 50x100 mm were made in the composition 1:1:6:1.55 (cement: lime: sand: water) using 0%, 2.5% and 5% of natural fibers and fibers treated with sodium hydroxide (soda) in relation to the mass of cement. The fibers were chemically, physically, mineralogically and morphologically characterized. The mixtures were evaluated for their consistency in the fresh state, in addition to properties in the hardened state, such as compressive strength, modulus of elasticity, diametral compressive strength, water absorption and density. In the fiber characterization results, it was observed that the soda treatment increased the fiber crystallinity from 46.7% in the natural fiber to 74.3% in the treated fibers. There was also an increase in the cellulose content, from 59.8% to 63.5%. These results are important because they indicate greater compatibility of the fibers with the cement matrix. Regarding the properties evaluated in the mortars, it was observed that the treatment with soda allowed the application of corn straw fibers, since the compositions with natural fibers showed a reduction in compressive strength, while the compositions with treated fibers showed equivalence statistic. The treatment also provided a reduction in the water absorption of the mortars, a positive factor due to the fiber hygroscopicity. In addition, there was a stiffness reduction in the cement matrix, identified by the modulus of elasticity that reduced from 133.30 MPa in the reference composition to 36.52 MPa in the composition with 5% soda treated fiber. Thus, it can be concluded that the corn straw fiber is viable for use in mortars for coating and laying blocks only after treatment with soda, which even improves problematic properties of cementitious materials, such as high stiffness.