Fibrocimentos híbridos reforçados com sisal quimicamente tratado e nanoargila

Abstract

The addition of natural fibers in cementitious composites can enhance certain mechanical properties, such as flexural tensile strength, toughness, and fracture toughness. However, these fibers may undergo a hydrolysis mechanism due to the highly alkaline environment of the cement, which may require fiber sealing treatment or the addition of a pozzolan to reduce the pH of the hydrating cement. In order to mitigate the negative effects caused by the cementitious matrix and enhance the reinforcing function of plant fibers, employing both mentioned strategies synergistically, the main objective of the present study was to evaluate the mechanical performance of cementitious composites incorporated with nano clay, reinforced with chemically treated sisal fibers, and with partial substitution of the cement by limestone. The fibers were treated with poly-furfuryl alcohol (AF) at a 50% percentage and introduced into a cement paste (water/cement ratio of 0.4) at a quantity of 2% relative to the cement mass. Nano clay was added at percentages of 1% and 5%. The fibers were examined through optical microscopy, chemical composition (wet chemical analyses), infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). The studied composites underwent tests in the plastic state (regarding their rheology and water affinity) and in the hardened state (regarding physical and mechanical properties). The evaluated mechanical characteristics included flexural tensile strength, compressive strength, and fracture toughness, with results indicating good compatibility between AF, fibers, and nano clay. In the fresh state tests, the strategies tested (fiber treatment and pozzolan addition) mitigated the negative effects related to their addition in cementitious matrices, improving workability. In the hardened state, the combined addition of nano clay and AF maintained values of paste porosity and water absorption, except for composites with 1% nano clay (NC1) and 50% alcohol (FA50), which experienced increases (13% and 33% for porosity and 23% and 25% for water absorption, respectively). In terms of density, the composites maintained slightly reduced values (4%). The synergy of the actions of treated fibers and nano clay resulted in increased flexural strength (12- 19%) compared to the control composite, as well as a reduction in brittle behavior (observed by the behavior of the curves). In terms of toughness and modulus of elasticity, the combination of AF and nano clay showed an increase (8% and 97%) in the toughness of composites with 1% nano clay and 50% alcohol (NC1FA50) and with 5% nano clay and 50% alcohol (NC5FA50), respectively, while, concerning the modulus of elasticity, an increase of 158% and a reduction of 10% were obtained, relative to the composites. In the fracture toughness test, there was also evident improvement in resistance, especially in composites with combined addition of AF and nano clay.