Avaliação das propriedades físico-mecânicas e reológicas de compósitos de cimento de fosfato de magnésio com adição de fibras de aço, de sisal (agave sisalana) e de pva

Abstract

Magnesium phosphate cement (MPC) is an acid-base binder with superior physical mechanical properties compared to conventional hydraulic cements, yet it still presents many gaps, aiming at its development and wider application. This study evaluates the physical, mechanical, and rheological performance of MPC composites reinforced with PVA, sisal, and steel fibers in different proportions, aiming to reduce the brittleness and low deformability of the cementitious matrix. The MPC raw materials (calcined MgO, ammonium dihydrogen monophosphate - ADP, sodium tripolyphosphate – STP, and boric acid), sand, and steel (metallic), polymeric (PVA), and sisal (vegetable) fibers were characterized in terms of physical, chemical, and mineralogical aspects to optimize the formulation and allow evaluations of the composites in the fresh and hardened states. In the fresh state, setting time, pH, calorimetry, and rheological analysis tests were performed on the reference matrix and samples with different fiber contents. After molding and curing, the samples were subjected to phase formation analysis by XRD and thermogravimetry (TG/DTA), in addition to physical-mechanical analysis (specific mass, apparent porosity, capillary absorption, dimensional stability, axial compressive strength, and flexural tensile strength). The results showed that the addition of steel fibers to the CFM promoted significant gains in flexural tensile strength and compressive strength, with emphasis on the increase in toughness, evaluated by the I10 factor, indicating a more ductile post-cracking behavior and an efficient redistribution of stresses. While the addition of natural fibers to the composites resulted in a loss of mechanical performance, contributing to reduced strength values and increased variability in results, possibly due to high water absorption and low interfacial adhesion with the matrix, the chemical acetylation treatment showed promise in improving the mechanical properties of CFM composites with sisal fibers. The insertion of PVA fibers into the CFM matrix provided a modest improvement in mechanical strength compared to the reference matrix and superior performance to that of composites containing natural sisal fibers.