Engenharia de materiais sustentáveis: desenvolvimento e avaliação de ligante de óxido de magnésio e resíduo agroindustrial

Abstract

Portland cement is widely used in the stabilization of soils, hazardous waste, mining tailings, and other materials. However, this binder has low resistance to attack by certain contaminants, and its production chain is responsible for high extraction of natural resources, energy consumption, and CO₂ emissions. Given this, this study developed and evaluated an alternative binder produced from magnesium oxide (MgO) and rice husk ash (RHA) as a more sustainable option compared to Portland cement. An experimental design was conducted to investigate the unconfined compressive strength (UCS) of the mixtures, considering different contents of the dispersant sodium hexametaphosphate (SHMP) and varying MgO/RHA ratios. The curing time and temperature were fixed at 7 days and 23 °C. The chemical, mineralogical, and microstructural characteristics of the mixtures were evaluated using FTIR, XRD, and SEM/EDS. The results indicated that UCS is significantly influenced by all investigated factors, particularly the SHMP content. The highest recorded strength was 8.19 MPa, achieved with an MgO/RHA ratio of 1.5 and 4% SHMP. However, the most economical formulation, with statistically equivalent mechanical performance, was obtained with an MgO/RHA ratio of 1 and 3% SHMP (8.03 MPa). Chemical analysis revealed the progressive formation of M–S–H gel, while mineralogical analysis indicated the presence of brucite (a product of MgO hydration) and cristobalite (derived from RHA). Microstructural analysis, in turn, pointed to the gradual formation of M–S–H and the persistence of unreacted phases in the matrix.