INFLUÊNCIA DA ADIÇÃO DE ÓXIDO DE NIÓBIO CALCINADO NA RESISTÊNCIA À COMPRESSÃO DE MATRIZES CIMENTÍCIAS

Abstract

The incorporation of nanoadmixtures into cementitious matrices has been extensively investigated to optimize the performance and mechanical properties of Portland cement. In this context, given the national scenario and the abundance of reserves, niobium oxide (Nb₂O₅) emerges as a promising alternative for the modification of cementitious matrices. However, the scientific literature lacks systematic investigations on the combined effect of addition content, temperature, and calcination thermal treatment duration on the mechanical behavior of these matrices. Therefore, the present study investigated the influence of calcined Nb₂O₅ additions at contents of 0.1%, 0.3%, and 0.5% (by cement mass), calcined at temperatures of 400 °C, 600 °C, and 800 °C for 30, 45, and 60 minutes, on the axial compressive strength of cementitious matrices at 28 days of curing, encompassing 27 experimental combinations. One-way ANOVA followed by Tukey's test (α = 0.05) was applied, adopting RF1 (0.5% uncalcined Nb₂O₅; fc = 21.78 MPa) as the reference, with 15 combinations identified as statistically significant. The highest strength gain was achieved at a content of 0.1% calcined at 400 °C for 30 minutes (+38.9%). It is concluded that the polymorphic transformations of Nb₂O₅ — from the amorphous phase (<500 °C) to the orthorhombic (600 °C) and monoclinic (800 °C) phases, govern the reactivity of the oxide within the matrix in a non-linear manner, acting as a coupled function of addition content, calcination temperature, and exposure time.