Amostras de hidroxiapatita foram sintetizadas por meio da precipitação de soluções aquosas contendo os íons precursores. O precipitado obtido foi lavado, seco, desaglomerado e peneirado com o intuito de se obter amostras em forma de pó e com granulometria homogênea. O material foi sinterizado em diferentes temperaturas e posteriormente caracterizado por difração de raios X, espectroscopia no infravermelho, microscopia eletrônica de varredura, análise termogravimétrica e termodiferencial e a quantificação da área superficial específica e porosidade foi realizada por meio dos métodos Brunauer-Emmett-Teller e Barret-Joyner-Halenda, respectivamente. Os pós apresentaram modificações na cristalinidade, morfologia e nas propriedades texturais com o aumento da temperatura. Novas fases foram identificadas nos difratogramas de raios X devido à decomposição do material, corroborando com resultados reportados. Houve o crescimento dos cristais, aumento da cristalinidade e diminuição da área de superfície específica, comprovando que as modificações ocorreram devido aos processos de sinterização, uma vez que a força motriz para esse processo é a diminuição da área de superfície específica.

This article analyzes the effect of the rehydration method on the physical–mechanical properties of accelerated carbonation-cured magnesium-based fiber cement boards. The rehydration process of the boards was analyzed in conjunction with the analysis of the pre-curing time before accelerated carbonation (24, 48, and 72 h before carbonation), resulting in eight different curing parameters used in this investigation. The physical–mechanical performance and microstructural characteristics of magnesium oxysulfate boards before and after carbonation were investigated by water absorption, apparent porosity, and bulk density using the four-point bending test, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. According to the results, the accelerated carbonation process improved the mechanical properties of the boards. The samples that carbonated after 48 h showed a higher modulus of rupture. The rehydration process of the composites before carbonation led to enhancements in the pre-cured boards for 48 and 72 h, demonstrating that carbonation occurred more effectively after water rehydration. The mechanical improvements were associated with the formation of hydration products, which preferentially formed in the pores and voids of the fiber cement matrix. These carbonation products altered the physical properties of the composites, increasing the density of the boards and reducing the void volume. The decomposition of the formed carbonates was confirmed by thermogravimetric analysis, which indicated that the rehydration process favored the carbonation of the composites.

In the pursuit of unconventional binders that can reduce energy consumption in production, magnesium oxysulfate (MOS) cement emerges as a viable alternative. Moreover, carbon dioxide (CO₂) has been employed in the curing process of certain MOS cement products, such as magnesia fiber cement, due to its capacity to enhance their performance. This study aims to assess the impact of pre-curing prior to accelerated carbonation on the physical-mechanical properties of magnesium oxide fiber cement boards. These boards were manufactured using the Hatschek process simulation and subjected to pre-curing periods of 24, 48, and 72 h post-production. The relationship between microstructural alterations and the physical-mechanical properties was examined through analyses including water absorption, apparent porosity, apparent density, four-point bending tests, X-ray diffraction, and scanning electron microscopy analyses. The results indicated that pre-curing had an influence on the physical-mechanical attributes of the manufactured boards. After 72 h, the carbonated materials exhibited a decline in mechanical performance, a phenomenon attributed to the carbonation reactions between CO₂ and the hydration products responsible for enhancing the mechanical strength of the cementitious materials.

This study investigated the effects of substituting magnesium oxide (MgO) with dolomitic limestone (DL) on the mechanical and physical properties of magnesium oxysulfate (MOS) cement. Additionally, the hydration formation phases and the influence of the molar ratio on the MOS cement’s performance were examined. The corresponding action mechanisms were identified and explored by compressive strength tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), isothermal calorimetry, and a thermogravimetric analysis (TGA). The results showed that replacing MgO with DL decreased the reaction speed and heat release rate generated in the hydration process of the MOS cement. This substitution also reduced the quantity of non-hydrated MgO particles and delayed the formation of Mg(OH)₂. The diminished formation of Mg(OH)₂ contributed to an increase in the apparent porosity of pastes containing DL, thus alleviating internal stresses induced by Mg(OH)₂ formation and enhancing their mechanical strength after 28 days of curing. Conversely, the increased porosity improved the CO₂ diffusion within the structure, promoting the formation of magnesium carbonates (MgCO₃). Through the characterization of the cement matrix (XRD and TGA), it was possible to identify phases, such as the brucite, periclase, and 318 phases. The obtained results revealed the potential of incorporating mineral fillers like limestone as a promising approach to producing MOS cement with a reduced environmental impact and better properties at higher curing ages.