Effect of the Rehydration Method on the Physical-Mechanical Properties of CO2-Cured Magnesium-Based Fiber Cement Boards

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.