## 1 Introduction
In natural conditions, the complete carbonation of engineering sized components takes many years but only a few hours or days under laboratory conditions by increasing the CO\({}_{2}\) concentration, especially in case of application of a pressure gradient to facilitate transport processes and dissolution of CO\({}_{2}\)[14; 18]. Controlling surrounding relative humidity (RH) is very important to accelerate the carbonation process. [PERSON] et al. showed that carbonation was more rapid at a relative humidity of 50-70% and decreased at higher and lower relative humidity [19; 20]. The increase of temperature (up to 60 \({}^{\circ}\)C) increases the CO\({}_{2}\) uptake due to the leaching of Ca\({}^{2+}\) ions from the solid phases [21]. Finally, the initial conditions of the cementitious materials are also important such as the water to cement ratio, the initial porosity, and density. In this study, we changed the initial physical characteristics of the specimen by changing the rolling pressure during the Hatschek process. The Hatschek process consists of producing fiber-cement sheets by stacking thin laminas made from a suspension of cement, fibers, mineral admixtures, and water. Consequently, there are many parameters (e.g., CO\({}_{2}\) concentration, temperature, and relative humidity) to be optimized in the accelerated carbonation curing process to obtain a high-performance composite. Only a few studies have been reported in the literature in which accelerated CO\({}_{2}\) curing is considered for fiber-cement composites under different conditions. [PERSON] et al. [22] studied carbonated cementitious specimens reinforced with bleached eucalyptus pulp, with a climate chamber set to 60 \({}^{\circ}\)C temperature, 90% RH, and atmospheric CO\({}_{2}\) concentration (15 vol %) for two days. The results showed that the mechanical properties were better for the composites subjected to accelerated carbonation at early stages of hydration and carbonated samples presented higher values of mechanical properties for all aging tests (400 accelerated aging cycles and 1 year of natural weathering). For the non-carbonated samples, the highest modulus of rupture (MOR) was found for the samples that were exposed to one year of natural weathering (CO\({}_{2}\) from the atmosphere). [PERSON] et al. [23] studied the accelerated carbonation process in cementitious specimens reinforced with bleached cellulosic pulp and synthetic fibers, with the same carbonation conditions as [PERSON] et al. for ten hours. Even with such a short curing time, the carbonated products exhibited a good fiber-matrix bonding, improved mechanical properties with a reduction of composite degradation. [PERSON] et al. [16] studied the supercritical carbonation of extruded fiber-cement reinforced with bleached eucalyptus pulp and residual sisal chopped fibers, with specimens placed in a chamber with total saturation (close to 100% concentration) of supercritical CO\({}_{2}\) at 20 MPa with the chamber immersed in water at 45 \({}^{\circ}\)C. The results showed that the supercritical carbonation treatment for only 2 h could significantly improve the physical characteristics and mechanical performance. It has been proved that carbonation of fiber-cement composites may improve the interfacial transition zone (ITZ) between cement paste and fiber [24], which significantly enhances the tensile strength of fiber-cement composites. In particular, nanofibrilated cellulose based fiber-cement composites show significantly better mechanical behavior compared to the composites without nanofiber. This improvement is attributed to the better bonding between the nanofibrils and the cement matrix. However, under accelerated aging by carbonation, the composites with or without nanofibers do not reduce the mechanical performance due to the lower alkalinity provided by the accelerated carbonation. Therefore, the nanofibrilated cellulose appears to be a promising material to be used as nano-reinforcement of the extruded hybrid cement-based composites [25].