###### Abstract  
This research presents a sensitivity analysis of various parameters that affect the carbonation of recycled aggregates (RAs), namely CO\({}_{2}\) concentration, temperature, and relative humidity. The range of parameter values is close to that found in cement plant chimneys with regard to the forced carbonation of RAs. With this purpose, the main characteristics of flue gas streams (CO\({}_{2}\) concentration, temperature, and relative humidity) from two Portuguese cement plants were identified and used in this research. The results indicated that temperatures around 60 \({}^{\circ}\)C and CO\({}_{2}\) concentrations around 25% accelerate the carbonation reaction and increase CO\({}_{2}\) absorption in mixed recycled aggregates (MRAs). CO\({}_{2}\) absorption consistently decreased as the relative humidity was reduced from 60% to 40%. The highest amount of CO\({}_{2}\) captured was by a recycled concrete aggregate (RCA) in the conditions of 23 \({}^{\circ}\)C, 60% RH, and 25% CO\({}_{2}\). Overall, the RAs were able to capture a significant amount of CO\({}_{2}\), ranging from 52 to 348 kg of CO\({}_{2}\) per tonne of cement paste, depending on the nature of the RA. These findings drawn from a parametric campaign provide valuable insights into the potential enforcement of carbonation for recycled aggregates under conditions that closely reflect those found in cement plants. os 2  
materials, such as ettrinigite and calcium aluminates, resulting in the formation of calcium carbonate (CaCO\({}_{3}\)) [2,5]. The formation of calcium carbonate within the pores of the cement matrix increases density and reduces water absorption [6]. When water and CO\({}_{2}\) are present, carbonic acid is produced. This acid lowers the pH of the cement, causing the release of Ca\({}^{2+}\) ions from hydrated cement compounds [4]. Consequently, CaCO\({}_{3}\) is formed [7]. The reaction with CO\({}_{2}\) can also occur with other hydrated phases of cementitious materials, such as calcium silicate hydrate (C-S-H), ettrinigite, and calcium aluminates [7]. The carbonation of C-S-H results in the formation of calcium carbonate and amorphous silica gel [8,9]. Furthermore, anhydrous cement compounds like tricalcium silicate (alite) and dicalcium silicate (belite) can also undergo carbonation. This process leads to the formation of calcium carbonate and, in some cases, silica gel [5,9,10]. The carbonation of recycled aggregates (RAs) has the potential to enhance material properties and contribute to environmental sustainability. RAs from construction and demolition waste often have uncarbonated cementitious compounds. This makes them well suited for accelerated carbonation. During this process, the aggregates are strengthened by filling voids and microcracks with calcium carbonate [10,11,12]. In addition, greenhouse gas emissions are mitigated by sequestering CO\({}_{2}\). By optimizing the carbonation process in recycled aggregates, their mechanical properties--such as their crushing index--can also be improved, making them more competitive compared to natural aggregates. Furthermore, incorporating CO\({}_{2}\) curing into the production of RA supports the industry's broader efforts to develop sustainable building practices and reduce the carbon footprint of construction activities [13]. This study investigated the CO\({}_{2}\) capture of recycled aggregates under different carbonation conditions to understand how each reaction factor, such as relative humidity, temperature, and CO\({}_{2}\) concentration, influences the amount of CO\({}_{2}\) captured [6,14,15,16,17,18,19,20]. The test campaign was divided into three parts: variation in relative humidity; variation in temperature; and variation in CO\({}_{2}\) concentration. The experimental conditions selected for this study aimed to approach the typical operating conditions encountered in Portuguese cement plants and were based on data provided by cement companies operating in Portugal.