## 3 Results and Discussion  
### Testing the Carbonation Products Formed in the Pastes  
The XRD analyses were conducted on the samples extracted from the colorless and purple regions of the pastes. Figure 3a,b at 24 h and 72 h and Figure 4a,b at 24 h and 72 h, respectively, show the XRD results for the non-carbonated (purple) inner regions and the carbonated (colorless) outer side regions of the blocks. For the sample with no \(\gamma\)-C\({}_{2}\)S supplementation, C\({}_{2}\)S0, the principal phase reacting in the carbonation of the pastes was portlandite (Ca(OH)\({}_{2}\)) and, to a lesser extent, alite (C\({}_{3}\)S) and belite (C\({}_{2}\)S). The presence of portlandite (Ca(OH)\({}_{2}\)) in all the paste blocks was mainly indicated by the characteristic XRD 2-theta-degrees peaks at 20 = 18.09\({}^{\circ}\), 28.76\({}^{\circ}\), 32.2\({}^{\circ}\), 47.23\({}^{\circ}\), 50.89\({}^{\circ}\), 54.45\({}^{\circ}\), and 71.93\({}^{\circ}\)[5]. From Figure 3a at 24 h and Figure 3b at 72 h, 3 out of the 6 possible (because the 20 reading stopped at 60\({}^{\circ}\)) peaks at 20 = 18.09\({}^{\circ}\), 28.76\({}^{\circ}\), and 47.23\({}^{\circ}\) were clearly visible, thereby representing the Ca(OH)\({}_{2}\) content inside the paste blocks. The presence of CaCO\({}_{3}\) in the paste blocks in Figure 3a,b was indicated by the characteristic peaks of calcite (CaCO\({}_{3}\)) at 20 = 23.08\({}^{\circ}\), 29.39\({}^{\circ}\), 36.04\({}^{\circ}\), 39.46\({}^{\circ}\), 42.23\({}^{\circ}\), 47.42\({}^{\circ}\), 48.5\({}^{\circ}\), 57.51\({}^{\circ}\), 60.76\({}^{\circ}\), and 64.8\({}^{\circ}\)[9; 10]. However, despite the range of 20 having stopped at 60 \({}^{\circ}\) and excluding 1 peak, only 2 peaks were visible out of the possible 6 peaks, at 20 = 23.08\({}^{\circ}\) and 48.5\({}^{\circ}\). Notably, the XRD intensities for both Ca(OH)\({}_{2}\) and CaCO\({}_{3}\) for their clear peaks at 24 h were not significantly higher than their corresponding peaks at 72 h after carbonation, thereby indicating that the portlandite in the purple regions of the blocks barely reacted with the CO\({}_{2}\) from the onset of carbonation, through the 24 h to 72 h test times, and hence the near equality of the intensities at the characteristic 20 peaks. The same observation was made for the alite and belite phases in all the purple-colored parts of the specimens (inner regions), as their peaks at 20 degrees of approximately 32 to 33 barely changed in intensity between the test periods of 24 and 72 h. This indicates that 72 h was not sufficient for the CO\({}_{2}\) to diffuse to the inner parts of the paste specimens. However, most of the inner regions of the discarded mortar test samples were carbonated for 72 h.  
Figure 2: Experimental schematic of diffusion of CO\({}_{2}\). Figure 4: XRD results on the carbonated (colorless) outer regions of the blocks (**a**) at 24 h and (**b**) 72 h. P = portlandite (Ca(OH)2); C = calcite (CaCO3); B = belite (C2S); A = alite (C3S). Figure 3: XRD results on the non-carbonated (purple) inner regions of the blocks (**a**) at 24 h and (**b**) 72 h. P = portlandite (Ca(OH)2); C = calcite (CaCO3); B = belite (C2S); A = alite (C3S). When the XRD analyses for the outer parts of the paste specimens were examined in Figure 4a at 24 h and Figure 4b at 72 h, the characteristic peaks for portlandite (20 degrees of about 18.09\({}^{\circ}\), 28.76\({}^{\circ}\), and 34.23\({}^{\circ}\)) significantly decreased from the test time of 24 h to 72 h, and the peaks characteristic of the alite and belite phases (20 degrees between 32\({}^{\circ}\) and 33\({}^{\circ}\)) decreased; however, in the same figure and time interval, the characteristic peaks for calcite (CaCO\({}_{3}\)) at 20 = 29.39\({}^{\circ}\) were enhanced significantly, whereas its peaks at 20 = 23.08\({}^{\circ}\) and 39.46\({}^{\circ}\) appreciably increased, thereby indicating the carbonation reactions occurring on both the portlandite on one part and on the alite and belite phases on the other, from the outer regions of the blocks going inward.