*3.3. E*ff*ect of Hydration by the X-ray Di*ff*raction of Pastes*

The hydration of the reference paste (cement paste without admixture of cellulose ether) is model-like, which means that, in this case, significant amounts of Portlandite are formed (Figure 5). The largest amount of Portlandite in the C-0 paste and the smallest intensity of the peaks of the phases of alite and belite are related to their faster reaction as a result of the hydration process, which was confirmed in calorimetric studies [38,39]. Diffraction patterns of pastes modified with cellulose ether after 48 h of setting indicate that the admixture inhibits the hydration process of cement and cement-lime pastes. In the case of the diffractograms of the samples from C-0.3-MV to CL-0.175-HV, a lower intensity of Portlandite can be seen compared to the diffractogram of the C-0 and C-0.05-MV pastes. It can be seen that the hydration of the cement paste with an admixture of 0.05% with a viscosity of 25,000 MPa·s (C-0.05-MV) does not differ from the hydration of the C-0 paste. Hence, the conclusion that HEMC added in the amount of 0.05% does not have such a large impact on the setting process as in other cases. The lowest amount of Portlandite was observed for the cement paste modified with an admixture of 0.3% with a viscosity of 25,000 MPa·s. These experiments confirmed that the admixture viscosity does not have such a large influence on the changes in the hydration process as its amount, regardless of the type of binder.

For cement-lime pastes, the increase of calcite peaks is also characteristic, which may indicate of the partial lime binder carbonation. Due to a binder composition, alite and belite have less intense peaks in these pastes.

The diffractograms of the pastes after 40 days of maturation were shown in Figure 6. It can be seen that the process of setting individual pastes is similar. There are few significant differences (between the individual pastes) in the intensity of portlandite, alite, and belite peaks, as could be observed for the measurements carried out after two days of hydration of the samples. A similar conclusion for cement pastes was observed in literature reports [22]. Only for the C-0.3-MV and C-0.175-HV pastes, differences for the characteristic peaks of Portlandite are clearly visible. In both cases, the peak for 18.04◦ 2θ is significantly higher and the peak for 34.05◦ 2θ is lower than in the other pastes. The least intense Portlandite peak was obtained for CL-0.3-MV.

**Figure 5.** X-ray patterns of all pastes for 48 h. Denotation: A–alite, B–belite, Br–brownmillerit, C–calcite, E–ettringite, P–portlandite, H–C-S-H.

However, comparing the diffraction patterns after two days and after 40 days, it is possible to notice the different intensity of Portlandite and calcite. A greater amount of Portlandite after 40 days may be caused by the hydration process, and an increased amount of calcite is associated with the formation of calcium carbonate CaCO3 and the progressive carbonation process. In Table 6, the percentage changes of the intensity of Portlandite peaks for 18.04◦ 2θ after 40 days of pastes hydration were shown. In the case of calcite, the difference in peak intensity between the diffractograms made after two days and after 40 days is also visible, although not as large as in the case of Portlandite. However, the results are consistent with the studies carried out by Izaguirre et al. [27]. In the case of the sample with cellulose ether, a significant increase in the amount of free water, Ca(OH)2 and CaCO3 were seen in TG analysis. Percent content H20, Ca(OH)2, and CaCO3 after 28 and 91 days was bigger than after 7 days maturation (compared to a reference sample), which confirm the ongoing carbonation processes. On the other hand, percent content of Ca(OH)2 and CaCO3 after 7 days was smaller in the case of the sample with cellulose ether than the reference sample, which may indicate a delay of reaction of carbonation processes caused by the admixture.

**Figure 6.** X-ray patterns of all pastes for 40 days. Denotation: A–alite, B–belite, Br–brownmillerit, C–calcite, E–ettringite, P–portlandite.

**Table 6.** Percentage changes in Portlandite intensity after 2 and 40 days of maturation for all pastes (according to Table 3).

