## 3 Results
### The Effect of DE on the Hydration Process of Cement Mortar
#### 3.5.2 The Impact of DE on the Phase Composition of Hydration Products in Cement Mortar  
The hydration products of cement mortar mainly consist of Ca(OH)\({}_{2}\) crystals and C-S-H gels. Among them, there are many types of C-S-H gels, most of which exist in an amorphous state in cement paste. It is difficult to detect C-S-H gels through XRD, but the changes in CH crystals are very obvious in the diffraction patterns. Therefore, to further analyze the impact of internal curing with diatomic earth on the hydration products of cement mortar, see Figure 9 for the XRD patterns of mortars with different dosages of DE and the XRD patterns of mortars with different ages after the addition of DE.  
As can be seen from Figure 9a, the development law of the diffraction peaks of crystalline hydration products in each group with different dosages of DE is basically similar, while the height of the diffraction peak mainly varies according to the dosage of DE. The diffraction peak of SiO\({}_{2}\) is the highest in the spectra, but the difference among samples is not significant. This is mainly because a large amount of RS is contained in the cement paste, which cannot be avoided during sampling and testing. Therefore, the change in the SiO\({}_{2}\) peak is not significant in each sample. C-S-H belongs to gels and exists in cement paste in an amorphous state with low crystallinity, so its diffraction peak is not obvious and difficult to distinguish in the XRD pattern. Therefore, the diffraction peak is not quantified, but the existence of C-S-H is observed in the pattern, which proves that C-S-H is generated during the hydration process of mortar. In Figure 9a, the difference in the Ca(OH)\({}_{2}\) peak is the most obvious, and the peak decreases with the increase in DE dosage. This is mainly because the incorporated internal curing material DE has volcanic ash activity. Under alkaline conditions, SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) in DE can react with Ca(OH)\({}_{2}\) to produce secondary hydration products such as C-S-H gel and AFt. In the spectra, the existence of the AFt peak can be observed. Although the change is not significant, it can be observed that the peak increases with the increase in DE dosage. This phenomenon can explain why the incorporation of DE can delay the \"second expansion stage\" of autogenous shrinkage during the hydration period of cement mortar, which is caused by the production of a large amount of expansive AFt crystals during the hydration period of cement mortar.  
Figure 9: XRD patterns. (**a**) XRD patterns of mortar with different DE contents; (**b**) XRD patterns of mortar at different ages after incorporation of DE.  
As shown in the spectra of Figure 9b, the peak value of SiO2 gradually decreases while the peak value of Ca(OH)2 gradually increases as the age increases. This is mainly due to the hydration reaction, during which the internal relative humidity of mortar decreases. The difference in the relative humidity gradient stimulates diatomic to release stored water, which results in the secondary hydration of cementing materials, generating more Ca(OH)2. This enhances the alkalinity inside the cement paste, stimulating the potential activity of diatomic. As a result, its structure is destroyed, leading to reactions between SiO2, Al2O3 and Ca(OH)2 inside it, producing a large amount of C-S-H gel. This reduces the content of Ca(OH)2 and improves the degree of hydration of the mortar, which is consistent with the results of the chemically bound water content tests.