## 3 Results and Discussion
### Xrd  
To further analyze the effects of NC and AS on the hydration products of the hardened single OPC and OPC-CSA, XRD was applied to reveal the consumption of cement clinkers and the precipitation of hydration products after 3 d and 28 d hydration, as shown in Figures 6 and 7. It should be noted that, because each XRD measurement was operated with the same detecting parameters, the intensities of characteristic XRD reflexes can be compared to semi-qualitatively reflect the amount of crystalline hydration products [37].  
Regarding the OPC system after 3 d of hydration, no obvious peaks corresponding to the aluminate-contained phase (mainly C\({}_{3}\)A and C\({}_{4}\)AF) were observed due to its fast hydration speed compared to the silicate phases (mainly C\({}_{2}\)S and C\({}_{3}\)S). Besides, a slightly decreased peak height of C\({}_{2}\)S and an enhanced CH peak height were observed with the addition of NC. However, an obvious increase in the peak height of AFt was found with the addition of AS, which is attributed to the massive hydration of the aluminate-contained phase accelerated by AS (Figure 4). Obvious AFt peaks and even an AFm peak were found in OPC-CSA binary blended cement (Figure 6b). However, the peak height of silicate phases remains quite high, which proves the depressed silicate phases hydration by the rapid reaction of aluminate-contained phases. With the extended curing age to 28 d, a  
Figure 5: Cumulative heat of OPC and OPC-CSA binary blended cement paste with or without the addition of NC and AS; (**a**,**b**) single OPC; (**c**,**d**) OPC-CSA.  
higher reduction in the peak height of silicate phases was found. Consistent with the 3 d hydration, samples with the addition of NC still showed a slightly decreased height of the C2S peaks, while the incorporation of CSA and AS increased the AFt peak height.  
Figure 6: XRD patterns of the hardened OPC (**a**) and OPC-CSA (**b**) cement paste with or without the addition of NC and AS after hydration for 3 d.  
Figure 7: XRD patterns of the hardened OPC (**a**) and OPC-CSA (**b**) cement paste with or without the addition of NC and AS after hydration for 28 d.  
When we compared the intensity originating from the formation of CH and AFt after 3 d of hydration, the addition of NC showed a negligible effect on the intensity of CH and AFt for the OPC without the addition of AS. While in the presence of AS, the addition of NC caused an obvious reduction in the intensity of CH, which may be due to the accelerated reaction between NC and CH by AS [38; 39]. However, the addition of NC has a limited effect on the intensity of AFt.  
Compared to the OPC system, a lower CH intensity was observed in OPC-CSA binary blended cement, regardless of the addition of AS or not, which may be attributed to the depressed silicate phase hydration shown in Figure 4. In addition, compared to that without AS, it is worth noting that the presence of AS can always lead to a very low intensity of CH, which may be attributed to the following two mechanisms: On the one hand, in the OPC-CSA sample with only the addition of AS, the low intensity of CH may be caused by the seriously depressed silicate phase hydration (Figure 4), in which the formation of CH is rare. On the other hand, in the OPC-CSA sample with the combined addition of NC and AS, the addition of NC promoted silicate phase hydration (Figure 4), while the formed CH was then consumed by the accelerated reaction between NC and CH by AS. Meanwhile, the addition of AS to OPC-CSA binary blended cement can enhance the intensity of AFt due to the strongly accelerated aluminate-contained phase hydration (Figure 4). Along with the extended curing age to 28 d, the same phenomenon was found in the intensities of CH and AFt. In addition, the OPC-CSA sample with the combined addition of NC and AS exhibited a reduced CH intensity compared to the sample with the only addition of AS, which proves that AS can accelerate the reaction between NC and CH.