## 3 Results and Discussion
### Analysis of Hydration Characteristics of Composite Mortar
Compared with the OPC group, the diffraction peaks of the hydration products Ca(OH)\({}_{2}\) and AFt of the specimens in the A0 group were significantly weaker, which indicated that the incorporation of SS inhibited the hydration reaction of the slurry and led to the reduction of the hydration products. Compared with group A0, the diffraction peak intensity of Ca(OH)\({}_{2}\) in group A1 was significantly lower, which was mainly because the admixture of RM promoted the hydration reaction of SS, accelerated the absorption of Ca\({}^{2+}\) and reduced the content of Ca(OH)\({}_{2}\). For the group A1-A6, in comparison, the diffraction peak of AFt was gradually enhanced with the increase of EMR admixture, which was mainly due to the higher content of SO\({}_{4}\)\({}^{2}\)- in EMR, which could further react with the calcium aluminate gel generated by the hydration reaction to produce AFt [22]. Figure 6 shows the TG-DTG curves of composite net pulp at 28 d of age, and the mass loss rates are shown in Table 5. From the TG diagram, it can be learned that the total mass loss rate of each group of composite net pulp is in the order of A6 group \(>\) A4 group \(>\) A5 group \(>\) A3 group \(>\) A2 group \(>\) A1 group \(>\) A0 group from the largest to the smallest. Corresponding to the DTG diagram, it can be seen that four main decomposition peaks exist in each group of composite net pastes: the decomposition peaks existing before 60\(\sim\)300 \({}^{\circ}\)C correspond to the initial dehydration of C-S-H gels and the early thermal decomposition of AFt; the mass loss existing between 400\(\sim\)600 \({}^{\circ}\)C is mainly attributed to the thermal decomposition of Ca(OH)\({}_{2}\); the mass loss existing between 600\(\sim\)750 \({}^{\circ}\)C is mainly caused by the thermal decomposition of calcite (CaCO\({}_{3}\)) produced by carbonization of the specimens during the hardening process [5; 23]. From this, it can be judged that the content of hydration products Ca(OH)\({}_{2}\), Aff, and C-S-H gel is significantly reduced in the specimens of group A0 compared to group OPC. Compared to the A0 group, the content of AFt and C-S-H gels gradually increased and the content of Ca(OH)\({}_{2}\) gradually decreased in the A1-A6 group, which indicates that the compounding of suitable proportions of RM and EMR can promote the hydration reaction of the slurry, consume Ca(OH)\({}_{2}\), and generate AFt and C-S-H gels that are more favorable to the development of mechanical properties, which is consistent with the XRD test results. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Second Exothermic** & **Third Exothermic** & **72 h Total Heat** \\  & **Peak/h** & **Peak/h** & **Release /J**-g**\({}^{-1}\) \\ \hline OPC & 10.0 & — & 258.5 \\ A0 & 10.9 & — & 225.0 \\ A1 & 8.2 & — & 227.7 \\ A2 & 9.2 & — & 246.2 \\ A3 & 9.5 & 17.9 & 236.6 \\ A4 & 10.0 & 26.2 & 237.3 \\ A5 & 10.1 & 46.1 & 228.9 \\ A6 & 9.9 & — & 199.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Compound mortar exothermic peak occurrence time and its 72 h total exothermic heat. Figure 5: XRD pattern of composite net pulp: (**a**) 3 d; (**b**) 28 d.  
seen that the approximate cumulative pore volume size is in the order of C5 group > OPC group > C6 group > C4 group > C2 group > A0 group > C3 group > C1 group. [PERSON] [24] classified the mortar strength according to the degree of harm caused by the size of pores, which was mainly divided into four categories: harmless pores (<20 nm), less harmful pores (20-50 nm), harmful pores (50-200 nm), and multiharmful pores (>200 nm). The pore size distribution of composite mortar at 28 d age is shown in Table 6. It can be seen from the figure that the percentage of multiharmful pores > 200 nm in the specimens of the A0-A6 group decreased significantly and the percentage of nonharmful pores less than 20 nm increased significantly compared to the specimens of the OPC group.