## 3 Results and Discussion  
### Compressive Strength  
Figure 3 shows the compressive strength test results of the mortar specimens at 1, 3, 7, and 28 days. The compressive strength increases as the curing period increases. The use of SCMs mainly affects cement hydration through dilution, filling, and nucleation effects [30]. When the curing age was 1, 3, and 7 days, the compressive strength of the mortar specimens decreased with the increase in QZ and FA substitution. However, the compressive strength of the QZ group was higher than that of the FA group. The main reason is that QZ and FA have low initial reaction activity [31]. Therefore, the dilution effect increases the effective water-cement ratio of the mixed mortar, speeding up the cement reaction rate [32] and negatively impacting the formation of compressive strength [33]. The difference in compressive strength mainly depends on the strength of the filling and nucleation effects. The particle size distribution of QZ has a finer range of particle size distribution than that of FA. The finer particle size makes the nucleation effect of QZ more significant than that of FA. In addition, finer QZ can fill finer pores, making the internal structure of the mixed mortar denser at an early stage, thereby obtaining higher compressive strength than the FA group. During the initial stage, FA has low reactivity, which hardly accelerates the formation of early compressive strength [31]. In addition, FA also reduces the hydration rate, which delays the process of the mixed mortar turning into a solid, thus affecting early compressive strength [34]. FA accelerates cement strength development mainly in the late stage [35]. When the curing age reached 28 days, the compressive strength of 10 FA, 20 FA, and 10 FA10 QZ increased rapidly and reached a level comparable to that of the control group. The following is a summary that explains the reasons behind the results: First, when the curing age is reached, the pozzolanic effect of FA is activated. This means that Al\({}_{2}\)O\({}_{3}\) and SiO\({}_{2}\) in FA can react with CH to produce substances such as C-S-H. The gel produced by the pozzolanic effect can fill the capillaries in the concrete and thus effectively accelerate  
Figure 3: Compressive strength results. the formation of strength [36; 37]. Secondly, the secondary hydration products of FA adhere to its surface, making the surface of FA rough, improving the interface with cement, and optimizing the overall mechanical properties of cement materials. When the curing time is prolonged beyond 28 days, the mechanical strength and durability properties of the test specimens continue to exhibit incremental improvements, attributed to the characteristic delayed pozzolanic reactivity of FA [38]. The compressive strength values of the 10 FA10 QZ group at all stages achieved satisfactory results. This group can improve strength through the filling and nucleation effects of QZ in the early stage and through the secondary hydration reaction of FA in the late stage. In the same reaction system, these two SCMs can demonstrate their respective advantages at different ages and jointly accelerate the consolidation of cement strength. To quantitatively describe the relationship between the addition of FA and QZ and the 28-day compressive strength (Table 3), a quadratic polynomial model was constructed using regression analysis, with the general form as follows:  
\[\text{y}=\text{a}_{0}+\text{a}_{1}\text{x}_{1}+\text{a}_{2}\text{x}_{2}+\text {a}_{11}\text{x}_{1}^{2}+\text{a}_{22}\text{x}_{2}^{2}+\text{a}_{12}\text{x}_ {1}\text{x}_{2}+\varepsilon \tag{1}\]  
In the model, the dependent variable y is the dependent variable representing the 28-day compressive strength. x\({}_{1}\) and x\({}_{2}\) represent the proportions of FA and QZ, and k represents the number of independent variables.