## 3 Experimental Analysis of Steam Curing and Orthogonal Matching Ratio
### Steam Curing Test Analysis
These results suggest that while a moderate increase in curing temperature promotes early hydration and strength development, excessively high temperatures may adversely affect mid-to-late strength, potentially due to internal structural defects, microcracking, or unstable hydration products. Therefore, based on the above findings, the optimal curing temperature is determined to be 50 \({}^{\circ}\)C.  
(5) The constant temperature time is also one of the important factors affecting the strength of fly ash cement mortar. The specific test plan and results are shown in Table 12.  
As shown in Table 12, under constant temperature durations of 12, 24, 36, 48, and 60 h, the 3-day compressive strength of the specimens increased by 12.52%, 37.87%, 44.46%, 45.06%, and 47.57%, respectively, compared to standard curing; the 7-day strength rose by 8.43%, 28.09%, 32.65%, 30.49%, and 31.44%; the 14-day strength increased by 2.69%, 14.19%, 16.42%, 18.02%, and 19.43%; and the 28-day strength improved by 2.30%, 10.99%, 12.23%, 13.22%, and 15.95%. It is evident that the compressive strength increased most rapidly between 3 and 7 days, and gradually stabilized with age. Extending the constant temperature duration from 12 to 24 h led to increases of 22.52%, 18.13%, 11.50%, and 8.49% in compressive strength at 3, 7, 14, and 28 days, respectively, while further extending it from 24 to 60 h resulted in additional increases of 7.95%, 2.62%, 4.95%, and 4.47%, although the growth rate declined significantly. These findings indicate that compressive strength increases most significantly between 12 and 24 h of constant temperature curing, after which the rate of increase gradually diminishes and stabilizes. Therefore, considering both strength improvement and curing efficiency, the optimal constant temperature curing duration in this experiment is determined to be 24 h.  
In summary, with a fly ash content of 20% by mass of the cementitious material, the optimal steam curing parameters are as follows: a static curing duration of 18-24 h, a heating rate of 20 \({}^{\circ}\)C/h, a constant temperature of 50 \({}^{\circ}\)C, and a constant temperature \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & **Resting** & **Heating** & **Constant** & **Constant** & \multicolumn{3}{c}{**Compressive Strength**} \\ \cline{3-10}  & **Time (h)** & **Rate (\({}^{\circ}\)C/h)** & **Temperature (\({}^{\circ}\)C)** & **Temperature Time (h)** & **3 d** & **7 d** & **14 d** & **28 d** \\ \hline HW-40 & 24 & 20 & 40 & 24 & 19.78 & 27.24 & 29.67 & 31.48 \\ HW-50 & 24 & 20 & 50 & 24 & 23.01 & 29.78 & 32.26 & 33.75 \\ HW-60 & 24 & 20 & 60 & 24 & 23.45 & 30.56 & 31.78 & 32.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Summary table of test plans and test results. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & **Resting** & **Heating** & **Constant** & \multicolumn{3}{c}{**Constant**} & \multicolumn{3}{c}{**Compressive Strength**} \\ \cline{3-10}  & **Time (h)** & **Rate (\({}^{\circ}\)C/h)** & **Temperature (\({}^{\circ}\)C)** & **Temperature Time (h)** & **3 d** & **7 d** & **14 d** & **28 d** \\ \hline HS-12 & 24 & 20 & 50 & 12 & 18.78 & 25.21 & 29.01 & 31.11 \\ HS-24 & 24 & 20 & 50 & 24 & 23.01 & 29.78 & 32.26 & 33.75 \\ HS-36 & 24 & 20 & 50 & 36 & 24.11 & 30.84 & 32.89 & 34.13 \\ HS-48 & 24 & 20 & 50 & 48 & 24.21 & 30.34 & 33.34 & 34.43 \\ HS-60 & 24 & 20 & 50 & 60 & 24.84 & 30.56 & 33.74 & 35.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Summary table of test plans and test results. duration of 24 h. This parameter set effectively enhances the mechanical performance of fly ash cement mortar, achieving a balance between early- and late-stage strength development.