## 3 Experimental Analysis of Steam Curing and Orthogonal Matching Ratio
### Steam Curing Test Analysis  
(1) To evaluate the performance of the test specimens, three distinct curing schemes were implemented, The compressive strength was measured by NYL-2000 microcomputer controlled electronic universal testing machine produced by China Nanjing Speiker Test Instrument Co., Ltd. (Nanjing, China). The test scheme and corresponding rock mechanics results are presented in Table 8:  
According to China's \"Code for design of concrete structures\" (GB 50010) [24], the strength of concrete specimens was tested at the age of 3 d, 7 d, 14 d and 28 d to ensure that the strength of the concrete structures meets the requirements. As shown in Table 8, under steam curing conditions, the compressive strength of specimens at 3, 7, 14, and 28 days increased by 74.4%, 54.6%, 40.05%, and 32.21%, respectively, compared to the non-cured condition; while compared to standard curing, the increases were 38.47%, 28.00%, 14.12%, and 10.95%, respectively. Additionally, the compressive strength of specimens cured for 3 days reached 90% of that of specimens cured for 28 days without curing, indicating that elevated temperature significantly accelerated cement hydration and effectively activated the early reactivity of fly ash. (2) The curing stage refers to the interval between demolding the blocks and initiating the thermal curing process. The test plan and corresponding results are presented in Table 9:  
Figure 5: Demolded fly ash cement mortar test specimen. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{\
\begin{tabular}{c} **Maintenance** \\ **Methods** \\ \end{tabular} } & \multirow{2}{*}{**Maintenance Process**} & \multicolumn{4}{c}{**Compressive Strength/MPa**} \\ \cline{3-6}  & & **3 d** & **7 d** & **14 d** & **28 d** \\ \hline \multirow{6}{*}{
\begin{tabular}{c} steam curing \\ **Methods** \\ \end{tabular} } & After resting for one day, place the test & & & & \\  & piece in a steam curing chamber and raise & & & & \\  & its temperature to 50 \({}^{\circ}\)C at a rate of 20 \({}^{\circ}\)C & 23.11 & 29.76 & 32.24 & 33.74 \\  & per hour, then maintain a constant & & & & \\  & temperature for 24 h. & & & & \\ standard & After demolding the test specimen, cure it & 16.69 & 23.25 & 28.25 & 30.41 \\ maintenance & under standard conditions for 24 h. & & & & \\  & After demolding, the test specimens are & 13.25 & 19.25 & 23.02 & 25.52 \\ maintenance-free & placed outdoors for curing. & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Summary table of maintenance methods and intensity values. As shown in Table 9, after static curing durations of 6, 12, 18, and 24 h, the 3-day compressive strength of the specimens increased by 8.6%, 15.94%, 27.38%, and 37.87%, respectively, compared to standard curing; the 7-day strength increased by 3.83%, 12.39%, 18.54%, and 28.09%; the 14-day strength rose by 0.96%, 3.93%, 13.17%, and 14.19%; and the 28-day strength improved by 0.53%, 2.33%, 9.27%, and 10.98%. Extending the static curing time from 6 to 18 h led to a 13% increase in 28-day strength; further extending it to 24 h resulted in an approximate 19% increase relative to the 6 h curing period. This indicates that when the steam curing period is insufficient, the reactive components in the fly ash mortar do not fully participate in hydration, thereby limiting early strength development and resistance to thermal effects. Therefore, to ensure desirable mechanical performance in fly ash cement mortar, the static curing duration should be maintained between 18 and 24 h.  
(3) The heating rate has a significant effect on the strength development of the test specimens.