## 4 Results and Discussion
### Effect of Leading Time on Compressive Strength  
Figure 10 illustrates the compressive strength of the specimen after a mineralization reaction for 3 h under different soaking times. The specimen without any soaking treatment exhibited the lowest compressive strength of 0.099 MPa. However, as the soaking time exceeded 12 h, the compressive strength significantly increased. Notably, the specimens soaked for 24 and 48 h displayed the highest strengths of 0.658 MPa and 0.592 MPa, respectively, which is nearly six times higher than the strength of the specimen without soaking treatment. The compressive strength of specimens subjected to soaking for 12 to 72 h is higher compared to those without soaking treatment. The trend in compressive strength with soaking time indicates an initial sharp increase, followed by a slight decrease. This increase in strength is attributed to the soaking of fly ash, leading to the continued dissolution and diffusion of the alkaline metal ions into the liquid environment. This process promotes mineralization reactions, enhancing the degree of mineralization. Prolonged soaking results in higher concentrations of alkaline ions in the liquid environment, leading to an increased generation of carbonate and amorphous calcium silicate hydrate (CSH) through the mineralization reactions. This densities the specimen, consequently increasing its strength. Consequently, the growth rate of compressive strength gradually diminishes. Figure 8: Original fly ash (**a**), fly ash without mineralization after soaking (**b**), mineralization without soaking (**c**), mineralization after soaking 24 h (**d**), mineralization after soaking 48 h (**e**), mineralization after soaking 72 h (**f**). Figure 9: The energy spectra of the sample. For instance, compressive strength increases by 565% when soaking time rises from 0 to 24 h, but the growth rate slows down as the carbonization time extends from 24 to 72 h.  
Figure 11 presents the mineral pressure strength of the specimen during mineralization reaction with supercritical CO2 at different soaking times. The compressive strength of the specimen without any soaking treatment is the lowest, measuring 0.519 MPa. However, when the soaking time exceeds 12 h, there is a significant increase in compressive strength. Notably, the specimens soaked for 24 h and 48 h exhibit the highest strengths, measuring 1.324 MPa and 1.059 MPa, respectively, which is more than twice the strength of the specimen without soaking treatment. Furthermore, the compressive strength of the specimens with immersion times ranging from 12 to 72 h is higher than that of those without immersion treatment. The overall trend of compressive strength with immersion time indicates a sharp increase initially, followed by a slight decrease, and eventually stabilizing. Comparatively, compressive strength is doubled when compared to non-supercritical CO2 reactions. This can be attributed to the similar density of supercritical CO2 and water, requiring minimal critical energy to overcome surface tension. Consequently, it enhances the transport capacity of CO2 in water, facilitating rapid diffusion into the liquid environment to provide the necessary reactive substances for mineralization. Figure 11: Effect of soaking time on the UCS of specimens (supercritical CO2). Figure 10: Effect of soaking time on the UCS of specimens. Figure 12 illustrates a linear relationship between the degree of mineralization and the compressive strength in the experimental specimens, where higher mineralization correlates with greater strength. As soaking time increases, the rate of ion leaching decreases, reaching a maximum ion concentration and slowing down the reaction speed. The fly ash specimens prepared by the reaction of fly ash and carbon dioxide mineralization have good uniaxial compressive strength and pore structure.