## 3 Results and Discussion
### Physical Activation Process Test Results
According to the Chinese standard JG/T 315-2011 [2], which  
Figure 8: Flexural (**a**) and compressive (**b**) strength activity indices with different specific surface areas at different ages. Figure 7: Flexural (**a**) and compressive (**b**) strength curves of volcanic powder with different specific surface areas at different ages. requires a 28-day activity index of \(\geq\)65%, only the sample with a specific surface area of 735 m\({}^{2}\)/kg met the specification. Throughout the age period, the flexural activity index varied between 66% and 99%, which is significantly higher than the range of 55-80% for the compressive activity index. This shows that the volcanic rock powder had a high flexural compression ratio, and the property of the high flexural compression ratio indicated a better toughness of the concrete [52; 53]. Also, the finer the fineness of the volcanic rock powder, the higher the contribution to the flexural strength. From the microscopic point of view, the volcanic rock powder particles tended to show an irregular morphology with a rough surface and sharp edges. This feature helped to increase the friction between particles, effectively dispersed and reduced the influence of bending stress, and reduced the stress concentration phenomenon, thus playing a positive role in improving the flexural strength. Scanning electron microscopy (SEM) and energy spectrum analysis (EDS) methods were employed to determine the microscopic morphology and hydration products of the natural volcanic rock powders at 3 days and 28 days. The specific surface areas of the powders were S1 = 480 m\({}^{2}\)/kg, S2 = 560 m\({}^{2}\)/kg, and S3 = 640 m\({}^{2}\)/kg, as depicted in Figures 9-14. Figure 10: SEM (**a**) and EDS (**b**) patterns of volcanic rock powder with a specific surface area of 560 (m\({}^{2}\)/kg) at 3 days. Figure 9: SEM (**a**) and EDS (**b**) patterns of volcanic rock powder with a specific surface area of 480 (m\({}^{2}\)/kg) at 3 days. Figure 11: SEM (**a**) and EDS (**b**) patterns of volcanic rock powder with a specific surface area of 640 (m\({}^{2}\)/kg) at 3 days. Figure 4:0 SEM (**a**) and EDS (**b**) patterns of volcanic rock powder with a specific surface area of 480 (m\({}^{2}\)/kg) at 28 days. Figure 4:1 SEM (**a**) and EDS (**b**) patterns of volcanic rock powder with a specific surface area of 560 (m\({}^{2}\)/kg) at 28 days. 3D SEM images (Figures 9a, 10a and 11a) revealed that the hydration products comprised reticulated C-S-H, thin platelet Ca(OH)\({}_{2}\), and a small amount of acicular AFt. During the initial hydration process, the voids within the products were large, indicating that the hydration reaction had not yet progressed sufficiently. As the specific surface area of the volcanic rock powder increased, the hydrated calcium silicate gel gradually aggregated and intertwined into a network, resulting in decreased pore size and a denser structure. EDS images (Figures 9b, 10b and 11b) indicated that the calcium-silica ratios of 1.88%, 2.21%, and 2.31%, as well as the aluminium-silica ratios of 0.16%, 0.21%, and 0.26% at 3 days, were enhanced with the increase in specific surface area. This suggests that a larger active surface area facilitated more effective reactions between the cement and water molecules, leading to the production of additional C-S-H gels, and thus contributing to the accelerated strength development observed at 3 days. Moreover, with the increase in calcium and aluminium content, more aluminium atoms replaced silicon in the C-S-H structure, resulting in the formation of C-A-S-H. This product shares similar properties with C-S-H and significantly contributes to structural strength, particularly flexural strength [54].