## 3 Results and Discussion
### Chemical Activation Process Test Results
#### 3.2.3 Pore Structure, XRD, and SEM Analysis  
The pore size distribution reflected the dimensions of the pores within the material structure and served as a crucial indicator for evaluating the characteristics of cement-based hardened slurry. According to research conducted by the Chinese scholar [PERSON] [60], pores were categorized into four levels: harmless pores (\(<\)20 nm), less harmful pores (20 nm to 50 nm), harmful pores (50 nm to 200 nm), and more harmful pores (\(>\)200 nm). Based on this classification and the mercury injection test data from the mortar specimen, the calculated pore size distribution curve is depicted in Figure 20.  
Figure 20: Pore size distribution curves of samples at different ages. As the age increases, the number of harmful and more harmful pores in HS-4 decreased significantly. Compared to the 7-day age, at 28 days, the proportion of less harmful pores in the pore structure of HS-4 increased by 9%, while the distribution proportion of harmless pores also increased slowly by 3%. At 60 days of age, the proportion of harmful pores decreased to 7%, whereas the proportion of harmless pores increased rapidly to 12%. Overall, as time progressed, the pore structure of HS-4 became increasingly dense and optimized, indicating that the internal structure of the material was improving, porosity was being reduced, and the stability of the material had been significantly enhanced. Comparing the intensities of the physical phase diffraction peaks of HS-4 (6% CaO + 2% CaCO3 + 2% CaCO4 2H2O) with those of the H-1 (cement + 30% volcanic rock powder) test group (Figure 21), the main manifestations were the changes in the intensities of Ca(OH)2, AFt, and C3S/C2S diffraction peaks. Figure 21 shows that for HS-4 (7 days), the diffraction peaks of Ca(OH)2 near 20 = 18\({}^{\circ}\) and 34\({}^{\circ}\) had very high intensities, and by 28 days, despite the enhancement of the peaks of Ca(OH)2, their overall intensities were still lower than that of the H-1 sample. In addition, the diffraction peaks of AFt showed an increasing trend, indicating that the addition of chemical reagents accelerated the secondary hydration process and the consumption of Ca(OH)2, which promoted the enhancement of AFt generation. The diffraction peaks of C3S/C2S were significantly reduced in HS-4 (28 days), which further verified that the chemical reagents not only accelerated the rate of Ca(OH)2 consumption, but also accelerated the conversion of C3S/C2S to C-S-H in the gel conversion process. In contrast, although Ca(OH)2 increased in the H-1 sample without chemical reagent intervention at 28 days, the increase in the AFt diffraction peak was not significant, indicating that the secondary hydration reaction was more sluggish and the transformation rate of C3S/C2S to C-S-H was slower than that in the HS-4 sample. Figure 22 shows the morphology of the hydration products of H-1 (cement + 30% volcanic rock powder) and HS-4 (6% CaO + 2% CaCO3 + 2% CaCO4 2H2O) at 7 and 28 days. Figure 21: XRD patterns of H-1 (**a,b**) and HS-4 (**c,d**) at 7 d and 28 d.  
Combined with the crystal composition and content changes shown in the XRD pattern, we observed the morphological characteristics of the hydration products in the SEM images, which mainly included flake, flocculent, or fibrous CSH gel, hexagonal plate or flake Ca(OH)\({}_{2}\) crystals, and needle-shaped or columnar AF crystals. By evaluating the production amount and structural density of hydration products, it was found that the CSH gel network of HS-4 was more complete at 28 days, the AFt crystals were thicker, the structural density was improved, and the overall structure was more complete. This change in microstructure is reflected in the improvement of the mechanical properties of the material at the macro level. Specifically, at the age of 28 days, the flexural strength of HS-4 reached 6.8 MPa, which was 23.6% higher than H-1's 5.5 MPa, while its compressive strength was 36.0 MPa, which was higher than H-1's 30.1 MPa, an increase of 19.6%.