# Preparation and Characterization of Polymer-Modified Sulphoaluminate-Cement-Based Materials
## 3 Results and Discussion
### Characterization
#### 3.3.3 Field Emission Scanning Electron Microscopy (SEM) Analysis  
After 7 days of curing, SEM testing was conducted on both specimens: (a) the sulphoaluminate cement specimen and (b) polymer-modified sulphoaluminate cement specimen, with the results shown in Figure 5. Photos of these specimens are presented in Figure 6. When comparing SEM images under 5000\(\times\) magnification (Figure 5), it can be observed that there was a distinct disparity between the sulphoaluminate cement specimen (a) and polymer-modified sulphoaluminate cement specimen (b). In case of the sulphoaluminate cement specimen (a), loose rigid network structures consisting of numerous needle-shaped ettrinigite crystals, rod-shaped ettrinigite crystals, and reticular gel were formed as hydration products. Additionally, there were obvious micro-cracks and cracks on the surface of cement hydration products. A large amount of ettrinigite was exposed in the spatial structure, and the connection with the hydrated gel material was not tight, resulting in poor structural compactness of the material.  
Figure 4: XRD patterns of polymer modification group and benchmark group.  
On the contrary, in the case of the polymer-modified sulphoaluminate cement specimen, acrylamide formed a network structure via in situ polymerization, which interpenetrated with rigid structures formed by cement hydration, leading to the formation of a dense double network structure. The material exhibited an absence of obvious cracks, and there was a minimal space leakage phenomenon for ettringite, indicating its close connection with gel materials as well as polymers.  
By combining FT-IR, XRD, and SEM analysis, it can be concluded that the in situ polymerization of acrylamide resulted in the formation of a more stable network structure with the cement hydration product. The amide groups of the polymer exhibited strong reactivity, while the hydrolyzed -COOH- groups demonstrated significant adsorption ability and reacted with ions in cement hydration products. The carboxyl group reacted and became fixed, leading to a relatively stable structure formed by polymers and cement hydration products. Compared to the sulphoaluminate cement specimen group, polymer-modified cement-based materials showed improved material properties. The in situ polymerization of acrylamide led to the formation of an organic macromolecular polymer, which intertwined, penetrated, and condensed with the spatial network structure formed by polymers and cement hydration products to create a complex three-dimensional network structure. This polymer wrapped around ettringite surfaces as well as hydrated  
Figure 5: SEM images of the sulphoaluminate cement specimen (**a**) and polymer-modified sulphoaluminate cement specimen (**b**).  
Figure 6: Photos of the sulphoaluminate cement specimen (**a**) and polymer-modified sulphoaluminate cement specimen (**b**).  
gel materials while filling cracks and structural gaps within cement stone. Its network structure exhibited excellent compatibility with cement-based materials due to its adhesion properties through new chemical bonds formed between cement hydration products. Furthermore, this three-dimensional spatial network structure demonstrated high density, compatibility, and adhesion characteristics. This study provides a theoretical foundation for enhancing our knowledge of macroscopic properties.