In this study, phospho-silica (SiO2) particles with different characteristic particle sizes were added as raw materials to manufacture β-hemihydrate gypsum (β-HPG) through high-temperature firing and pulverization. The effect of patterns and mechanisms of nano-SiO2 with different particle sizes and loading levels (0 to 1.5 %) on the hydration and curing processes of semi-hydrated gypsum, as well as the macroscopic properties and microstructure of cured products, were systematically investigated. The phase composition, chemical structure, pyrolysis behavior, and microstructure evolution of hydrated products were comprehensively characterized by combining them with microscopic analysis methods through tests of macroscopic properties. Results show that the addition of nano-SiO2 significantly reduced the standard consistent moisture requirement of β -semi-hydrated gypsum and optimized the rheological properties of the slurry, while effectively improving the physical properties of cured products, reducing moisture absorption and improving water resistance. Among them, nano-SiO2 with a particle size of 30 nm showed an optimal comprehensive modification effect. The novelty of this study lies in the systematic evaluation of particle-size-dependent effects (15 nm-2 μm) of ultrafine SiO2 on the hydration, mechanical performance, and water resistance of β-hemihydrate gypsum, and the elucidation of why 30 nm particles exhibit optimal comprehensive modification. This study provides a systematic theoretical basis and technical support for the high-value utilization of phosphogypsum and the development of high-performance gypsum-based building materials.

Abstract
1. Introduction
2. Experimental Procedure
    2.1. Materials
    2.2. Sample Preparation and Mixing Ratio
    2.3. Test Method
3. Results and Discussion
    3.1. Standard Consistency W/H
    3.2. Compressive strength
    3.3. Softening Coefficient
    3.4. Water Absorption Rate
    3.5. XRD analysis
    3.6. Infrared Testing
    3.7. Thermal Analysis
    3.8. Microstructural Analysis
    3.9. Mechanism Analysis
4. Conclusion
Acknowledgement
References
Author Information

• Wenrong Yuan(Anhui Construction Engineering Road & Port Construction Group Equipment & New Materials Co., Ltd., Hefei 231600, China)
• Qianbao Chen(China Railway Shanghai Engineering Group Materials Industry & Trade Co., Ltd., Shanghai 201906, China)
• Renguo Dou(China Railway Shanghai Engineering Group Materials Industry & Trade Co., Ltd., Shanghai 201906, China) Corresponding author
• Jiacan Lin(Anhui Province Engineering Laboratory of Advanced Building Materials, Anhui Jianzhu University, Hefei 230601, China, Anhui Province Key Laboratory of Advanced Building Materials, Anhui Jianzhu University, Hefei 230601, China)
• Liangting Geng(Anhui Province Engineering Laboratory of Advanced Building Materials, Anhui Jianzhu University, Hefei 230601, China, Anhui Province Key Laboratory of Advanced Building Materials, Anhui Jianzhu University, Hefei 230601, China)
• Xuan Wu(Anhui Province Engineering Laboratory of Advanced Building Materials, Anhui Jianzhu University, Hefei 230601, China, Anhui Province Key Laboratory of Advanced Building Materials, Anhui Jianzhu University, Hefei 230601, China)
• Won-Chun Oh(Department of Advanced Materials Science & Engineering, Hanseo University, Seosan 31962, Republic of Korea) Corresponding author