Impact of Inorganic Salts on Rheology, Strength, and Microstructure of Excess-Sulfate Phosphogypsum Slag Cement
Excess-sulfate phosphogypsum slag cement (EPSC), offering the potential for large-scale phosphogypsum (PG) utilization, has drawn significant attention. However, its susceptibility to salt erosion in marine/saline environments remains unquantified, hindering engineering applications. This study, the...
Guardado en:
| Autores principales: | , , , , , , , |
|---|---|
| Formato: | Artículo |
| Lenguaje: | inglés |
| Publicado: |
MDPI AG
2025-07-01
|
| Colección: | Buildings |
| Materias: | |
| Acceso en línea: | https://www.mdpi.com/2075-5309/15/13/2348 |
| Etiquetas: |
Agregar Etiqueta
Sin Etiquetas, Sea el primero en etiquetar este registro!
|
| Sumario: | Excess-sulfate phosphogypsum slag cement (EPSC), offering the potential for large-scale phosphogypsum (PG) utilization, has drawn significant attention. However, its susceptibility to salt erosion in marine/saline environments remains unquantified, hindering engineering applications. This study, therefore, systematically investigates the effect of various salts (NaCl, MgCl<sub>2</sub>, KCl, and Na<sub>2</sub>SO<sub>4</sub>) at different concentrations (0.5–1.5%) on the hydration mechanism and performance of EPSC using rheometry, strength tests, and microstructural characterization (XRD/SEM-EDS). The findings reveal that EPSC exhibits low initial yield stress and plastic viscosity, both of which increase over time. The addition of Na<sup>+</sup>, Cl<sup>−</sup>, and SO<sub>4</sub><sup>2−</sup> ions promotes hydration and flocculent structure formation in the EPSC paste, thereby enhancing the yield stress and plastic viscosity. In contrast, Mg<sup>2+</sup> and K<sup>+</sup> ions inhibit the hydration reaction, although Mg<sup>2+</sup> temporarily increases the plastic viscosity by forming Mg(OH)<sub>2</sub> during the initial stage of the reaction. Both Na<sub>2</sub>SO<sub>4</sub> and NaCl improve mechanical properties when their concentrations are within the 0.5–1.0% range; however, excessive amounts (>1%) negatively impact these properties. Significantly, adding 0.5% NaCl significantly improves the mechanical properties of EPSC, achieving a 28-day compressive strength of 51.06 MPa—a 9.5% increase compared to the control group. XRD and SEM-EDX analyses reveal that NaCl enhances pore structure via Friedel’s salt formation, while Na<sub>2</sub>SO<sub>4</sub> promotes the early nucleation of ettringite. However, excessive ettringite formation in the later stages of the hydration reaction due to Na<sub>2</sub>SO<sub>4</sub> may negatively affect compressive strength due to the inherent abundance of SO<sub>4</sub><sup>2−</sup> in the EPSC system. Therefore, attention should be paid to the effect of excessive SO<sub>4</sub><sup>2−</sup> on the system. These results establish salt-type/dosage thresholds for EPSC design, enabling its rational use in coastal infrastructure where salt resistance is critical. |
|---|---|
| ISSN: | 2075-5309 |