Toughness properties of polyvinyl alcohol powder-modified magnesium potassium phosphate cement

Magnesium potassium phosphate cement (MKPC) is widely used in civil engineering repairs owing to its rapid setting and high early strength. However, its application is constrained by inherent brittleness and low impact resistance. This study investigated the toughening effects and mechanisms of a non-fibrous, water-soluble polyvinyl alcohol (PVA) powder on MKPC, leveraging the film-forming properties of PVA. The influence of PVA content (1%, 2%, 3%, 4%, 5%) was assessed through setting time, tensile-compressive ratio, flexural toughness, and impact resistance. Results showed that 2–3% PVA provided the most effective toughening: at 2% PVA, the 7-day impact energy increased by 66.6% (relative to PVA-0), whereas at 3% PVA, the 7-day tensile–compressive ratio and flexural toughness factor increased by 30.5% and 19.8%, respectively. Microstructural analysis indicated that PVA increased total porosity and optimized pore structure by reducing large and small pores while increasing medium pores, thereby promoting stress dispersion. XRD confirmed that PVA did not alter the main hydration product (MgKPO₄·6H₂O), while SEM and EDS mapping revealed that PVA formed continuous films. The toughening mechanism was attributed to PVA's synergistic actions, which include enhancing interfacial adhesion and crack resistance via film formation and pore-filling, absorbing energy through film deformation, and dissipating energy through pore compaction and fracture. This study proposed a "film interfacial encapsulation and pore deformation energy dissipation" mechanism, supporting PVA’s application in toughening MKPC.