Effect of anionic polyacrylamide on magnesium phosphate cement grouting materials

To enhance the anti-washout performance of magnesium phosphate cement-based grouting materials (MPCG), this study investigates the incorporation of anionic polyacrylamide (APAM) as a functional additive. The effects of the water-to-binder ratio (0.20–0.30) and APAM dosage (0–1.5 wt% of the combined mass of magnesia and phosphate) on the workability (fluidity, setting time and bleeding rate), mechanical properties (compressive strength, flexural strength and tensile bond strength) and microstructural characteristics of MPCG were systematically investigated. The results indicate that APAM significantly reduces the bleeding rate of the slurry while extending the setting time. It also greatly enhances resistance to water-induced dispersion, with acceptable workability retained. When the APAM content was 0.5 wt% and the water-to-binder ratio was 0.25, the suspension turbidity decreased by 66.3% compared to the control, while the fluidity remained at 250 mm and the setting time was 14 min. At this composition, the 3-day compressive strength, flexural strength, and tensile bond strength reached 21.25 MPa, 5.41 MPa and 2.71 MPa, respectively. Microstructural analysis revealed that APAM retarded the hydration process, altered the crystal morphology and pore structure and facilitated the formation of K-struvite as a hydration product.