Regulatory Effect of Polyacrylate Emulsion on the NaCl Attack Behavior of Cement-Based Grouting Materials

Cement-based grouting materials with a high water-to-cement ratio are susceptible to connected pore development, chloride ingress, and mechanical degradation in chloride-bearing groundwater and marine environments. To improve resistance to NaCl attack, this study compared an unmodified cement-based grouting material (NC) with a polyacrylate-emulsion-modified material (PA). Mechanical properties, surface wettability, pore structure, phase assemblage, thermal behavior, functional groups, and microstructure were investigated under different NaCl concentrations (0%, 5%, 10%, and 15%) and immersion durations (28 and 90 d). This study systematically evaluates the coupled evolution of mechanical strength retention, surface wettability, pore structure, chloride-bearing phases, and microstructure in a bulk PA-emulsion-modified high-water-to-cement-ratio grouting material under graded NaCl exposure. The results showed pronounced concentration- and time-dependent effects. Low NaCl concentrations were associated with continued hydration and reaction-product filling, whereas higher concentrations and prolonged exposure led to pore coarsening and strength loss. PA modification improved the mechanical stability of the material in NaCl environments. After 90 d of immersion in 15% NaCl, the compressive and flexural strengths of the PA group were 23.60% and 22.53% higher than those of the NC group, respectively, while the corresponding strength-retention ratios were higher by 9.06 and 10.40 percentage points. Contact-angle and MIP results showed that PA reduced surface wettability and mercury-accessible porosity. After 15% NaCl exposure, the contact angle of the PA group remained 72.5°, compared with 40.1° for the NC group, while the porosity decreased from 38.11% in the NC group to 30.98% in the PA group. XRD, TG-DTG, and FTIR analyses indicated the formation and evolution of Friedel's salt or other chloride-bearing AFm phases after NaCl exposure. Combined with SEM observations, the results indicate that PA mitigates NaCl-induced deterioration through reduced surface wettability, refined pore structure, regulated chloride-bearing product distribution, and improved matrix integrity. Overall, the findings establish a coupled surface-pore-phase-microstructure framework for understanding the enhanced NaCl resistance of PA-modified cement-based grouting materials.