Hydration and Microstructure Evolution of Acrylamide-Modified Tunnel Slag Mortar Under Various Curing Conditions

The preparation of tunnel slag mortar (TSM) represents a sustainable strategy to enhance the resource utilization efficiency of tunnel slag. Toughening TSM via the in situ polymerization of acrylamide (AM) is effective in mitigating the risk of cracking during service. However, the limited understanding of the temperature and humidity sensitivity of AM-modified TSM poses challenges in establishing optimal curing regimes. In this study, low-field nuclear magnetic resonance (LF-NMR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to systematically investigate the evolution of hydration kinetics, hydration products, pore structure, and micromorphology of AM-modified TSM under various curing conditions. The results indicate that AM incorporation retards early hydration but does not alter the types of hydration products. Increasing the curing temperature can alleviate this adverse effect, and a 3% AM dosage exhibits a stronger hydration-promoting effect at 40–60 °C. The efficacy of AM on pore refinement is highly environment-dependent: a 3% dosage yields optimal pore refinement at 20 °C, whereas high temperatures induce pore coarsening. Furthermore, compared to conventional TSM, AM-modified TSM exhibits higher sensitivity to curing humidity, underscoring that adequate moisture is critical for optimizing its pore structure.