Self-sealing and -healing performance and environmental adaptability of concrete cracks using superabsorbent polymers

Concrete structures often suffer from cracking under environmental stress, compromising durability and service life. Superabsorbent polymers (SAPs) have emerged as promising additives for autonomous crack sealing, yet their long-term performance under cyclic exposure remains unclear. This study investigates the self-sealing performance and durability of concrete modified with two SAP types (SAP1 and SAP2) subjected to freeze-thaw and dry-wet cycles. Crack width, permeability, and mass loss were monitored to assess sealing performance. SAP1 showed better early-stage sealing due to its high swelling capacity and gel formation but suffered from increased permeability and material loss after cycling. In contrast, SAP2 exhibited lower initial sealing but better long-term stability. SEM-EDS analysis revealed that SAP1 formed hydration-rich, amorphous gels, whereas SAP2 developed compact, carbonate-rich layers. These differences may be interpreted thermodynamically: SAP1 likely forms metastable gels prone to disruption, while SAP2 favors stable crystalline phases with stronger interfacial retention. A novel “Mass Sealing Efficiency” (E_m) metric was proposed to integrate permeability and material loss into a unified performance indicator. These findings reveal critical trade-offs between sealing intensity and environmental resilience, offering practical insights for the tailored design of SAP-based self-healing systems in concrete infrastructure.