Mechanically robust super-absorptive hydrogels for grouting treatment of water inrush via a dual fixing-sliding effect of physical entanglements

• A physical entanglement strategy simultaneously enhances hydrogel swelling capacity and mechanical strength. • Rate-dependent fixing-sliding effect of physical entanglement is revealed. • Entanglement-reinforced hydrogels exhibit superior swelling ratios (∼1663 g/g to ∼618 g/g) and improved mechanical strengths (> ∼7 MPa). • 24 g of hydrogel blocks 1 L/min water flow in 5 minutes, demonstrating critical efficacy for water inrush disasters. Water inrush is a major disaster in civil infrastructures extensively located in geologically unstable and water-rich regions, which demand grouting hydrogels to expansively block geological fractures and to be robust against the impact of rushing water. However, the traditional strategy of reinforcing hydrogels via fixed crosslinking sites inevitably interferes with their swelling properties. In this study, physical entanglement is employed as a reinforcing strategy to prepare a mechanically robust super-absorptive hydrogel, aiming to address this challenging dilemma. A rate-dependent fixing-sliding effect is revealed to exist in physical entanglement-reinforced hydrogels by comprehensively analyzing the rheological, mechanical, and swelling properties. Under high-velocity external forces such as water stream impact, polymer chains are frozen to fix the physical entanglement sites, thereby strengthening the hydrogels; during relatively slower water absorption, polymer chains are movable to allow sliding, achieving a higher swelling ratio. Accordingly, the hydrogels exhibit robust mechanical compressive strength (> ∼7 MPa) and a remarkable swelling ratio (∼1663 g/g to 618 g/g), which can effectively plug gushing water (1 L/min) with only usage of 24 g in the model water inrush test device. This work presents a useful strategy to design hydrogels combining seemingly incompatible swelling and mechanical properties, providing insightful guidance for developing not only grouting hydrogels but also a wide range of robust yet super-absorptive polymer-based materials.