Aging properties and mechanism of GINA gaskets on immersed tunnel element joint subjected to seawater environment: A multi-scale experimental study

GINA gasket, as the principal waterproofing component of element joints, plays a crucial role in the waterproofing of subsea immersed tunnels. In this study, the GINA gasket seawater aging test was designed and carried out. Subsequently, macroscopic properties tests including Shore A hardness, density and compression reaction force were conducted. Meanwhile, microcosmic appearance tests including scanning electron microscope were carried out. Moreover, molecular structure tests including dynamic mechanics analysis, crosslinking density, infrared spectroscopy, thermogravimetric analysis, and glass transition temperature were performed. Finally, the seawater aging process and mechanism of GINA gaskets were revealed through multi-scale aging properties analysis. The findings from the experimental investigation demonstrate that the Shore A hardness and density of GINA gaskets increased by 9.09 % and 4.94 % after aging, respectively. The compression reaction force initially increases by 11.46 % of the initial value, and then decreases by 26.29 % with aging time. Considering the aging effect, the contact stress of GINA gasket after 100 years is predicted to be 2.32 MPa, which is larger than the designed waterproofing index (0.61 MPa). The seawater aging process of GINA gaskets occurs with crosslinking, oxidation, hydrolysis and chain scission. Additionally, the aging process was divided into three stages, transitioning from increased elasticity to decreased property. The storage modulus, crosslinking density, maximum weight loss rate temperature, and final residual rate all show a trend of initial increasing and then decreasing. During the aging process, particulate matter, cracks, holes, and delamination gradually appear, leading to a degradation in the material properties of GINA gaskets.