Encapsulated anti-aging approach on rubber sealing gasket of shield tunnel segment joint: a multiscale comparative experimental study

The performance of Ethylene Propylene Diene Monomer (EPDM) sealing gaskets directly impacts the waterproofing safety and long-term durability of shield tunnels. Mechanistic analysis of rubber thermo-oxidative aging revealed that chain scission reactions of molecular oxygen dominate, while thermal energy primarily acts as a catalytic accelerator by reducing activation energy barriers. To enhance durability, an encapsulated anti-aging technique isolating oxygen was proposed, using a coating layer composed of S06-N-1 polyurethane primer and S04-60 semi-gloss acrylic polyurethane topcoat. Comparative thermo-oxidative aging tests were performed on anti-aging and normal EPDM sealing gaskets to evaluate performance differences. Multiscale characterization, including macroscopic metrics (density, hardness, stress relaxation, compression set), SEM micromorphology analysis, and microscopic property evaluation (DMA, FTIR, TG), was conducted to assess material behavior across hierarchical levels. Service life predictions for both gaskets were conducted based on contact stress relaxation test data. Results showed that the anti-aging EPDM sealing gasket exhibited lower hardness and density, with surface defects (cracks, holes, voids, delamination) occurring later and at smaller dimensions. Antioxidant treatment enhanced molecular stability by reducing functional group changes, resulting in improved physical properties (lower storage modulus , loss modulus , and glass transition temperature). FTIR confirmed chemical structure stability, and TG results demonstrated superior thermal stability and mass retention compared to normal gaskets. The mechanism of the encapsulated anti-aging approach was attributed to its ability to inhibit oxidation reactions, reduce alcohol, ether, and ester formation, and maintain molecular chain flexibility. After 100 years, the anti-aging gaskets retained 17.6 % more contact stress (0.536) than normal gaskets (0.458).