Compressed thermal aging and enhanced long-term performance prediction of EPDM flat-bottomed gaskets in shield tunnels

This study investigated the long-term waterproof performance of ethylene propylene diene monomer (EPDM) flat-bottomed gaskets in shield tunnels, with a focus on the effects of compression force. EPDM gaskets play a crucial role in preventing water leakage at tunnel joints; however, their performance deteriorates over time. To investigate this phenomenon, thermal oxidative aging tests were performed on EPDM gaskets under various conditions, assessing temperatures from 295 K to 363 K, aging durations between 24 and 120 hours, and different compression levels (0 mm to 8 mm openings). The analysis involved height measurements, compression testing, and scanning electron microscopy (SEM), with a focus on permanent deformation, compression performance, and surface damage mechanisms. The results demonstrate that compression force significantly accelerates the aging process, leading to increased permanent deformation and a reduction in closure pressure. Aging initially softens the material, reducing pressure, but prolonged aging can increase pressure due to material hardening. Notably, aging results in permanent deformation and reduces the closure pressure by decreasing the amount of compression. SEM analyses revealed that compression altered surface damage mechanisms, exacerbating degradation. To improve the accuracy of long-term performance predictions, this study introduces a novel dual annealing algorithm to enhance the time temperature superposition (TTS) method. This algorithm outperformed traditional quadratic fitting methods, improving the prediction accuracy by 13%. On the basis of the experimental data, a closure pressure prediction model was developed that incorporates the effects of both compression force and aging time. This model provides a reliable method for predicting the long-term waterproof performance of EPDM gaskets under various service conditions.