Experimental Evaluation of Aging Characteristics of EPDM as a Sealant for Undersea Shield Tunnels

The degradation mechanism of ethylene-propylene-diene monomer (EPDM), when used as a sealant material for shield tunnels, must be known to assess of the service life of sealant gaskets. This paper presents a series of experimental investigations on the degradation performance of EPDM due to aging under artificial seawater and hot air conditions. The mechanical properties of EPDM (such as hardness, tensile strength, and elongation at break) are investigated first. Then, microchemical analyses, such as scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR), are conducted to investigate the variations in the microstructure during aging. The tensile strength and elongation at break under hot air or artificial seawater conditions at different temperatures decrease with aging time, whereas the hardness of EPDM under hot air or artificial seawater conditions increases with aging time. However, at 25C, the hardness decreases gradually with aging time under artificial seawater conditions. The microscopic results show that the microstructure changes can be attributed to the fracture degradation of the molecular chains, oxidation reactions, and the formation of Câ•O/Câ" Oâ" C.