ABSTRACT
EPDM (Ethylene Propylene Diene Monomer) rubber gaskets were widely used as the waterproofing component at the joints of shield tunnels that are expected to serve for decades. However, the alterations in surface roughness of EPDM rubber gaskets due to ageing introduce an aspect that is not yet comprehensively understood in terms of its implications for sealant performance. In this study, a series of AFM (Atomic Force Microscope) tests were conducted on 6 groups of squared EPDM thin slices, each of which had been oxidatively aged to different levels before the tests. The analysis encompassed the determination of both the fractal dimension and the RMS (Root Mean Square)-slope of the surfaces. Supplementary tests utilizing Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) were performed to elucidate the mechanisms governing surface roughening. The results show that the mean value of fractal dimension of EPDM specimens first decreased to 2.16 after 11.2-hour ageing and then increased to 2.42 after 39h-ageing. The evolution of RMS-slope exhibited similar tendencies, escalating from 0.55 to 1.16. Finally, a theoretical model to prognosticate the long-term waterproof capacity based on the percolation theory was proposed, which explicitly incorporated the impact of surface roughness. The outcomes underscore the considerable hydraulic deterioration resulting from surface roughening over a prolonged duration, ultimately leading to the complete loss of waterproof capacity in large opening scenarios.
