Effects of the physico-mechanical properties on water tightness performance of ethylene propylene diene monomer-based tunnel segment gasket

Water tightness is a critical concern for tunnels during both construction and operation. In industry, ethylene propylene diene monomer (EPDM) gaskets are commonly used at tunnel joints to prevent groundwater infiltration. This study investigates the influence of physical and mechanical properties, particularly about filler content, on the waterproofing performance of EPDM segmental gaskets. EPDM compounds with carbon black (CB) and calcium carbonate (CaCO₃) fillers were prepared using an internal mixer and hot press, followed by various physical, mechanical, morphological, and water-tightness tests. The hardness of the compounds ranged from 68 to 71 Shore A, while densities varied from 1.16 to 1.28 ± 0.04 g/cm³, indicating no significant change with different filler amounts. However, tensile strength decreased from 12.7 to 6.3 MPa, and elongation-at-break values dropped from 415 to 294% as filler loading increased. Compression sets rose from 9.7% to 49.6% with higher filler content. Stress-relaxation tests revealed that stress losses increased when filler quantities exceeded 50%, with formulations containing less filler exhibiting superior performance. Water-tightness tests showed that the compound with lower filler content could withstand up to 28 bar of water pressure with a 6 mm offset, while the compound with higher filler content only tolerated 10 bar with a 2 mm offset. Morphological analysis indicated a more homogeneous distribution in compounds with lower levels of fillers. Therefore, EPDM–CB–CaCO₃ compounds with lower filler content may be preferred in tunnel segmental joints, offering improved water tightness and mechanical performance.