Prediction of Aging Characteristics in Natural Rubber Bearings Used in Bridges

Rubber bearings used in bridges are exposed to the air and easily attacked by oxygen, even at room temperature, and heat, light, dynamic strain, and liquids. It is usually known that the degradation of polymers often occurs as a nonuniform or heterogeneous process because aged rubber will prevent deterioration from progressing into the inner rubber bearing. Thermal oxidation tests were carried out on natural rubber (NR) blocks at different elevated temperatures using the modulus profiling method. The development of the heterogeneous property profiles in aged rubber bearings is revealed. The NR blocks display the features of a diffusion-limited oxidation and the properties change most significantly at the surface. However, in the interior region beyond the critical depth, NR does not change. The property variations at the block surface and the interior are quantitatively examined, based on which, the relations are clarified among property variation, temperature, aging time, and relative position inside a rubber bearing. An appropriate aging model is established, which is able to predict the aging characteristics in NR bearing.