Crumb Rubber-Bitumen Interactions: Diffusion of Bitumen into Rubber

A method for reusing discarded tires is to process them into crumb-sized particles for use in flexible pavement applications by incorporating crumb rubber (known as crumb rubber modifier) into asphalt mixtures. Understanding of the interaction between rubber and bitumen is an important requirement. The work reported here is the development of a test method suitable for studying the diffusion of bitumen into rubber by determining the rate of bitumen ingression into the rubber (diffusion coefficient) and the solubility of bitumen (concentration at equilibrium or the solubility coefficient). The test method developed is extension of a method employed in adhesion science. The test method has been used to obtain diffusion data of various types of bitumen and two types of rubber from discarded tires to predict the variation of the concentration of bitumen in commercially produced particles of crumb rubber modifier. No such work has been reported in the literature before.