Numerical investigation of rubber swelling in bitumen

Crumb rubber modified bitumen (CRMB) has been utilized in the asphalt paving industry for decades due to its various benefits. The main mechanisms of bitumen-crumb rubber interaction include rubber particle swelling and chemical degradation. Crumb rubber modifier (CRM) swelling plays a dominant role in controlling the property development of CRMB during the traditional interaction process. To have a better understanding of the swelling behavior of rubber in bitumen, this study developed a finite element model capable to simulate the multiphysics swelling phenomenon consisting of mass diffusion and volume expansion. The effects of various factors including material characteristics and process conditions on the rubber swelling in bitumen were investigated. The results indicate that the coupled diffusion-expansion model can predict the swelling behavior of rubber in bitumen. A good correlation between the simulation results and the previously reported evidences was observed. The effects of bitumen composition, rubber type and size, interaction temperature and time on swelling were successfully demonstrated by using the developed model with dedicated input parameters. With this study as a foundation, the estimated rubber swelling behavior in bitumen can be implemented into suitable micromechanical models to predict the viscoelastic properties of CRMB and consequently to optimize the design and process of bitumen-rubber blends.