History dependence of water diffusion in asphalt binders

Despite the importance of hysteresis of water diffusion in polymeric materials, only limited literature is available on this subject. The FT-IR-ATR spectroscopy technique was used to investigate the effect of cycling moisture boundary conditions on the diffusivity of moisture of three asphalt binders. Each sample passed through three hydration cycles and two dehydration cycles. The existence of hysteresis of moisture diffusivity in asphalt binders is validated. The increase in moisture diffusivity is primarily attributed to the change in microstructure of the asphalt binder after being exposed to moisture. This is supported by atomic force microscope images of asphalt binder before and after exposure to water. Evidence to an increase of water trapped in the form of vapour even after dehydration was observed, and this may also contribute to the increase in diffusivity. This topic is still under investigation by this research group.