Structural change of bitumen in the recycling process by using rheology and NMR

The mechanical properties of bitumen are the result of the chemical composition and arrangement of the molecular structures (phases present). The loss of elasticity of the bitumen with aging is mainly due to the oxidation of aromatic compounds and resins. This work deals with the recycling process of bitumen, by following the changes in the bitumen structure. Fresh, aged, and doped recycled bitumens were investigated. Rheology and nuclear magnetic resonance were used to monitor the differences between the bitumens and the role of the additives. As a novel approach to the understanding of the colloidal nature of the bitumen, an inverse Laplace transform of the NMR spin-echo decay (T-2) was applied. The results indicate that the rejuvenating additives have little influence on the solid-liquid transition. However, they help to restructure the aged bitumen, thus facilitating workability at a lower temperature. Two-dimensional maps of the structure distributions were reconstructed.