Temperature-dependent bitumen softening studied by NMR

Abstract

The study of the temperature-dependent bitumen softening by thenuclear magnetic resonance (NMR) techniques of proton NMR line shape andspin-lattice relaxation is presented. The increased molecular translationaland rotational mobility on bitumen softening results in a dynamictransition of the NMR line shape from a static rigid-lattice spectrum to amotionally narrowed spectrum that is accompanied by a drastic decrease ofthe spectral width by a factor of 300. In the type of bitumen investigated,which is of high industrial importance for the road construction industry,the majority of the line width change (and thus the softening) happens inthe temperature interval between + 40 °C and -20 °C (~310-250 K). This is exactly the range of the summer-winter atmospherictemperature variations in most geographical regions on Earth. Thetemperature-dependent curves of the full width at half height of the protonNMR spectrum (that we propose to call the bitumen `NMR melting curves')represent an accurate analytical tool for the study of the bitumensoftening process. Due to its simplicity, high accuracy and ease ofimplementation in industrial laboratories, the method shows the potentialto become a standard analytical tool for the bitumen basic research. It mayalso serve as an on-line bitumen quality control method in industrialprocesses, like the asphalt covering of roads and highways.