Viscous properties, storage stability and their relationships with microstructure of tire scrap rubber modified asphalt

• The relationship of microstructure with viscous behavior and storage stability is uncovered.
• The flow behavior tends to turn into non-Newtonian fluid with increasing particle size.
• The features of dispersed rubber particles in asphalt are elongated or strip-type.
• Viscosity increase with particle size owing to ratio of length and diameter increasing.

Recycled-polymer modified asphalt has been extensively used in road construction, especially the recycled tire scrap rubber-modified asphalt (TSRMA). However, the main problem during the application of TSRMA is poor storage stability which finally affects the service performance of the pavement. The objective of this work is to evaluate viscous properties, storage stability and morphology of TSRMA and to reveal the relationship of microstructure with rheological behavior and storage stability. With this aim, two different penetration grade asphalts were modified by rubber particles with various mean diameter in a four-paddle mixer at 170 °C. Steady state flow measurements, frequency sweep tests in linear viscoelastic region, storage stability tests as well as fluorescence microscopy were carried out on mixes. Rheological evaluation reveals that the addition of tire scrap rubber to asphalt lead to a significant increase in viscosity at 60 °C, improving rutting or permanent deformation resistance. Furthermore, the increase in particle size causes an enhancement in viscosity and the steady flow behavior tend to turn into non-Newtonian fluid with increasing particle size and temperature. Storage tests presented that the viscosity of samples obtained from the bottom section of a tube are always higher and the difference also becomes significant as the increase of rubber particles size, tending to poor stability. Fluorescence microscopy shows that dispersed particles in asphalt are the elongated features or strip-type and the aspect ratio (length/diameter) increases with particle size. In addition, smaller particle tend to be unobvious in matrix under microscopy view, indicating improved compatibility between rubber and asphalt.

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