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Optical characterization of temperature‐ and composition‐dependent microstructure in asphalt binders
Author(s) -
RAMM A.,
SAKIB N.,
BHASIN A.,
DOWNER M.C.
Publication year - 2016
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/jmi.12353
Subject(s) - microstructure , materials science , optical microscope , hysteresis , composite material , scattering , characterization (materials science) , volume fraction , asphalt , light scattering , thermal , optics , scanning electron microscope , nanotechnology , condensed matter physics , thermodynamics , physics
Summary We introduce noncontact optical microscopy and optical scattering to characterize asphalt binder microstructure at temperatures ranging from 15°C to 85°C for two compositionally different asphalt binders. We benchmark optical measurements against rheometric measurements of the magnitude of the temperature‐dependent bulk complex shear modulus| G *( T ) | . The main findings are: (1) Elongated (∼5 × 1 μm), striped microstructures (known from AFM studies as ‘bees’ because they resemble bumble‐bees) are resolved optically, found to reside primarily at the surface and do not reappear immediately after a single heating–cooling cycle. (2) Smaller (∼1 μm 2 ) microstructures with no observable internal structure (hereafter dubbed ‘ants’), are found to reside primarily in the bulk, to persist after multiple thermal cycles and to scatter light strongly. Optical scattering from ‘ants’ decreases to zero with heating from 15°C to 65°C, but recovers completely upon cooling back to 15°C, albeit with distinct hysteresis. (3) Rheometric measurements of| G *( T ) |reveal hysteresis that closely resembles that observed by optical scatter, suggesting that thermally driven changes in microstructure volume fraction cause corresponding changes in| G *( T ) | .