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Correlated time‐variation of bulk microstructure and rheology in asphalt binders
Author(s) -
RAMM A.,
SAKIB N.,
BHASIN A.,
DOWNER M.C.
Publication year - 2018
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.12715
Subject(s) - microstructure , dynamic shear rheometer , materials science , isothermal process , rheology , volume fraction , hysteresis , rheometer , composite material , optical microscope , infrared , shear modulus , shear (geology) , thermodynamics , optics , scanning electron microscope , condensed matter physics , physics
Summary We use near‐infrared dark‐field optical microscopy to probe isothermal time variation of the volume fraction of naturally‐occurring, subsurface microstructures in PG 64‐22 asphalt binders at temperature T = 30 ∘ C , following a rapid heating (cooling) increment| Δ T | = 20 ∘ C from initial temperatureT 0 =10 ∘ C( 50 ∘ C ) . We compare these microstructure variations with isothermal time variations of the magnitude|G 30 ∗ ( t )|of the bulk complex shear modulus measured for identical sample conditions with a Dynamic Shear Rheometer. The main findings are: (1) Microstructure volume fraction (inferred from intensity I ( t ) of near‐infrared optical scatter) and|G ∗ ( t )|both continue to change appreciably long after measurable changes of binder temperature cease. Moreover, delayed time variations in I ( t ) and|G ∗ ( t )|(2) correlate closely with each other; (3) evolve on three distinct time scales – several minutes, ∼1 h, >1 day; (4) depend on binder aging; (5) are more pronounced after a cooling step ( Δ T = − 20 ∘ C ) than after a heating step ( Δ T = + 20 ∘ C ); and (6) account for hysteresis in I ( t ) and|G ∗ ( t )|curves observed during heating–cooling cycles.