ANALYSIS OF INHERENT ANISOTROPY IN ASPHALT CONCRETE MIXTURES

Asphalt Concrete mixtures were characterized by one of mechanistically modeling
technique, inherent anisotropy of the material. The performance of AC
mixtures is influenced by the arrangement of aggregates and their associated
air voids. The main objective of this study to analyze aggregate orientation
and evaluates inherent anisotropy in AC mixtures using X-ray CT images
by means of microstructure parameter. There are three AC mixture designs:
coarse graded CMHB Type C, gap graded PFC and fine graded Superpave
Type C AC mixtures. They are prepared with hard limestone aggregate and
compacted with SGC, having a PG 76-22 modified binder.
Digital image processing algorithm is adopted for this study to process X-ray
CT scanned images and effectively separate the connected or overlapping aggregates
using MATLABr 2018b, image processing toolbox. It includes for
both coarse and fine aggregate particles ranging from 1.18 mm to 19 mm. The
aggregate orientation, size and area can be used to define internal structure
parameters (i.e., modified Vector magnitude) to evaluate inherent anisotropy
of AC mixtures.
Aggregates have three dominant average orientations having 20% of the aggregates
has an inclination angle between (-10o-10o), 65% of the aggregates
have an inclination angle between (-45o-45o) and 15% of aggregates have
an inclination angle between (-45o-90o) for three AC mixtures. Small inclination
angle indicates the aggregates lies flat in the horizontal direction that
is perpendicular to the compaction direction. In addition, statistical analysis
was performed for AC mixtures within AC layers. It results, aggregate
orientation varies within AC layers. Variation of aggregates orientation is
performed using Scheffe multi-comparison test.