Page 56 - Mechanics of Asphalt Microstructure and Micromechanics

Mechanical Proper ties of Constituents 49

It should be noted that the above mechanical properties are referred to as the prop-
erties of bulk materials. For individual granular particles these properties may be
slightly different from those of bulk materials. Nevertheless, it is very difficult to char-
acterize these properties for individual particles.

2.2.2 Morphological Properties
Shape, angularity, and texture are three related concepts in morphology analysis. They
represent spatial variations (irregularities) in different dimension scales. Shape repre-
sents variation in the large dimension; angularity represents variation in the medium
dimension super-imposed on shape; and texture represents variation in the small di-
mension super-imposed on angularity. In the frequency domain, large spatial varia-
tions are related to low frequency and small spatial variations are related to large fre-
quency. Due to the different dimension scales, shape, angularity, and texture affect
material properties in different ways. For example, the local curvature of particles at
the contact is important in load transfer among the skeleton, while the texture at the
interface between aggregates and binder is important for durability. There is a need to
separate the shape, angularity, and texture. One of the most efficient methods is the
Fourier morphological analysis.

Rock for cmax Anisotropy Ratio R c
Fractured sandstone 90° 6.37
Diatomite 90° 3.74
Green River shale 0°, 90° 1.37
Kota sandstone 0° 1.12
Arkansas sandstone 0° 1.10
Sandstone-A (fine grained) 90° 1.75
Sandstone-B (fine grained) 90° 1.62
Sandstone-C (fine grained) 90° 1.15
Sandstone-D (medium grained) 90° 1.34
Sandstone-E (medium grained) 90° 1.23

Siltstone-A 90° 1.94
Siltstone-B 90° 2.30
Quartzitic 90° 2.19
Carbonaceous 90° 2.19
TABLE 2.7 Strength anisotropy ratio R c for different rocks at unconfined compression
(from Ramamurthy, 1993 and Zhang, 2005).