Quantification of Shape, Angularity, and
Surface Texture of Base Course Materials
VINCENT C. JANOO
INTRODUCTION
irregularities and the effect of these irregularities
on the performance of base course materials. A
The base course layer is identified as that un-
summary of the methods used by geologists to
bound layer between the surface course (asphalt
describe aggregates has been included. Even
concrete or portland cement concrete) and the
though these methods may not be practical for
subgrade. This layer is sometimes subdivided
everyday engineering work, they have been used
into two parts: the upper layer, called the base,
by researchers for quantifying base course perfor-
and the bottom, the subbase. The base is usually
mance (Barksdale and Itani 1994). A review of
constructed with coarse gravel or crushed stone,
current methods used by engineers, including a
and the subbase with either gravel or sand. Sever-
discussion on the usage of image analysis for de-
al factors affect the performance of these layers.
scribing particle shape and roughness, is also pre-
The common factors usually cited are gradation,
sented.
degree of compaction, amount of fines, moisture
content, and permeability. The shape, angularity,
and surface texture of the aggregates also have a
CHARACTERIZATION OF COARSE
significant effect on the engineering response of
AGGREGATE SHAPE, ANGULARITY,
the layer.
AND SURFACE ROUGHNESS
Quantification of the shape, angularity, and
The description of the aggregate particles can
surface texture of aggregates is difficult but not
be conducted directly using petrological methods
impossible. There are several methods that in-
or by using image analysis. The effect of particle
volve either direct measurement of the aggre-
shape, angularity, and surface texture on the
gates or indirect inference from aggregate proper-
engineering properties can also be inferred.
ties. For example, geologists have developed a
sophisticated system that involves physical mea-
Petrological methods
surements of the aggregates, and engineers have
The shape of the aggregate can be described by
developed visual classification methods for char-
its length, width, thickness, sphericity, round-
acterization, shape, and angularity or index tests
ness, and angularity. The surface texture is diffi-
that use some engineering properties, such as po-
cult to quantify and several visual charts and
rosity, to speculate on the shape, angularity, and
some sophisticated test methods have been pro-
surface texture of aggregates. However, none of
posed. A description of these methods is presented
the index tests developed by engineers make it
below.
possible to quantify separately the shape, angu-
larity, or surface texture. Usually these character-
Description of aggregate shape
istics are lumped together as geometric irregular-
Sedimentary petrologists have described the
ities.
shape of particles using methods developed as
This report reviews test methods currently
long ago as 1930. The description involves mea-
available to quantify the aggregate geometric
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