The aggregate base layer is a vital part of the flexible pavement system. Unlike rigid
pavements, the base layer provides a substantial contribution to the load bearing capacity in
flexible pavements, and this contribution is complex: stress dependent, moisture dependent,
particle size dependent, and is anisotropic in nature. Furthermore, the response of the
aggregate layer in the pavement structure is defined not only by resilient properties of the
base layer but also by permanent deformation properties of the aggregate layer. Before the
benefits of revolutionary changes in the typical pavement structures, such as deep unbound
aggregate base (UAB) layers under thin hot mix asphalt surfaces and inverted pavement
systems can be justified, an accurate assessment of the UAB is required.
Several researchers identified that in order to properly assess the contribution of the
UAB in the pavement structure, it is necessary to consider not only the vertical modulus but
also the horizontal modulus as this substantially impacts the distribution of stresses within
the pavement structure. Anisotropy, which is defined as the directional dependency of the
material properties in unbound granular bases, is inherent even before the aggregate layer is
subjected to traffic loads due to random arrangement of particles upon compaction.
Distribution of particle contacts is dominated by the geometry of the aggregates as well as
the compaction effort at the time of construction.
Critical pavement responses and therefore performance of flexible pavements are
significantly influenced by the level of anisotropy of aggregate layers. There are several ways
to characterize the level of anisotropy in unbound aggregate systems. Previous research at Texas A&M University suggests functions of fitting parameters in material models (kvalues)
as characterizers of the level of anisotropy. In the realm of geotechnical engineering,
the ratio of the horizontal modulus to vertical modulus is commonly referred to as the level
of anisotropy. When the vertical and horizontal moduli are equal, the system is isotropic, but
when they differ, the system is anisotropic.
This research showed that the level of anisotropy can vary considerably depending on
aggregate mix properties such as gradation, saturation level, and the geometry of the
aggregate particles. Cross anisotropic material properties for several unbound and stabilized
aggregate systems were determined. A comprehensive aggregate database was developed to
identify the contribution level of aggregate features to the directional dependency of material
properties. Finally a new mechanistic performance protocol based on plasticity theory was
developed to ensure the stability of the pavement foundations under traffic loads.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-08-7103 |
| Date | 2009 August 1900 |
| Creators | Salehi Ashtiani, Reza |
| Contributors | Little, Dallas N. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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