dc.description.abstract |
Fatigue in asphalt pavements is the incremental damage that asphalt materials suffer as
they receive multiple variable loadings that do not necessarily exceed their yield
strength. Accurate prediction of asphalt fatigue comes in handy in the development of
asphalt materials with high fatigue life as well as in the estimation of fatigue life of
asphaltic pavement materials. This review paper looks at the phenomenological models,
dissipated energy models and fracture mechanics models, which are the three models
that have been used over the years to model asphalt fatigue behaviour in the laboratory.
The phenomenological models relate the numbers of load cycles applied on an asphalt
sample and the resultant asphalt tensile strains. The approach has been found to be
deficient in tracking crack initiation and progression. The dissipated energy models on
the other hand are based on the premise that work is done whenever a material is
loaded. The models have been successfully used to track crack initiation and
propagation and to isolate dissipated energy that goes into fatigue from that which
performs mechanical work. Despite that success, the dissipated energy coefficients have
been noted to change with the mode and frequency of loading as well as the
temperature. The third approach, fracture mechanics models, is based on the premise
that asphaltic materials have inherent discontinuities that form the basis of crack
initiation. Fracture mechanics models predict asphalt fatigue using either linear fracture
mechanics approach or non-linear fracture mechanics approach. The Linear fracture
mechanics method assumes that asphalt will always operate within the linear-elastic
region while non-linear fracture mechanics method assumes that it will at times be
loaded beyond the linear elastic region. The non-linear fracture mechanics approach
comes across as the most promising method as it considers both the inherent materials
discontinuities and the loading regimes that are expected in the field. Both linear and
non-linear fracture mechanics approaches face challenges in finding specimen geometry
that match laboratory sample preparation procedures to field coring shapes. The three
models reviewed are 2-dimensional and do not consider seasonal and diurnal
temperature dynamics in laboratory work. A 3-dimensional model using non-linear
elastic fracture mechanics approach
is suggested as an alternative. |
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