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CE 4650 LECT. 5
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Flashcards
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Terms in this set (28)
what are the types of HMA pavement distresses?
ravelling
cracking
rutting
stripping
___ is progressive disintegration of HMA layer from the surface downward as a result of the dislodgment of aggregate particles.
ravelling
what are the causes of ravelling?
- deficient asphalt binder content
- lack of construction compaction (high air voids)
- insufficient fine aggregate matrix
- excessively aged asphalt
why do different asphalts age at different rates?
higher air voids accelerate aging in the mixture
what two groups categorize cracking?
load & non-load associated
what are the four geometric descriptions of cracking?
longitudinal
transverse
polygon (alligator)
block
what are the three mechanic descriptions of cracking?
slippage
shrinkage
reflection
the principal class of load associated cracking is ___ cracking.
fatigue
how does fracture occur in load associated cracking?
it occurs under repeated stress level that is less than the tensile strength of the material
in load assoc. cracking, constant stress (load) tests are suitable for ___ HMA pavements more than 5". A(n) ___ mixture stiffness ___ fatigue life by using ___ penetration and ___ viscosity.
thick
increased
increases
lower
higher
in load assoc. cracking, constant strain (deformation) tests, are suitable for ___ HMA pavements. A(n) ___ stiffness ___ fatigue life by using ___ penetration and ___ viscosity. (*may cause rutting*)
thin
increased
decreases
higher
lower
what is fatigue cracking affected by?
asphalt binder
aggregates
pavement structure
longer fatigue life consists of ___ materials and a ___ stress/strain level, and shorter fatigue life consists of __ materials and a ___ stress/strain level.
flexible
low
stiff
high
what are the two exceptions concerning fatigue behavior?
thick pavements
non-deflecting support layers
the primary class of non-load assoc. cracking is ___ cracking.
low temperature cracking
what is low temperature cracking? and what is it primarily affected by?
it happens when there's rapid chilling at the surface, and stresses/strains are induced by temperature change.
asphalt binder
What improvements can be used for low temperature cracking?
use less stiff asphalt binder
use asphalt binder less prone to aging
construct HMA with proper air voids
what is rutting?
it represents an accumulation of small amounts of deformation that occur each time a load is applied
where can rutting occur?
in the subgrade, base, or asphalt layer
what is rutting in the asphalt layer affected by?
asphalt binder
aggregate
___, a moisture induced damage, is the loss of bond between the aggregates and asphalt binder in the presence of water.
stripping
how does stripping occur?
it begins at the bottom of the HMA layer and moves upward
___ mechanisms are based on aggregate's surface affinity for water.
stripping
in stripping, what can be used to change the surface of the aggregate?
additives from hydrophilic to hydrophobic
in stripping, the cohesive failure occurs within the ___.
AC
what are the mechanisms of stripping?
detachment due to dirty aggregates
displacement due to water
pore pressure due to trapped water & traffic
hydraulic scouring at surface by traffic
what are the causes of stripping?
presence of water
physiochemical aggregate property
asphalt characteristics (absorption of functional groups)
environment/traffic
why does higher viscosity help stripping?
it induces the compaction of aggregates, thus reducing permeable air voids.
**it must be limited to fatigue and low temp. cracking**
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