uniaxial testing on asphalt wafers poster
TRANSCRIPT
The Fatigue Performance of Asphalt Under Uniaxial Tensile Cyclic Loading
Fidez Oreta and Catherine Mills
Supervisors: Dr. Doug Wilson and Dr. Tam Larkin Project Number: 124
Group: Transport Infrastructure
Results A total of 44 samples were tested. One way analysis of variance was used to
compare the following fatigue characteristics:
Introduction Many structural aspects of asphalt pavements, especially
when utilising New Zealand aggregates, are not fully
understood. Fatigue cracking is a major distress mode in
asphalt and it is necessary to gain a better understanding
of fatigue behaviour before asphalt pavements become
widely implemented in New Zealand.
Crack Development Photographs were used to examine fatigue cracking in the
samples. The following crack behavior was observed:
Conclusions • AC20 60/70 mix had the longest fatigue life.
• AC14 60/70 had the largest strain at failure and shortest
fatigue life.
• 20mm nominal aggregate size had longer fatigue lives
compared to 14mm.
• No difference was observed between the fatigue life of
polymer modified binder and conventional 60/70 binder.
• Stiffness is constant at low stresses.
• Using crack initiation as the failure point produced shorter
fatigue lives compared to the 50% reduction in stiffness.
Tensile
Str
ain
Cycle
s
Cycle
s
Nominal Aggregate Size (mm)
Cycle
s
Binder Type
Two methods were used to determine fatigue life:
1) 50% reduction in initial stiffness;
2) Crack initiation.
The two methods produced similar trends. Results using the reduction in
stiffness method are shown above. Graphical techniques for identifying
failure are illustrated below.
• Fatigue life;
• Effect of nominal aggregate size;
• Strain at failure;
• Effect of polymer modified binder. 1. Crack development near elongated aggregates
2. Crack propagation along surfaces of large aggregate
3. Cracking through aggregate cleavage planes
Before testing During testing
Before testing During testing
Before testing During testing
Objectives • Explore the feasibility of cyclic uniaxial tensile testing as
a fatigue testing method.
• Compare fatigue behaviour between four asphalt mixes.
Methodology
A 60/70 binder and a polymer-
modified binder were mixed
with 20 and 14mm nominal
aggregate gradations.
Slabs were compacted using a kneading
compactor and cut with a diamond saw.
Samples were epoxied to
steel plates and stacked
on a jig to cure.
Samples were bolted to
the MTS via a pin
connection and a camera
was used to take photos of
the samples cracking.
0
50
100
150
200
0 1800 3600 5400 7200
Str
ess
(k
Pa
)
Number of Cycles
74 - 10 kPa (2Hz) 154 - 10 kPa (2Hz)
164 - 10 kPa (2Hz)
Samples were subject to a three-stage
controlled stress loading regime until
they fractured into two pieces.
From To Peak Trough
0 1800 10 74
1801 5400 10 154
5401 failure 10 164
Cyclic Range Stress (kPa)
Mix Variables AC14 AC20
60/70 AC146070 AC206070
DHD AC14DHD AC20DHD
DEPARTMENT OF CIVIL AND
ENVIRONMENTAL ENGINEERING
THE UNIVERSITY OF AUCKLAND
FACULTY OF ENGINEERING