Ron Glaser Fred Turner, et al.Western Research Institute
P3 2014
Oxidation, Rheology, and Durability
An overview of the primary effects of oxidation on pavements
Oxidation, Rheology, and Durability
• There is a road in Saudi Arabia
• No Traffic, but falling apart
• Comments indicate few had any idea why
• I know exactly why
LinkedIn discussion
• Long time frame failure
• Why?
• Mechanical Fatigue?
• Nope
• Thermal Fatigue? (getting closer)
Durability
• The combination of mechanical property changes in time and
• Thermal Fatigue
• Oxidation is to blame
• (Damn free radicals)
Oxidation, Rheology, and Durability
• As oxidation progresses, failure stress occurs at higher and higher temperatures when cooling at comparable rates
The short answer
• Of course this is only a concern in cold places like Saudi Arabia and Phoenix, Arizona
The short answer
Master Curve changes with oxidation
1000
10000
100000
1000000
10000000
10000000
1E+09
1.0E-03 1.0E+01 1.0E+05 1.0E+09
Com
plex
Mod
ulus
frequency
DSR Master Curves
0 days, 25 Celcius
84 days, 25 Celcius
Master Curve changes with oxidation
1000
10000
100000
1000000
10000000
10000000
1E+09
-40 -20 0 20 40 60
Com
plex
She
ar M
odul
us
Temperature Celcius
1 Rad/s DSR results
0 days, 1 Rad/s
84 days, 1 Rad/s
Relaxation changes with oxidation
1
10
100
1000
10000
100000
1000000
10000000
10000000
1E+09
0 900 1,800 2,700 3,600
Shea
r Mod
ulus
(Pa)
Time (s)
G with oxidation
0 days, 25 Celcius
84 days. 25 Celcius
0 days, -20 Celcius
84 days, -20 Celcius
10 X Fresh Binder
Relaxation changes with oxidation
• Computational footnote
• The relaxation is so slow it looks like a constant
• The convolution integral can be approximated by an equivalent Young’s modulus
• Elastic calculations are adequate in the time frame of thermal stress events
• Other annoying problems
• Aging gradient
• Aging gradient causes unusual stress gradient
• Shift in neutral axis
The short answer
Property Gradients
New Pavement
Old Pavement
Thermal Stress with depth (cold) and traffic load
Permeable Pavement
Tight Pavement
Thermal Stress with depth (cold) and traffic load
Static-Elastic Modeling of Thermal Stresses… Aging and Block Cracking
Static-Elastic Modeling of Thermal Stresses… Aging and Block Cracking
0
1
2
3
4
5
6
7
0 20 40 60 80 100 120
Stre
ss, M
Pa
Block Size, feet
Oxidation
Static-Elastic Modeling of Thermal Stresses… Aging and Block Cracking
AZ1 Distress Data
0
100
200
300
400
500
600
0 50 100 150 200 250 300
Long
itud
inal
, m
Transverse, m
AZ1-1 Total
AZ1 Distress Data
0
20
40
60
80
100
120
0 2 4 6 8 10 12
Crac
king
Rat
e, m
/y
Pavement Age, y
LongitudinalTransverse
AZ1 Distress Data
0
100
200
300
400
500
600
700
800
900
0 2 4 6 8 10 12
Tota
l Cra
ck L
engt
h, m
Time, years
AZ1-1 TotalSingle event longitudinal
AZ1 Distress Data
1
10
100
1000
0 2 4 6 8 10 12
Long
itud
inal
/Tra
nsve
rse
Rati
o, m
/m
Years
AZ1-1
AZ1-2
AZ1-3
AZ1-4
• Better binder and mix characterization
• Pavement Monitoring for timing and treatment
• Better oxidation-mechanical models (FEM)
• Treatments
• Better Binder design
What to do ?
• Focusing on rapid tests- PDSC, SAR-AD, IR, GPC
Better Binder Characterization
• Focusing on small samples from small cores or hammer drill cuttings combined with IR or SAR-AD chemometrics. PDSC may be helpful here as well.
Pavement Monitoring
• Hybrid fundamental modeling of chemistry and physics combined with multivariable empirical fitting appears to be the best route to robust methods that provide full kinetics needed for model computation.
Inputs for FEM models
• We are engaged in extensive public and privately funded studies of rejuvenators for RAP
Treatments
• We are engaged in studies to modify the oxidation chemistry and/or modify the micro structural response to oxidation
Better Binder Design
• Understanding oxidation will aid in technology developments to improve flexible pavement durability
• Flexible pavements will continue to be the material of choice for most roadway applications.
Conclusions
• Federal Highway Administration
• NCHRP
• ARC
• The asphalt research community in general –YOU!
Acknowledgements