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