PERFORMANCE TESTING OF
ASPHALT PAVEMENTS
SPECIFYING LOW-TEMPERATURE
CRACKING PERFORMANCE FOR
HOT-MIX ASPHALT
January 22, 2012
TRB Workshop
Tim Clyne, MnDOT
Presentation Topics





Brief Project History
Phase I Major Findings
Phase II Research
Mixture LTC Specification
The Road Ahead
Affects Ride Quality
Project History
Initial Studies

Low Temperature Cracking of Asphalt Concrete
Pavements
 Introduced
SCB test method
 Developed models for crack spacing and propogation

Low Temperature Cracking Performance at
MnROAD
 Evaluated

field performance of ML and LVR cells
Investigation of the Low-Temperature Fracture
Properties of Three MnROAD Asphalt Mixtures
 PG
58-28, 58-34, 58-40
Pooled Fund Project Phase I
National TAP – August 2003
Pooled Fund Project Phase I



Investigation of Low Temperature Cracking in Asphalt
Pavements National Pooled Fund Study TPF-5(080)
16 Authors from 5 entities!
Large Laboratory Experiment

10 Asphalt Binders


2 Aggregate Sources


Limestone and Granite
2 Air Void Levels


Neat and Modified, PG 58-40 to 64-22
4% and 7%
2 Asphalt Contents

Optimum Design and + 0.5%
Pooled Fund Project Phase I

Field Samples
 13

pavement sections around region
Experimental Modeling
Laboratory Test Procedures

Indirect Tensile Test (IDT)
 Test

protocol AASHTO T 322-03
Semi Circular Bend (SCB)
 Proposed

AASHTO Test
Disk Shaped Compact Tension
 ASTM
D 7313-06
Asphalt Binder Testing




Bending Beam Rheometer
Direct Tension
Double Edge Notched Tension
Dilatometric (Volume Change)
Phase I Major Findings
Fracture Mechanics Approach
Asphalt Mixture Testing

Binder gives a good start, but doesn’t tell whole story
Binder Grade


Modified vs. Unmodified
High temperature grade
Aggregate Type

Granite generally better than Limestone
Air Voids

Lower air voids = slightly better performance
Binder Content

More asphalt = better performance
Phase II Research
Objectives

Develop LTC mix specification
 Test
field additional field samples
 Various mix types, binder grades & modifiers, RAP

Supplementary data from 12 MnROAD mixtures
and 9 binders from 2008
 SCB,
IDT, BBR, DTT, DENT
 Porous, Novachip, 4.75 mm Superpave, WMA, Shingles

Improved modeling capabilities
DCT vs. SCB
Item
DCT
SCB
Even
Equipment needed
x
Cost of test setup
x
Test time
requirement
Ease of sample
preparation
Repeatability of
results
Loading mode
Loading rate
Lab vs. Field
Ability to test thin
lifts in field
OVERALL CHOICE
x
x
x
?
?
x
x
DCT vs. SCB
DCT vs. SCB
DCT vs SCB for 4% void specimens
800
PGLT+10C
35
700
34
SCB [J/m2]
600
20
77
500
33 21
400
22
300
Pearson's r = 0.41
200
200
300
400
500
600
DCT [J/m2]
700
SCB = DCT if you remove creep!
800
Reproducibility
Reproducibilty of DCT test
1000
900
UIUC UMN
800
Gf [J/m2]
700
600
500
400
300
200
100
0
20-7-18
21-4-18
21-4-28
22-7-24
22-7-34
Equipment Cost
Item
Loading fixtures
X‐Y Tables to facilitate coring and sawing
CMOD Extensometer (Epsilon)
Temperature‐Chamber
Temperature modules and thermocouples
PC for Data Acquisition
Labview Based Interface Board
Coring barrels (qty = 5)
Labview Software for Data Acquisition
Labview Programming
Dual water cooled masonry saws
Dual saw system for flat face and notching
TOTAL
Cost
$3,000
$1,500
$1,400
$20,000
$400
$1,000
$700
$500
$1,500
$3,000
$10,000
$7,000
$50,000
Phase II Major Findings

Conditioning / Aging
 None

Binder Modification
 SBS


> Elvaloy > PPA
RAP
 No

> Long Term Lab = Field
RAP > RAP = FRAP
Air Voids not significant
Test Temperature was significant
ILLI-TC Model

Modeling can provide:
 True
performance
prediction (cracking vs.
time)
 Input for maintenance
decisions
 Insight for policy
decisions
LTC Specification
Draft Mixture Specification

Prepare sample during mix design
 Eventually





perform on behind paver samples
Prepare specimens at 7% air voids
Long term condition per AASHTO R 30
Perform 3 replicate tests at PGLT + 10°C
Average Gf > 350 J/m2
Make adjustments if mix fails & retest
Specification Limit
Possible Mixture Adjustments

Binder grade
 Reduce
Low PG (-34 vs -28)
 Different modifier or supplier

Aggregate source
 Granite/taconite
instead of limestone/gravel
 Reduce RAP/RAS content

Aggregate gradation
 Finer
gradation
 Increase binder content
What’s Next?

Use pilot spec on select projects in 2012 or 2013
 Implement

in cooperation with Bituminous Office
HMA Performance Testing project – University of
Minnesota Duluth
 Phase
I – Review of Literature & State Specifications
 Phase II – Lab Testing & Field Validation (begin spring
2012)

Extend to other types of cracking
 Fatigue,
Top Down, Reflective
Thank You!
Tim Clyne
651-366-5473
tim.clyne@state.mn.us
www.mndot.gov/mnroad