PERFORMANCE TESTING OF ASPHALT PAVEMENTS SPECIFYING LOW-TEMPERATURE CRACKING PERFORMANCE FOR HOT-MIX...

PERFORMANCE TESTING OF ASPHALT

PAVEMENTS

SPECIFYING LOW-TEMPERATURE

CRACKING PERFORMANCE FOR HOT-MIX ASPHALT

Tim Clyne, MnDOTJanuary 22,

2012TRB Workshop

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 Neat and Modified, PG 58-40 to 64-22

2 Aggregate Sources Limestone and Granite

2 Air Void Levels 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 EvenEquipment

needed    x

Cost of test setup

    x

Test time requirement

    x

Ease of sample

preparation  x  

Repeatability of results

x    

Loading mode     ?Loading rate     ?Lab vs. Field x    Ability to test

thin lifts in field

  x  

OVERALL CHOICE

DCT vs. SCB

20

21

22

33

34

35

77

200

300

400

500

600

700

800

200 300 400 500 600 700 800

SC

B [J

/m2 ]

DCT [J/m2]

DCT vs SCB for 4% void specimens

PGLT+10C

Pearson's r = 0.41

DCT vs. SCB

SCB = DCT if you remove creep!

0

100

200

300

400

500

600

700

800

900

1000

20-7-18 21-4-18 21-4-28 22-7-24 22-7-34

Gf[J

/m2 ]

Reproducibilty of DCT test

UIUC UMN

Reproducibility

Equipment Cost

Item CostLoading fixtures $3,000 X‐Y Tables to facilitate coring and sawing $1,500 CMOD Extensometer (Epsilon) $1,400 Temperature‐Chamber $20,000 Temperature modules and thermocouples $400 PC for Data Acquisition $1,000 Labview Based Interface Board $700 Coring barrels (qty = 5) $500 Labview Software for Data Acquisition $1,500 Labview Programming $3,000 Dual water cooled masonry saws $10,000 Dual saw system for flat face and notching $7,000 TOTAL $50,000

Phase II Major Findings

Conditioning / Aging None > Long Term Lab = Field

Binder Modification SBS > Elvaloy > PPA

RAP No 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 Clyne651-366-5473tim.clyne@state.mn.

us

www.mndot.gov/mnroad