PERFORMANCE TESTING OF ASPHALT PAVEMENTS SPECIFYING LOWTEMPERATURE CRACKING

PERFORMANCE TESTING OF ASPHALT PAVEMENTS SPECIFYING LOWTEMPERATURE CRACKING PERFORMANCE FOR HOTMIX ASPHALT January 22, 2012 TRB Workshop Tim Clyne, Mn. DOT

Presentation Topics q q q 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 Mn. ROAD Evaluated field performance of ML and LVR cells Investigation of the Low-Temperature Fracture Properties of Three Mn. ROAD 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

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 Mn. ROAD 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 Equipment needed Cost of test setup 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 DCT SCB Even x x x x x x ? ? x

DCT vs. SCB

DCT vs. SCB = DCT if you remove creep!

Reproducibility

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 > Long Term Lab = Field Binder Modification SBS > Elvaloy > PPA RAP No RAP > RAP = FRAP Air Voids not significant Test Temperature was significant

ILLI-TC 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/m 2 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