LOW TEMPERATURE CRACKING Tim Clyne, MnDOT Dec 7, 2011 MAAPT

Presentation Topics  Project History  Phase I Major Findings  Phase II Research  Mixture LTC Specification  The Road Ahead

Affects Ride Quality

We’re Making Progress Current spec Initial Superpave

Project History

Initial Project  Low Temperature Cracking of Asphalt Concrete Pavements ( )  Mihai Marasteanu, Xue Li, Timothy Clyne, Vaughan Voller, David Timm, David Newcomb  Introduced SCB test method  Developed two models  Crack spacing  Damage and crack propagation

Phase I Field Performance  Low Temperature Cracking Performance at MnROAD  Brief for 2007 MnROAD Lessons Learned project  Tim Clyne, Ben Worel, Mihai Marasteanu  Evaluated field performance of ML and LVR cells

LVR Superpave Cells  Investigation of the Low-Temperature Fracture Properties of Three MnROAD Asphalt Mixtures  University of Minnesota  Xinjun Li, Adam Zofka, Xue Li, Mihai Marasteanu, Timothy R. Clyne

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 776  16 Authors from 5 entities!  Large Laboratory Experiment  10 Asphalt Binders Neat and Modified, PG to  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

Indirect Tensile Test  Developed during SHRP program  In current MEPDG  Determines Creep Stiffness & Tensile Strength  Test protocol AASHTO T

Creep & Strength Data

Semi Circular Bend  Apply constant Crack Mouth Opening Displacement  Determines Fracture Energy & Fracture Toughness  Proposed AASHTO Test Method

SCB Data

Disk Shaped Compact Tension  Similar to SCB except for geometry and loading rate  Determines Fracture Energy  Test protocol ASTM D

DCT Data

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

Work Plan  Updated literature review  Test additional field samples  Various mix types, binder grades & modifiers, RAP  Develop LTC mix specification  Improved modeling capabilities  Model thermal cycling effects  Validate new mixture specification  Final Report

Supplementary Data  Asphalt Mixture and Binder Fracture Testing for 2008 MnROAD Construction  University of Minnesota  Mihai Marasteanu, Ki Hoon Moon, Mugurel Turos  Tested 12 MnROAD mixtures and 9 binders, reported data  SCB, IDT, BBR, DTT, DENT  Porous, Novachip, 4.75 mm Superpave, WMA, Shingles

DCT vs. SCB ItemDCTSCBEven Equipment 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. Fieldx Ability to test thin lifts in field x OVERALL CHOICE

DCT vs. SCB

Equipment Cost ItemCost Loading 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

Reproducibility

Aging Plays a Role

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 G f > 400 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  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 (proposed fall 2011)  Extend to other types of cracking  Fatigue, Top Down, Reflective

Thank You! Tim Clyne