Low Temperature Cracking Mixture Specifications

reelingripebeltUrban and Civil

Nov 15, 2013 (3 years and 6 months ago)

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PERFORMANCE TESTING OF
ASPHALT PAVEMENTS


SPECIFYING LOW
-
TEMPERATURE
CRACKING PERFORMANCE FOR
HOT
-
MIX ASPHALT

Tim Clyne, MnDOT

January 22, 2012

TRB 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

Even

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. 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
SCB [J/m
2
]
DCT [J/m
2
]
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
G
f
[J/m
2
]
Reproducibilty of DCT test
UIUC
UMN
Reproducibility

Equipment Cost

Item

Cost

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

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

> 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