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DCT – How it Affects Pavement

Mix Design

Eshan Dave, Chelsea Hanson, Chelsea Hoplin,

and Ben Helmer

59th Annual Asphalt Contractors’ Workshop

02/19/2015

1

Outline

1. Low temperature cracking and fracture energy

2. Disk-shaped compact tension (DCT) test for

fracture energy

3. Low temperature cracking mix specifications

4. Current and future research

2

Low Temperature Cracking (LTC) ProblemLTC is a major cause of pavement deterioration in regions with

severe winter climates

3

Why do we need specify LTC performance of asphalt mix?

Binder is important, but does not completely control material behavior:– Aggregate/mastic effects on mixture creep/fracture properties

– Effects of RAP, RAS, WMA, and other additives

– Mixture volumetrics and aggregate effects – voids, aggregate size and gradation

– Plant/field aging

– Structural effects of fracture process

Mix testing can provide:– Improved comparisons between cracking performance of asphalt

mixes

– Inputs for performance prediction models

– Input for maintenance decisions

– Insight for policy decisions

4

Cracking of Asphalt Materials

5

Load

Load

CMOD

Crack

formation

CrackingDamage Zone

Onset of damage

δc

σt

Work, Wf

Lo

ad

Quasi-brittle fracture

Softening

Crack Mouth Opening Displacement (CMOD)

Outline

1. Low temperature cracking and fracture energy

2. Disk-shaped compact tension (DCT) test for

fracture energy

3. Low temperature cracking mix specifications

4. Current and future research

6

Disk-Shaped Compact Tension, DCT Test

ASTM D7313-13

Loading Rate:– Crack Mouth Opening Displacement

– CMOD = 1.0-mm/min

Measurements:– CMOD

– Load

7

P

P

CMOD, u

Wf

Crack Mouth Opening Displacement (CMOD), u

Lo

ad

, P

Quasi-brittle fracture

Softening(damage)

Results from Low Temperature Cracking Pooled Fund Study

8

Results for TH371 Sections

9

RPNorth Bound Crack

CountSouth Bound Crack

CountFracture Energy

[J/m2]

6 3 4 453.4417 12 8 356.18

21.5 10 57 330.59

0

50

100

150

200

250

300

350

400

450

500

RP 6 RP 17 RP 21.5

Frac

ture

En

erg

y [J

/m2]

Field Cores (TH371)RP6: Good performing section (2005 construction)RP17/21.5: Poor performing section (2004 construction)

Field Core Testing

10

Field Cracking Performancevs. Fracture Energy

11

0

200

400

600

800

1000

0 10 20 30 40 50 60 70

Fra

ctu

re E

ne

rgy (

J/m

2)

TCTotal (%)

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8Pe

rce

nt

Cra

ck

ing

(M

nD

OT

)

Years in Service

RP 10

RP 5

182

326

0

50

100

150

200

250

300

350

400

450

500

550

Fra

ctu

re E

ne

rgy (

J/m

2)

RP 10 (PP)

RP 5 (GP)

Effects of Mix Composition on Fracture Energy

12

0

200

400

600

800

1000

1200

PG 58-28 PG 64-28 PG 58-34 PG 70-34

Fra

ctu

re E

ne

rgy (

J/m

2)

0

100

200

300

400

500

4.3% 4.5% 4.7% 4.9% 5.1% 5.3% 5.5%

Fra

ctu

re E

ne

rgy (

J/m

2)

Asphalt Binder (%)

0

200

400

600

800

1000

1200

12.0% 14.0% 16.0% 18.0% 20.0%

Fra

ctu

re E

ne

rgy (

J/m

2)

VMA (%)

0

100

200

300

400

500

7.0 8.0 9.0 10.0 11.0

Fra

ctu

re E

ne

rgy (

J/m

2)

Adj. Asphalt Film Thickness (micron)

Outline

1. Low temperature cracking and fracture energy

2. Disk-shaped compact tension (DCT) test for

fracture energy

3. Low temperature cracking mix specifications

4. Current and future research

13

LTC Performance Specifications

Based on traffic levels

14

Limits

Project Criticality / Traffic Level

High

(> 30M ESALs)

Medium

(10 – 30M ESALs)

Low

(< 10M ESALs)

DCT Fracture Energy

(J/m2)690 460 400

IlliTC Cracking

Prediction (m/km)< 4 < 64 Not required

Marasteanu et al., 2012

15

Refinement and Implementationof Specification

Implementation of

Performance-based

Specification (MnDOT)

Refinement Efforts (Spec. finalization,

conditioning process, training etc.)

Determine sensitivity of fracture energy to

thermal cracking performance

DCT Spec. Implementation

DCT based specifications are currently being implemented:

– Minnesota DOT (discussed here)

– Wisconsin DOT (next presentation)

– Chicago DOT (ASTM version)

– Illinois Tollways (ASTM version)

16

ASTM D7313-13 MnDOT Modified WisDOT Modified

Specimen Prep Minor Differences

Test Equipment No Difference

Specimen

Conditioning: AgingN/A AASHTO R30 (oven aging)

Specimen

Conditioning:

Temperature

8 - 16 hr @ test temp.

± 0.2ºCDiscussed later

Initial Cond.: 8 - 16 hr @

-12ºC±5ºC

Final Cond.: 1.5±0.5 hr @

test temp.

Data Analysis No Difference

Test Temperature

Recommendation:

PGLT + 10ºC

No requirement

98% Reliability Low

Temperature + 10ºC

(Use LTPPBind 3.1 software)

10±0.5ºC warmer than

WisDOT plan specified lower

temperature grade.

MnDOT DCT Specifications

“MnDOT Modified”

– Current version used by MnDOT

GOAL: Improve ease, practicality and repeatability of

test procedure

Several changes/additions to ASTM specification

Revisions made to temperature conditioning

of specimens:

– Specimens must reach test temperature in no faster than

0.75 hours, but within 1.5 hours.

– Specimens must stay in conditioning chamber for a minimum

of 2 hours before testing.

– All testing must be finished within 5 hours of initial placement

into conditioning chamber

17

Temperature Conditioning and InterlabVariability Studies

18

Field sampled material (I-94)

Samples tested at MnDOT and UMD

Temperature conditioning: Room to Chamber is

comparable to 1/3 deg. C/minute

Interlab differences:

– Fracture Energy: 2.4 – 8.1%

– Peak Load: 0.7 – 4.6%

Outline

1. Low temperature cracking and fracture energy

2. Disk-shaped compact tension (DCT) test for

fracture energy

3. Low temperature cracking mix specifications

4. Current and future research

19

Projects

Variety of climates,

binders, construction

– D2 – TH 310, FDR +

Overlay, PG 58-34

– D3 – TH 371,

Reconstruct, PG 64-34

– Metro – TH 10, Mill &

Overlay, PG 64-28

– D6 – TH 56, SFDR +

Overlay, PG 58-34

– D6 – TH 69, Mill &

Overlay, PG 58-28

20

21

334292 310

195

318

257

317

627

444

324

549 543

470

0

100

200

300

400

500

600

700F

rac

ture

En

erg

y (

J/m

2)

22

334292 310

195

318

257

317

627

444

324

549 543

470

0

100

200

300

400

500

600

700F

rac

ture

En

erg

y (

J/m

2)

TH 56 – SPWEA340C, tested @ -24CNote production decrease relative to mix design;Adjustment made: 0.1% additional binder.

23

334292 310

195

318

257

317

627

444

324

549 543

470

0

100

200

300

400

500

600

700F

rac

ture

En

erg

y (

J/m

2)

TH 310 – SPWEB340C, tested @ -30CNote low value in first mix design;Adjustment made: eliminate 20% RAP, stockpile feeds adjusted.

24

334292 310

195

318

257

317

627

444

324

549 543

470

0

100

200

300

400

500

600

700F

rac

ture

En

erg

y (

J/m

2)

TH 10 – SPWEB440E, tested @ -24CNo adjustment made;Note drop in fracture energy at mix production.

25

334292 310

195

318

257

317

627

444

324

549 543

470

0

100

200

300

400

500

600

700F

rac

ture

En

erg

y (

J/m

2)

TH 69 – SPWEA440F, tested @ -24CNo mix design data;Adjustment made: reduce RAP from 30% to 20%, stockpile feeds adjusted.

26

334292 310

195

318

257

317

627

444

324

549 543

470

0

100

200

300

400

500

600

700F

rac

ture

En

erg

y (

J/m

2)

TH 371 – SPWEB340B, tested @ -18CNo adjustment required;Note drop in fracture energy at mix production;

Summary

2 projects (TH10 and TH371) passed at mix design

– Both Level 4 designs (Higher amounts of crushed agg.)

– Both polymer modified

3 failed at mix design

– TH 69, 58-28, 30% RAP, 324 J/m2

Adj. 58-34, 20% RAP, 549 J/m2

– TH 56, 58-34, 20 % RAP, 292 J/m2

Adj. + 0.1% new AC, 310 J/m2

– TH 310, 58-34, 20% RAP, 257 J/m2

Adj. 58-34, 0% RAP, 317 J/m2

Old oil in mix design, 195 J/m2

Need to make sure that same materials are used for

mix design and production (esp. binder)

27

• Training of lab staff

• Round robin (inter-laboratory) repeatability study

• Samples collected this fall, with testing to start this

spring

• Participating labs include AET, Braun, MnDOT,

and UMD

28

On-going Work

• Study analyzing source of drop in fracture energy from mix design to production and placement

• Samples collected from 8 projects throughout the state

29

On-going Work

Future Efforts

• State Transportation Innovation Councils (STIC) project

• FHWA program through TERRA

• Review state of practice and current studies being

undertaken by neighboring states

• Performance reviews of pilot implementation sections

of 2013 and for samples from 2014 construction

season

• Database of DCT results

• Continued implementation efforts

• Additional pilot projects

• Training of lab staff

• Workshops and webinars

30

Summary In light of newer asphalt technologies (high recycling,

WMA, additives) performance based specifications

are becoming necessary

– Low risk on agencies, high innovation from industry

Fracture energy has and is continuing to show high

potential as cracking performance indicator

Stay tuned:

– 2015: Improve breadth of DCT result

database

– 2016: Continue with pilot projects

– 2017: Goal of implementation

Plan to target wear courses

New and re-construction

Possibly on thick overlays

Stand-alone testing equipment

is available 31

Thank you for your attention

Questions?

Acknowledgments:

– Bill Buttlar

– Dave Van Deusen

– Shongtao Dai

– Joe Voels

– Luke Johanneck

32

Sponsoring agencies for present work:US Department of Transportation (FHWA)

Minnesota Department of TransportationTERRA

Contact:Eshan V. Daveeshan.dave@unh.edu603-862-5268

Chelsea HansonChelsea.hanson@state.mn.us651-366-5482

Appendix

33

Objective: Determine the allowable variability

in fracture energy for purposes of job specification

– Req. fracture energy = 400 J/m2 (if actual is

375 J/m2 is it too low?)

Approach:

– Simulate performance of various fracture energies

using IlliTC and different combinations of:

Minnesota climates

Asphalt mixtures

Pavement structures

Use of IlliTC to Determine Sensitivity of Thermal Cracking to Fracture Energy

34

Simulation Variables

35

Asphalt Mix PG28R PG34R PG34

MnROAD Cell Cell 21 Cell 22 Cell 35

Virgin Binder

GradePG 58-28 PG 58-34 PG 58-34

Total Percent AC 5.2% 5.2% 5.6%

Recycled Binder as

Percent of Total AC28% 28% 0%

Amount of RAP 30% 30% 0%

Fracture Energy (J/m2)

Pavement Thickness (in.)

Climate

Asphalt Mix PG28R

Cold

4

300 350 375 400 425 450

6 8

Intermediate Warm

Results from Sensitivity Study

Variation of fracture energy by 25 J/m2 might be

sufficient in changing the thermal cracking performance

of the pavement

36

Asphalt Mix PG28R PG28R PG34R PG34

Climate Warm Case-1 Warm Case-2 Intermediate Cold

Pavement Thickness (cm) 10 15 20 15

Fracture Energies (J/m2) Corresponding to Thermal Cracking Performance Levels

No Damage (ND) No data No data No data ≥425

Damaged (D) 450 425-450 375-450 300-375

Cracked (C) ≤425 ≤400 ≤350 No data

MnDOT 2013 Implementation Project

Contractor provide samples at mix design

– TSR pucks, 7% AV, +/- 0.5%

UMD perform DCT tests

– If mix passes, approve for paving

Passing value of Gf > 400 J/m2

If mix fails, adjust mix & try again

– MnDOT paid for difference in

cost (D-I funds)

– Adjusted mix was used for paving

a section of project

Testing is also conducted on

production mixes

37

Possible Mixture Adjustments

Binder grade

– Reduce low PG (-34 vs -28)

Different modifier or supplier

Aggregate source and crushing

– Granite/taconite instead of

limestone

Aggregate Gradation

– Finer gradation

– Increase binder content

38