Permeable Friction Course (PFC) Mixtures are Different!

36th Rocky Mountain Asphalt Conference and Equipment Show

1st Annual Flexible Pavement Research Symposium

Amy Epps Martin, Allex E. Alvarez

February 18, 2009

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OUTLINE

1. Introduction

2. Current Research

3. Experimental Design and Results

4. Summary and Recommendations - Future

Work

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1. Introduction1. Introduction

Dense-graded mixtures Dense-graded mixtures VsVs Porous friction course mixtures Porous friction course mixtures (PFC or OGFC) as (PFC or OGFC) as surface coursessurface courses

Kringos et al., 2007

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PFC AdvantagesPFC Advantages• Reduce splash and sprayReduce splash and spray• Improve skid resistance in wet conditionsImprove skid resistance in wet conditions• Decrease noiseDecrease noise• Produce cleaner runoffProduce cleaner runoff

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2. Current Research2. Current Research

Improve TxDOT Improve TxDOT PFC mix design procedure and PFC mix design procedure and

recommend construction practices recommend construction practices based on: based on: Volumetrics Durability Drainability Densification Effects

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3. Experimental Design and Test Results3. Experimental Design and Test Results

Selected MixturesSelected Mixtures

Mixture Asphalt TypeOAC (%)

AggregateOther

Materials

I-35

PG 76-22

6.1 Sandstone, Limestone

Lime (1%), Fibers (0.3%)

US-59Y 5.8 Limestone

IH-30 6.6 Sandstone

US‑83 6.4 Limestone

IH-20 6.5 Limestone

US-59 5.9 Granite, Limestone

US-281Asphalt Rubber

8.1 Sandstone, Limestone

NoneUS-290 8.3 Sandstone

US-288 8.0 Granite, Limestone

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3.1 Volumetrics3.1 Volumetrics

Gmm: theoretical max. specific gravity of the mixture

Gmb: bulk specific gravity of the compacted PFC mixture

(%)100*1

mm

mb

G

GContentAVTotal

a. Total AV Content

Current practice:Current practice:

• Total AV content (or corresponding density)

• Vacuum method or dimensional analysis for Gmb

• Measured Gmm

Theoretical Max. Specific Gravity, Theoretical Max. Specific Gravity, GGmmmm

mixture at the design asphalt range (6 to 10%)

mixwmixpycwpyc

mixmm WWW

WGMeasured

,,

Method 1-measured Gmm

Method 2-calculated Gmm

b

b

mm

bse

G

P

G

PG

100100

b

b

se

bmm

G

P

G

PGCalculated

100

100

ormixture at low binder content (3.5 to 4.5%)

w

tmb

VW

DimG

Method 2-dimensional

Vt=*r2*h

CF

WWWW

WVacuumG

bwbsb

mb

,

Bulk Specific Gravity, Bulk Specific Gravity, GGmbmb

Method 1-vacuum

GGmmmm Comparison and Variability, AR Mixtures Comparison and Variability, AR Mixtures

Calculated Gmm: less variability and less asphalt-loss error

2.25

2.292.33

2.37

2.412.45

2.49

3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Asphalt Content (%)

Th

eore

tica

l M

axim

um

Sp

ecif

ic G

ravi

ty

Average Meas. Gmm Calculated Gmm

Gmm-Ignition Sample Gmm Compacted Sample

Shift due to asphalt loss

2.252.29

2.332.37

2.412.45

2.49

3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Asphalt Content (%)

Th

eore

tica

l M

axim

um

S

pec

ific

Gra

vity

Calculated Gmm Measured GmmStandard deviation

0.00

0.01

0.02

0.03

Sta

nd

ard

De

via

tio

n

Results and DiscussionResults and Discussion

GGmbmb Dim: Dim:Simpler, faster, less expensive, cleaner, required equipment is readily available, and data can be directly used to analyze X-ray CT images

(%)100

)(

dim

td

w

std

ensional V

WWV

WAAV

(%)100*)(_

,

,

CFW

WWW

WWCFW

WWWAVWA

bwbsb

SVb

wbsb

b. Connected AV Content

Water-Accessible AV ContentWater-Accessible AV Content

Method 1-vacuum method

Method 2-dimensional analysis

Interconnected AV Content - Interconnected AV Content - X-ray Computed X-ray Computed Tomography and Image AnalysisTomography and Image Analysis

SourceDetector

Object

Grayscale image B&W image

3D render

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Comparison of Water-Accessible AV and Comparison of Water-Accessible AV and Total AV Content Total AV Content

50

70

90

110

12 16 20 24 28Total Air Voids (%)

Ra

tio

Wa

ter-

Ac

ce

s. A

V/T

ota

l AV

(%

)

Vacuum, PG Vacuum, ARDimensional, PG Dimensional, AR

Most AV in PFC are water accessible

10

15

20

25

30

10 15 20 25 30Water-Accessible AV (%)

Inte

rco

nn

ec

ted

AV

, W

ith

Su

rfa

ce

AV

(%

) Equality LinePMLC-PGPMLC-ARCores-PGCores-AR

Dimensional analysis with vacuum

Good agreement for interconnected AV and

water-accessible AV

Summary and Recommendations-VolumetricsSummary and Recommendations-Volumetrics

• Use dimensional analysis for determining both Gmb and water-accessible AV content

• Use calculated Gmm

• The methods used for determining Gmm and Gmb affect: OAC, mixture aggregate gradation, and fibers content

Include mixture-durability test for PFC mix design

Future work:Future work:• Explore the use of connected AV content for mix design and evaluation

2.4’’

3.2 Durability3.2 Durability

0

4

8

12

16

0 5000 10000 15000Number of Cycles

Ru

t (m

m)

Wet ConditioningWet Conditioning

Hamburg Wheel-Tracking Test (Hamburg)Hamburg Wheel-Tracking Test (Hamburg)

Current practice:Current practice:• No durability test applied

TTI Overlay Test (Overlay)TTI Overlay Test (Overlay)

No Conditioning (dry)No Conditioning (dry)

Zhou et al., 2003Zhou et al., 2003

-300

-200

-100

0

100

200

300

400

500

0 50 100 150 200

Number of Cycles

Lo

ad

(lb

)

Cracking life

Cantabro Loss Test (Cantabro)Cantabro Loss Test (Cantabro)

100*W-W

(%) Loss Cantabro fo

oW

No Conditioning (dry)No Conditioning (dry)

300 rev.Before (W0) After (Wf)

4.5’’

TestSpecimen

Preparation

Air Voids Variability

(COV)

Availability of Equipment (in

Texas)

Testing Time

(hours)

Results Variability

(COV)

Hamburg Saw trimming 0.030 Medium 5 0.02 to 0.57

Overlay

Saw cutting, drying, final AV checking, and

gluing

0.030 Low 2 0.22 to 1.17

Cantabro Not required 0.016 High 0.3 0.07 to 0.36

Comparison of Comparison of Mixture Evaluation TestsMixture Evaluation Tests

Additional Cantabro Testing: Additional Cantabro Testing: wet (24 hrs @ 60C + drying), cold (3C), & aged (3 & 6 months @ 60C)

Results and DiscussionResults and Discussion

Cantabro Results - Effect of ConditioningCantabro Results - Effect of Conditioning

PG 76-22 mixtures

0

20

40

5.5 5.7 5.9 6.1 6.3 6.5 6.7

Ca

nta

bro

Lo

ss

(%)

Asphalt Content (%)

Dry WetLow Temp. 3 Months Aged6 Months Aged

Summary and Recommendations-DurabilitySummary and Recommendations-Durability

• Cantabro Loss test recommended• Cantabro test results suggest: Mixture resistance to disintegration is affected more by aggregate than binder properties The test can be used as a screening tool for PFC mix design, but it may not provide enough sensitivity for selecting the OAC Cantabro Loss values showed a direct relationship with water-accessible AV content

Future work:Future work:• Evaluate relationships between field and lab. responses• Use analytical performance models to improve PFC mix design

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3.3 Drainability3.3 Drainability

Current practice - design (SGC specimens):Current practice - design (SGC specimens):

• Ensure total AV content (min. 18%)

• Measure lab permeability (min. 100 m/day)

Current practice - fieldCurrent practice - field

• Measure field drainability: water flow value (max. 20 secs)

Field drainabilityField drainability

Water flow value(outflow time)

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Lab drainabilityLab drainability

Coefficient of permeability (k)

Laboratory and Field Measurement of DrainabilityLaboratory and Field Measurement of Drainability

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Evaluation of Current PracticeEvaluation of Current Practice

Lack of correlation can be related to differences in: (i) Total AV content,(ii) Specimen thickness, and(iii) Internal structure of the mixture

0

100

200

16 20 24 28 32 36Total Air Voids (%)

Pe

rme

ab

ilty

(m

/da

y)

SGC - PGCores - PGNCAT Minimum

Best fit lines

Watson et al.' relationship

Results and DiscussionResults and Discussion

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Alternatives EvaluatedAlternatives Evaluated

(i) Relationship of water-accessible AV content and

lab-measured permeability,

(ii) Relationship of lab and field drainability, and

(iii) Analytical prediction of permeability (Expected value of

permeability using modified Kozeny-Carman Eq.)

(ii) Relationship of lab (ii) Relationship of lab and field drainabilityand field drainability

R2 = 0.82, PG

R2 = 0.75, AR

10

100

1000

1 10 100 1000Water Flow Value (s)

Co

re P

erm

ea

bili

ty

(m/d

ay

)

PG MixturesAR Mixtures

NCAT Minimum

0

100

200

0 100 200

E[k

] a

nd

Ca

lcu

late

d

Pe

rme

ab

ility

(m/d

ay)

Measured Permeability (m/day)

Expected Value of Perme.Calculated Perme.Equality line

0

100

200

0 100 200

E[k

] a

nd

Ca

lcu

late

d

Pe

rme

ab

ility

(m

/da

y)

Measured Permeability (m/day)

Expected Value of Perme.Calculated Perme.Equality Line

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(iii) Expected Value of Permeability (iii) Expected Value of Permeability ((EE[[kk]) ]) and Calculatedand CalculatedPermeability Permeability (Modified Kozeny-Carman Equation) (Modified Kozeny-Carman Equation)

Road cores

Parameters for E[k]:• Average and variance of both aggregate-particle size (gradation) and total AV content (X-ray CT)• Covariance of aggregate-particle size and total AV content• Empirical calibration coefficient• Aggregate, asphalt and fluid (water) parameters

SGC specimens

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Summary and Recommendations-DrainabilitySummary and Recommendations-Drainability

• Current practices led to poor drainability evaluation of field-compacted mixtures• Water-accessible AV content may be used as a surrogate of the total AV content to indirectly assess permeability• Use the Expected value (E[k]) as an estimator of permeability. Alternatively, the WFV can be used to asses field drainability

Future WorkFuture Work• Further assess permeability of field-compacted mixtures using laboratory-compacted mixtures

Current CCurrent Construction Controlonstruction Control Asphalt content, gradation Asphalt content, gradation Visual inspection: density, material variability, segregationVisual inspection: density, material variability, segregation Minimum smoothnessMinimum smoothness

• No field density requirements for PFCNo field density requirements for PFC

Assess effects of densification on PFC based on:Assess effects of densification on PFC based on:

Internal structure (air voids [AV] characteristics)Internal structure (air voids [AV] characteristics)

Macroscopic response (durability and functionality)Macroscopic response (durability and functionality)

FOR TWO COMPACTION LEVELSFOR TWO COMPACTION LEVELS

ObjectiveObjective

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3.4 Densification Effects3.4 Densification Effects

Comparison of Total AV ContentComparison of Total AV Content

Field Vs Lab (SGC) air voids content

14

18

22

26

30

34

I-35-PG

US-59Y-PG

IH-30-PG

US-83-PG

US-281-AR

US-290-AR

US-288-AR

To

tal

Air

Vo

ids

(%)

Road Cores PMLC Specimens

AV Design Range

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Results and DiscussionResults and Discussion

Field AV content reproduced at 15 gyrations of the SGC

Distribution of AV contentUS-59Y mixture

0

25

50

75

100

10 20 30 40Air Voids Content (%)

Po

siti

on

(m

m)

Core, Total AV15G Total AV50G Total AV50G Interc. AV

Ongoing Research! Ongoing Research!

0

1

2

3

4

5

6

0 10 20 30 40 50Number of Gyrations, N

Ch

an

ge

in H

eig

ht

(mm

)

US-59Y-PG-50G

US-59Y-PG-15G

US-290-AR-50G

US-290-AR-15G

Compaction Curve and Stone-on-Stone ContactCompaction Curve and Stone-on-Stone Contact

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US-59Y-PG mixture30

35

40

45

0 5 10 15Replicate Specimen

VC

A-M

ix a

nd

-D

RC

(%

) VCA-Mix 12G VCA-Mix 15GVCA-Mix 50G

VCA-DRC

Stone-on-Stone Contact

DRCmix VCAVCA

Ongoing Research! Ongoing Research!

Effect of Densification on DurabilityEffect of Densification on Durability

0

10

20

30

40

50

Dry Wet LowTemper.

Aged 3Months

Aged 6Months

Can

tab

ro L

oss

(%

) 50 Gyrations

15 Gyrations

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0

25

50

75

100

0 10 20 30 40 50 60

Number of Gyrations

Cra

ckin

g L

ife

(Cyc

les)

Replicate Result

Average

MixtureSGC

GyrationsTotal AV Content

Cycles to Failure @ 12.5 mm

Rut Depth @ 20000 Cycles (mm)

12 22 - 11.4112 22.3 - 8.9650 17.6 - 4.8250 16.2 - 5.43

US-59Y-PG

Hamburg-Wheel Tracking test

Cantabro test Overlay test

Effect of Densification on DrainabilityEffect of Densification on Drainability

Laboratory permeability

0

100

200

300

16 19 22 25 28Total Air Voids (%)

Wat

er P

erm

eab

ilit

y (m

/day

)

US-290-AR-15GUS-290-AR-50GUS-59Y-PG-15GUS-59Y-PG-50G

Field drainability (WFV)

0

10

20

30

0 1 2 3 4 5 6 7

Number of Static Roller Passes

Wa

ter

Flo

w V

alu

e (

s)

US-290-AR US-59Y-PG

Total AV=21.7%

Total AV=26.7%3 Passes

Total AV=23.4%

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• High levels of densification (after reaching stone-on-stone contact) are required for mixture durability

• These findings suggest the necessity of:

Checking stone-on-stone contact during mix designIncluding a construction density control

Short-term action: Increase efforts to establish required roller patterns

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Summary and Recommendations-DensificationSummary and Recommendations-Densification

Future WorkFuture Work• Develop techniques (e.g., nondestructive methods) to evaluate the field density and enforce a density specification• Improve the current SGC compaction protocol• Evaluate long-term mixture performance to obtain final recommendations for field density control

Thank you!

Questions?

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Total AV Content Comparison Based on Total AV Content Comparison Based on GGmmmm and and

GGmb mb Calculations Calculations

-5

0

5

-2.0 0.0 2.0

Zone I

Zone IVZone III

Zone II

AV (vacuum Gmb, calculated Gmm) –

AV (vacuum Gmb, measured Gmm)

AV

(va

cuu

m G

mb,

calc

ula

ted

Gm

m)

–

AV

(d

imen

sio

nal

Gm

b,

calc

ula

ted

Gm

m)

Effect of Volumetric Parameters on OAC Effect of Volumetric Parameters on OAC

US-281-AR lab. mixture

Dim Gmb-Meas. Gmm Dim Gmb-Calc. Gmm

Vacuum Gmb-Meas. Gmm Vacuum Gmb-Calc. Gmm

Asphalt Content (%)

To

tal

AV

Co

nte

nt

(%)

14

16

18

20

22

7.9 8.1 8.3 8.5 8.7 8.9 9.1

OAC

Hamburg ResultsHamburg Results

PG 76-22 mixtures

4

8

12

16

5.5 5.7 5.9 6.1 6.3 6.5 6.7Asphalt Content (%)

Ru

t D

epth

at

2000

0 C

ycle

s (m

m)

AVERAGE I-35-PG I-35-PG COV

0.00

0.20

0.40

0.60

CO

V

Asphalt-rubber mixtures

2000

6000

10000

14000

18000

7.5 7.7 7.9 8.1 8.3 8.5 8.7Asphalt Content (%)

Cyc

les

to F

ailu

re a

t 0

.49

in (

12.5

mm

)

AVERAGE US-281-AR US-281-AR COV

0.00

0.15

0.30

0.45

0.60

CO

V

Results and DiscussionResults and Discussion

Overlay ResultsOverlay Results

0

250

500

750

1000

5.5 5.7 5.9 6.1 6.3 6.5 6.7

Asphalt Content (%)

Cra

ckin

g L

ife

(Cyc

les)

AVERAGE, I-35-PG COV, I-35-PG

0.0

0.3

0.6

0.9

1.2

CO

V

PG 76-22 mixtures 0

250

500

750

1000

7.5 7.7 7.9 8.1 8.3 8.5 8.7Asphalt Content (%)

Cra

ckin

g L

ife

(Cyc

les)

AVERAGE, US-281-AR COV, US-281-AR

0.0

0.3

0.6

0.9

1.2

CO

V

Asphalt- rubber mixtures

Cantabro Results (Dry)Cantabro Results (Dry)

PG 76-22 mixtures

0

10

20

30

40

5.5 5.7 5.9 6.1 6.3 6.5 6.7

Asphalt Content (%)

Can

tab

ro L

oss (

%)

0.0

0.1

0.2

0.3

0.4

CO

V

Asphalt-rubber mixtures

0

10

20

30

40

7.5 7.7 7.9 8.1 8.3 8.5 8.7

Asphalt Content (%)

Can

tab

ro L

oss (

%)

0.0

0.1

0.2

0.3

0.4

CO

V

AR

PG

Sandstone, 100%

Lim./San., 50/50%

Limestone, 100%

0

10

20C

anta

bro

Lo

ss (

%)

NA

NA

US-281-AR

US-290-AR-15G

I- 35-PG

US-59Y-PG-15G

Cantabro Results - Effect of Material QualityCantabro Results - Effect of Material QualityD

UR

AB

ILIT

Y

Cantabro Results - Effect of AV Content Cantabro Results - Effect of AV Content

PG 76-22 & Asphalt-rubber mixtures

0

15

30

45

14 16 18 20 22 24 26

Total Air Voids (%)

Can

tab

ro L

oss

(%

)

0

15

30

45

14 16 18 20 22 24 26 28

Water Accessible Air Voids (%)

Ca

nta

bro

Lo

ss

(%

)

Linear (Vacuum)

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Internal Structure of the MixtureInternal Structure of the Mixture

0

25

50

75

100

1 2 3 4Average Air Voids Radius (mm)

Po

sit

ion

(m

m)

2-PG-P12-PG-C23-PG-P13-PG-C1

0

25

50

75

100

12 16 20 24 28 32 36Air Voids Content (%)

Po

sit

ion

(m

m)

2-PG-P12-PG-C23-PG-P13-PG-C1

AV design range

Effect of Densification on Cantabro LossEffect of Densification on Cantabro Loss

US-59Y-PG mixture

US-290-AR mixture

0

10

20

30

40

50

Dry Wet LowTemper.

Aged 3Months

Aged 6Months

Can

tab

ro L

oss

(%

) 50 Gyrations

15 Gyrations

0.8

7.3

0.8

5.1

0.6

0

4

8

Dry Wet LowTemper.

Aged 3Months

Aged 6Months

Can

tab

ro L

oss

(%

) 50 Gyrations

15 Gyrations

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Effect of Densification on Hamburg-WheelEffect of Densification on Hamburg-WheelTracking TestTracking Test

MixtureSGC

GyrationsTotal AV Content

Cycles to Failure @ 12.5 mm

Rut Depth @ 20000 Cycles (mm)

12 19.9 7550 -

50 16.9 16700 -

12 22 - 11.41

12 22.3 - 8.96

50 17.6 - 4.82

50 16.2 - 5.43

US-290-AR

US-59Y-PG

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Effect of Densification on Overlay ResultsEffect of Densification on Overlay Results

US-59Y-PG mixture

US-290-AR mixture

0

25

50

75

100

0 10 20 30 40 50 60

Number of Gyrations

Cra

ckin

g L

ife

(Cyc

les)

Replicate Result

Average

0

250

500

750

1000

0 10 20 30 40 50 60

Number of Gyrations

Cra

ckin

g L

ife

(Cyc

les)

Replicate Result

Average

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3.5 Stone-on-Stone Contact (SOS Contact)3.5 Stone-on-Stone Contact (SOS Contact)

Current practiceCurrent practice• No test applied• Assessment methodology available (NCAT, 2002) based on voids in coarse aggregate (VCA)

Ongoing Research ApproachOngoing Research Approach

1; nnVCA

VCA

DRC

mix

VCAmix = AV in the coarse aggregate of the compacted mixture

VCADRC = AV in the coarse aggregate using dry-rodded unit weight

Determination of Breaking-Sieve SizeDetermination of Breaking-Sieve Size

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0.6

0.8

1.0

1.2

1-P

G

2-P

G

3-P

G

4-P

G

5-P

G

6-P

G

1-A

R

3-A

R

Ra

tio

VC

Am

ix/V

CA

DR

C

No 4 sieveSlope of gradation10% sieve

Mechanical modeling based on Discrete Element Model

(DEM)

Ongoing Research ApproachOngoing Research Approach