Progress in Evaluating Asphalt Mixture Polishing

John Zaniewski,

Danielle Hoyer & Allison Givens

40th Paving Conference

Charleston WV

February 19, 2020

Objectives

1. Develop procedure for asphalt mixture polishing and friction evaluations

2. Provide evaluation of current approved WVDOH surface mixtures

3. Verify results

4. Experiment – varying skid aggregate amounts

Friction

• Interaction between tire and pavement surface

Texture

• Characteristics of the pavement surface that contributes to friction

Polishing

• Change in texture due to traffic or laboratory process

Texture

Pavement Surface Microtexture and

Macrotexture (Liang, 2013)

MacrotextureRepresents the

space b/w

aggregates in a

mixture

Microtexture

Represents the

texture of

aggregate

surface

High Speed Low Speed

Polishing Devices

MIWT

(Erukulla, 2011)NCSU CTPM

(ASTM E660)

NCAT TWPD

(NCAT, 2016)

Field Friction Evaluation

• High speed: locked wheel, fixed slip, variable slip, and side force

• WVDOH currently uses locked wheel (ASTM E274)

Locked Wheel Skid Trailer

(Kuttesch, 2004)

Laboratory Friction and Texture Measurements

Dynamic Friction Tester

(Haider and Sajedi, 2017)

British Pendulum

Tester (BPT)

Circular Track/Texture Meter

(Hanson and Prowell, 2004)

BPT Minimum

(Lu and Steven, 2006)

BPN = 47

Virginia min.

Materials

Polishing Equipment

• Modeled after NCSU machine

• Includes 12 sample housings

• Clamping and height adjustment Specimen removal openings

• 4 wheels rotating on central shaft

• Toe-In/Toe-out adjustments

• Tire size = 11x6x5 in.

• Variable rotation speed (~30 rpm for this project)

Specimen Preparation

• Compacted at 4% and 8% air void contents (VTM) and 90mm height

• Label top and bottom

Polishing Procedure• Allow specimens to fully dry before

polishing

• Place randomly in polisher

• Vertically aligned and flush with surface deck plate

• Record specimen and tire surface

temps.

• Distribute 2g Silicon Carbide

abrasive powder on surface

• Lower wheel assembly and add two

25-lb weights on each

Polishing Procedure

• Set drive to ~30 rpm (as marked)

• Start polisher

• Stop after 8000, 16000, 32000, and 48000 wheel passes

Friction Measurement

• Measure BPN after 8000, 16000, 32000, and 48000 wheel passes

BPT Field Procedure

• Procedures followed similar to lab (ASTM E303)

• 5-in slider contact path

• Wet surface

• 5 measurements (1st not recorded)

• Level equipment according to roadway surface

• Measurements recorded according to field extraction site (for comparison purposes)

Test variables

TiresToe angleSample orientationSample air voidsThree replicatesFour mix types

Friction vs Polishing Cycles

Average BPN Measurements for Asphalt Mixtures at 4% VTM Polished at Low Toe Angles

0

10

20

30

40

50

60

70

80

90

0 8000 16000 32000 48000

BP

N

Number of Wheel Passes

Mix 1 12.5mm Skid-RAP

Mix 2 W1-RAP

Mix 3 W1H

Mix 4 12.5mm Skid-RAP

BPN

47

Average BPN Measurements for Laboratory and Field Core Mix 12.5mm Skid-RAP

0

10

20

30

40

50

60

70

0 8000 24000 48000

BP

N

Number of Wheel Passes

Mix 1 Laboratory Compacted

Mix 1 I-79 Field Core

BPN

47

Laboratory, Field Core, and Field Measurements for Mix 1 12.5mm Skid-RAP

0

10

20

30

40

50

60

70

80

BP

N

Mix 1 Laboratory Compacted

Mix 1 I-79 Field Core

Mix 1 I-79 Field BPN Measurement

BPN

47

Polishing Prediction

• Trend plots reversed (x-axis = BPN; y-axis = number of wheel passes)

• Power function fitted to data

• Predicted number of wheel passes to reach BPN 47

Prediction of Required Wheel Passes at BPN Limits for Mix 3 W1H Specimens (Top Surfaces) at 8%

VTM After 48,000 Wheel Passes

y = 5E+34x-18.04

R² = 0.9769

0

20000

40000

60000

80000

100000

120000

140000

0 10 20 30 40 50 60 70 80 90

Nu

mb

er o

f W

hee

l P

asse

s

BPN

Specimen 13T

Specimen 14T

Specimen 15T

Mix Average

Power (Mix Average)

Predicted Number of Wheel Passes to Achieve BPN of 47

0

100000

200000

300000

400000

500000

600000

700000

4% VTM Low Toe 8% VTM Low Toe 4% VTM High Toe 8% VTM High Toe

Nu

mb

er o

f W

hee

l P

asse

s

Testing Parameters

Mix 1 12.5mm Skid-RAP

Mix 2 W1-RAP

Mix 3 W1H

Mix 4 12.5mm Skid-RAP

Predicted Number of Wheel Passes at BPN of 47 for JFA Laboratory Compacted and Field Core Specimens

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Nu

mb

er o

f W

hee

l P

asse

s

JFA Laboratory Compacted I-79 Field Core

Statistical Analysis

• T-test

• 95% confidence (α = 0.05);

•Ho assuming equal means

• Compare BPN after 48,000 wheel passes

Statistical Comparisons

Conclusions – BPN Analysis

• Decreased BPN with increased polishing

• Asymptotic behavior after 48,000 wheel passes

• Generally higher BPN for Mix 2 W1-RAP and Mix 4 12.5mm Skid-RAP

• Higher initial BPN for field measurements

• High toe = lower BPN

Conclusions – Statistical Analysis

• Insignificant factors:

• VTM

• Contractor

• Lab vs. Field Core

• NMAS

• Significant factors:

• Tire toe angles

• Field Core vs. Field Measurements

Procedure Recommendations

• Hoosier R80 tires

• High toe → accelerated polishing

• 7% VTM

• 48,000 wheel passes• Asymptotic behavior shown

• Decrease friction measurement increments for efficiency

• Track top and bottom surfaces

Replicate Experiment

Verify two technicians obtain compatible results.

SKID Aggregate Experiment

Percent Skid Aggregates

AggregatesMashey

Gap Skid

8's

Elkins 9'sElkins

Sand

Bag House

Fines

Mix Type 40% 10% 49% 1%

Total %

Skid

All Skid Skid Skid Skid 99

Intermediate Skid Skid 59

Per Design Skid 40

No Skid 0

Gradation and binder content the same for all mixes

Average BPN Numbers for 9.5 mm SKID Studyat 7% VTM with High Toe

Benjamin M. Statler College of Engineering and Mineral Resources

0

10

20

30

40

50

60

70

80

90

0 8000 16000 32000 48000 80000

BP

N

Wheel Passes

0% 40% 59% 99%

Varying the amount of skid aggregate was NOT significant

Wow! We can stop using skid aggregate!

British pendulum only sensitive to microtexture

ORMixes are the same at LOW speeds

Good News Bad News

Polisher works

Should upgrade

Texture British Pendulum sensitive to microtextureFor mix evaluation need to

measure macrotexture

Measures texture

Measures friction

Standard test methods

State of the art

Used by leading researchers –NCAT

Thank you