Mixture Polishing John Zaniewski, Danielle Hoyer & Allison - - PowerPoint PPT Presentation

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)

Macrotexture

Represents 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

Tires Toe angle Sample orientation Sample air voids Three replicates Four mix types

Friction vs Polishing Cycles

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

10 20 30 40 50 60 70 80 90 8000 16000 32000 48000

BPN 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

10 20 30 40 50 60 70 8000 24000 48000

BPN 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

10 20 30 40 50 60 70 80

BPN

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

20000 40000 60000 80000 100000 120000 140000 10 20 30 40 50 60 70 80 90

Number of Wheel Passes BPN

Specimen 13T Specimen 14T Specimen 15T Mix Average Power (Mix Average)

Predicted Number of Wheel Passes to Achieve BPN of 47

100000 200000 300000 400000 500000 600000 700000 4% VTM Low Toe 8% VTM Low Toe 4% VTM High Toe 8% VTM High Toe

Number of Wheel Passes 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

500 1000 1500 2000 2500 3000 3500 4000 4500

Number of Wheel Passes 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

Aggregates

Mashey Gap Skid 8's Elkins 9's Elkins 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

Gradation and binder content the same for all mixes

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

Benjamin M. Statler College of Engineering and Mineral Resources

10 20 30 40 50 60 70 80 90 8000 16000 32000 48000 80000

BPN 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

OR

Mixes are the same at LOW speeds

Good News Bad News

Polisher works Should upgrade

Texture

British Pendulum sensitive to microtexture

For mix evaluation need to measure macrotexture

Measures texture Measures friction

Standard test methods State of the art Used by leading researchers – NCAT

Thank you