Progress in Evaluating Asphalt Mixture Polishing John Zaniewski, Danielle Hoyer & Allison Givens 40 th 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 Macrotexture Microtexture Represents the Represents the space b/w texture of aggregates in a aggregate mixture surface High Speed Low Speed Pavement Surface Microtexture and Macrotexture (Liang, 2013)
Polishing Devices NCAT TWPD MIWT (NCAT, 2016) (Erukulla, 2011) NCSU CTPM (ASTM E660)
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 Circular Track/Texture Meter British Pendulum (Haider and Sajedi, 2017) (Hanson and Prowell, 2004) Tester (BPT)
BPT Minimum BPN = 47 Virginia min. (Lu and Steven, 2006)
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 (1 st 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 90 Mix 1 12.5mm Skid-RAP 80 Mix 2 W1-RAP Mix 3 W1H 70 Mix 4 12.5mm Skid-RAP 60 50 BPN BPN 40 47 30 20 10 0 0 8000 16000 32000 48000 Number of Wheel Passes
Average BPN Measurements for Laboratory and Field Core Mix 12.5mm Skid-RAP 70 Mix 1 Laboratory Compacted 60 Mix 1 I-79 Field Core 50 BPN 47 40 BPN 30 20 10 0 0 8000 24000 48000 Number of Wheel Passes
Laboratory, Field Core, and Field Measurements for Mix 1 12.5mm Skid-RAP 80 70 60 50 BPN 47 BPN 40 30 Mix 1 Laboratory Compacted 20 10 Mix 1 I-79 Field Core 0 Mix 1 I-79 Field BPN Measurement
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 140000 y = 5E+34x -18.04 120000 R² = 0.9769 100000 Number of Wheel Passes 80000 Specimen 13T 60000 Specimen 14T Specimen 15T 40000 Mix Average 20000 Power (Mix Average) 0 0 10 20 30 40 50 60 70 80 90 BPN
Predicted Number of Wheel Passes to Achieve BPN of 47 700000 Mix 1 12.5mm Skid-RAP Mix 2 W1-RAP 600000 Mix 3 W1H Mix 4 12.5mm Skid-RAP 500000 Number of Wheel Passes 400000 300000 200000 100000 0 4% VTM Low Toe 8% VTM Low Toe 4% VTM High Toe 8% VTM High Toe Testing Parameters
Predicted Number of Wheel Passes at BPN of 47 for JFA Laboratory Compacted and Field Core Specimens 4500 4000 3500 3000 Number of Wheel Passes 2500 2000 1500 1000 500 0 JFA Laboratory Compacted I-79 Field Core
Statistical Analysis • T-test • 95% confidence ( α = 0.05); • H o 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: • Significant factors: • VTM • Tire toe angles • Contractor • Field Core vs. Field Measurements • Lab vs. Field Core • NMAS
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 Gradation and binder Aggregates content the Mashey same for all Elkins Bag House Gap Skid Elkins 9's mixes Sand Fines 8's Total % Mix Type 40% 10% 49% 1% Skid All Skid Skid Skid Skid 99 Intermediate Skid Skid 59 Per Design Skid 40 No Skid 0
Average BPN Numbers for 9.5 mm SKID Study at 7% VTM with High Toe 90 0% 40% 59% 99% 80 70 60 50 BPN 40 30 20 10 0 0 8000 16000 32000 48000 80000 Wheel Passes Benjamin M. Statler College of Engineering and Mineral Resources
Varying the amount of skid aggregate was NOT significant British pendulum only Wow! We can stop sensitive to microtexture using skid aggregate! Mixes are the same at LOW speeds OR
Bad News Good News Should upgrade Polisher works
Texture British Pendulum sensitive to microtexture For mix evaluation need to measure macrotexture
Standard test methods State of the art Used by leading researchers – NCAT Measures Measures friction texture
Thank you
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