Research Findings from the NCAT Test Track

APAI Winter ConferenceIndianapolis, December 14, 2010

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NCAT Pavement Test Track

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• 1.7 mile oval asphalt track• 45 experimental test sections, each 200 ft. long• A pooled-fund project with test sections sponsored by

highway agencies and businesses to evaluate specific materials and/or pavement design strategies

• Realistic traffic applies 10 million ESALs in each two year cycle

• Currently 60% complete with the 4th cycle

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Lab Testing

• Fine and coarse Superpave mixes perform similarly

• Modified binders cut rutting approximately 50%, densify less under traffic, enable high binder content

• Aggregate specification assessments– F&E for SMA & OGFC– Polishing prone aggregates– Elimination of Restricted Zone– Gravel performs well in SMA & OGFC

Test Track Research Findings

• Benefits of OGFC: safety, noise, smoothness• Lowering Ndesign is O.K.• High RAP content mixes perform well• Criteria for Lab Performance Tests

– Air voids– Asphalt Pavement Analyzer– Flow Number– Energy Ratio for top-down cracking

Test Track Research Findings

• Mechanistic pavement models validated and calibrated – Measured vs. predicted HMA tensile stresses – Seasonal effects on pavement layers– Compressive stresses in unbound layers– Transfer functions for strain damage– Field fatigue threshold– Validation of pavement temperature models– Traffic wander– Speed vs strain / load pulse

Test Track Research Findings

9Track Conference – 2/10/092006 Indiana Low QC Voids Study

2006 Indiana Low QC Voids Study

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y = 98.74e-0.83x

R2 = 0.69

0

5

10

15

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25

30

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45

50

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5QC Air Voids (% Gmm)

Max

imum

Mea

sure

d A

RA

N A

vg R

ut D

epth

(mm

)

- All mixes shown produced with PG67 binder- Green control section placed in September 2006- Red treatment sections placed in October 2006- Blue replacement sections placed in February 2008- More rutting expected in blue replacement sections- Design gradations shown with round symbols- Closed gradations shown with triangle symbols- Black diamonds show PG67 RAP study sections- Yellow squares show 2000 limestone/slag mixes

Track Layout

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2009 Thinner Structural Test Sections

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Perpetual Pavement on Soft Clay

N8 Strain = 21.487e0.0335*Temperature

R2 = 0.96

N9 Strain = 11.496e0.0298*Temperature

R2 = 0.9217

0

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600

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1000

1200

1400

0 20 40 60 80 100 120 140Mid-Depth Temperature, F

Tens

ile M

icro

stra

in

N8 N9

10”

14”

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Perpetual Pavement on Soft Clay

Visible Cracks on Pavement Surface

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25

50

75

100

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0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

IRI (

inch

es p

er m

ile)

MESALs

N8 N9

Cracks appearon surface

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Perpetual Pavement on Soft Clay

• 14” pavement looks great after 16.2 million ESALs

• 10” pavement recently rehabilitated for 2nd time– In need of 1st rehabilitation after 10 million ESALs– 5” mill/inlay failed again after 3.5 million ESALs– 1.6 million ESALs on 5-3/4” high polymer inlay

Perpetual Pavements

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• 24 inch perpetual (original) Track foundation• Designed with ‘93 Guide for MANY cycles

• Two 9 inch thick structural sections in 2003• ‘93 Guide predicted failure near 10M ESALs• 26.2M ESALs to date (perpetual expectation)

• 15 inches of wasted (excess) thickness?

• 14 inches required on N9 soft subgrade

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Layer Coefficient Recalibration

0

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1,000,000 10,000,000 100,000,000 1,000,000,000

ESALs

HM

A D

epth

(in)

a1 = 0.44a1 = 0.5418.5% Thinner

Layer Coefficient Recalibration

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• Technology has improved since AASHO Road Test

• Need to recalibrate coefficients• Increase a1 from 0.44 to 0.54 based on all

structural sections on the Track• 18.5 percent thinner structural designs• Alabama saving $25M to $50M annually

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2009 Group Experiment (+)

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2009 Group Experiment (+)

High RAP Mixes on the NCAT Test Track

• 2006: – 45% RAP surface mix with four different virgin

binder grades• 2009:

– 2006 high RAP sections continued– 45% RAP surface mix from Mississippi– 50% RAP HMA & 50% RAP WMA in structural

sections

Group Experiment – High RAP (N10 & N11)

Control HMA Section

50% RAP Section

50% RAP WMA Section

PFC Surface Cracks (Tack Method)

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PFC Surface Cracks (Tack Method)

• 2006 crack susceptible dense Superpave mix– Surface cracks after 1.9M ESALs (Rehab at 5.6M)

• 2009 PFC surface placed with conventional tack– Surface cracks after 2.2M (cracking/pumping at 6.2M)

• 2009 bonded PFC surface placed with spray paver– Surface cracks after 4.1M (very good at 6.2M)

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PFC Surface Permeability

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PFC Surface Noise

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SBS vs GTR Mill/Inlay: Rutting

GTR

SBS

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Pavement Preservation (S13)

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Temperature Reduction (S13)

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Reflective Cracking (S13)

Web Performance Reports

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www.pavetrack.com

Profiler Certification Program

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• 9.5 mm coarse granite PG67-22 mix (TSR ≈ 0.3!)

• Laboratory performance of plant produced mix– Flow number, dynamic modulus, APA– IDT, overlay tester, bond strength, PG grading– TSR, stripping via boiling, Hamburg (aged & unaged)

• Field performance on Pavement Test Track– Hot-mix control, immediate traffic (1 year thereafter)– Weekly rutting, roughness, macrotexture– Final report within 18 months of commitment

National WMA Certification Program

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Thank Youwww.NCAT.us