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Research Findings from the NCAT Test Track APAI Winter Conference Indianapolis , December 14, 2010. NCAT Pavement Test Track. 1.7 mile oval asphalt track 45 experimental test sections, each 200 ft. long

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research findings from the ncat test track apai winter conference indianapolis december 14 2010

Research Findings from the NCAT Test TrackAPAI Winter ConferenceIndianapolis, December 14, 2010

ncat pavement test track

NCAT Pavement Test Track

  • 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

2

test track research findings
Test Track Research Findings
  • 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
slide7

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
slide8

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
perpetual pavement on soft clay
Perpetual Pavement on Soft Clay

1400

1200

10”

1000

0.0335*Temperature

N8 Strain = 21.487e

800

2

R

= 0.96

Tensile Microstrain

600

N8

N9

0.0298*Temperature

N9 Strain = 11.496e

400

2

R

= 0.9217

14”

200

0

0

20

40

60

80

100

120

140

Mid-Depth Temperature, F

perpetual pavement on soft clay1

200

175

150

125

100

IRI (inches per mile)

75

50

25

0

0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

MESALs

N8

N9

Perpetual Pavement on Soft Clay

Visible Cracks on Pavement Surface

Cracks appear

on surface

perpetual pavement on soft clay2
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

15

perpetual pavements
Perpetual Pavements
  • 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

16

layer coefficient recalibration1
Layer Coefficient Recalibration
  • 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

18

high rap mixes on the ncat test track
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
slide22

Group Experiment – High RAP (N10 & N11)

Control HMA Section

50% RAP Section

50% RAP WMA Section

pfc surface cracks tack method1
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)

24

national wma certification program
National WMA Certification Program
  • 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

34