research findings from the ncat test track apai winter conference indianapolis, december 14, 2010
TRANSCRIPT
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
20
25
30
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40
45
50
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
QC Air Voids (% Gmm)
Max
imu
m M
easu
red
AR
AN
Avg
Ru
t D
epth
(m
m)
- 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
200
400
600
800
1000
1200
1400
0 20 40 60 80 100 120 140
Mid-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
0
25
50
75
100
125
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175
200
0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
IRI (
inc
hes
pe
r 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
2
4
6
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10
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1,000,000 10,000,000 100,000,000 1,000,000,000
ESALs
HM
A D
ep
th (
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