Inverted Pavements
A TRB Webinar
(AFP70 – Mineral Aggregates)
TRB Webinar - July 18, 2016
Inverted Pavement
1
Why now?
The IP topic was briefly reviewed in NCHRP
Synthesis 445 – Practices for Unbound
Aggregate Pavement Layers (Erol Tutumluer,
Deb Mishra and Rick Boudreau).
download from the TRB website:
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp
_syn_445.pdf
We received tremendous audience feedback
following the TRB Webinar presented June
24, 2015 (Erol Tutumluer, Andrew Dawson, Deb
Mishra and Rick Boudreau).
TRB Webinar - July 18, 2016
Inverted Pavement
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Invited Speaker Session
TRB 95th Annual Meeting
Sponsored by AFP70 – Mineral Aggregates
(E. Tutumluer – Chair)
•
•
•
•
•
•
Rick Boudreau (Moderator) – Boudreau Engr.
Kevin Vaughan – Vulcan
Wynand Steyn – South Africa
David Frost – Georgia Tech
Reza Ashtiani – UTEP
Bryce Symons – N. Mexico
TRB Webinar - July 18, 2016
Inverted Pavement
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Invited Speaker Session
TRB 95th Annual Meeting
Sponsored by AFP70 – Mineral Aggregates
(E. Tutumluer – Chair)
•
•
•
•
•
•
Rick Boudreau (Moderator) – Boudreau Engr.
Kevin Vaughan – Vulcan
Wynand Steyn – South Africa
David Frost – Georgia Tech
Reza Ashtiani – UTEP
Bryce Symons – N. Mexico
TRB Webinar - July 18, 2016
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Outline
•
•
•
•
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Introduction and Background (Boudreau)
Design Considerations (Frost)
Construction Methods (Vaughan)
Performance Assessment (Frost)
Summary Comments (Boudreau)
TRB Webinar - July 18, 2016
Inverted Pavement
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Inverted Pavement - Alias
•
•
•
•
•
Inverted Base Pavement (IBP)
Inverted G1-Base Pavement (South Africa)
Stone Interlayer Pavement (Louisiana)
Upside Down Pavement
Sandwich Pavement
TRB Webinar - July 18, 2016
Inverted Pavement
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Inverted Pavement - Defined
•
•
•
•
Alternative flexible pavement structure
Relatively thin upper AC layer(s)
Layered stiffness profile does not decrease
with depth
Structure typically looks like this (from
bottom up):
•
•
•
•
Compacted Subgrade
Cement-Treated Base (CTB w/ 2-5% cement)
Unbound Aggregate Base (UAB)
Relatively thin Asphalt Concrete (AC)
TRB Webinar - July 18, 2016
Inverted Pavement
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Inverted Pavement Compared to
Conventional Pavement
Conventional Pavement Section
7-8 inches AC (HMA)
8-12 inches UAB
12 inches well-compacted
Subgrade Soil
TRB Webinar - July 18, 2016
Inverted Pavement
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Inverted Pavement Compared to
Conventional Pavement
Inverted Pavement Section
Conventional Pavement Section
3-4 inches AC (HMA)
7-8 inches AC (HMA)
6-10 inches UAB
8-12 inches UAB
8-12 inches CTB
12 inches well-compacted
Subgrade Soil
12 inches well-compacted
Subgrade Soil
TRB Webinar - July 18, 2016
Inverted Pavement
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Inverted Pavement Compared to
Conventional Pavement
Inverted Pavement Section
Conventional Pavement Section
Can reach up to 25% less $ to build the inverted
compared with conventional for similar performance
3-4 inches AC (HMA)
7-8 inches AC (HMA)
6-10 inches UAB
8-12 inches UAB
8-12 inches CTB
12 inches well-compacted
Subgrade Soil
12 inches well-compacted
Subgrade Soil
TRB Webinar - July 18, 2016
Inverted Pavement
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Inverted Pavement Compared to
Conventional Pavement
Inverted Pavement Section
Conventional Pavement Section
Can reach up to 25% less $ to build the inverted
compared with conventional for similar performance
3-4 inches AC (HMA)
7-8 inches AC (HMA)
6-10 inches UAB
$0.75
8-12 inches UAB
$1.00
8-12 inches CTB
12 inches well-compacted
Subgrade Soil
12 inches well-compacted
Subgrade Soil
TRB Webinar - July 18, 2016
Inverted Pavement
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Inverted Pavement Compared to
Conventional Pavement
Inverted Pavement Section
TRB Webinar - July 18, 2016
Conventional Pavement Section
Stiffness (layer modulus)
Inverted Pavement
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Inverted Pavement Compared to
Conventional Pavement
Inverted Pavement Section
TRB Webinar - July 18, 2016
Conventional Pavement Section
Stiffness (layer modulus)
Inverted Pavement
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Inverted Pavement Compared to
Conventional Pavement
Inverted Pavement Section
Conventional Pavement Section
Stiffness (layer modulus)
Still trying to
minimize strains
TRB Webinar - July 18, 2016
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Inverted Pavement Compared to
Conventional Pavement
Inverted Pavement Section
Conventional Pavement Section
As a result of the
stiff CTB layer,
higher densities
can be achieved in
the UAB layer
during
installation.
This results in higher
stiffness properties,
and the UAB layer
remains in
compression.
TRB Webinar - July 18, 2016
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Inverted Pavement Compared to
Conventional Pavement
Inverted Pavement Section
Conventional Pavement Section
1993 AASHTO Design Guide
hypothetical example
E = 80,000psi
ai = 0.24
E = 30,000psi
ai = 0.14
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Improving the Chance of Success
Unbound Aggregate Base (UAB) Layer
•
•
•
Equipment: Mixing should be accomplished by stationary plant such as a pugmill or
by road mixing using a pugmill or rotary mixer. Mechanical spreaders should be
utilized to avoid segregation and to achieve grade control. Suitable vibratory
compaction equipment should be employed.
Mixing and Transporting: The aggregates and water should be plant mixed
(stationary or roadway) to the range of optimum moisture plus 1% or minus 2% and
transported to the job site so as to avoid segregation and loss of moisture.
Spreading: The material should be placed at the specified moisture content to the
required thickness and cross section by an approved mechanical spreader. At the
engineer's discretion, the contractor may choose to construct a 500-ft long test
section to demonstrate achieving adequate compaction without particle
degradation for lift thicknesses in excess of 13 in. The engineer may allow thicker
lifts on the basis of the test section results.
Allen, et al. ICAR 501-5 (1998)
TRB Webinar - July 18, 2016
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Improving the Chance of Success
Unbound Aggregate Base (UAB) Layer
•
•
•
•
Equipment: Mixing should be accomplished by stationary plant such as a pugmill
or by road mixing using a pugmill or rotary mixer. Mechanical spreaders should be
utilized to avoid segregation and to achieve grade control. Suitable vibratory
compaction equipment should be employed.
Mixing and Transporting: The aggregates and water should be plant mixed
(stationary or roadway) to the range of optimum moisture plus 1% or minus 2%
and transported to the job site so as to avoid segregation and loss of moisture.
Spreading: The material should be placed at the specified moisture content to the
required thickness and cross section by an approved mechanical spreader. At the
engineer's discretion, the contractor may choose to construct a 500-ft long test
section to demonstrate achieving adequate compaction without particle
degradation for lift thicknesses in excess of 13 in. The engineer may allow thicker
lifts on the basis of the test section results.
Slushing: South African method to increase packing density of layer by careful
over-watering during the compaction process (slush acts as a lubricant to increase
density while the slush or cream exudes to the surface).
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Design …………
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The US Road System is vast and suffers from
insufficient funding.
Vast network
Depleted funding
Federal Funds
$2.0b
$1.0b
$0.0b
Wikipedia.org
GDOT
‘04 ‘06 ‘08 ‘10 ‘12
Poor condition
Solution Sources
• Innovative designs
• Optimal use of materials
TRB Webinar - July 18, 2016
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An inverted base pavement (IBP) is an innovative technology
that can optimize the use of materials.
Conventional Flexible Pavement
Inverted Base Pavement
Stiffness
Stiffness
asphalt concrete
asphalt concrete
unbound
aggregate base
asphalt base
cement-treated
base
unbound
aggregate base
subgrade
subgrade
• Stiffness contrast between layers
• Granular base : close to load  demand for exceptional performance
(After Papadopoulos, 2015)
TRB Webinar - July 18, 2016
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South Africa has developed and utilized inverted base
pavements for half a century.
Crushed stone base pavement development
Accelerated Testing
Slushing
No Slushing
G1 Base
G2 Crushed Stone Bases
Crusher Run
Macadam / gravel
1940
1950
1960
1970
1980
Jooste & Sampson (2005)
Slushing after
compaction
“Ping” when
struck with
rock hammer
www.Vti.se
Kleyn, 2012
(After Papadopoulos, 2015)
TRB Webinar - July 18, 2016
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US experience with inverted base pavements had also
been long but sparse.
•
•
•
•
•
•
•
•
New Mexico (1960s)
USACE (1970s)
Georgia Tech (1980s)
Louisiana (1990s)
Morgan County GA quarry (2000s)
Lagrange GA bypass (2000s)
Bull Run VA highway (2010s)
Pineville NC quarry (2010s)
0.9
Accelerated Testing, LA
FWD measurements
Deflection [mm]
Reps. to failure [103]
2,000
1,500
IBP
1,000
500
Conventional
pavement
0.6
Conventional
Morgan Co
0.55
IBP-Lagrange
0.3
IBP-Morgan Co
0.21
0.0
0
0
1
2
3
4
Structural Number SN
TRB Webinar - July 18, 2016
5
0.27
Data from Lewis et al 2009
(Adapted from Papadopoulos, 2015)
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Top quality unbound aggregate base is the
fundamental block of IBPs.
South Africa G1 base
CALTRANS base
GDoT GAB
Fines
LL<25%, PI<4
Sand Equivalent <21
Sand Equivalent <20
Shape
flakiness (sphericity) <35%
N/A
elongated particles <10%
Density
86-88% of apparent solid density
(~102% mod Proctor)
95% of CTM 231
98% mod. Proctor
% passing
80
60
Resilient modulus [MPa]
100
GDOT
CALTRANS
G1 South Africa
40
20
0
0.01
1mm=
39mils
0.1
1
10
Grain diameter [mm]
100
900
Crushed stone
600
300
Gravel
0
0
100
200
300
mean stress p´ [kPa]
400
(After Papadopoulos, 2015)
TRB Webinar - July 18, 2016
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Key component of Inverted Pavement construction is
slushing technique
Slushing
• Process to wash away excess fines to achieve optimum fine to coarse soil matrix
• Water migrates to surface by capillary action carrying excess fines
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Comprehensive laboratory – field – numerical study that
expanded understanding of IPB component performance.
Compaction
Lab Characterization
In situ testing
Inverted Base Pavements
Study completed in 2014
Mechanistic analysis
TRB Webinar - July 18, 2016
Inverted Pavement
(After Papadopoulos, 2015)
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Field: fully documented construction project provides
basis for long-term IBP performance assessment.
LaGrange By-Pass
Test section:
0.65 miles long
2 lanes
PCC typical section
IBP test section
Construction
completed in
2009
Super Pave
Graded Aggregate Base
Cement Treated Base
Subgrade
TRB Webinar - July 18, 2016
Inverted Pavement
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.
6
5
””
1
0
”
6
”
Portland Cement Concrete
Graded Aggregate Base
Subgrade
9
.
5
”
1
0
”
6
”
27
Field: fully documented construction project provides
basis for long-term IBP performance assessment.
780
1000
760
Elevation [ft]
Cut
Fill
720
Specific Surface [m2·g-1]
Cut
740
700
Montmorillonite
Specific Surface
100
10
Kaolinite
680
Fill
1
280
660
285
290
295
300
305
310
300
305
310
300
305
310
300
305
310
Station
640
280
285
290
295
300
305
310
120%
LL & m/c
Liquid Limit
Station
In-situ
100%
Water Content [ ]
80%
Elevation [ft]
800
60%
40%
20%
0%
750
280
285
290
295
Station
700
2500
2000
280
285
290
295
300
305
Dry Density [kg∙m-3]
650
310
Station
1500
1000
Dry Density
500
0
280
285
290
295
Station
100%
2500
GSD
60%
P-wave Velocity
2000
VP [m·s-1]
Percent Passing
80%
40%
1500
1000
500
0
20%
280
285
290
295
Station
0%
0.01
0.1
1
Particle Size [mm]
10
Laboratory Characterization of Subgrade
(Data from Santamarina, 2015)
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Field: fully documented construction project provides basis
for long-term IBP performance assessment.
-1
PR (mm·blow )
-1
PR (mm·blow )
5
10
15
0
20
5
15
-1
-1
PR (mm·blow )
PR (mm·blow )
20
0
5
10
15
0
20
0
10
10
10
10
20
20
20
20
30
30
30
30
40
50
60
40
50
60
40
50
60
Depth (cm)
0
Depth (cm)
0
5
10
15
20
40
50
60
70
70
70
70
80
80
80
80
90
90
90
90
100
100
100
100
100000
Constrained Modulus [Mpa]
10
0
Depth (cm)
Depth (cm)
0
(Data from Santamarina, 2015)
10000
1000
100
10
Subgrade
Stabilized Subgrade
CTB
GAB
1
280
285
290
295
300
305
310
300
305
310
Station
Elevation [ft]
800
750
700
650
280
285
290
295
Station
Extensive lab and field characterization studies for various layers
TRB Webinar - July 18, 2016
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Field and Lab: current laboratory methods do not account
for the complex nature of aggregate base stiffness.
Inherent Anisotropy
Stress-Dependent Stiffness
Stiffness
F
Force
Cortes 2010
•
In-chamber compaction.
•
Independent control of the 3
principal stresses.
•
P-wave instrumentation in
each direction.
(After Papadopoulos, 2015)
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Lab: stress ratio has small influence on the small-strain
stiffness as long as the material is away from failure.
Horizontal propagation x
2000
Isotropic Compression
𝛔𝛔𝐳𝐳 = 𝛔𝛔𝐲𝐲 = 𝛔𝛔𝐱𝐱
𝐕𝐕𝐩𝐩 [m/s]
1500
1000
500
Triaxial Extension
𝛔𝛔𝐱𝐱 = 𝛔𝛔𝐲𝐲
𝛔𝛔𝐳𝐳 = 𝟗𝟗𝟗𝟗𝟗𝟗𝟗𝟗𝟗𝟗
Triaxial Compression
𝛔𝛔𝐳𝐳 = 𝛔𝛔𝐲𝐲 = 𝟗𝟗𝟗𝟗𝟗𝟗𝟗𝟗𝟗𝟗
0
500
0
1000 1500
Horizontal Stress 𝛔𝛔𝐱𝐱 [kPa]
Characterization of unbound aggregate base stiffness:
• Granular Bases: inherent & stress-induced anisotropy exist.
• Mmax : function of normal stress
(Adapted from Papadopoulos, 2015)
• Loading conditions: almost no effect on Mmax
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Field and Lab: Soil compaction is omnipresent in
construction and has known impact on performance.
Inadequate compaction results
Post-placement changes in material
Pavement Interactive
Lab-field discrepancies
≠
test-llc.com
TRB Webinar - July 18, 2016
Heavyequipment.com
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Lab: an extensive lab study was conducted to assess
the compaction process in terms of stiffness.
•
•
Specimens compacted using Modified Proctor (Adapted from Papadopoulos, 2015)
Stress-dependent stiffness for different water contents
Piezocrystal
Signal Generator
Digital Oscilloscope
Effect of compaction on granular base stiffness:
• 𝛒𝛒𝐝𝐝𝐝𝐝𝐝𝐝 : not sufficient to assess compaction
• Granular base stiffness not affected by water content
• Water content affects permanent deformation
• Velocity changes reflect accumulation of deformation
TRB Webinar - July 18, 2016
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Field: Two new field tests were conceived to measure the
stiffness of as-built aggregate bases.
Measure stiffness of as-built unbound aggregate bases
Crosshole
Uphole
Dump Truck
Dump Truck
AC
AC
GAB
GAB
Piezopads
CTB
CTB
Subgrade
Subgrade
Accelerometer
Actuator
(After Papadopoulos, 2015)
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Field: Successive forward simulations were conducted to
determine the state of stress in the pavement.
AC
GAB
CTB
Subgrade
Two configurations to capture anisotropic stiffness – 2 case histories
•
In situ GAB: anisotropic stress-dependent stiffness
•
Field values ≠ lab values: Due to preconditioning and compaction
method (field versus lab)
•
Field-Compacted GAB: great stiffness
(Adapted from Papadopoulos, 2015)
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Modeling: Numerical simulations were conducted to
compare IBP’s to conventional pavements.
Inverted Base Pavement
Conventional
Low structural capacity
asphalt concrete
asphalt concrete
160 mm
aggregate base
GAB
aggregate base
GAB
200mm
cement-treated base
CTB
25mm
150mm
250mm
High structural capacity
Mechanistic analysis
asphalt concrete
190mm
asphalt concrete
aggregate base GAB
aggregate base
GAB
305mm
cement-treated base
CTB
100mm
150mm
300mm
(Adapted from Papadopoulos, 2015)
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Aggregate base stiffness in IBP is high due to the
℄
confinement provided by the CTB.
Constitutive model:
• Anisotropy, stress-dependency, shear
softening
AC
Inverted base pavements:
• Unique load-bearing mechanism
Granular base:
• Underutilized in conventional
pavements
• Great contribution in inverted base
pavements
Thin asphalt layers:
• Potential for economic savings
• Caution when subjected to strong shear
(Adapted from Papadopoulos, 2015)
TRB Webinar - July 18, 2016
Tangent Vertical Young’s
modulus Ev (MPa)
Inverted Pavement
𝐭𝐭𝐀𝐀𝐀𝐀 = 190mm
𝐭𝐭𝐆𝐆𝐆𝐆𝐆𝐆 = 305mm
85
105
130
℄
AC
240
90
390
CTB
𝐭𝐭𝐀𝐀𝐀𝐀 = 100mm
𝐭𝐭𝐆𝐆𝐆𝐆𝐆𝐆 = 150mm
𝐭𝐭𝐂𝐂𝐂𝐂𝐂𝐂 = 300mm
37
Construction ………..
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Inverted Pavement Construction
• Standard construction methods may be used for
most layers in an inverted pavement
• Subgrade, Cement Treated Base and Asphalt may
be constructed in the normal way
• Unbound Aggregate Base course may take a little
more effort to ensure the higher density required
• South African methods vs. traditional
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Subgrade Construction
• Generally use standard subgrade requirements
• Remove/correct saturated soils, organics,
unsuitable, etc.
• Typical density requirements
• Variety of subgrades have been used in US inverted
pavements
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Subgrade Construction
• South Africa
• 90% to 93% Modified Proctor
• Georgia
• Mixed in graded aggregate base to improve CBR to 15
• New Mexico
• Lime treated subgrade
• Luck Stone – Virginia
• Standard VDOT subgrade requirements
• Vulcan – North Carolina
• Standard NCDOT subgrade
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Vulcan North Carolina Subgrade
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New Mexico Subgrade Construction
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Cement Treated Base
• Can generally use traditional CTB requirements
• Relatively low level of strength & cement
• South Africa requires 100 to 200 psi
• Pugmill or mix in place
• Recommend spreader box to reduce segregation
• Typical density requirements
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Cement Treated Base
• Pugmill system works
well if available
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Cement Treated Base
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Cement Treated Base
• Asphalt paver used in
NM for CTB
• Good control over
depth and segregation
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Cement Treated Base
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Cement Treated Base
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Cement Treated Base
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Cement Treated Base
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Cement Treated Base
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Inverted Pavement
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Cement Treated Base
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Cement Treated Base
• Seal with emulsified
asphalt tack coat
• Allow to cure for 7 days
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Unbound Aggregate Base
• Typical laydown
• Spreader box should be required for thickness and
consistency
• Density requirements higher than normal
• How is this achieved
• South Africa requires “slushing”
• Will normal methods work?
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Unbound Aggregate Base
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Unbound Aggregate Base
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Unbound Aggregate Base
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Unbound Aggregate Base
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Slushing Process
• What is slushing?
• After initial compaction – UAB flooded with water
• Rolled at high speed to “suck” the fines out of the UAB
• Fines and water act as a lubricant
• As they are removed, larger particles are consolidated for high
density and stiffness
• Excess fines collect on top of the UAB
• Excess fines broomed off
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Slushing Process
No vibration
High speed rolling
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Slushing Process
15 to 17 ton minimum –
27 to 37 ton towards end of cycle
High speed rolling “sucking” fines from
saturated layer
Fines being expelled
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Slushing Process
Notice air being expelled
= interlocking taking place
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Slushing Process
Initial slush/fines same color as
parent rock
Dried fines
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Slushing Process
Well-knitted mosaic being
exposed
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Bristles of broom should just touch surface
Inverted Pavement
65
Slushing Process
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Unbound Aggregate Base
• To Slush or not to Slush…that is the question
• First test section in Georgia saw no benefit to
slushing
• New Mexico specified slushing
• All others used traditional compaction methods
• Easily achieved 102 to 103% of modified Proctor
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67
Unbound Aggregate Base
• On Vulcan section, the
UAB on the
conventional & inverted
sections compacted
same time
• Density on
conventional: 99.8%
• Density on inverted:
103.4%
• 86.4% of apparent
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Unbound Aggregate Base
• Used the same
compaction techniques
on both
• Roller operated
commented that the
inverted section caused
more “bouncing” when
compacting with
vibration
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Hot Mix Asphalt
• Normal HMA
construction in
accordance with local
DOT requirements
• Nothing new
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Vulcan Final Density Comparison
Inverted
Layer Densities
Required
9.5mm A
90% of Gmm
9.5mm B
92% of Gmm
102% of Mod.
Proc.
97% of Mod.
Proc.
UAB
CTB
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Conventional
Layer Densities
Achieved
9.5mm B
94.3% 19.0mm
90.8%
103.4%
UAB
Required Achieved
92% of Gmm
93.2%
92% of Gmm
93.1%
100% of
Mod. Proc.
99.8%
99.2%
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Construction Summary
• Subgrade – standard methods
• Cement Treated Base – standard methods
• Unbound Aggregate Base – requires higher density
• Standard methods have been shown to work
• Slushing will work, but may not be required
• Asphalt Paving – standard methods
• QA/QC: Stiffness-based measurements vs densitybased measurements
• Intelligent Compaction (IC)
• LWD, PLT, DCP …..
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Performance Assessment
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Test sections with well documented loading over
15 year period (Morgan County Quarry).
Seven Islands Road
Quarry Entrance Road
Station 0+50 through Station 10+00
Conventional Haul Road
Station 10+00 through Station 14+00
South African Base
Station 14+00 through Station 18+00
Georgia Base
Construction completed in 2001
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FWD evaluations of test sections (2009).
Performance Evaluation: 853,719 ESAL’s (63.5% design life cycle)
Lewis et al., 2012
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Surface distress study using imaging and LiDAR (2016).
3D Laser Imaging System
Range Image
Detected Crack Map
The GDOT’s Pavement Condition Evaluation System (PACES) is used for
conducting the annual asphalt pavement condition surveys in Georgia.
– Ten different distress types and their severity levels are defined.
– Four of them are crack related distresses: load cracking, B/T cracking,
edge distress, and reflective cracking.
(Courtesy of James Tsai)
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Surface distress study using Imaging (2016).
Abnormal sections
due to truck
braking at main exit
Abnormal sections due to
truck braking at
temporary crossing
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Surface distress study using Imaging (2016).
Georgia Inverted
Conventional
South Africa Inverted
Inbound
Outbound
1800’
Fine transverse crack
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0’
1000’
1400’
Transverse and
longitudinal crack
Block cracking
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Alligator cracking
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Pavement surface distress study using imaging.
•
Load cracking is caused by repeated
heavy loads and always occurs in the
wheel paths:
•
Severity Level 1 usually starts as
single longitudinal cracks in the
wheel path.
•
Severity Level 2 has a single or
double longitudinal crack with a
number of 0-2 feet transverse cracks
intersecting.
•
Severity Level 3 shows an increasing
number of longitudinal and
transverse cracks in the wheel paths.
This level of cracking is marked by a
definite, extensive pattern of small
polygons.
•
(Courtesy of James Tsai)
(a) Severity Level 1
(b) Severity Level 2
(c) Severity Level 3
Severity Level 4 has the definite
“alligator hide” pattern but has
deteriorated to the point that the
small polygons are beginning to pop
out.
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(d) Severity Level 4
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Surface distress study using imaging (2016).
Inbound
Outbound
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Surface distress study using imaging (2016).
Conventional
Less severe cracking
Conventional
Severe cracking
Load
Cracking
1
2
3
1
Block
Cracking
Max Rutting (1/8”)
Average Rating
Rating Range
Conventional
Inbound
Outbound
32.5 %
25.8%
0%
5. %
0%
12.5%
52.5%
31.7%
0
79
71-85
4
68.7
43-80
South African IP
Inbound
Outbound
33.8%
37.5%
0
0
0
0
32.5%
31.3%
0
81.8
81-83
0
80.5
76-86
Georgia IP
Inbound
Outbound
20 %
32.5%
0
0
0
0
32.5%
30%
1
85.5
GA IBP
82-89
2
81.5
79-86
SA IBP
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Rutting study using LiDAR (2016).
Load
Cracking
1
2
3
1
Block
Cracking
Max Rutting (1/8”)
Average Rating
Rating Range
Conventional
Inbound
Outbound
32.5 %
25.8%
0%
5. %
0%
12.5%
52.5%
31.7%
0
79
71-85
4
68.7
43-80
South African IP
Inbound
Outbound
33.8%
37.5%
0
0
0
0
32.5%
31.3%
0
81.8
81-83
0
80.5
76-86
Georgia IP
Inbound
Outbound
20 %
32.5%
0
0
0
0
32.5%
30%
1
85.5
82-89
2
81.5
79-86
Comparable rating
for SA IBP and GA
IBP – far superior to
conventional design.
Less rutting with SA
IBP than with GA
IBP – possible link to
benefits of slushing?
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Laboratory simulation study of slushing process.
Ongoing laboratory simulation study to examine evolution of aggregate
shape, pore structure and load path during slushing
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Laboratory study of slushing on cracking and rutting.
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Selected References
•
Cortes, D. D. (2010). "Inverted Base Pavement Structures." Ph.D., Georgia Institute of Technology, Atlanta, GA.
•
Terrell, R.G., Cox, B.R., Stokoe II, K.H., Allen, J.J., and Lewis, D. (2003). Transportation Research Record, No.
1837, pp. 50-60.
•
Papadopoulos, E. (2014). "Performance of Unbound Aggregate Bases and Implications for Inverted Base
Pavements." Ph.D., Georgia Institute of Technology, Atlanta.
•
Cortes, D.D., Shin, H.S. and Santamarina, J.C. (2012), Numerical Simulation of Inverted Pavement Systems, ASCE
J. Transportation Engineering, vol. 138, no. 12, pp. 1507-1519.
•
Cortes, D.D. and Santamarina, J.C. (2013), Inverted Base Pavement Case History (LaGrange, Georgia):
Construction, Characterization and Preliminary Numerical Analyses, International J. Pavement Engineering,
International Journal of Pavement Engineering vol. 14, 463-471
•
Lewis, D.E. and Jared, D.M. (2012). "Construction and Performance of Inverted Pavements in Georgia."
Proceedings of 91st TRB Meeting, Washington D.C., Paper # 12-1872.
•
Papadopoulos, E., D. Cortes, and Santamarina J.C., (2015). "In Situ Assessment Of The Stress-Dependent
Stiffness Of Unbound Aggregate Bases: Application In Inverted Base Pavements”, International Journal
Pavement Engineering., http://dx.doi.org/10.1080/10298436.2015.1022779
•
Papadopoulos, E. and Santamarina J.C., (2015). "Analysis Of Inverted Base Pavements With Thin Asphalt
Layers", International Journal of Pavement Engineering, http://dx.doi.org/10.1080/10298436.2015.1007232
•
Papadopoulos, E., and Santamarina, J. C. (2014). "Optimization of Inverted Base Pavement Designs with Thin
Asphalt Surfacing." Geo-Congress 2014 Technical Papers, ASCE, Atlanta, GA, 2996-3004.
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In Conclusion ………….
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Pooled fund study to leverage current knowledge to expedite
implementation of IBP design specifications for US state DOT’s.
GDOT Led Pooled-Fund Study:
Closing Sept 25, 2016
http://www.pooledfund.org/Details/Solicitation/1416
IBP Test Sections
Objective:
• To expedite the implementation of inverted base pavement
design specifications for state DoT’s and to make IBP a
practical and reliable alternative design approach for
highway pavements.
Broad Tasks:
• Further study of existing field cases with detailed construction
records and long-term performance monitoring data
• Advanced material characterization and modeling with emphasis on granular base
• Numerical simulation of IBP performance
• Relevant calibrations for design within framework of Mechanistic-Empirical Pavement design Guide
(MEPDG)
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Pooled fund study to leverage current knowledge to expedite
implementation of IBP design specifications for US state DOT’s.
GAPS in knowledge:
• Improved understanding of IBP component performance,
particularly of unbound granular base, through advanced
material characterization and modeling
• Better understanding of relationship between
construction and long-term performance of CTB, in
particular, and IBP, in general, through continued
assessment of test sections and associated numerical
simulations
BARRIERS to implementation:
• Need for reliable framework for assessment of economics
of IBP for both construction and performance stages
• Need for material model calibrations and damage
functions suitable for IBP designs in MEPDG
• Guidelines for implementation through all phases of
design, construction and maintenance
PROPOSED POOLED-FUND STUDY CAN RESOLVE GAPS AND ELIMINATE BARRIERS
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