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Oklahoma DOT Perpetual Pavement Test Sections at the NCAT Test Track
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Transcript of Oklahoma DOT Perpetual Pavement Test Sections at the NCAT Test Track
Oklahoma DOT Perpetual
Pavement Test Sections at the
NCAT Test Track
Compression
Tension
Perpetual Pavement
Structure and materials are designed to provide a long service life (50 years +)
Early Texas Perpetual Pavements
1.5” PFC2.0” SMA
3.0” 19 mm SP
10.0” 25 mm SP
4.0” 19 mm2% air voids
6.0” crushed stone
3.0” SMA
3.0” 19 mm SP
8.0” 25 mm SP
2.0” 12.5 mm2% air voids
Waco Cotulla McAllen
10.0”, 19 mmor
25 mm SP
3.0” 12.5 mm2% air voids
1.5” PFC2.0” SMA
8.0”lime-treated
salvaged aggregate
1.5” PFC2.0” SMA
3.0” 19 mm SP
10.0” 25 mm SP
4.0” 19 mm2% air voids
6.0” crushed stone
3.0” SMA
3.0” 19 mm SP
8.0” 25 mm SP
2.0” 12.5 mm2% air voids
Waco Cotulla McAllen
10.0”, 19 mmor
25 mm SP
3.0” 12.5 mm2% air voids
1.5” PFC2.0” SMA
8.0”lime-treated
salvaged aggregate
20.5” Total HMA
16” Total HMA
16.5” Total HMA
How thick is too thick?
Cost of 5 Miles of Pavement
Assume 80’ width, $50 per ton
Save 1” in over-design: $650,000
Save 2” in over-design: $1,300,000
Save 4” in over-design: $2,600,000
How thin is too thin?
If the perpetual pavement structure is designed too thin, the risk of bottom-up cracking increases dramatically, defeating the purpose of the design and resulting in an expensive rebuild.
To design the appropriate pavement thickness, stresses and strains
Max Flexural Strain
Pavement Foundation
High ModulusRut Resistant Material
(Varies As Needed)
} 3”3”toto6”6”
High ShearHigh ShearZoneZone
1.5-3 in. PFC, SMA, etc.
To design against potential bottom-up cracking, certain strain thresholds cannot be exceeded.
Limiting Strain Theory
• Based on laboratory beam fatigue data
• “Small” strains will never induce cracking
• Limiting strain at 75 to 125 microstrains
• No bottom-up cracking below this level
These strains can be calculated based on total pavement thickness and material properties.
However, the calculations would be based on assumptions made from previously collected data.
There are large deviations in the types of environment around the country, the types of materials used and the types of pavement specified. These deviations decrease the reliability of the assumptions made to calculate strains.
If the strains could be measured directly, using Oklahoma materials and mix designs, the data would be much more reliable.
Est
imat
ed
Str
ain
National Center for Asphalt Technology (NCAT) Test Track
ODOT’S PERPETUAL PAVEMENT STRUCTURAL SECTIONS AT NCAT TEST TRACK
PLAN VIEW
SECTION N8 – 150’ SECTION N9 – 150’
25’ TRANSITION 50’ TRANSITION 25’ TRANSITION
PLAN VIEW
SECTION N8 – 150’ SECTION N9 – 150’
25’ TRANSITION 50’ TRANSITION 25’ TRANSITION
PROFILE VIEW
2” SMA w/PG 76-28
3” SuperPave 19.0mm w/PG 76-28
3” SuperPave 19.0mm w/PG 64-22
3” SuperPave 19.0mm w/PG 64-22 2” RBL w/PG 64-22
3” RBL w/PG 64-22
*RBL = RICH BOTTOM LAYER
ODOT’S PERPETUAL PAVEMENT STRUCTURAL SECTIONS AT NCAT TEST TRACK
Structural Study Test Sections
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
22.0
24.0
N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 S11
As
Bu
ilt T
hic
kne
ss, i
n.
PG 67-22 PG 76-22 PG 76-22 (SMA) PG 76-28 (SMA)
PG 76-28 PG 64-22 PG 64-22 (2% Air Voids) PG 70-22
Limerock Base Granite Base Type 5 Base Track Chert Soft Subgrade
Florida Alabama & FHWAOklahoma
FHWAMissouri Alabama
Max Flexural Strain
Pavement Foundation
High ModulusRut Resistant Material
(Varies As Needed)
1.5-3 in. PFC, SMA, etc.
The maximum flexural strain is directly measured using a series of strain gauges installed at the bottom of the asphalt section.
MIC
RO
ST
RA
IN
10” 14” 16”
?
If we have determined the strain for a 10” and 14” thick pavement, the thickness at the critical strain level can be interpolated / extrapolated
Instrumentation – N8
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12
Tranverse Offset from Center of Outside Wheelpath, ft
Lon
gitu
din
al O
ffse
t fr
om C
ente
r of
Arr
ay, f
t .
Earth Pressure CellAsphalt Strain Gauge
Edge StripeOutside WheelpathInside WheelpathCenterline
Direction of Travel
Temperature probe
Laser
1 2 3
4 5 6
7 8 9
10 11 12
13
14
15
Accelerated Loading
• Compress 10-15 years into 2 years
• Heavy triples optimize safety and efficiency
• Each axle loaded to federal legal bridge limit
• Heavier loads induce unrealistic damage
• No bridge spans to overload on NCAT track
• Average gross vehicle weight 155k pounds
Long Term Response Measurements
• Weekly - three passes of 5 trucks– Steer axle (12 kip), tandem (40 kip), 5 single axles (20
kip/axle)– 45 MPH
• Measure strain• Measure pressure• Measure temps• Characterize long-term trends in strain response
Transverse Strain
-10
0
10
20
30
40
50
60
70
80
90
0 0.5 1 1.5 2 2.5 3
Time (sec)
Mic
ro S
trai
n
To design the appropriate pavement thickness, stresses and strains
Max Flexural Strain
High ModulusRut Resistant Material
(Varies As Needed)
Vertical Compressive Strain
1.5-3 in. PFC, SMA, etc.
The vertical compressive strain is directly measured using pressure plates installed at the top of the subgrade.
Moisture sensors were also placed in the subgrade to continuously monitor soil conditions
Temperature probes were placed in the pavement to continuously monitor temperature at various depths
A datalogger is used to collect information from the different pavement sensors.
In addition to the normal “slow speed” mode that continuously gathers data, a “high speed” mode can be used to collect 40,000 data points per second.
Additional Testing - Surface Map Cracking
3/21/2005N2
0
1
2
3
4
5
6
7
8
9
10
11
1225 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175
Longitudinal Distance from Far End of Section (ft)
Tran
sver
se D
ista
nce
from
Cen
terl
ine
(ft)
0
1
2
3
4
5
6
7
8
9
10
11
12
Thic
knes
s of
Exp
erim
enta
l Pav
emen
t Lift
s (in
)
Cracking Coring Random Testing Avg Wheelpaths Gauge Array Avg Thickness
FWD Testing
Rut Testing
Skid Testing
Inertial Profiler –RuttingSmoothnessSurface Texture
N8 and N9 – Strain vs. Date
0
200
400
600
800
1000
120011
/1/2
006
12/1
/200
6
12/3
1/20
06
1/30
/200
7
3/1/
2007
3/31
/200
7
4/30
/200
7
5/30
/200
7
6/29
/200
7
7/29
/200
7
8/28
/200
7
9/27
/200
7
10/2
7/20
07
11/2
6/20
07
12/2
6/20
07
1/25
/200
8
Date
Lo
ng
itu
din
al M
icro
stra
in
0
1
2
3
4
5
6
Rat
io o
f S
trai
n (
N8/
N9)
N8 (Meas)
N9 (meas)
Ratio (N8 / N9)
Average Ratio (N8/N9) = 2.6
Effect of Depth (N9)
0
50
100
150
200
250
300
350
10/10/2006 11/29/2006 1/18/2007 3/9/2007 4/28/2007 6/17/2007 8/6/2007 9/25/2007 11/14/2007 1/3/2008 2/22/2008
Date
Lo
ng
itu
din
al M
icro
stra
in
Bottom of HMA
Bottom of Lift 2
Bottom of Lift 3
Temperature Normalized Response
0
50
100
150
200
250
300
350
400
Averageof N1
Averageof N2
Averageof N4
Averageof N6
Averageof N7
Averageof N8
Averageof N9
Averageof N10
Averageof S11
Mic
rost
rain
s
Normal Operations• 55% of Strains below threshold
0
20
40
60
80
100
120
140
10/10/2006 12/24/2006 3/9/2007 5/23/2007 8/6/2007 10/20/2007 1/3/2008 3/18/2008
Date
Tem
per
atu
re (
oF
)
0
100
200
300
400
500
600
700
Mic
rost
rain
T2_AVG
Strain
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12
Tranverse Offset from Center of Outside Wheelpath, ft
Lon
gitu
din
al O
ffse
t fr
om C
ente
r of
Arr
ay, f
t
Earth Pressure CellAsphalt Strain Gauge
Gauges 16 - 19Top of HMA Lift 1
Gauges 20 - 23Top of HMA Lift 2
Gauges 24 - 27Top of HMA Lift 3
Gau
ges
Nu
mb
ered
16
- 27
Edge StripeOutside WheelpathInside WheelpathCenterline
Direction of Travel
Laser
N9 Instrumentation(Multi-Depth Array)
Supplemental FHWA
Experiment
N9 Cross Section and Supplemental Instrumentation
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
De
pth
, in
.
Full Depth HMA Section
Asphalt Strain Gauge
Thermistor
SMA
PG 76-28
PG 64-22
PG 64-22
PG 64-22Rich Bottom
Asphalt Strain GaugePlan View
OWPCL
Strain vs. Speed and Temperature (ODOT and FHWA)
• Primary Objectives– Study a perpetual pavement under a wider set
of conditions• Primarily look at speed and temperature effects
Data Collected
• 4 Speeds Tested– 15-45 mph (10 mph increments)
• 4 Dates– April – May 2007
• Measured– Temperature– Tensile Strain
Investigations
• Studied relationships– Speed-Strain– Temperature-strain– Combined
• Strain Threshold
• Load Durations– Relate to Frequency
Relationships
• Speed-Strain– Strain at bottom of HMA– Decrease with speed
• Temperature-Strain– Strain at bottom of HMA– Increase with temperature
bva ln dTce
deva cT lnR2: 0.955-0.986
Strain Threshold
• Tensile strain threshold: 100με
0
100
200
300
400
500
600
700
20 40 60 80 100 120 140
Temperature
Mic
rost
rain
15 mph
25 mph
35 mph
45 mph
65 mph
Strain Threshold
THANK YOU!
QUESTIONS?