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					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
   Waco            Cotulla          McAllen
  1.5” PFC         3.0” SMA          1.5” PFC
  2.0” SMA                           2.0” SMA
                 3.0” 19 mm SP
3.0” 19 mm SP
                                   10.0”, 19 mm
                                         or
                 8.0” 25 mm SP      25 mm SP
10.0” 25 mm SP
                 2.0” 12.5 mm      3.0” 12.5 mm
 4.0” 19 mm      2% air voids      2% air voids
 2% air voids                            8.0”
     6.0”                            lime-treated
 crushed stone                   salvaged aggregate
   Waco            Cotulla          McAllen
  1.5” PFC         3.0” SMA          1.5” PFC
  2.0” SMA                           2.0” SMA
                 3.0” 19 mm SP
3.0” 19 mm SP                      10.0”, 19 mm
                                         or
                 8.0” 25 mm SP      25 mm SP
10.0” 25 mm SP
                 2.0” 12.5 mm      3.0” 12.5 mm
 4.0” 19 mm      2% air voids      2% air voids
 2% air voids                            8.0”
                  16” Total
     6.0”                            lime-treated
 crushed stone
                    HMA          salvaged aggregate

20.5” Total
                                  16.5” Total
   HMA
                                     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
     To design against potential bottom-up
     cracking, certain strain thresholds
     cannot be exceeded.



                  }
                                              1.5-3 in. PFC, SMA, etc.
                           3”
                                 High Shear
                           to
                                    Zone
                           6”                        High Modulus
                                                 Rut Resistant Material
                                                  (Varies As Needed)


Max Flexural Strain




                     Pavement Foundation
       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.
  Estimated
    Strain




If the strains could be measured directly, using
Oklahoma materials and mix designs, the data
would be much more reliable.
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
        ODOT’S PERPETUAL PAVEMENT STRUCTURAL
             SECTIONS AT NCAT TEST TRACK
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
      2” RBL w/PG 64-22                 3” SuperPave 19.0mm w/PG 64-22
                                                  3” RBL w/PG 64-22
 *RBL = RICH BOTTOM LAYER
                                  Structural Study Test Sections
                                                                                                   Oklahoma
                                         Florida                    Alabama & FHWA
                                                                                                                  Missouri Alabama
                                                                                                         FHWA
                                    N1             N2   N3     N4        N5      N6      N7      N8        N9      N10      S11
                           0.0
                           2.0
                           4.0
                           6.0
As Built Thickness, in.




                           8.0
                          10.0
                          12.0
                          14.0
                          16.0
                          18.0
                          20.0
                          22.0
                          24.0
                                           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
 The maximum flexural strain is directly
 measured using a series of strain gauges
 installed at the bottom of the asphalt
 section.
1.5-3 in. PFC, SMA, etc.


     High Modulus
 Rut Resistant Material
  (Varies As Needed)



Max Flexural Strain




                    Pavement Foundation
If we have determined the strain for a 10” and
14” thick pavement, the thickness at the critical
strain level can be interpolated / extrapolated
   MICROSTRAIN




                       ?




                 10”       14”      16”
                                                              Instrumentation – N8
                                                                                            12
                                                                                                                   Edge Stripe
                                                                                            10                     Outside Wheelpath
                                                                                                                   Inside Wheelpath
Longitudinal Offset from Center of Array, ft .




                                                                                             8                     Centerline
                                                                                                    14
                                                                                             6
                                                                                                                Temperature probe
                                                                                       10    4 11        12

                                                                                       7     2 8         9

                                                                                             0
                                                                                        4       5        6
                                                 -12   -10   -8    -6      -4          -2       0        2     4       6      8        10   12
                                                                                        1    -2 2        3

                                                                                             -4                               Laser 15
                                                                                                    13
                                                                                             -6
                                                                        Direction of
                                                                          Travel             -8               Earth Pressure Cell
                                                                                                              Asphalt Strain Gauge
                                                                                            -10

                                                                                            -12
                                                                  Tranverse Offset from Center of Outside Wheelpath, ft
          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

               90

               80

               70

               60
Micro Strain




               50

               40

               30

               20

               10

                0

               -10 0   0.5   1          1.5          2   2.5   3

                                       Time (sec)
To design the appropriate pavement thickness, stresses and strains
 The vertical compressive strain is directly
 measured using pressure plates installed
 at the top of the subgrade.
                                              1.5-3 in. PFC, SMA, etc.



                                                     High Modulus
                                                 Rut Resistant Material
                                                  (Varies As Needed)


Max Flexural Strain


                                           Vertical Compressive Strain
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
N2                                                                                                     Longitudinal Distance from Far End of Section (ft)                                   3/21/2005
                                                25   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
                                           12                                                                                                                                                       12


                                           11                                                                                                                                                       11


                                           10                                                                                                                                                       10




                                                                                                                                                                                                         Thickness of Experimental Pavement Lifts (in)
                                           9                                                                                                                                                        9
Transverse Distance from Centerline (ft)




                                           8                                                                                                                                                        8


                                           7                                                                                                                                                        7


                                           6                                                                                                                                                        6


                                           5                                                                                                                                                        5


                                           4                                                                                                                                                        4


                                           3                                                                                                                                                        3


                                           2                                                                                                                                                        2


                                           1                                                                                                                                                        1


                                           0                                                                                                                                                        0

                                                                    Cracking             Coring             Random Testing          Avg Wheelpaths      Gauge Array      Avg Thickness
FWD Testing

Rut Testing

Skid Testing

Inertial Profiler –
     Rutting
     Smoothness
     Surface Texture
                                Longitudinal Microstrain




                    0
                        200
                              400
                                                                       600
                                                                             800
                                                                                                     1000
                                                                                                                              1200
        11/1/2006


        12/1/2006


       12/31/2006
                                                                                                                  N8 (Meas)
                                                                                                      N9 (meas)
                                                                                   Ratio (N8 / N9)


        1/30/2007


         3/1/2007


        3/31/2007


        4/30/2007


        5/30/2007




Date
        6/29/2007


        7/29/2007


        8/28/2007


        9/27/2007


       10/27/2007


       11/26/2007
                                                                                                                                     N8 and N9 – Strain vs. Date




       12/26/2007
                                         Average Ratio (N8/N9) = 2.6




        1/25/2008
                    0
                        1
                              2
                                                                       3
                                                                             4
                                                                                                     5
                                                                                                                              6




                                    Ratio of Strain (N8/N9)
                                                     Effect of Depth (N9)
                           350




                           300




                           250
Longitudinal Microstrain




                           200




                           150                                                                                                    Bottom of HMA
                                                                                                                                  Bottom of Lift 2
                                                                                                                                  Bottom of Lift 3


                           100




                            50




                             0
                           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
Temperature Normalized Response
                 400

                 350

                 300
  Microstrains




                 250

                 200

                 150

                 100

                 50

                  0
                       Average Average Average Average Average Average Average Average Average
                        of N1   of N2   of N4   of N6   of N7   of N8   of N9 of N10 of S11
                                    Normal Operations
• 55% of Strains below threshold
                       140                                                                                                   700

                                                                                                              T2_AVG
                                                                                                              Strain

                       120                                                                                                   600




                       100                                                                                                   500
    Temperature (oF)




                        80                                                                                                   400




                                                                                                                                   Microstrain
                        60                                                                                                   300




                        40                                                                                                   200




                        20                                                                                                   100




                         0                                                                                                   0
                       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
                                                                                                                                         30

                                                                                                                                         28


                                                                           Earth Pressure Cell                                           26
                                                                           Asphalt Strain Gauge
                                                                                                                                         24              Gauges 24 - 27
                                                                                                                                                       Top of HMA Lift 3


 Supplemental                                                                                                                            22

                                                                                                                                         20


    FHWA                                                                                                                                 18
                                                                                                                                                         Gauges 20 - 23
                                                                                                                                         16

  Experiment
                                                                                                                                                       Top of HMA Lift 2




                      Longitudinal Offset from Center of Array, ft
                                                                                                                                         14




                                                                                                          Gauges Numbered 16 - 27
                                                                                                                                         12

                                                                                                                                         10
                                                                                                                                                         Gauges 16 - 19
                                                                                                                                                       Top of HMA Lift 1
                                                                                                                                          8

                                                                                                                                          6

                                                                                                                                          4



N9 Instrumentation                                                                                                                        2

                                                                                                                                          0


(Multi-Depth Array)                                                  -12   -10     -8      -6       -4                              -2
                                                                                                                                          -2
                                                                                                                                               0   2      4      6         8       10   12



                                                                                                  Direction of
                                                                                                                                          -4                               Laser
                                                                                                    Travel
                                                                                                                                          -6                  Edge Stripe
                                                                                                                                                              Outside Wheelpath
                                                                                                                                          -8                  Inside Wheelpath
                                                                                                                                         -10
                                                                                                                                                              Centerline

                                                                                                                                         -12
                                                                                          Tranverse Offset from Center of Outside Wheelpath, ft
N9 Cross Section and Supplemental Instrumentation
                                          Full Depth HMA Section
              0
              1                                                    SMA
                   Asphalt Strain Gauge
              2
                   Thermistor
              3                                                    PG 76-28
              4
              5
              6                                                    PG 64-22
Depth, in.




                  Asphalt Strain Gauge
              7
                      Plan View
              8
              9                                                    PG 64-22
             10
             11
             12                                                    PG 64-22
                                                                   Rich Bottom
             13
             14          CL      OWP
             15
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                 • Temperature-Strain
  – Strain at bottom of HMA        – Strain at bottom of HMA
  – Decrease with speed            – Increase with temperature

     a ln v  b                         ce   dT




                 a ln v  e  d  cT

                      R2: 0.955-0.986
                             Strain Threshold
• Tensile strain threshold: 100με
                  700


                  600


                  500
                                                                       15 mph
                                                                       25 mph
    Microstrain




                  400
                                                                       35 mph
                                                                       45 mph
                  300
                                                                       65 mph
                                                                       Strain Threshold
                  200


                  100


                   0
                        20   40   60       80        100   120   140
                                       Temperature
THANK
 YOU!




        QUESTIONS?