Concrete Overlay Research

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					                    Concrete Overlay Research
                          Shelley Stoffels, D.E., P.E.
                          Lin Yeh, PhD

                                        SCI
                                                            Gears
                Performance




                           Layer                      Measured Responses
                     Interactions



FAA Airport Pavement Working Group PavementApril 2012
                       FAA Airport Meeting, Working Group Meeting, April 2012   1 1
  CC4 conducted through IPRF consisted of
  two overlapping experiments (QES)
                              Baseline Experiment—2006
                                 9 inch OL   7.5 inch OL    6 inch OL
                                                            10 inch SL
                                             7.5 inch UL
                                 6 inch UL
     Low-strength Subgrade            Medium-strength Subgrade           High-strength Subgrade




                   SCI Validation Study—2007/2008
                                 9 inch OL    7.5 inch OL   6 inch OL
                                                            10 inch SL
                                              7.5 inch SL
                                 6 inch SL
      Low-strength Subgrade           Medium-strength Subgrade           High-strength Subgrade




FAA Airport Pavement Working Group Meeting, April 2012                                            2 2
  Experimental design included thickness variations,
  matched and mismatched joints




       NORTH                                                                             SOUTH
                  12.5                 12.5                   10          12.5          12.5




              5          12.5                  12.5                12.5          12.5          5




                                6-inch P-154 Aggregate Base



FAA Airport Pavement Working Group Meeting, April 2012                                             3 3
North test items were loaded with                              10.25 in.
triple dual tandem and South test
items with dual tandem
   Test       Structural Overlay Slab Underlay Slab
                                                                     Loading Gear
   Item        Section Thickness, mm Thickness, mm
                                                                   Triple Dual
     N1             1                  229               152
                                                                   Tandem
     N2             2                  190               190       Dual Tandem
                                                                   Triple Dual
     N3             3                  152               254
                                                                   Tandem
     S1             1                  229               152       Dual Tandem
                                                                   Triple Dual
     S2             2                  190               190
                                                                   Tandem
     S3             3                  152               254       Dual Tandem

FAA Airport Pavement Working Group Meeting, April 2012                           4 4
                                                         Test Item N1
                                                         UL SCI = 100             8.6-in PCC OL
  12                                            6
                                                         Date Passes SCI
                                                          Final OL UL
                                                         Passes
                                                         08/01/06    SCI
                                                                    2046   SCI
                                                                            80    6.3-in PCC UL
  11                                            5        08/03/06
                                                            5146    2574
                                                                      14    73
                                                                            32   5.6-in Aggregate Base
                                                         08/04/06   2574    73
                                                         08/10/06   2772    68   Subgrade k=135 pci
                                                         08/11/06   3234    63
  10                                            4
                                                         08/24/06   3234    57
                                                                                  Triple Dual Tandem
                                                         08/28/06   3234    46
                                                                                            54 in
                                                         09/13/06   3234    39
  9                                             3        09/14/06   3744    31
                     8
                         10 10 10
                                    8
                                                         09/19/06   4552    24      57 in

             4
                 6                      6
                                            4
                                                         09/22/06   5146    19
                                                         09/29/06   5146    16
  8                                             2                                   57 in
                                                         10/02/06   5146    14
                                                         10/03/06   5146    12

  7                                             1                                   50,000 lbs/wheel
                                                                                   230 psi tire pressure
-30    -25   -17.5 -12.5                        -5   0
                                                         Test Item S1
                                                         UL SCI = 100            8.7-in PCC OL
        6                                           12
                                                                   OL SCI
                                                           Final Passes UL
                                                         Date
                                                         Passes SCI SCI
                                                         08/04/06 3168
                                                                     93          6.3-in PCC UL
        5                                           11   08/08/06 3432
                                                           12142     7     85
                                                                          39    5.8-in Aggregate Base
                                                         08/09/06 3894    78
                                                         08/10/06 4356    76    Subgrade k=135 pci
                                                         08/11/06 4818    67
        4                                           10   09/13/06 5016    54
                                                                                     Dual Tandem
                                                         09/14/06 5526    51
                                                         09/19/06 8116    50
                                                                                           54 in
        3                                           9    09/22/06 8116    46
                        10 10 10                         09/26/06 9370    32
                    8              8
                6                      6                 09/29/06 11020   22       57 in
            4                              4
                                                         10/02/06 11614   16
        2                                           8
                                                         10/03/06 12142   7
                                                         10/31/06 12142   7
                                                                                   50,000 lbs/wheel
    1                                               7                             230 psi tire pressure

0   5           12.5 17.5                      25   30
FAA Airport Pavement Working Group Meeting, April 2012   7 7
FAA Airport Pavement Working Group Meeting, April 2012   8 8
         Transition




                                    12/18/06

1N-12U    1N-6U   1S-12U   1S-6U
                                       02/20/07

1N-11U    1N-5U   1S-11U   1S-5U




1N-10U    1N-4U   1S-10U   1S-4U


                                   Structural
1N-9U     1N-3U   1S-9U    1S-3U


                                   Section 1
1N-8U     1N-2U   1S-8U    1S-2U




1N-7U     1N-1U   1S-7U    1S-1U



         Transition
                                                         Test Item N1
                                                                                    9.3-in PCC OL
  12                                            6
                                                         Date       Passes SCI
                                                         11/14/07     3696   88     6.3-in PCC UL
                                                         11/19/07     4422   83
  11                                            5                                  5.6-in Aggregate Base
                                                         11/21/07     4950   77
                                                         12/03/07     7194   68
                                                         12/05/07     7986   55    Subgrade k=135 pci
                                                         12/07/07     8712   51
  10                                            4
                                                         12/10/07     9108   48
                                                                                    Triple Dual Tandem
                                                         12/11/07     9504   42
                                                                                              54 in
                                                         12/19/07    11286   27
  9                                             3        01/11/08    13398   26
                         10 10 10                        01/16/08    14850   24
                 6
                     8              8
                                        6
                                                         01/18/08    15510   12       57 in

             4                              4
                                                         Underlay            SCI
  8                                             2
                                                         Beginning            25      57 in

                                                         Final                 3

  7                                             1                                      42.5k lbs/wheel
                                                                                     230 psi tire pressure
-30    -25   -17.5 -12.5                        -5   0
                                                         Test Item S1
                                                                                    9.3-in PCC OL
        6                                           12
                                                         Date       Passes SCI
                                                         12/13/07     9966    88    6.3-in PCC UL
                                                         01/16/08    14850    80
        5                                           11
                                                         01/23/08    16316    80   5.8-in Aggregate Base
                                                         02/01/08    19008    70
                                                                                   Subgrade k=135 pci
                                                         02/04/08    19602    63
        4                                           10   02/25/08    20328    58
                                                         03/05/08    24684    52        Dual Tandem
                                                         03/11/08    27126    46
                                                         03/20/08    30096    31              54 in
        3                                           9    03/21/08    30756    29
                        10 10 10                         03/24/08    31350    23
                    8              8
                6                      6                 03/26/08    32604    20      57 in
            4                              4
                                                         04/02/08    33264    18
        2                                           8    Underlay            SCI
                                                         Beginning            23
                                                         Final                 8       42.5k lbs/wheel
    1                                               7                                230 psi tire pressure

0   5           12.5 17.5                      25   30
      Final Loading Status
     Test            Baseline             Baseline            SCI Val.      SCI Val.
     Item            Passes, k            SCI                 Passes, k     SCI
     North 1                    5,100                     5        15,500          12
     North 2                    5,100                    24        35,300          29

     North 3                    5,100                    21        35,300          27

     South 1                  12,100                      5        33,300          18

     South 2                  16,400                     11        42,800          66

     South 3                  12,100                     23        35,300          39

                        50,000-lb wheel load                   42,500-lb wheel load

FAA Airport Pavement Working Group Meeting, April 2012                                   12
                                                                                        12
  SCI Validation Study:
  Approximate Passes to SCI Values

                                                     Passes
                  N1         S1            N2               S2          N3       S3
     SCI         9”/6”      9”/6”       7.5”/7.5”        7.5”/7.5”    6”/10”   6”/10”

      80          5000 15000                 10000            23000    12500    24000


      60          7500 20000                 15000         >42000      16000    30000


      40         10000 30000                 21000              ???    25000    35000


FAA Airport Pavement Working Group Meeting, April 2012                              13
                                                                                   13
  Preliminary Findings from CC4
  Observations from Distress Surveys

     For unbonded overlay over intact slabs, the initial cracks
       were longitudinal, and longitudinal cracking, both top-
       down and bottom-up, predominated throughout testing.

     For unbonded overlay over damaged slabs, the initial
       cracks were longitudinal, but a variety of cracking
       progressed. Greatest distress concentrations in overlay
       over greatest distress in underlying.




FAA Airport Pavement Working Group Meeting, April 2012              14
                                                                   14
  Preliminary Findings from CC4
  Observations from HWD

     Continued deterioration of the underlay slabs, in place
       throughout both experiments, could be seen in the
       progressive decrease of backcalculated moduli.

     After placement of the new overlay, the backcalculated
       stiffness for the upper layer was fully recovered.
       However, some of the underlying layers also exhibited an
       apparent (temporary) stiffened effect.

     The load transfer efficiency at mismatched joints
       deteriorated less than at matched joints in the same test
       item.


FAA Airport Pavement Working Group Meeting, April 2012              15
                                                                   15
  Preliminary Findings from CC4
  Observations from Instrumentation
     The soil pressure cells during loading of the second overlay
       experienced significantly greater (normalized) responses
       than those in the initial testing.
     The ratio in magnitude of peak strain produced by the
       triple dual tandem and twin dual tandem gears is not
       inversely proportional to the number of passes to failure.
       The ratio of passes to achieve a given SCI is greater than
       can be explained only by the peak magnitude of the
       measured strains.
     For all ratios of overlay to underlay thickness, the peak
       strains from instrumentation were larger in the overlay
       than in the underlay. This corresponds to the observed
       relative distress progression.

FAA Airport Pavement Working Group Meeting, April 2012               16
                                                                    16
  Preliminary Findings from CC4
  Comparisons to Design Models
     The test items loaded with the twin dual tandem consistently
       required more passes to achieve a given SCI level than the test
       items loaded with the triple dual tandem at the same wheel load.
       This reinforces that gross aircraft weight is an important factor.
     The thin overlay over thick overlay cross section performed better
       than anticipated. While the overlay deteriorated at a rate similar
       to that of the other test items, the underlay slabs had only minor
       distress at the end of the testing.
     The unbonded overlay data, consolidated from both experiments,
       did not follow the pattern of slowing deterioration shown by the
       Rollings relationship between Cn and SCI, instead following an
       almost linear trend. A likely explanation is the corresponding
       deterioration of the underlying slabs, resulting in decreasing
       support with increased cumulative passes.


FAA Airport Pavement Working Group Meeting, April 2012                     17
                                                                          17
  Preliminary Findings from CC4
  Relative Comparison to FAARFIELD

     The thick-over-thin test items did not perform as well as
       predicted.

     The effects of underlying cracking, in terms of reducing relative
       passes to an SCI of 80, were not as significant as expected.

     The relative differences in passes to an SCI of 80 for the twin dual
       tandem as compared to the triple dual tandem were greater.

     Stress estimations from FAARFIELD, in terms of relative values,
       corresponded to the relative degree of damage to the underlay
       versus overlay that was observed in the Baseline Experiment.



FAA Airport Pavement Working Group Meeting, April 2012                     18
                                                                          18
FAARField


    Damaged slab
    material
    characterization
    for stress
    computation




    Failure model
    for traffic
    prediction for
    concrete
    overlays
A. Structure and Materials
           Relationship between pavement condition and
           materials characterization

FAARFIELD Cracked Slab Model (Rollings)
E-Ratio = 0.02 + 0.0064 X SCI + (0.00584 X SCI)2
E-Ratio: Damaged Modulus / Intact Modulus
SCI: A rating based upon the observed structural distress (ASTM D5320)
          Based on data of six
           individual slab-on-subgrade
           structures (WES)
          Assumed 50% of a test item
           would have that distress to
           compute SCI

FAA Airport Pavement Working Group Meeting, April 2012             20
                                                                  20
 Model Assessment
 Backcalculation (BAKFAA)




                As-built thickness from level surveys supplemented
                 with core data
                Seed modulus = design modulus
                Average modulus of 12 slabs = modulus of a test item

FAA Airport Pavement Working Group Meeting, April 2012                 21
                                                                      21
Underlay Modulus vs SCI




FAA Airport Pavement Working Group Meeting, April 2012    22
                                                         22
Underlay Modulus vs SCI




FAA Airport Pavement Working Group Meeting, April 2012    23
                                                         23
     Relationship between SCI and elastic modulus based upon
        backcalculation results and distress surveys.
       Should relationships from backcalculations with elastic
        layer analysis be valid for use in finite element forward
        calculations?
       Rollings used only the maximum deflection due to the
        crack discontinuities.
       It is suggested that additional sensors be used for
        unbonded overlays. Relationship was developed for single
        slab, assuming half would be deteriorated. Field SCIs
        based upon sample units.
       Is SCI the only parameter having a significant effect on
        variation of elastic modulus?
       A key area of investigation is the re-examination of the SCI
        and modulus relationship and the possible development of
        a modified cracked slab model.
FAA Airport Pavement Working Group Meeting, April 2012              24
                                                                   24
 The Modulus “Side of the Equation”
   Backcalculation Approaches
      Layered elastic
      Plate theory
      3D finite element
   Backcalculation Considerations
      Interlayer effects
      Interface conditions (bonded, unbonded)
      Overlay cracking
   Sources of Data
      Slab test data (WES)
      Full-scale rigid pavement data (CC2)
      Full-scale UBOL data (CC4)

FAA Airport Pavement Working Group Meeting, April 2012    25
                                                         25
The Distress “Side of the Equation”
Exploratory Statistical Analysis
Predictive Variables Selection
                 Overlay Data                                      Underlay Data
    Independent Variables            P-value               Independent Variables   P-value

           Intercept                        0.00                Intercept                    0.14

   Overlay Thickness, HOL                   0.79                   NP                        0.93

              LTE                           0.48                   CD                        0.02

               NP                           0.97                  NP^2                       0.11

              CD                            0.01                  CD^2                       0.01

         Test Item SCI                      0.18                   SCI                       0.83

             CD^2                           0.04                  SCI^2                      0.46

             NP^2                           0.89                SCI*HUL                      0.31

             SCI^2                          0.86         Underlay Thickness, HUL             0.58

              ISM                           0.88                 HBASE                       0.21

FAA Airport Pavement Working Group Meeting, April 2012                                    26
                                                                                         26
FAA Airport Pavement Working Group Meeting, April 2012    27
                                                         27
  Model Development
  Distress Type Effect (Failure Index)




FAA Airport Pavement Working Group Meeting, April 2012    28
                                                         28
 D. Failure Model

        SCI = 80 is defined as failure (i.e. 50% low severity
         longitudinal crack)
        Current failure model has been developed based
         on rigid pavement. Can the same failure model
         be applied to unbonded concrete overlay design?
        The damage accumulation and failure model for
         unbonded concrete overlays is being reassessed.
         Given the two concrete pavement layers and the
         interaction of relative deterioration, another
         model may be more effective than that used for
         original pavements.

FAA Airport Pavement Working Group Meeting, April 2012        29
                                                             29
 Traffic
 Prediction
 Model




         DF: Ratio between flexural strength and 75%
            of maximum tensile stress at bottom of a
            free slab under edge loading
FAA Airport Pavement Working Group Meeting, April 2012    30
                                                         30
                                             (Rollings, 1988)
FAA Airport Pavement Working Group Meeting, April 2012           31
                                                                31
FAA Airport Pavement Working Group Meeting, April 2012    32
                                                         32
FAA Airport Pavement Working Group Meeting, April 2012    33
                                                         33
Traffic Prediction Model
Development Explorations




                  Proposed Design Factor for UBOL




FAA Airport Pavement Working Group Meeting, April 2012    34
                                                         34
Traffic Prediction Model
Explorations




FAA Airport Pavement Working Group Meeting, April 2012    35
                                                         35
Traffic Prediction Model                                 THANK YOU!
Explorations




FAA Airport Pavement Working Group Meeting, April 2012            36
                                                                 36

				
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