Structural Overlay Design Using NDT Methods

7/31/2019 Structural Overlay Design Using NDT Methods

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Structural Overlay Design

Using NDT MethodsZhong Wu, Ph.D., P.E.Louisiana Transportation Research Center2007 Transportation Engineering ConferenceBaton Rouge, February 11-14, 2007


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OutlineBackgroundObjective

Overview of Overlay Design MethodsResearch ProjectsSummaryRecommendations


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BackgroundAsphalt overlay has been considered assimplest and fastest means of restoring the distressedsurfaces of rigid and flexible pavements

A quality overlay designimprove the roadways rideabilityrestore the pavement structural stability.

Structural overlay thickness design requestsExisting subgrade conditionExisting pavement strengthEngineering judgment


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Background (cont)Current DOTD overlay thickness designthe 1993 AASHTO Pavement design guide software (DARWin)

One required design input, subgrade resilient modulus value,Mr,

the pre-assigned parish-map valuesnot base on in-situ soil properties

Uses component analysis (layer co-efficients) method todetermine the existing pavements structure number

SN eff = a ihiSuch method can lead to design errors (over- or under-estimated overlay thickness)

since design values do not represent actual field conditions


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Overlay Design Example

-30 -20 -10 0 10 20 30 40 50 60 70 80Change in M r (MPa)

-150

-100

-50

0

50

100

150

D i f f e r e n c e

i n o v e r

l a y

t h i c k n e s s

( m m

)

-4000 -2000 0 2000 4000 6000 8000 10000Change in M r (psi)

Hot mix asphaltD1 =102 mm, a 1 =0.0165/mm

Base courseD2 =241 mm, a 2 =0.0063/mm

SubbaseD3 =457 mm, a 3 =0.0040/mm

Subgrade soil

Typical pavement section

W 18 =5,000,000 ESALsR=95 %

PSI=1.9S0 =0.35Design M r=34.5 MPaDesign SN=5

Mr = 2,000 psi

=> Underestimated ACthickness of 1.5 in

Mr = -2,000 psi

=> Overestimated ACthickness of 2.0 in


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Objectiveto establish a methodology for mechanisticpavement overlay design, based on

in-situ pavement conditions, andutilizing non destructive test (NDT) methods,specifically the FWD and/or Dynaflect.

Dynatest 8002 model Falling Weight Deflectometer Dynaflect


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Overview of Overlay Design MethodsEffective Thickness (ET) Approach

1993 AASHTO Pavement Design GuideAsphalt Institute (AI) ET Method (MS-17)

Deflection-based ApproachAI Benkelman Beam Deflection Method (MS-17)Caltran Flexible Pavement Rehabilitation

Mechanistic-Empirical (M-E) ApproachEVERPAVE (WsDOT)New M-E Pavement Design Guide


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Effective Thickness (ET) Approach- Asphalt Institute (MS-17)

Thickness of Overlay = Tn - TeTn, new pavement thickness, determined from AI

Design Chart for Full-depth Asphalt Concrete, usingESAL d and MrTe , effective thickness of existing pavementstructure

Te= C ih iwhere, hi=thickness of the ith layer of the existingpavement;C

i=conversion factor associated with the ith existing layer


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Effective Thickness (ET) Approach

-1993 AASHTO Pavement Design GuideOverlay Thickness Equation

SN f from AASHTO pavement design equationwhere Mr is a required input, which can be determined from

Laboratory TestingBackcalculation from NDT measurementsApproximate relationships ( used by DOTD )

The effective structure number of existing pavement, SN eff NDT methodComponent analysis method ( used by DOTD )Remaining life method

OL

eff f

OL

OLOL a

SN SN

aSN

h


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Deflection-Based Approach

- Asphalt Institute Benkelman Beam (MS-17)Pavement is modeled as a two-layer system

Layer 1: AC OverlayLayer 2: Existing pavement

Overlay thickness is determined as following steps:Determine Representative Rebound Deflection (RRD)

Layer 2s elastic modulus is determined from RRD.

Compute Design Rebound Deflection (DRD) based on theallowable ESAL: DRD=1.0363 (ESAL )-0.2438

Other Deflections (e.g. FWD, Dynaflect) can beconverted into Benkelman beam deflections, such as

Benkelman Beam = 1.61 * FWDBenkelman Beam = 20.63 * Dynaflect


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Mechanistic-Empirical (M-E) Approach

Modeled pavement as multi-layered elasticor visco-elastic structure

Pavement materials described by theirstiffness and strengths at different times of the year

Determine the critical stress, strain, ordeflection by mechanistic methodsPredict resulting damages by empirical

failure criteria, e.g. fatigue cracking, rutting.


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Mechanistic-Empirical (M-E) Approach-EVERPAVE

Developed by Washington DOTSteps:

Backcalculate layer moduli using FWD dataAnalyze and determine the two failure criteria parameters.

Fatigue crackingRutting

Compute allowable repetitions to failure at each seasonCompute damage at each season and sum the seasonaldamage ratio.Determine the overlay thickness based on the sum of the

damage ratio is less than or equal to one.

)log(854.0)log(291.382.14log act f E N

4843.418 )(10077.1log V f N


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EVERPAVE Design Input


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New M-E Pavement Design Guide

Developed underNCHRP 1-37ANew Traffic inputEnhanced IntegratedClimatic Model(EICM)

Season variationsNew Distress ModelsNeed Calibration

Dr. Matthew W. Witczak (2003)


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NDT Overlay Design SurveyState Method Software

Arkansas Equivalent Thickness ROADHOG

Mississippi Equivalent Thickness ELMOD5

Alabama 1993 AASHTO Spreadsheet program

Maryland 1993 AASHTO Spreadsheet program(VDOT)

Virginia 1993 AASHTO Spreadsheet program

California Deflection-based Design Manual

North Carolina AI Deflection-based Spreadsheet program

South Carolina Deflection-based Spreadsheet program

Idaho M-E WinFlex

Minnesota M-E MNPAVE

Oregon M-E /

Texas M-E FPS-19W

Washington M-E EVERPAVE


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Project SelectionFour in-service pavements

I-12 (ESAL d=24,400,000, life=15yrs)

LA28 (ESAL d=1,513,000, life=10yrs)LA74 (ESAL d=700,590, life=10yrs)LA44 (ESAL d=353,256, life=10yrs)

Each project about 3 to 5 miles long


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Design PlanBased on current DOTD overlay designmethod (Mr-parish map, SN eff -estimated)

I-12 4.5 AC overlay + 2 cold planningLA28 4.5 AC Overlay + 2 cold planningLA44 3.5 AC overlay + 2 cold planning

LA74 3.5 AC overlay + 2 cold planning


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NDT TestsFWD and Dynaflect tests were performed oneach project site

at 0.1 mile intervalon both traffic directions

8 4 6 6 12 12 12 12

d1 d2 d3 d4 d5 d6 d7 d8 d9

FWD Load


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Dynaflect Deflection AnalysisKinchen and Temple(1980) developed aPavement EvaluationChart for Louisiana

SN of existing pavementsSubgrade Modulus

Routinely use inpavement researchprojects

Pavement Evaluation Chart


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FWD Analysis (D0 & D9)

LA 44

0

5

10

15

20

25

1 . 0

1 . 2

1 . 4

1 . 6

1 . 8

2 . 0

3 . 1

3 . 3

3 . 5

3 . 7

3 . 9

6 . 0

6 . 2

6 . 4

6 . 6

6 . 8

7 . 0

Station (miles)

F W D D e f

l e c t

i o n

( m i l s D0 (NB)

D0 (SB)

D9 (NB)

D9 (SB)

LA 74

0

10

20

30

40

50

0 . 1

0 . 3

0 . 5

0 . 7

0 . 9

1 . 1

1

1 . 3

1 . 5

1 . 7

1 . 9

2 . 1

2 . 3

2 . 5

2 . 7

2 . 9

3 . 1

Station (miles)

F W D D e f

l e c t

i o n

( m i l s

D1(EB)D0 (WB)D9 (EB)D9 (WB)


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Dynaflect (SN)


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Overlay ThicknessDeflection-Based Approach (AI Method)

3.5"3.5"

4.5"4.5"

2"

4"4.5"

3"

2"

3"2"

3"

0

2

4

6

8

I-12 LA28 LA74 LA44Project

O

v e r

l a y

T h i c k n e s s

( i n

Current PlanAI (NB/EB)AI (SB/WB)


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Equivalent Thickness Method(Arkansas ROADHOG)

3.5"3.5"

4.5"4.5"

2.8"2.7"

4.2"

2"2.6"2.2"

2.9"2"

0

2

4

6

8

I-12 LA28 LA74 LA44Project

O

v e r

l a y

T h i c k n e s s

( i n

Current PlanROADHOG(NB/EB)ROADHOG(SB/WB)


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Based on M-E Design Approach

Only 0 or 1 overlay thickness required for allfour projects.

Possible explanations:Backcalculated modulus too highDefault values used in distress models (no

Calibrated)Not fully understand how to choose arepresentative design value


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Summary (Deflection-based method)

Simple to use (e.g. AI method)Needs to verify and calibrate the relationship

between FWD (or Dynaflect) measureddeflections and BB rebound deflectionsRelationship between allowable rebound

deflection and ESAL d also needs to beverified and calibrated


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Summary (Equivalent Thicknessmethod)

Simple to use (e.g. AASHTO and ROADHOG)1993 AASHTO NDT-based method generallyunderestimate the overlay thickness, due to over-estimate the existing pavement SN.ROADHOG uses its own relationship in estimationof SNeff.

Such relationships between SNeff and delta(D) may ormay not be applicable to Louisiana condition


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Summary (M-E design method)Complicate to use.M-E-based overlay design method needs

sophisticate inputs, which usually are notavailable directly from in-situ NDT testsThe fatigue and rutting models used in any M-

E base design software must be verified andcalibrated before any locally implementation.


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Proposed NDT-based Overlay DesignProcedure for Louisiana

Use Effective Thickness approachThe future Structure Number (SN future )determined from 1993 AASHTO designequation

Mr determined from in-situ tests (DCP, FWD orDynaflect)

SN eff determined from FWD or Dynaflect testIf FWD used, SN eff (FWD) needs to be scaleddown to SN eff (Dynaflect) for LouisianaCondition

Overlay thickness = (SN future -SN eff )/a AC


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Future WorksFurther validate the Dynaflect deflectiondetermined SNeff

The proposed overlay design procedure willbe automated into a EXCEL spreadsheet-based program

Documents

Structural Overlay Design Using NDT Methods