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The Asphalt Pavement Alliance Presents:A Five‐Part Webinar Series On Mechanistic Empirical Pavement Design Guide (MEPDG) Implementation Specific to Asphalt Pavements

Part 1: Pavement Design, Where We’ve Come From and What We’re Trying to Accomplish

Part 2: Local Calibration

Part 3: Individual Distress Models

Part 4: Major Inputs – Where Do They Come From & How Do We Get Them?

Part 5: Moving Beyond Data Input (Advanced)

The Asphalt Pavement Alliance Presents:A Five‐Part Webinar Series On Mechanistic Empirical Pavement Design Guide (MEPDG) Implementation Specific to Asphalt Pavements

• Today’s Webinar: Part‐3The Individual Distress Models

•Speaker:Kevin Hall, PhD., P.E.Professor and Head of the Department of Civil Engineering at the University of Arkansas

• Moderator:Mike Kvach, APA

Webinar Protocol:

• Audio Quality

• All attendees have been muted upon joining.

• Questions & Answers• Questions Box – Make sure to change the drop‐

down menu to “Organizer & Panelists Only”

•Recorded Webinars• www.asphaltfacts.com/webinars/

• Click on:  “View Webinars”

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•Speaker:Kevin Hall, PhD., P.E.Professor and Head of the Department of Civil Engineering at the University of Arkansas

Part 3: Individual Distress Models

•Panelist:David Newcomb, Ph.D., P.E.Senior Research Scientist with the Texas Transportation Institute

Flexible Pavement Performance Modelsin Pavement‐METM

Kevin D. Hall, Ph.D., P.E.Professor and Head, Dept. of Civil Engineering21st Century Leadership Chair in Civil Engineering

Dave Newcomb, Ph.D., P.E.Senior Research EngineerTTI / Texas A&M University

Pavement‐METM Webinar SeriesPresentation #3Asphalt Pavement AllianceSeptember 9, 2013

Quick note about terms: “Pavement-ME” is the software package which contains the “Mechanistic-Empirical Pavement Design Guide” (MEPDG). We will use the terms rather interchangeably…

Trial Design

Str

uct

ura

lM

od

el

Transfer Functions

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What we WILL discuss◦ Pavement response models and transfer functions◦ Applicability of the models◦ Sensitivity of performance predictions to model

inputs◦ Implications◦ Reliability (time permitting)

What we WILL NOT discuss◦ “Why” the model forms are what they are

Example: ‘Traditional’ Asphalt Institute:Asphalt Fatigue

Nf = 0.0796*(r)-3.291 E-0.854

r = tensile strain in ACRutting (subgrade)

Nf = 1.365*10-9 (z)-4.477

z = vertical strain in subgrade

Nf = load applications to “failure”

Extension of Miner’s Hypothesis◦ Pavement ‘damage’ caused by each load is

proportional to the predicted Nf (loads to failure)◦ Incremental damage(s) are additive

For Design: total accumulated damage < 1.0

1.0

For each “n” applications of a load/axle configuration which causes a stress/strain related to Nfcycles to failure…

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Key Question: what factors influence the performance prediction?

HMA thickness = Alligator Crackingi.e.

Binder Content = Rutting

One-at-a-Time (OAT)

“Local” Analysis

HMA thicknessAlligator Cracking

i.e.

Binder Content Rutting

GLOBALSensitivity Analysis

(GSA)

GradationChange

IRI

Lee and Hall, 2004 Kim, Ceylan and Heitzman, 2005 Graves and Mahboub, 2006 Tran and Hall, 2007 Buch et al. 2008 Li, Pierce, Hallenbeck and Uhlmeyer, 2009 Sayyady et al. 2010 Orobio, 2010 Mallela, 2011 Zapata and Salim, 2012 NCHRP 1-47: Schwartz, et al

GLOBALSensitivity Analysis

(GSA)

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HS: Hyper-SensitiveVS: Very SensitiveS: Sensitive

Negative values inverselyproportional, e.g.property = distress

Statistical Property isNormalized SensitivityIndex (NSI)-- scaled with the distress;

(relative values can becompared acrossdistress types)

Asphalt Master Curve (E*) Parameters

Terminal IRI (in/mile)AC top‐down fatigue cracking (ft/mile)AC bottom‐up fatigue cracking (percent)AC thermal fracture (ft/mile)Permanent deformation – total pavement (in)Permanent deformation – AC only (in)Reflective cracking (percent)

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Wheel Load

Repeated Tensile Strain

Fatigue Cracking / Pot Holes

Leads to

Wheel Load

Repeated Tensile / Shear Strains

Top-Down Cracking

Leads to

www.pavementinteractive.org

32 281.19492.3

1

1100432.0

ff

ECN

tff

MC 10

69.084.4

ba

b

VV

VM

where Nf = number of repetitions to fatigue cracking

t= tensile strain at the

critical locationE = stiffness of the materialC = laboratory to field

adjustment factorVb = effective binder content (%)Va = air voids (%)fi = Calibration coefficients

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T

i i

i

N

nD

1

60

1*

1

6000_..

))100*(10*log**( '22

'11 DCCCCe

upbottomCF

C1=1.0C2=1.0C2’= -2.40874-39.748*(1+hac)-2.856

C1’= -2*C2’hac= AC thickness

T

i i

i

N

nD

1

56.10*1

1000_.. )log*( 21

DCCedowntopCF

D = top-down damage, C1= 7, C2=3.5.

Master Curve Parameters

Expected…

????

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Master Curve Parameters

Expected…????Expected…

ac

f

hCNC

/log400

Cf = amount of thermal cracking (ft/500 ft) N = standard normal distribution at ( )C = crack depth (in)hac = thickness of asphalt layer (in)

nnt KAkC 1

C = change in crack depth due to a cooling cyclek = regression coefficient determined through

field calibrationBt = calibration coefficentA, n = fracture parameters for asphalt mixtureK = change in stress intensity factor due to

a cooling cycleE = mixture stiffnessm = undamaged mixture tensile strength

nE mA log(52.2389.410

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There is no prediction of thermalcracking when the appropriatebinder grade is selected…

Wheel Load

Repeated Vertical Strain

Rutting

Leads to

nsublayers

i

iiphRD

1

ipih

= pavement total permanent deformation

= number of sublayers

= total plastic strain in sublayer i

= thickness of sublayer i

i

RD

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32 4791.05606.135412.31 10* rr NTk rz

r

p

p = accumulated plastic strain

= resilient strain of HMA(function of loading time, mixture, temp)

= depth parameter (to account for confiningpressure at various depths)

= Temperature (F)

= Number of load applications

= Calibration Coefficients

k1

T

r

Nri

= depth parameter (to account for confiningpressure at various depths)

kz

ach

depthdepthCCk 328196.0*)*( 211

342.17*4868.2*1039.0 21 acac hhC

428.27*7331.1*0172.0 22 acac hhC

= AC thickness

32 4791.05606.135412.31 10* rr NTk rz

r

p

N

rvsa ehkN 0

11)(

where

a

0

rv

1s

= permanent deformation for the layer/sublayer (in)N = number of traffic repetitions

= material properties= calibration factor= resilient strain from laboratory tests (in/in)= average vertical resilient strain in the layer/sublayer

as obtained from the primary response model (in/in)h = thickness of the layer/sublayer (in)k1 = material coefficient (granular: 2.03 fine: 1.35)

, , and

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Master Curve Parameters

????!!!!!

Expected…

Master Curve Parameters

????

!!!!!Expected…

Rutting (under HMA) only slightly sensitive to Unbound layer stiffness!

TL

age

TCeSFIRIIRI )(00119.010463.0 200

MHSNWPT LCBC )(00115.0)(00736.0 TRD FCCOV )(00384.0)(1834.0

IRI = IRI at any given time, m/kmIRI0 = initial IRI, m/kmSF = site factorCOVRD = coefficient of variation of the rut depths(TCL)T = total length of transverse cracking, m/km(FC)T = fatigue cracking in wheel path, percent(BC)T = area of block cracking as a percent of total lane area(LCSNWP)MH = length of moderate and high severity sealed longitudinal cracks

outside wheelpath, m/km

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TFCFIAgeIRIIRI )(00235.0)(0005183.0)(0099947.00

HHS

PTC

)(9694.0)(

136.18

(TCS)H = average spacing of high severity transverse cracking, m(P)H = average of high severity patches, percent of total lane area, %

TLRDT TCSDFCIRIIRI )(0001449.0)(07647.0)(00732.00

MHNWPT LCBC )(002115.0)(00842.0

(LCNWP)MH = medium and high severity sealed longitudinal cracking outside the wheel path, m/km.

SDRD = standard deviation of the rut depth, mm

Master Curve Parameters

????Expected…

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Performance Prediction Models◦ Bottom-up fatigue cracking, thermal cracking, rutting, IRI

appear functional at this time◦ Top-down cracking, reflection cracking appear to be less

functional at this time Hyper-sensitive or Very Sensitive for “most” (4 out of

5) distress predictions:◦ E* alpha & E* delta (in other words…Dynamic Modulus)◦ HMA thickness◦ Surface shortwave absorptivity◦ Poisson’s ratio

Very Sensitive for multiple distress predictions:◦ Air Voids◦ Effective Binder Volume◦ Traffic Volume

“Reliability” : Standard Deviations

AC Rutting:                         0.24*Pow(RUT,0.8026)+0.001

Thermal Cracking:             0.3972*THERMAL+20.422  (Level 3)

Unbound Rutting(Granular):                          0.1477*Pow(BASERUT,0.6711)+0.001

Unbound Rutting(Fine):                                  0.1235*Pow(SUBRUT,0.5012)+0.001

AC Top‐Down Cracking:    200+2300/(1+exp(1.072‐2.1654log(TOP+0.0001)))

AC Bottom‐Up Cracking:   1.13+13/(1+exp(7.57‐15.5log(BOT+0.0001)))

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“Reliability”

Distress

Time

50% R

Selected R

Std. Deviation

Thank You!

Part 4:  Major Inputs – Where Do They Come From & How Do We Get Them?

Next Webinar: Wednesday, September 11th

Register at:  www.asphaltfacts.com/webinars/