mechanistic pavement guide

Guide for Mechanistic-Empirical Design Guide for Mechanistic-Empirical Design of New and Rehabilitation of New and Rehabilitation

Pavement StructuresPavement Structures

By Matt MasonBy Matt Mason

OverviewOverview

ObjectiveObjective Current UseCurrent Use JustificationJustification Flexible Pavement Design ProcessFlexible Pavement Design Process Input Levels and SelectionInput Levels and Selection Required InputsRequired Inputs Design ProcedureDesign Procedure Pavement Response ModelsPavement Response Models Current StatusCurrent Status

ObjectiveObjective

““The overall objective of the Guide for the Mechanistic-The overall objective of the Guide for the Mechanistic-Empirical Design for New and Rehabilitated Pavement Empirical Design for New and Rehabilitated Pavement Structures is to provide the highway community with a Structures is to provide the highway community with a state-of-the-practice tool for the design and state-of-the-practice tool for the design and rehabilitated pavement structures, based on rehabilitated pavement structures, based on mechanistic-empirical principles.”mechanistic-empirical principles.”

Dictionary DefinitionsDictionary Definitions Mechanistic- Anything explained in terms of physical forcesMechanistic- Anything explained in terms of physical forces Empirical- Depending upon experience or observation aloneEmpirical- Depending upon experience or observation alone

Current UseCurrent Use

80% of States use the 1972, 1986, or 80% of States use the 1972, 1986, or 1993 AASHTO guides1993 AASHTO guides

Iowa Department of Transportation currently Iowa Department of Transportation currently uses the 1993 Guideuses the 1993 Guide

Development from empirical performance Development from empirical performance equations from the 1950s AASHO Road testequations from the 1950s AASHO Road test

AASHO Road TestAASHO Road Test

LocationLocation Ottuwa, IllinoisOttuwa, Illinois

TimeTime 1958-19601958-1960

Test FacilitiesTest Facilities 6 two-lane test loops6 two-lane test loops Loop 1 controlLoop 1 control

SoilsSoils A-6 and CBR approximately 2-4A-6 and CBR approximately 2-4

Justification for a New Design Justification for a New Design GuideGuide

RehabilitationRehabilitation ClimateClimate SoilsSoils Surface Material – HMA & PCCSurface Material – HMA & PCC Truck CharacteristicsTruck Characteristics Design Life – short duration of road testDesign Life – short duration of road test PerformancePerformance Reliability – AASHTO 1986 guideReliability – AASHTO 1986 guide

Design of New and Design of New and Reconstructed Reconstructed

Flexible PavementsFlexible Pavements Flexible PavementsFlexible Pavements

ConventionalConventional

Deep StrengthDeep Strength

Full DepthFull Depth

““Semi-Rigid”Semi-Rigid”

Design ProcessDesign Process

Design Input LevelsDesign Input Levels

Level 1Level 1 Site and/or material specific inputsSite and/or material specific inputs

Level 2Level 2 Use of correlations to establish or determine Use of correlations to establish or determine

the required inputsthe required inputs

Level 3Level 3 Use of national or regional default values to Use of national or regional default values to

define the inputsdefine the inputs

Input Level SelectionInput Level Selection

Sensitivity of the pavement performance Sensitivity of the pavement performance to a given inputto a given input

The criticality of the projectThe criticality of the project Information available at the time of Information available at the time of

designdesign Resources & time available to the Resources & time available to the

designer to obtain the inputsdesigner to obtain the inputs

InputsInputs

General informationGeneral information Site/Project IdentificationSite/Project Identification Analysis ParametersAnalysis Parameters TrafficTraffic ClimateClimate Drainage and Surface PropertiesDrainage and Surface Properties Pavement StructurePavement Structure

General InformationGeneral Information

Design LifeDesign Life

Base/subgrade construction monthBase/subgrade construction month

Pavement construction monthPavement construction month

Traffic opening monthTraffic opening month

Site/Project IdentificationSite/Project Identification

Project LocationProject Location Project IdentificationProject Identification Functional ClassFunctional Class

Principal Arterial – Interstate & Defense routesPrincipal Arterial – Interstate & Defense routes Principal Arterial – OtherPrincipal Arterial – Other Minor ArterialMinor Arterial Major CollectorMajor Collector Minor CollectorMinor Collector Local Routes & StreetsLocal Routes & Streets

Analysis ParametersAnalysis Parameters

Initial IRIInitial IRI Performance CriteriaPerformance Criteria

Surface-down fatigue crackingSurface-down fatigue cracking Bottom-up fatigue crackingBottom-up fatigue cracking Thermal crackingThermal cracking Fatigue fracture of chemically stabilized layersFatigue fracture of chemically stabilized layers Total permanent deformationTotal permanent deformation Smoothness Smoothness

TrafficTraffic

ESAL ApproachESAL Approach Data requiredData required

Base year truck traffic volumeBase year truck traffic volume Vehicle operation speedVehicle operation speed Truck traffic directional and lane distribution factorsTruck traffic directional and lane distribution factors Vehicle class distributionVehicle class distribution Axle load distribution factorsAxle load distribution factors Axle and wheel base configurationsAxle and wheel base configurations Tire characteristics & Inflation pressuresTire characteristics & Inflation pressures Truck lateral distribution factorTruck lateral distribution factor Truck growth factorsTruck growth factors

Traffic CollectionTraffic Collection

Agency’s typically collectAgency’s typically collect Weigh in Motion (WIM)Weigh in Motion (WIM) Automatic Vehicle Classification (AVC)Automatic Vehicle Classification (AVC) Vehicle countsVehicle counts

Iowa Department of TransportationIowa Department of Transportation Two-way AADTTwo-way AADT Percentage of trucks in design lanePercentage of trucks in design lane Operational speedOperational speed Monthly adjustment factorsMonthly adjustment factors Vehicle class distribution informationVehicle class distribution information Weigh in Motion Weigh in Motion Reasonable assumptions about number of axles & axle Reasonable assumptions about number of axles & axle

spacing for each truck classspacing for each truck class Tire inflation pressure & wheel wander data is not collectedTire inflation pressure & wheel wander data is not collected

Traffic Input LevelsTraffic Input Levels

Level 1Level 1 Site specific vehicle classification & axle weight dataSite specific vehicle classification & axle weight data

Level 2Level 2 Site specific vehicle classification & regional axle Site specific vehicle classification & regional axle

weight dataweight data

Level 3Level 3 Regional vehicle classification & axle weight dataRegional vehicle classification & axle weight data

Level 4Level 4 Default vehicle classification & axle load distributionDefault vehicle classification & axle load distribution

Traffic Module Data AnalysisTraffic Module Data Analysis

AVC – Vehicle ClassificationAVC – Vehicle Classification WIM – Axle Load DistributionWIM – Axle Load Distribution AADTTAADTT AADTAADT Percent TrucksPercent Trucks Truck Traffic Classification (TTC)Truck Traffic Classification (TTC)

Truck Traffic ClassificationTruck Traffic Classification

Functional ClassificationFunctional Classification Distribution of trucksDistribution of trucks

Traffic Module Data AnalysisTraffic Module Data Analysis

Loading detailsLoading details Tire pressuresTire pressures Tire & axle loadTire & axle load Axle & tire spacingAxle & tire spacing Average number of Average number of

axles per vehicle axles per vehicle classificationclassification

Traffic factorsTraffic factors Time distribution Time distribution

factorsfactors Weekday & Weekend Weekday & Weekend

truck factorstruck factors Directional Directional

DistributionDistribution Lane DistributionLane Distribution Lateral DistributionLateral Distribution Traffic growth functionTraffic growth function

Lateral DistributionLateral Distribution

Accounts for the Accounts for the wander of trucks wander of trucks across one lane across one lane of trafficof traffic

ClimateClimate

Weather informationWeather information Hourly air temperatureHourly air temperature Hourly precipitationHourly precipitation Hourly wind speedHourly wind speed Hourly percentage of sunshineHourly percentage of sunshine Hourly ambient relative humidityHourly ambient relative humidity Seasonal or constant water table depthSeasonal or constant water table depth

Drainage & Surface PropertiesDrainage & Surface Properties

Pavement shortwave absorptivityPavement shortwave absorptivity Ratio of the amount of solar energy absorbed by the Ratio of the amount of solar energy absorbed by the

pavement surfacepavement surface Typical valuesTypical values

0.80-0.90 for weathered0.80-0.90 for weathered 0.90-0.98 for new pavement 0.90-0.98 for new pavement

Potential for InfiltrationPotential for Infiltration At this time does not allowAt this time does not allow Recommend subdrainage Recommend subdrainage

Pavement cross slopePavement cross slope Length of drainage pathLength of drainage path

Pavement StructurePavement Structure

Layer PropertiesLayer Properties defined by userdefined by user

4-6 layers4-6 layers Maximum of 10 Maximum of 10

is recommendedis recommended

subdivide layerssubdivide layers 12-15 sub layers12-15 sub layers Maximum of 19Maximum of 19


Asphalt Concrete & Asphalt Stabilized layersAsphalt Concrete & Asphalt Stabilized layers Specify maximum of 3 HMA layersSpecify maximum of 3 HMA layers Asphalt aging modeled only for top sub layerAsphalt aging modeled only for top sub layer Layer inputsLayer inputs

Layer thicknessLayer thickness Poisson’s ratioPoisson’s ratio Thermal conductivityThermal conductivity Heat capacityHeat capacity Total unit weightTotal unit weight


Dynamic Modulus, E*Dynamic Modulus, E* Stiffness propertyStiffness property Function ofFunction of

TemperatureTemperature rate of loadingrate of loading AgeAge binder stiffnessbinder stiffness aggregate gradationaggregate gradation binder contentbinder content air voidsair voids

InputsInputs Asphalt mixture Asphalt mixture

propertiesproperties Asphalt binderAsphalt binder Air voidsAir voids


BedrockBedrock Presence within 10 feet of the pavement Presence within 10 feet of the pavement

surface influences the structural response of surface influences the structural response of the pavement layersthe pavement layers

InputsInputs Layer thickness (infinite)Layer thickness (infinite) Unit weightUnit weight Poisson’s ratioPoisson’s ratio Layer modulusLayer modulus

Design ProcedureDesign Procedure

Predict a variety of distress typesPredict a variety of distress types Asphalt fatigue factureAsphalt fatigue facture Permanent deformationPermanent deformation HMA thermal fractureHMA thermal fracture Chemically stabilized load associated fatigue Chemically stabilized load associated fatigue

fracturefracture

Design ProcedureDesign Procedure

Select an initial trial pavement structureSelect an initial trial pavement structure Identify pavement cross sectionIdentify pavement cross section Specify layer material types & thicknessSpecify layer material types & thickness Is Seasonal Analysis required?Is Seasonal Analysis required?

NO – constant values for modulus & Poisson's ratioNO – constant values for modulus & Poisson's ratio YES – Two optionsYES – Two options

EICM EICM Monthly Seasonal valuesMonthly Seasonal values

Pavement Response ModelsPavement Response Models

Determines structural responses of the Determines structural responses of the pavement systempavement system

Outputs are the stresses, strains and Outputs are the stresses, strains and displacements within the pavement layersdisplacements within the pavement layers Tensile horizontal strain at the bottom of the HMA Tensile horizontal strain at the bottom of the HMA

layerlayer Compressive vertical stresses/strains within the Compressive vertical stresses/strains within the

HMA layerHMA layer Compressive vertical stresses/strains within the Compressive vertical stresses/strains within the

base/subbase layersbase/subbase layers Compressive vertical stresses/strains at the top of Compressive vertical stresses/strains at the top of

the subgradethe subgrade


Permanent DeformationPermanent Deformation 3 distinct stages of rutting behavior3 distinct stages of rutting behavior


Fatigue CrackingFatigue Cracking Both top-down & bottom-upBoth top-down & bottom-up Based on calculating the fatigue damage at Based on calculating the fatigue damage at

the surface & at the bottom of each asphalt the surface & at the bottom of each asphalt layerlayer

Based upon Miner’s LawBased upon Miner’s Law


Thermal FractureThermal Fracture Amount of transverse cracking expected is Amount of transverse cracking expected is

predicted by relating the crack depth to the predicted by relating the crack depth to the amount of cracking presentamount of cracking present

Enhanced version of model developed by Enhanced version of model developed by the SHRP A-005 research contractthe SHRP A-005 research contract

Current StatusCurrent Status

My involvementMy involvement Current ActivityCurrent Activity

Gyratory compactorGyratory compactor

QuestionsQuestions

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mechanistic pavement guide

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