By: Asst. Prof. Imran Hafeez

ContentsAncient Roads (5000 years ago)Modern Roads (17th & 18th Centuries)Evolution Of Pavement Design MethodologyModern Trends in DesignMechanistic-Empirical Design methodsPavement performance prediction modelsSuper-pave & Perpetual pavements conceptsPavement Performance Tests/Equipments

Engr. Imran Hafeez

Concept of Ancient Roads(5000 years ago)Definition: Paths treaded by animals and human beingsPavement Structure: Stone paved roads made of one or two rows of slabs 50 mm thick in central portion.,

Roman Roads

Types of Roman RoadsOrdinary roman roadsImportant Roman roadsBuilt in straight line regardless of gradientExcavated parallel trenches 40-ft apart for longitudinal drainage Foundation raised 3-ft above ground levelEmbankment covered with sand or mortar

CROSS-SECTION(Ordinary Roman Roads)Foundation layer (10-24inch),composed of large stonesFirm base 9-in thick made of broken stones,pebbles, cement and sandNucleus layer about 12-in thick using concrete made from gravel and coarse sandWearing surface of large stone slabs at least 6-in deepTotal thickness varied from 3ft to 6ft

Ordinary Roman roads

CROSS-SECTION(Important Roman Roads)Bottom coarse(25-40cm) made of large size broken stones in lime mortarBase coarse(25-40cm) made with smaller broken stones in lime mortarWearing coarse(10-15cm) of dressed large stone blocks/slabs set in lime mortar Total thickness varied 0.75 to 1.20 mHeavily crowned central carriage way 15ft wide(total width 35ft)

Important Roman roads

17th and 18th centuries.

MODERN ROADS(17th & 18th Centuries)TRESAGUET ROAD (1775)

CROSS-SECTIONTRESAGUET ROAD (1775)The subgrade was prepared in levelLayer of large foundation stone with large kerb stones at edgesBase coarse about 8cm of compacted small broken stonesTop wearing coarse 5cm at edges,thickness increased towards center for providing surface drainageSloping shoulders with side drain Total thickness about 30cm

TELFORD ROAD (1803)MODERN ROADS (17th & 18th Century)

CROSS-SECTION TELFORD ROAD (1803)Level subgradeLarge foundation stones of thickness 17-22cmTwo layers of angular broken stones compacted thickness of 10-15cm Lime mortar concrete instead of kerb stones at pavement edgesTop wearing coarse of 4cm thick gravel as binding layer

MACADAM ROAD (1827)MODERN ROADS (17th & 18th Century)

CROSS-SECTION TELFORD ROAD (1803)The subgrade is compacted with cross slopeSub-base of broken stone 5cm size were compacted to uniform thickness of 10 cmBase coarse of strong broken stone 3.75cm size compacted to 10cm uniform thicknessTop layer of stone 2cm size compacted to thickness of about 5cmTotal thickness approximately 25cm

(20th Century)

EVOLUTION OF PAVEMENT DESIGN METHODOLOGYPavement design :1) Mix design of material2) Thickness design of structural layers Pavement design philosophy:1) Empirical2) Mechanistic ( Theoretical , Analytical, Structural)3) Mechanistic-Empirical

Design ApproachesRoad Note 29 (TRRL, UK 1960, 1970, Empirical)Road Note 31The Asphalt Institute Manual SeriesAASHTO Guide for Design of Pavement Structures

ROAD NOTE 29A guide to the structural design of Pavements for new roads TRRL, UK 1960, 1970, Empirical Approach: study performance of experimental sections built into in-service road networkFoundation soil CBR .. Upto 7 %Traffic.. Upto 100 Million Eq. Standard AxlesSpecification of material given in table-4Design life..20mm rutting or severe cracking

ROAD NOTE 29Performance data interpreted in light of structural theory, mathematical modeling of pavement behavior, simulative testing of road materials and pavementsThe Structural Design of Bituminous Roads.. TRRL Laboratory Report 1132 published in 1984Structural design criteria:1) Critical stress and strain 2) Permissible strains induced by standard 40 KN wheel load at pavement temperature of 20o C

ROAD NOTE 31A guide to the structural design of bitumen-surfaced roads in tropical and sub-tropical countries ( Overseas Edition 1962,1966,1977)For traffic upto 30 msa in one direction, for >30 msa use TRRL 1132 with calibration to local conditionssubgrade strength by CBR method6 Sub-grade strength classes(2,4,7,14,29,30+)8 Traffic classes (0.3.0.7,1.5,3.0,6.0,10,17,30)Design charts for 8 type of road base/surfacing material

THE ASPHALT INSTITUTE (MS-1)Thickness Design-Asphalt Pavements for Highways and streets ( 1964,1981,1991)Initially developed from data of AASHO Road testDesign charts in latest edition developed using DAMA elastic layered pavement analysis program that modeled two stress strain conditions ( mechanistic based design procedure uses empirical correlations)Roadbed soil strength characterized by Mr AC by Modulus of Elasticity and Poissons ratioThe design charts for 3 MAAT/ computer program for full depth asphalt concrete or with emulsified base/ untreated aggregate base are given

AASHTO GUIDE FOR THE DESIGN OF PAVEMENT STRUCTURES

Approach : study performance of trial sections constructed to a wide range of overall thickness round a close loop trafficked by repetitions of known axle loadsDeveloped empirical model by regression analysis from data of ASSHO Road TestInterim guide 1961,1972, 1981ASSHTO Guide for the design of Pavement Structures (1986,1993)

AASHTO GUIDE..contd.Performance periodAnalysis periodTraffic ..Load Equivalence ValuesReliabilityStandard deviationServiceability

Roadbed soil resilient modulusResilient modulus for unbound materialElastic model for asphalt concreteLayer co-efficientDrainage

AASHTO GUIDE..contd.Log(W18)= Zr x So+9.36 log10 (SN+1)-0.20 +Structural design model/equation log10[PSI/4.2-1.5] 0.40 + 1094 ( SN+1)5.19 + 2.32x log10 ( Mr) 8.07 SN = a1D1 + a2 D2 m2 + a3D3m3

Load Distribution in Flexible PavementsFlexible Pavements150 psi3 psiWearing C.BaseSub-baseSub-gradePAVEMENT RESPONSES

PAVEMENT RESPONSESLoad related responses:1) Vertical ( compressive)stresses and strains2) Shear stresses and strain3) Radial ( compressive or tensile) stresses and strainTemperature induced responses:Shrinkage stresses and strains ( temp: cycling)Low temperature crackingThermal cracking

PAVEMENT RESPONSESCritical responses:1) horizontal tensile stress/strain at the bottom of bound layers2) Vertical compressive stress/strain at the top of sub-gradeCalculating responses:1) Using equations2) Graphical solutions3) Elastic layer computer programsi) CHEVRON ii) ELSYM5iii) ILLI-PAVEiv) MICH-PAVE

PAVEMENT PERFORMANCE PREDICTION MODELSPerformance prediction models are also called distress models or transfer functionsModels relate structural responses to pavement distress1) Fatigue cracking Model2) Rutting Model3) Thermal cracking Model

PAVEMENT PERFORMANCE PREDICTION MODELSFatigue cracking Model Nf = f1( t ) f2 ( Es)-f3 (General form)Nf = 0.0796( t ) 3.291 ( Es)-0.854 (A. Inst)Nf = 0.0685( t ) 5.671 ( Es)-2.363 (Shell)Nf = 1.66x 10-10 ( t ) 4.32 (TRRL)Nf = 5.0 x 10-6 ( t ) 3.0 (IDOT)

PAVEMENT PERFORMANCE PREDICTION MODELSRutting Model(subgrade strain model) Nf = f4( v ) f5 (General form)

Orgf4f5Allowable Rut Depth mmAsp Inst1.365 x 10-6 4.44713Shel1.94 x 10-74.0013TRRL 6.18 x 10-83.9510

PAVEMENT PERFORMANCE PREDICTION MODELSPermanent deformation model log p = a + b (log N) or p = A (N)b

a = Exp estb material/stress condition parameterA= antilog of ab= 0.1---0.2

PAVEMENT PERFORMANCE PREDICTION MODELSAsphalt concrete Rutting Model log p = Cv + C1(log N) +C2 (log N)+ C3 (log N) Cv depends on temp and deviator stress C1, C2 are constantsSub-grade Rutting Model log p = Cv + C1(log N) +C2 (log N)+ C3 (log N)Cv depends on moisture and deviator stress

PAVEMENT PERFORMANCE PREDICTION MODELSThermal Cracking ModelLow temperature crackingThermal fatigue cracking Models like that Shahin-McCullough model are quite complex , but examine both types of cracking.

SUPERPAVESuperior Performing Asphalt PavementsNew, comprehensive asphalt mix design and analysis system (SHRP 1987-1993) using SPGCDevelopment of Performance based AC specs (PG Grading) to relate lab Volumetric analysis with field performanceFour basic steps for Superpave asphalt mix design1)Material selection 2)Selection of design aggregate structure3) Selection of design asphalt binder content4) Evaluation of mixture for moisture sensitivity

Aggregate Properties

Aggregate crushing value (ACV)Ten percent fine value (TFV) Aggregate Impact value (AIV)Toughness Index (TI) Loss Angles Abrasion value (LAA) Polish Stone Value (PSV)Soundness value Sand equivalentSpecific gravity (Gsb)Porosity Flakiness Index (FI) Elongation Index (EI)

Binder Properties

Softening PointDuctility Flash & Fire PointPenetration ViscositySpecific gravities

Polar Molecular structureElastomeric /Plastomeric StiffnessShear modulusPhase angleAccumulated strain Strip off value

SUPERPAVEBinder tests: 1) Rolling Thin Film Oven ( RTFO) Test.. Aging during mixing 2) Pressure Aging Vessel in-service aging 3) Rotational Viscometer viscosity 4) Dynamic shear Rheometer visco-elastic property 5) Bending beam Rheometer.stiffness at low temp 6) Direct tension tester. Low temp tensile strain

PERPETUAL PAVEMENTS Long lasting(50yrs or more) asphalt pavements Full depth asphalt pavement constructed since1960sNeed periodic surface renewalPavements distress confined to top layerThe removed upper layer can be recycledMechanistic-based design,material selection,mixture design,performance testing,life cycle cost analysis

PERPETUAL PAVEMENTS HMA Base layerFatigued resistant layer No bottom up crackingIntermediate layerStable and durableWearing coarse resistant to surface cracking and rutting

Pavement Performance TestsThe Performance based tests can be classified as:

1) Dia-metral tests,2) Uni-axial tests,3) Tri-axial tests,4) Shear tests,5) Empirical tests,6) Simulative tests.7) Moisture Susceptibility tests.8) Friction tests.

1.Diametral testsa)Creep tests, b)Repeated load permanent deformation, c)Dynamic modulus, d)Strength test.

2.Uniaxial Creep Test

3.Triaxial Creep Testa) Uniaxial and Triaxial Repeated Load Testsb) Uniaxial and Triaxial Dynamic Modulus Tests

4.Shear Tests a) SST Repeated Shear at Constant Height Test b) Shear Dynamic Modulus c) Direct Shear Dynamic Modulus d) Direct Shear Strength Test

5.Empirical Test Marshall Stability and flow, Hveem stability, c GTM, and d Lateral pressure indicator (LPI).

6.Simulative Tests a The Asphalt Pavement Analyzer (APA) (Georgia Loaded Wheel Tester)b)Hamburg Wheel-Tracking Device (HWTD)c)Purdue University Laboratory Wheel Tracking Device Model Mobile Load Simulator Dry Wheel Tracker (Wessex Engineering) Rotary Loaded Wheel Tester (Rutmeter) and French Rutting Tester (FRT) 7. Moisture Susceptibility Tests

8.Friction Tests

State of the Art Equipment at TITE

Tri-axial Test systemDesign to perform following tests on Soil, aggregates and asphaltic samples Modulus of Resilience of soil and aggregates (Vacuum Triaxial test)Four point beam fatigue test on asphaltResistance to Permanent Deformation The repeated load Axial or Dynamic Creep testControlled Fatigue Stress & strains

Computerized ProfilographMeasures the profile of the road surface and display the results immediately on screen in the form of roughness index. Main Features:Compact and lightweightBattery operatedOn screen graphics displayOn screen display of Profile IndexImmediate resultsMeets all ASTM standardsEasily setup and operated by one personUser friendly menu driven softwareTransfer data to office PC for additional analysisEasily transported in a pickup or trailerBump Detection Warning System (BDWS)

Wheel TrackerWheel tracker is used to assess the resistance to rutting of asphaltic materials by simulating the in-site traffic and environmental conditions.Features:Integral temperature controlled cabinetTracks for specified number of passes or to specified rut depthDouble glazed doors for observation of testingAutomatic test stop/start and speed controlA loaded wheel tracks a sample under specified conditions of speed and temperatureDevelopment of the rut is monitored continuously during the testUser friendly Windows software

Accelerated Polishing MachineIt gives a Polished Stone Value for aggregates to be used in road surfaces and provides a measure of the resistance to skidding.Features:Machine polishes samples of aggregates, simulating actual road conditionsMeet the specifications of British standards & ASTMPredetermined revolution counterSpecimens manufactured and easily removed from accurately machined mouldsSpecimens located on Road Wheel by rubber rings and held by simple side fixingTired wheel easily removed for replacing tyresUsed abrasive and water collected in removable trayLoaded tire raised and lowered to the running surface by mechanical lifting device