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By: Asst. Prof. Imran Hafeez. MODERN TRENDS. IN. PAVEMENT DESIGN. Contents Ancient Roads (5000 years ago) Modern Roads (17 th & 18 th Centuries) Evolution Of Pavement Design Methodology Modern Trends in Design Mechanistic- Empirical Design methods Pavement performance prediction models

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By asst prof imran hafeez l.jpg
By: Asst. Prof. Imran Hafeez




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  • Ancient Roads (5000 years ago)

  • Modern Roads (17th & 18th Centuries)

  • Evolution Of Pavement Design Methodology

  • Modern Trends in Design

  • Mechanistic- Empirical Design methods

  • Pavement performance prediction models

  • Super-pave & Perpetual pavements concepts

  • Pavement Performance Tests/Equipments

Engr. Imran Hafeez

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Concept of Ancient Roads(5000 years ago)

Definition: “Paths treaded by animals and human beings”

Pavement Structure:

  • Stone –paved roads made of one or two rows of slabs 50 mm thick in central portion….,

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Roman Roads

Types of Roman Roads

  • Ordinary roman roads

  • Important Roman roads

  • Built in straight line regardless of gradient

  • Excavated parallel trenches 40-ft apart for longitudinal drainage

  • Foundation raised 3-ft above ground level

  • Embankment covered with sand or mortar

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CROSS-SECTION(Ordinary Roman Roads)

  • Foundation layer (10-24inch),composed of large stones

  • Firm base 9-in thick made of broken stones,pebbles, cement and sand

  • Nucleus layer about 12-in thick using concrete made from gravel and coarse sand

  • Wearing surface of large stone slabs at least 6-in deep

  • Total thickness varied from 3ft to 6ft

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CROSS-SECTION(Important Roman Roads)

  • Bottom coarse(25-40cm) made of large size broken stones in lime mortar

  • Base coarse(25-40cm) made with smaller broken stones in lime mortar

  • Wearing coarse(10-15cm) of dressed large stone blocks/slabs set in lime mortar

  • Total thickness varied 0.75 to 1.20 m

  • Heavily crowned central carriage way 15ft wide(total width 35ft)

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17th and 18th centuries.

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MODERN ROADS(17th & 18th Centuries)


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  • The subgrade was prepared in level

  • Layer of large foundation stone with large kerb stones at edges

  • Base coarse about 8cm of compacted small broken stones

  • Top wearing coarse 5cm at edges,thickness increased towards center for providing surface drainage

  • Sloping shoulders with side drain

  • Total thickness about 30cm

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MODERN ROADS(17th & 18th Century)


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  • Level subgrade

  • Large foundation stones of thickness 17-22cm

  • Two layers of angular broken stones compacted thickness of 10-15cm

  • Lime mortar concrete instead of kerb stones at pavement edges

  • Top wearing coarse of 4cm thick gravel as binding layer

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MODERN ROADS(17th & 18th Century)


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  • The subgrade is compacted with cross slope

  • Sub-base of broken stone 5cm size were compacted to uniform thickness of 10 cm

  • Base coarse of strong broken stone 3.75cm size compacted to 10cm uniform thickness

  • Top layer of stone 2cm size compacted to thickness of about 5cm

  • Total thickness approximately 25cm

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(20th Century)




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  • Pavement design :

    1) Mix design of material

    2) Thickness design of structural layers

  • Pavement design philosophy:

    1) Empirical

    2) Mechanistic ( Theoretical , Analytical, Structural)

    3) Mechanistic-Empirical

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Design Approaches

  • Road Note 29 (TRRL, UK 1960, 1970, Empirical)

  • Road Note 31

  • The Asphalt Institute Manual Series

  • AASHTO Guide for Design of Pavement Structures

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  • A 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 network

  • Foundation soil CBR .. Upto 7 %

  • Traffic.. Upto 100 Million Eq. Standard Axles

  • Specification of material given in table-4

  • Design life..20mm rutting or severe cracking

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  • Performance data interpreted in light of structural theory, mathematical modeling of pavement behavior, simulative testing of road materials and pavements

  • The Structural Design of Bituminous Roads.. TRRL Laboratory Report 1132 published in 1984

  • Structural design criteria:

    1) Critical stress and strain

    2) Permissible strains induced by standard 40 KN wheel load at pavement temperature of 20o C

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  • A 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 conditions

  • subgrade strength by CBR method

  • 6 Sub-grade strength classes(2,4,7,14,29,30+)

  • 8 Traffic classes (,1.5,3.0,6.0,10,17,30)

  • Design charts for 8 type of road base/surfacing material

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  • Thickness Design-Asphalt Pavements for Highways and streets ( 1964,1981,1991)

  • Initially developed from data of AASHO Road test

  • Design 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 Poisson’s ratio

  • The design charts for 3 MAAT/ computer program for full depth asphalt concrete or with emulsified base/ untreated aggregate base are given

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  • Approach : study performance of trial sections constructed to a wide range of overall thickness round a close loop trafficked by repetitions of known axle loads

  • Developed empirical model by regression analysis from data of ASSHO Road Test

  • Interim guide 1961,1972, 1981

  • ASSHTO Guide for the design of Pavement Structures (1986,1993)

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AASHTO GUIDE…………..contd.

  • Performance period

  • Analysis period

  • Traffic ..Load Equivalence Values

  • Reliability

  • Standard deviation

  • Serviceability

  • Roadbed soil resilient modulus

  • Resilient modulus for unbound material

  • Elastic model for asphalt concrete

  • Layer co-efficient

  • Drainage

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AASHTO GUIDE…………..contd.

  • Log(W18)= Zr x So+9.36 log10 (SN+1)-0.20 +

  • Structural design model/equation


    0.40 + 1094 ( SN+1) 5.19

    + 2.32x log10 ( Mr) – 8.07

  • SN = a1D1 + a2 D2 m2 + a3D3m3

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Given Wheel Load

Flexible Pavements

150 psi

Wearing C.



3 psi


Load Distribution in Flexible Pavements

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  • Load related responses:

    1) Vertical ( compressive)stresses and strains

    2) Shear stresses and strain

    3) Radial ( compressive or tensile) stresses and strain

  • Temperature induced responses:

    • Shrinkage stresses and strains ( temp: cycling)

    • Low temperature cracking

    • Thermal cracking

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Critical responses:

1) horizontal tensile stress/strain at the bottom of bound layers

2) Vertical compressive stress/strain at the top of sub-grade

  • Calculating responses:

    1) Using equations

    2) Graphical solutions

    3) Elastic layer computer programs

    i) CHEVRON ii) ELSYM5

    iii) ILLI-PAVE iv) MICH-PAVE

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  • Performance prediction models are also called distress models or transfer functions

  • Models relate structural responses to pavement distress

    1) Fatigue cracking Model

    2) Rutting Model

    3) Thermal cracking Model

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  • Fatigue cracking Model

  • Nf = f1( εt ) –f2 ( Es)-f3 (General form)

  • Nf = 0.0796( εt ) –3.291 ( Es)-0.854 (A. Inst)

  • Nf = 0.0685( εt ) –5.671 ( Es)-2.363 (Shell)

  • Nf = 1.66x 10-10( εt ) –4.32 (TRRL)

  • Nf = 5.0 x 10-6( εt ) –3.0 (IDOT)

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  • Rutting Model(subgrade strain model)

    Nf = f4( εv ) –f5 (General form)

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  • Permanent deformation model

    log εp = a + b (log N) or εp = A (N)b

    a = Exp estb material/stress condition parameter

    A= antilog of “a”

    b= 0.1---0.2

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  • Asphalt concrete Rutting Model

    log εp = Cv + C1(log N) +C2 (log N)+ C3 (log N)

  • Cv depends on temp and deviator stress

  • C1, C2 are constants

  • Sub-grade Rutting Model

    log εp = Cv + C1(log N) +C2 (log N)+ C3 (log N)

  • Cv depends on moisture and deviator stress

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  • Thermal Cracking Model

    • Low temperature cracking

    • Thermal fatigue cracking

    • Models like that Shahin-McCullough model are quite complex , but examine both types of cracking.

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  • Superior Performing Asphalt Pavements

  • New, comprehensive asphalt mix design and analysis system (SHRP 1987-1993) using SPGC

  • Development of Performance based AC specs (PG Grading) to relate lab Volumetric analysis with field performance

  • Four basic steps for Superpave asphalt mix design

    1)Material selection

    2)Selection of design aggregate structure

    3) Selection of design asphalt binder content

    4) Evaluation of mixture for moisture sensitivity

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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 equivalent

  • Specific gravity (Gsb)

  • Porosity

  • Flakiness Index (FI)

  • Elongation Index (EI)

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Binder Properties

  • Softening Point

  • Ductility

  • Flash & Fire Point

  • Penetration

  • Viscosity

  • Specific gravities

  • Polar Molecular structure

  • Elastomeric /Plastomeric Stiffness

  • Shear modulus

  • Phase angle

  • Accumulated strain

  • Strip off value

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  • Binder 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

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  • Long lasting(50yrs or more) asphalt pavements

  • Full depth asphalt pavement constructed since1960s

  • Need periodic surface renewal

  • Pavements distress confined to top layer

  • The removed upper layer can be recycled

  • Mechanistic-based design,material selection,mixture design,performance testing,life cycle cost analysis

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  • HMA Base layer

  • Fatigued resistant layer

  • No bottom up cracking

  • Intermediate layer

  • Stable and durable

  • Wearing coarse resistant to surface cracking and rutting

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Pavement Performance Tests

  • The 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.

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  • 1.Diametral tests

    • a) Creep tests,

    • b) Repeated load permanent deformation,

    • c) Dynamic modulus,

    • d) Strength test.

  • 2.Uniaxial Creep Test

  • 3.Triaxial Creep Test

    • a) Uniaxial and Triaxial Repeated Load Tests

    • b) 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

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Tri-axial Test system

  • Design 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 asphalt

  • Resistance to Permanent Deformation

  • The repeated load Axial or Dynamic Creep test

  • Controlled Fatigue Stress & strains

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Computerized Profilograph

Measures the profile of the road surface and display the results immediately on screen in the form of roughness index.

Main Features:

Compact and lightweight

Battery operated

On screen graphics display

On screen display of Profile Index

Immediate results

Meets all ASTM standards

Easily setup and operated by one person

User friendly menu driven software

Transfer data to office PC for additional analysis

Easily transported in a pickup or trailer

Bump Detection Warning System (BDWS)

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Wheel Tracker

  • Wheel 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 cabinet

  • Tracks for specified number of passes or to specified rut depth

  • Double glazed doors for observation of testing

  • Automatic test stop/start and speed control

  • A loaded wheel tracks a sample under specified conditions of speed and temperature

  • Development of the rut is monitored continuously during the test

  • User friendly Windows software

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Accelerated Polishing Machine

  • It 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 conditions

  • Meet the specifications of British standards & ASTM

  • Predetermined revolution counter

  • Specimens manufactured and easily removed from accurately machined moulds

  • Specimens located on ‘Road Wheel’ by rubber rings and held by simple side fixing

  • Tired wheel easily removed for replacing tyres

  • Used abrasive and water collected in removable tray

  • Loaded tire raised and lowered to the running surface by mechanical lifting device