Modern Trends In Pavement Design

transcript

By: Asst. Prof. Imran Hafeez

Engr. Imran Hafeez

Contents 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

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….,

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

CROSS-SECTION(Ordinary Roman Roads)

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

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

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

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

5) Total thickness varied from 3ft to 6ft

Ordinary 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)

CROSS-SECTION(Important Roman Roads)

Important Roman roads

17th and 18th centuries.

MODERN ROADS(17th & 18th Centuries)

TRESAGUET ROAD (1775)

CROSS-SECTIONTRESAGUET ROAD (1775)

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

TELFORD ROAD (1803)

MODERN ROADS(17th & 18th Century)

CROSS-SECTION TELFORD ROAD (1803)

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

MODERN ROADS(17th & 18th Century)

MACADAM ROAD (1827)

CROSS-SECTION TELFORD ROAD (1803)

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

(20th Century)

EVOLUTION OF PAVEMENT DESIGN METHODOLOGY

Pavement design :1) Mix design of material2) Thickness design of structural layers

Pavement design philosophy:1) Empirical2) Mechanistic ( Theoretical , Analytical, Structural)

3) Mechanistic-Empirical

Design Approaches

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

Road Note 31The Asphalt Institute Manual

SeriesAASHTO Guide for Design of

Pavement Structures

ROAD NOTE 29

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

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

ROAD NOTE 29

ROAD NOTE 31

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 (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 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

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 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)

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

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

Structural design model/equation log10[ΔPSI/4.2-1.5]

0.40 + 1094 ( SN+1) 5.19

+ 2.32x log10 ( Mr) – 8.07 SN = a1D1 + a2 D2 m2 + a3D3m3

AASHTO GUIDE…………..contd.

Given Wheel Load

Load Distribution in Flexible Pavements

Flexible Pavements

150 psi

Wearing C.BaseSub-baseSub-grade

PAVEMENT RESPONSES

PAVEMENT RESPONSES Load related responses:

1) Vertical ( compressive)stresses and strains2) Shear stresses and strain3) Radial ( compressive or tensile) stresses and

strain Temperature induced responses:

1) Shrinkage stresses and strains ( temp: cycling)

2) Low temperature cracking3) Thermal cracking

Critical responses:1) horizontal tensile stress/strain at the bottom of bound layers2) Vertical compressive stress/strain at the top of sub-grade

PAVEMENT RESPONSES

Calculating responses:1) Using equations2) Graphical solutions3) Elastic layer computer programs

i) CHEVRON ii) ELSYM5iii) ILLI-PAVE iv) MICH-PAVE

PAVEMENT PERFORMANCE PREDICTION MODELS

Performance prediction models are also called distress models or transfer functions

Models relate structural responses to pavement distress1) Fatigue cracking Model2) Rutting Model3) Thermal cracking Model

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)

Org f4 f5 Allowable Rut Depth mm

Asp Inst 1.365 x 10-6 4.447

Shel 1.94 x 10-7 4.00 13TRRL 6.18 x 10-8 3.95 10

Rutting Model(subgrade strain model)

Nf = f4( εv ) –f5 (General form)

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

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

Thermal Cracking Model1) Low temperature cracking2) Thermal fatigue cracking 3) Models like that Shahin-McCullough model

are quite complex , but examine both types of cracking.

SUPERPAVE 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 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 Aggregate crushing value (ACV)(ACV)

Ten percent fine value (TFV) Ten percent fine value (TFV) Aggregate Impact value (AIV)Aggregate Impact value (AIV) Toughness Index (TI)Toughness Index (TI) Loss Angles Abrasion value Loss Angles Abrasion value

(LAA) (LAA) Polish Stone Value (PSV)Polish Stone Value (PSV)

Soundness value Soundness value Sand equivalentSand equivalent Specific gravity (Gsb)Specific gravity (Gsb) Porosity Porosity Flakiness Index (FI) Flakiness Index (FI) Elongation Index (EI)Elongation Index (EI)

Binder Properties

Softening PointSoftening Point Ductility Ductility Flash & Fire PointFlash & Fire Point PenetrationPenetration ViscosityViscosity Specific gravities Specific gravities

Polar Molecular structurePolar Molecular structure Elastomeric /Plastomeric Elastomeric /Plastomeric

StiffnessStiffness Shear modulusShear modulus Phase anglePhase angle Accumulated strainAccumulated strain Strip off valueStrip off value

SUPERPAVE 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

PERPETUAL PAVEMENTS

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

HMA Base layer Fatigued resistant

layer No bottom up

cracking Intermediate layer Stable and durable Wearing coarse

resistant to surface cracking and rutting

PERPETUAL PAVEMENTS

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.

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

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 Testa Marshall Stability and flow, b 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 Devicea Model Mobile Load

Simulatorb Dry Wheel Tracker (Wessex Engineering)c Rotary Loaded Wheel

Tester (Rutmeter) andd French Rutting Tester (FRT)

7. Moisture Susceptibility Tests

8. Friction Tests

State of the Art Equipment at TITEState of the Art Equipment at TITE

Triaxial Test system Universal Testing Machine

Computerized Profilograph Benkelman Beam

Dynamic Modulus of Fill Accelerated Polishing machine

Surface Friction Tester Universal Testing Machine

Gyratory Compactor Wheel Tracker

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 asphaltResistance to Permanent Deformation The repeated load Axial or Dynamic Creep testControlled Fatigue Stress & strains

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 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 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 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 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 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