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Australian Long Life Pavements

Presented byGeoff Jameson ARRB Group

Institute of Road Engineering

6h November 2012

Presentation Outline

• Introduction

• Definition of heavily trafficked long life pavement

– Design period 40 years

• Foundation design

• Flexible pavements

– Surfacing types

– Structural design method (staged construction,

fatigue endurance limit)

– Specifications

• Concrete pavements

• Example designs

2

Australian context

• Large continent

• Wide range of climates

• each Australian state government has a pavement

design manual based on Austroads Guide

• tailored to local materials, performance, climates,

loadings, specifications

3

Austroads Guide

(www.austroads.com.au)

4

State road agencies have supplements

the Guide

5

Road agency design rules,

specifications, contracts

• Design inputs tailored to local climate

– Specifications

– Condition of Contract (warranties)

– Test methods

– Availability/ quality of materials

– Maintenance practices

– Past performance

6

Definition of long life pavements

• Pavements where no significant deterioration will

develop in the foundation or the road base layers over

a 40 year period provided that correct surface

maintenance is carried out

• Commonly called heavy-duty pavements in Australia

• Design periods

7

In Australia these heavy duty pavements

would be designed with a project reliability of

95% to 97.5%

8

Factors affecting performance

• Presentation discusses limited to pavement design issues

9

Foundation design

• Project delivered by design and construct contracts

• Contractors responsibility to design and construct the

foundation to carry the construction traffic

• In terms of providing a foundation for long term

performance, road agencies design Manuals provide

minimum foundation structures

10

Example : Roads and Maritime Services New

South Wales design manual

11

Presentation Outline

• Introduction

• Definition of heavily trafficked long life pavement

– Design periods 40 years

• Foundation design

• Flexible pavements

– Surfacing types

– Structural design method (staged construction,

fatigue endurance limit)

– Specifications

• Concrete pavements

• Example designs

12

Asphalt surfacing types and thickness

• Open graded asphalt (OGA)

• Dense graded asphalt (DGA)

• DGA Intersection mixes

• SMA – emerging

• Use of polymer modified PMB for high

stresses/loadings

13

Open graded asphalt

14

Road users benefits of open graded asphalt

15

16

Open graded asphalt

10mm

SAMI

Dense

graded

asphalt

Dense graded asphalt, size 14 mm

17

Nominal size and thickness of dense

graded asphalts

18

Nominal size and thickness of dense

graded asphalts

19

Guide to selection of binder types

20

Presentation Outline

• Introduction

• Definition of heavily trafficked long life pavement

– Design periods 40 years

• Foundation design

• Flexible pavements

– Surfacing types

– Structural design method

– Specifications

• Concrete pavements

• Example designs

21

Thickness design using mechanistic

approach in use of over 20 years

22

Elements of mechanistic design

method

23

Subgrade

Base Course/

Subbase Course

Asphalt

80 kN

Standard Axle

Nkb

=ε

(

Design Traffic (SAR)

Allowable load repetitions to distress

n

N

critical strain, ε

Damage =

Response

Model

Performance

Relationship:RF )

Mechanistic Design

Strains calculated under a 80 kN Standard Axle

Uniform stress

(equal to tyre

pressure)

1 Tensile strain at bottom of asphalt - asphalt fatigue

2 Tensile strain at bottom of cemented material - cement mat fatigue

3 Compressive strain at top of subgrade - rutting & shape loss

Denotes likely locations of critical strains due to applied loading

3 Subgrade

1 Asphalt

2 Cemented Material

Spacing of Dual Wheels – Full Axle Configuration

330mm

Crushed Rock

Features of pavement response model

• response to load is calculated using the linear

elastic theory and specifically the computer

program CIRCLY

Performance relationships relate

strains to allowable traffic loading

27

Summary of design process

• Step 1: select a trial pavement, desired project

reliability

• Step 2: elastic characterisation of materials

• Step 3: calculation of critical strains

• Step 4: calculation of allowable loadings

• Step 5: calculation of design traffic

• Step 6: compare allowable loading with design traffic

Types of heavy duty flexible pavements

29

Presentation Outline

• Introduction

• Definition of heavily trafficked long life pavement

– Design periods 40 years

• Foundation design

• Flexible pavements

– Surfacing types

– Structural design method

– Specifications

• Concrete pavements

• Example designs

30

Asphalt mix design performance tests

• Indirect tensile modulus

• Beam fatigue tests

• Rut resistance using small Wheel tracker

31

Cemented treated crushed rock

• 3-4% cement commonly used

• stiff working platform on which to construct asphalt layers

• 150 mm to 200 mm thick single layer

• common practice to assume it will fatigue crack early in

pavement life

• hence a post-cracked modulus of 500 MPa is used

• Unconfined compressive strength commonly specified,

ARRB has recently developed fatigue test

32

Lean concrete subbase

• composition

33

Aggregate size (nominal maximum)

Approximate proportion (by mass) of mix(1)

20 mm aggregate 31%

14 mm aggregate 6%

10 mm aggregate 6%

7 mm aggregate 6%

5 mm screened fines 2%

High fines - sand 37%

Lean concrete subbase

• placed wet and screeded as per concrete

• thicknesses min 150 mm to 230 mm

34

Lean concrete subbase

• 90 day flexural strength >2 MPa

• Design modulus 10 000 MPa

• Design to inhibit fatigue cracking

35

Need to inhibit cracking of lean mix

reflecting to pavement surface

• Overlying asphalt thickness ≥ 175 mm to inhibit reflection

cracking

36

Can use mechanistic approach to develop

design charts for routine use

37

Presentation Outline

• Introduction

• Definition of heavily trafficked long life pavement

– Design periods 40 years

• Foundation design

• Flexible pavements

– Surfacing types

– Structural design method

– Specifications

• Concrete pavements

• Example designs

38

Concrete pavement terminology

Lean concrete subbase

Capping/ select fill

Concrete base

Subgrade

• plain concrete

• jointed reinforced

• CRCP

debonding

layer

Concrete pavement types commonly

used

40

Plain concrete pavements (no dowels

at transverse joints)

concrete base

lean concrete subbase

Plain Concrete Pavements (PCP)

• Placed using slip form paver

42

tiebars

Longitudinal texture using hessian

dragged behind slip form paver

43

hessian

Transverse texture by tyning

44

Jointed reinforced concrete pavements

45

Continuously reinforced concrete

pavementReinforcing bars

subbase

base

Continuously reinforced concrete

pavement

47

Lean concrete (wet) subbase

48

Lean concrete subbase

Curing and debonding of concrete base and

subbase

49

Tied shoulders used

50

Presentation Outline

• Introduction

• Definition of heavily trafficked long life pavement

– Design periods 40 years

• Foundation design

• Flexible pavements

– Surfacing types

– Structural design method

– Specifications

• Concrete pavements

– Structural design method

• Example designs

51

Two distress types considered in flexible

pavement thickness design

• fatigue of cracking of concrete base

• erosion of fines of the subbase/subgrade arising from

repeated deflections at joints and planned cracks

Erosion

at joints

Fatigue

cracking

Thickness design based on simple prediction

models developed from finite element modelling

• critical stresses/displacement are determined under each

anticipated axle group type and axle group load

• not calculated directly in Austroads Guide,

stresses/displacement embedded in performance

relationships

103.0

3F2

4

SFe2 9.0)

35.41

10

F 4.45

PL,0max( 77.6 14.52 )N (F log

−

−=

Erosion predicted from slab corner displacements

Thickness design

• select a trial concrete base thickness

• calculate percentage damage by dividing expected load

repetitions by allowable repetitions

SINGLE AXLES / DUAL WHEELS (SADT)

Equivalent Stress 1.06Stress Ratio Factor 0.250 Erosion Factor 2.47

Fatigue Analysis Erosion Analysis

Axle Load(kN)

DesignLoad (kN)

ExpectedRepetitions

AllowableRepetitions

Fatigue(%)

AllowableRepetitions

Damage(%)

150 195.0 0 57,500 0.00 69,271 0.00

140 182.0 0 159,117 0.00 104,306 0.00

130 169.0 1,528 601,365 0.25 163,912 0.93

120 156.0 9,168 5,962,495 0.15 272,483 3.36

110 143.0 31,324 UNLIMITED 0.00 489,873 6.39

100 130.0 106,196 UNLIMITED 0.00 991,416 10.71

90 117.0 226,908 UNLIMITED 0.00 2,462,593 9.21

80 104.0 352,968 UNLIMITED 0.00 9,721,111 3.63

70 91.0 496,600 UNLIMITED 0.00 1,373,296,172 0.04

60 78.0 734,204 UNLIMITED 0.00 UNLIMITED 0.00

Thickness design

• sum damage over all axle group loads and axle group types

• if damage less than 100% for both erosion and fatigue,

pavement acceptable otherwise select another trial

pavement configurationSINGLE AXLES / DUAL WHEELS (SADT)

Equivalent Stress 1.06Stress Ratio Factor 0.250 Erosion Factor 2.47

Fatigue Analysis Erosion Analysis

Axle Load(kN)

DesignLoad (kN)

ExpectedRepetitions

AllowableRepetitions

Fatigue(%)

AllowableRepetitions

Damage(%)

150 195.0 0 57,500 0.00 69,271 0.00

140 182.0 0 159,117 0.00 104,306 0.00

130 169.0 1,528 601,365 0.25 163,912 0.93

120 156.0 9,168 5,962,495 0.15 272,483 3.36

110 143.0 31,324 UNLIMITED 0.00 489,873 6.39

100 130.0 106,196 UNLIMITED 0.00 991,416 10.71

90 117.0 226,908 UNLIMITED 0.00 2,462,593 9.21

80 104.0 352,968 UNLIMITED 0.00 9,721,111 3.63

70 91.0 496,600 UNLIMITED 0.00 1,373,296,172 0.04

60 78.0 734,204 UNLIMITED 0.00 UNLIMITED 0.00

Joint design

• Thickness design is dominated by traffic-induced

stresses

• Location and design of joints dominated by the need to

control stresses and strains due to changes in

temperature and moisture

56

Roads and Maritime Services, New

South Wales (www.rms.nsw.gov.au)

57

Need for experienced designers,

detailing critical to performance

58

Presentation Outline

• Introduction

• Definition of heavily trafficked long life pavement

– Design periods 40 years

• Foundation design

• Flexible pavements

– Surfacing types

– Structural design method (staged construction,

fatigue endurance limit)

– Specifications

• Concrete pavements

• Example designs

59

Design examples

• Location: Brisbane

• annual rainfall 1000 mm

• Urban freeway/motorway

• 40 year design traffic 100 MESA

• subgrade design CBR = 5%

60

Thick asphalt on crushed rock subbase

30mm Open graded asphalt

50mm DGA14

(SBS polymer modified binder)

290 mm DGA20

Pen 50/65 bitumen

(4.5% - 5% by mass)

150 mm crushed rock subbase

CBR ≥ 30%

150 mm Capping layer CBR ≥ 10%

subgrade material CBR = 5%

seal

Thick asphalt on cement treated crushed rock

subbase

30mm Open graded asphalt

50mm DGA14 (SBS polymer modified

binder

230 mm DGA20

Pen 50/65 bitumen

(4.5% - 5% by mass)

150 mm 3% cement treated crushed

rock subbase (E=500 MPa, cracked)

150mm Capping layer CBR ≥ 10%

subgrade material CBR = 5%

seal

Thick asphalt on lean concrete subbase

30mm Open graded asphalt

50mm DGA14 (SBS polymer modified

binder

125 mm DGA20

Pen 50/65 bitumen (4.5% - 5% by mass)

190 mm lean concrete subbase

(E= 10 000 MPa)

150 mm crushed rock subbase

CBR ≥ 30%

150mm Capping layer CBR ≥ 10%

subgrade material CBR = 5%

seal

Plain concrete on lean concrete subbase

270 mm concrete base

150 mm lean concrete subbase

(E= 10 000 MPa)

150 mm crushed rock subbase

CBR ≥ 30%

150mm Capping layer CBR ≥ 10%

subgrade material CBR = 5%

Debonding

treatment

Continuously reinforced concrete on lean

concrete subbase

250 mm concrete base

150 mm lean concrete subbase

(E= 10 000 MPa)

150 mm crushed rock subbase

CBR ≥ 30%

150mm Capping layer CBR ≥ 10%

subgrade material CBR = 5%

Debonding

treatment

Summary

• Summarised Australian pavement design

practice for heavily trafficked long life

pavements

• Austroads guidelines need to be considered in

context of the entire Design System:

– Specifications

– Test method

– Engineering policies

– Construction quality

– In service performance

66

Thank you

67