Guide to Pavement Technology Part 1:
Introduction to Pavement Technology
Sydney 2009
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
Publisher
Second edition project manager: Peter Balfe
Austroads Ltd.
Level 9, 287 Elizabeth Street
Sydney NSW 2000 Australia
Second edition prepared by: Kieran Sharp
Phone: +61 2 8265 3300
Abstract
The purpose of the Austroads Guide to Pavement Technology is to assemble
this knowledge into a single authoritative electronic publication that is readily
available, accessible, comprehensive and free resource for practitioners in
Australia and New Zealand. The target audience for the Guide to Pavement
Technology includes all those involved with the management of roads,
including industry, and students seeking to learn more about the fundamental
concepts, principles, issues and procedures associated with pavement
technology.
Keywords
Pavement technology, road management, history of roads, pavement type,
pavement design, pavement behaviour, pavement materials, guideline
austroads@austroads.com.au
www.austroads.com.au
About Austroads
Austroads is the peak organisation of Australasian
road transport and traffic agencies.
Austroads’ purpose is to support our member
organisations to deliver an improved Australasian
road transport network. To succeed in this task, we
undertake leading-edge road and transport
research which underpins our input to policy
development and published guidance on the
design, construction and management of the road
network and its associated infrastructure.
Austroads provides a collective approach that
delivers value for money, encourages shared
knowledge and drives consistency for road users.
Austroads is governed by a Board consisting of
senior executive representatives from each of its
eleven member organisations:
Edition 2.1 published August 2018
• Format updated
• Roads and Maritime Services New South Wales
Edition 2 published November 2009
• Roads Corporation Victoria
Edition 1 published 2005
• Queensland Department of Transport and Main
Roads
• Main Roads Western Australia
ISBN 978-1-921551-88-8
Pages 39
Austroads Project No. TP1048
Austroads Publication No. AGPT01-09
• Department of Planning, Transport and
Infrastructure South Australia
• Department of State Growth Tasmania
• Department of Infrastructure, Planning and
Logistics Northern Territory
© Austroads Ltd 2009
• Transport Canberra and City Services
This work is copyright. Apart from any use as permitted under the
Copyright Act 1968, no part may be reproduced by any process without
the prior written permission of Austroads.
• Australian Government Department of
Directorate, Australian Capital Territory
Infrastructure and Regional Development
• Australian Local Government Association
• New Zealand Transport Agency.
This Guide is produced by Austroads as a general guide. Its application is discretionary. Road authorities may vary their practice
according to local circumstances and policies. Austroads believes this publication to be correct at the time of printing and does not
accept responsibility for any consequences arising from the use of information herein. Readers should rely on their own skill and
judgement to apply information to particular issues.
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
Summary
Knowledge of pavement technology is of critical importance for all transport agencies in Australia and New
Zealand. Austroads and others (e.g. state road authorities, local government and industry) have amassed a
great deal of knowledge on pavement technologies, techniques and considerations. The purpose of the
Austroads Guide to Pavement Technology is to assemble this knowledge into a single authoritative
electronic publication that is a readily available, accessible, comprehensive and free resource for
practitioners in Australia and New Zealand.
The target audience for the Guide to Pavement Technology includes all those involved with the management
of roads, including industry, and students seeking to learn more about the fundamental concepts, principles,
issues and procedures associated with pavement technology.
Part 1 – Introduction to Pavement Technology – provides general information regarding the purpose and
function of pavements, pavement types and their components, pavement materials, the types of pavements
commonly in use today and an introduction to the fundamentals of pavement behaviour. A brief description
of the other nine parts of the guide is also presented. The development of road pavements in Australasia is
briefly discussed in a commentary.
This part is not intended to be referenced as a source document but rather it provides the background to the
guide as a whole.
Austroads 2009 | page i
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
Contents
1.
1.1
Introduction............................................................................................................................................. 1
Relationship to other Austroads Guides ................................................................................................... 3
2.
Purpose and Function of Pavements ................................................................................................... 4
3.
3.1
3.2
Pavement Types and Components....................................................................................................... 5
Pavement Types....................................................................................................................................... 5
Pavement Components ............................................................................................................................ 5
3.2.1 Wearing Surface ......................................................................................................................... 6
3.2.2 Base ............................................................................................................................................ 7
3.2.3 Subbase...................................................................................................................................... 7
3.2.4 Subgrade .................................................................................................................................... 8
4.
4.1
4.2
4.3
Pavement Materials ................................................................................................................................ 9
Unbound Granular Materials .................................................................................................................... 9
Modified Granular Materials ..................................................................................................................... 9
Bound Materials........................................................................................................................................ 9
4.3.1 Stabilised Materials .................................................................................................................. 10
4.3.2 Asphalt ...................................................................................................................................... 12
4.3.3 Concrete ................................................................................................................................... 13
5.
5.1
5.2
5.3
5.4
Pavement Types in Use Today............................................................................................................ 14
Unbound Granular Pavements ............................................................................................................... 14
Asphalt Pavements................................................................................................................................. 14
Rigid Pavements .................................................................................................................................... 15
Pavement Strengthening Treatments..................................................................................................... 17
5.4.1 Pavement Overlays .................................................................................................................. 17
5.4.2 In situ Stabilisation .................................................................................................................... 17
Unsealed Roads ..................................................................................................................................... 18
5.5
6.
6.1
Pavement Behaviour Under Load ....................................................................................................... 19
Structural Analysis .................................................................................................................................. 20
6.1.1 Flexible Pavements .................................................................................................................. 20
6.1.2 Rigid Pavements ...................................................................................................................... 21
7.
Pavement Life Cycle Costing .............................................................................................................. 22
8.
8.1
8.2
8.3
Brief Description of each part of Guide to Pavement Technology .................................................24
Part 2: Pavement Structural Design ....................................................................................................... 24
Part 3: Pavement Surfacings .................................................................................................................. 25
Part 4: Pavement Materials .................................................................................................................... 25
8.3.1 Unbound Granular Materials .................................................................................................... 25
8.3.2 Modified Granular Materials ..................................................................................................... 26
8.3.3 Bound Materials ........................................................................................................................ 26
Part 5: Pavement Evaluation and Treatment Design ............................................................................. 28
Part 6: Unsealed Pavements .................................................................................................................. 29
Part 7: Pavement Maintenance .............................................................................................................. 29
Part 8: Pavement Construction .............................................................................................................. 30
Part 9: Pavement Work Practices .......................................................................................................... 30
Part 10: Subsurface Drainage ................................................................................................................ 30
8.4
8.5
8.6
8.7
8.8
8.9
References ...................................................................................................................................................... 38
Austroads 2009 | page ii
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
Tables
Table 4.1:
Pavement material categories and characteristics ................................................................. 11
Figures
Figure 1.1:
Figure 2.1:
Figure 3.1:
Figure 5.1:
Figure 5.2:
Figure 5.3:
Figure 5.4:
Figure 6.1:
Figure 6.2:
Structure of Guide to Pavement Technology with focus on Part 1 ........................................... 2
Pavement structure and its role in the road formation .............................................................. 4
Components of flexible and rigid road pavement structures .................................................... 6
Typical longitudinal section of plain concrete pavement (PCP) steel fibre
reinforced concrete is sometimes used for PCP ..................................................................... 15
Typical longitudinal section of jointed reinforced concrete pavement (JRCP) .......................16
Typical longitudinal section of continuously reinforced concrete pavement ...........................16
Typical cross-section of dowelled plain concrete pavement (PCP-D) steel fibre
reinforced concrete is sometimes used for PCP-D ................................................................. 16
Dispersion of surface load through a granular pavement structure ........................................19
Responses of different bound pavement types to load ..........................................................20
Austroads 2009 | page iii
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
1.
Introduction
Knowledge of pavement technology is of critical importance for all transport agencies in Australia and New
Zealand. Austroads and others (e.g. state road authorities, local government and industry) have amassed a
great deal of knowledge on pavement technologies, techniques and considerations. The purpose of the
Austroads Guide to Pavement Technology is to assemble this knowledge into a single authoritative
electronic publication that is readily available, accessible, comprehensive and free resource for practitioners
in Australia and New Zealand.
The target audience for the guide includes all those involved with the management of roads, including
industry, and students seeking to learn more about the fundamental concepts, principles, issues and
procedures associated with pavement technology.
Figure 1.1 shows the structure of the guide. Part 1: Introduction to Pavement Technology provides general
information regarding the purpose and function of pavements, pavement types and their components,
pavement materials, the types of pavements commonly in use today and an introduction to the fundamentals
of pavement behaviour. A brief description of the other nine parts of the guide is also presented. This part is
not intended to be referenced as a source document but rather it provides the background to the guide as a
whole.
Each part is accompanied by ‘Commentaries’ which aim to amplify the principles and processes by use of
examples. For example, a summary of the historical development of road pavements in Australasia is
presented in Commentary 1.
There is no ‘Local Roads’ part in the guide because issues related to them span most guides (asset
management, road design, safety, traffic management, etc.) as well as pavement technology. Segmental
pavements are not addressed in the guide as their main use is in heavy duty industrial and local government
applications rather than highway applications and their adoption in local government applications is generally
confined to traffic control treatments or as a surfacing over an existing pavement. Relevant aspects relating
to geotextile and geogrids are addressed in Part 4G of this guide (see Figure 1.1), whilst non-pavement
related aspects are addressed in Part 7 (Geotechnical Investigation and Design) of the Guide to Road
Design.
As part of a developing series of live documents, it is recognised that there will be periodic revisions to this
document and other parts within the guide. The Austroads website should be referenced
(http://www.austroads.com.au) to ensure the reader is accessing the latest version of this document.
Austroads 2009 | page 1
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
Figure 1.1:
Structure of Guide to Pavement Technology with focus on Part 1
Austroads 2009 | page 2
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
1.1
Relationship to other Austroads Guides
Users of the Guide to Pavement Technology will need to ensure relevant parts of other guides, such as the
Asset Management, Bridge Technology and Project Delivery, are referred to where appropriate. For
example, whilst the Guide to Pavement Technology provides for decisions made at a detailed level about
issues specific to road pavements at the project level, the Guide to Asset Management aims to give
practitioners guidance for decision making with respect to good practice asset management at a network
level.
A ‘Glossary’ of commonly used terminology associated with pavement technology, and all the other guides,
is available on the Austroads website (http://www.austroads.com.au).
If a guide is properly designed, then there should not be a need for maintenance of similar guides and codes
within jurisdictions. Each development plan should be supported by a review of user needs for national
guidelines and should identify the extent to which there is current duplication of effort, why this occurs, and
what needs to be done to avoid it. On the other hand, it is recognised that procedures vary between Australia
and New Zealand and also within jurisdictions. For this reason, the Austroads Guide to Pavement
Technology does not prescribe particular processes. Instead it seeks to provide guidance on good practice,
and to promote consistent approaches to the achievement of this good practice.
Austroads 2009 | page 3
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
2.
Purpose and Function of Pavements
The contribution of a road pavement to the overall road formation is shown in Figure 2.1. The pavement must
serve two basic functions – it must perform as an engineering structure and at the same time meet functional
requirements.
In terms of structural performance, the pavement must be of sufficient thickness, and be composed of
materials of sufficient quality, to be able to withstand the various loads that are applied to it by heavy
vehicles.
In terms of functional performance, the pavement must have a good riding quality to ensure comfortable
travel for the road user and, in the case of surfaced pavements, a surface having adequate drainage, skid
resistance, reflectivity and line markings to ensure safe travel. The surface must also be capable of resisting
both vertical and horizontal surface stresses in order to maintain its integrity. If the surface is lost, or cracked,
then ride comfort is affected and water can enter the underlying base layers. It must also be capable of
withstanding environmental loads, including oxidation of bituminous binders.
Inherent in these demands is the need to ensure that construction and maintenance practices are adequate
for the demand to be placed upon the pavement.
Australia has about 800,000 km of roads, of which about two-thirds are unsealed (Austroads 2000) whilst
New Zealand has about 92,700 km of roads of which about 40% are unsealed (Transit New Zealand, Road
Controlling Authorities and Roading New Zealand 2005). Unsealed roads have different characteristics to
sealed roads and, in recognition of this they are addressed in a separate part of the Guide to Pavement
Technology.
Figure 2.1:
Pavement structure and its role in the road formation
Austroads 2009 | page 4
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
3.
Pavement Types and Components
3.1
Pavement Types
Pavements are classified as either flexible (containing unbound granular and/or stabilised materials and/or
asphalt) or rigid (concrete pavement with joints and/or steel reinforcement).
The term ‘flexible pavement’ is applied to all pavement structures other than those described as rigid
pavements, including unbound pavements with thin bituminous surfacings and bound (stabilised and
asphalt) pavements. They are designed and generally constructed as continua, without formal joints. The
most common sealed flexible pavement used in Australasia is the unbound granular pavement with a thin
bituminous seal. Their design is empirically based. The design of pavements incorporating a bound layer, or
full depth asphalt pavement, is mechanistic using elastic layer modelling. This relies on the stiffness
(modulus) properties of continuous layers, in a macro sense appropriate to potentially cracked media, rather
than material properties measured in the laboratory.
A rigid pavement consists of a relatively high strength concrete base (usually 30 MPa or more) and one of a
range of subbase materials (lean mix concrete, cement stabilised crushed rock, unbound granular material,
etc.). The various concrete base formats are: jointed unreinforced (plain concrete), jointed reinforced,
continuously reinforced, and steel fibre reinforced. With the exception, perhaps, of roller compacted
concrete, rigid pavements have formal jointing systems that are sealed against moisture. In the case of
continuously reinforced concrete pavements, there are longitudinal joints, but no regular transverse joints for
shrinkage and thermal strains. The thickness design method for rigid pavements takes into account the
presence of joints and edges.
Flexible pavements can be constructed in stages (staged construction) and, in many cases, repair of
underground services is simpler than for rigid pavements. There are advantages and disadvantages
associated with each pavement type. These need to be considered along with construction constraints,
material availability and costs, and the need to optimise the costs of the overall pavement system.
3.2
Pavement Components
The generic components of flexible and rigid road pavement structures are shown in Figure 3.1. A brief
description of each component follows.
Austroads 2009 | page 5
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
Figure 3.1:
Components of flexible and rigid road pavement structures
Source: Austroads (2004a).
3.2.1
Wearing Surface
The primary function of the surface course is to withstand the prevailing loading and environmental
(moisture, dust, etc.) effects and hence provide a safe and functional riding surface with reduced spray and
noise while at the same time protecting the underlying pavement courses from moisture ingress. The three
types of surface courses most commonly used on roads in Australasia are sprayed (or chip) seals, asphalt
and concrete. Interlocking concrete pavers have only very limited application in high speed traffic situations
and their use is limited to urban applications.
Austroads 2009 | page 6
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
The sprayed bituminous seal (or ‘chip seal’ 1) was developed in New Zealand in the 1930s (Hanson 1935). It
provides an economical solution to the surfacing problem. It consists of a thin film of bitumen sprayed on top
of a compacted base and incorporates a layer of single-sized stone. In the majority of cases they are used as
a surface over an unbound granular base. They are a low cost alternative to other forms of sealed
pavements such as asphalt.
Whilst spray seal surfacings mainly contribute to the functional performance of a pavements (i.e. provide a
safe, all-weather driving surface), asphalt and concrete also have roles to play in terms of the structural
performance of the pavement. Thin (30-50 mm) asphalt surfacings play a role in delivering functional
performance whilst thicker, including full depth asphalt, also deliver structural capacity.
3.2.2
Base
The base is the main ‘load carrying’ course within the pavement. An unbound basecourse is composed of
materials which are granular or mechanically stabilised or treated with binders to improve properties other
than strength (e.g. plasticity). An unbound basecourse therefore behaves under load as if its component
parts were not bound together although significant mechanical interlock can occur. In the majority of cases
an unbound granular basecourse is provided under a sprayed seal surfacing.
The quality of the base can be improved using stabilisation; the most common stabiliser used with unbound
granular materials is cement. In rural applications a sprayed seal surfacing is generally applied over the
stabilised base.
In terms of rigid pavements, the thickness of the concrete base will vary according to the type of shoulder
and joint/reinforcement details adopted. The selection of the overall pavement configuration is a matter for
decision by the designer based on its suitability for a particular project and economic considerations.
3.2.3
Subbase
The subbase in a flexible pavement is also a load carrying course; its lower quality is related to economics
and the lower stress levels than those near the pavement surface. The main role of the subbase is to provide
adequate support to the base and reduce the stress/strains applied to the subgrade. It may also be used to
reduce the pumping of subgrade fines through joints or cracks onto the surface of a pavement following the
action of traffic or ground water pressure.
The quality of the base can be also improved using stabilisation, including mechanical stabilisation or the use
of cement, lime or a bituminous binder. The practice is more common when the parent material is a marginal
or non-standard material, often won locally.
In terms of rigid pavements, the provision of a bound or lean mix concrete subbase is recommended to:
• resist erosion of the subbase and limit pumping at the joints and slab edges
• provide uniform support under the pavement
• reduce the magnitude of the deflection at joints and enhance load transfer across joints, especially if no
other load transfer devices, such as dowels, are provided
• assist in the control of shrinkage and swelling of high-volume-change subgrade soils.
1
The term ‘spray seal’ or ‘sprayed seal’ is commonly used in Australia, whilst the term ‘chip seal’ is widely used in New Zealand and
South Africa.
Austroads 2009 | page 7
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
3.2.4
Subgrade
The subgrade is the trimmed or prepared portion of the formation on which the pavement is constructed. The
subgrade may be the prepared in situ material but, particularly for heavy duty pavements, it may also include
selected materials which are placed above the in situ material.
Many factors must be considered in determining the subgrade support conditions, including the
consequences of premature distress, sequence of earthworks construction, target compaction moisture
content and field density achieved, moisture changes during the life of the pavement, subsurface drainage
and depth of the water table and the presence of weaker layers below the design subgrade level.
Subgrades are inherently variable in nature, reflecting the changes in topography, soil type and drainage
conditions that generally occur along an existing or prepared road alignment. The selection of the
appropriate design value for the subgrade requires a consideration of the degree of variability within a project
section and the quantity and quality of data on subgrade properties available to the designer.
Improved subgrades refer to subgrades that have had their properties ‘improved’ in order that they can
provide sufficient support to the upper layers and withstand the stresses applied to them under load. Other
practical considerations include the need to provide adequate access to construction traffic (i.e. a working
platform). Improvement can be achieved through stabilisation of the parent material or the introduction of an
imported material placed over the parent material.
A working platform can be considered either a subbase layer or an improved subgrade layer. For a low
formation height road containing few layers, the working platform may comprise a lower subbase layer but,
for a high formation, it would generally be described as an improved subgrade with embankment material to
be placed over it.
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Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
4.
Pavement Materials
Pavement materials can be classified into essentially five categories according to their fundamental
behaviour under the effects of applied loadings (see Table 4.1):
• unbound granular materials
• modified granular materials
• bound materials
– stabilised materials
– asphalt
– concrete.
The characterisation of these materials, other than concrete, is conducted using one of two currently
available design procedures: an empirical method and a mechanistic-empirical, or structural, method. The
former, which is limited to the design of pavements incorporating unbound granular materials only, requires
the materials to be characterised in terms of their strength. The latter, which is applicable to the design of
flexible pavements incorporating modified or bound materials (other than concrete), or unbound materials
having a thick asphalt surfacing, utilises a computerised analytical technique, CIRCLY (Mincad Systems
2004). This method models the pavement as a series of elastic layers and requires the materials to be
characterised in terms of their elastic properties – modulus and Poisson ratio.
4.1
Unbound Granular Materials
Unbound granular materials consist of gravels or crushed rocks which have a grading that makes them
mechanically stable, workable and compactable. Their performance is largely governed by their shear
strength, stiffness and resistance to material breakdown under construction and traffic loading. The most
common modes of distress are rutting and shoving due to insufficient resistance to deformation through
shear and densification, and disintegration through breakdown.
4.2
Modified Granular Materials
unconfined compressive strength
Modified granular materials are granular materials to which small amounts of stabilising binder have been
added to improve stiffness or to correct other deficiencies, such as high plasticity, without causing a
significant increase in tensile capacity (i.e. producing a bound material). Examples include chemically
modified materials and cement, lime, lime/fly ash or slag modified materials. For example, unbound materials
modified with cement will typically result in a material having a UCS value of less than 1 MPa. Modified
materials are considered to behave as granular materials though in practice this can be difficult to achieve
unless the stabilised material is reworked after most of the cementing action has occurred.
4.3
Bound Materials
A bound material is one in which the particles are strongly bound together by binders such as lime, cement
or bitumen. Under loading, they behave as a continuous system able to develop tensile stresses without
material separation.
Austroads 2009 | page 9
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
The choice between bound and unbound materials is usually based on function, cost and construction
constraints. Whilst the volumetric cost of bound course will be higher, less material will be required and the
overall cost may be lower. Bound courses may often be the only alternative if the water table is high,
drainage is poor, a working platform is needed or pavement thickness or construction time is limited due to
other constraints, including level constraints (much more common in urban areas than rural areas).
4.3.1
Stabilised Materials
Stabilised materials involve mixing a chemical binding agent into the pavement material and then compacting
and curing the material to form a bound pavement layer. The stabilising binder may consist of lime, Portland
cement, blended cement, bitumen or other pozzolanic materials. The binder should be added in sufficient
quantity to produce a bound layer with significant tensile strength.
Austroads 2009 | page 10
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
Table 4.1:
Pavement material categories and characteristics
Pavement Material Category
Characteristics
Unbound Granular
Modified Granular
Bound
Stabilised
Asphalt
Concrete
Material types
•
•
•
•
crushed rock
gravel
soil aggregate
mechanically stabilised
materials
• chemically modified
materials
• cement, lime, lime/fly
ash or slag modified
materials
• lime stabilised materials
• cement stabilised
materials
• bitumen stabilised
materials
• lime/fly ash stabilised
materials
• slag stabilised materials
• slag/lime stabilised
materials
• dense graded asphalt
• open graded asphalt
• stone mastic asphalt
• plain concrete
• lean mix concrete
• fibre reinforced concrete
Behaviour
characteristics
• development of shear
strength through
particle interlock
• no significant tensile
strength
• development of shear
strength through
particle interlock
• no significant tensile
strength
• development of shear
strength through particle
interlock and chemical
bonding
• significant tensile strength
• development of shear
strength through particle
interlock and cohesion
• significant tensile strength
• properties are
temperature sensitive
• development of shear strength
through chemical bonding and
particle interlock
• very significant tensile strength
Distress modes
• deformation through
shear and densification
• disintegration through
breakdown
• deformation through
shear and densification
• disintegration through
breakdown
• cracking developed
through shrinkage, fatigue
and over-stressing
• erosion and pumping in
the presence of moisture
• cracking developed
through fatigue,
overloading
• permanent deformation
• cracking developed through
shrinkage, fatigue and erosion
of subbase
Input parameters
for design
• modulus
• Poisson’s ratio
• degree of anisotropy
• modulus
• Poisson’s ratio
• degree of anisotropy
• modulus
• Poisson’s ratio
• modulus
• Poisson’s ratio
• 90 or 28 day flexural strength or
28 day compressive strength
Performance
criteria
• current materials
specifications
• current materials
specifications
• fatigue relationships
• fatigue relationships
• fatigue and erosion relationships
Austroads 2009 | page 11
Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
Lime stabilised materials
Lime stabilisation refers to the use of hydrated or quicklime (calcium hydroxide) rather than agricultural lime
(calcium carbonate). Lime stabilisation is widely used to improve clay material having plasticity index (PI)
values greater than 10. The addition of lime results in an immediate increase in strength, makes the soil
more friable and reduces its moisture sensitivity.
Cement stabilised materials
In cement stabilisation, hydration of the cement occurs in association with cement-clay interaction: the
hydrated cement fills voids in the soil by both diffusion and volumetric growth of the resulting compounds.
Cement contents obviously vary depending on the soil type being stabilised and the required application. In
general, the strength increases as the cement content increases, with an increase in unconfined
compressive strength (UCS) between 0.5-1.0 MPa being achieved for each 1% of cement added. Elastic
moduli can also vary greatly depending on the parent soil and amount of binder. Moduli up to 10,000 MPa
can be achieved in heavily bound pavements. Once the cement has been added, the material should be
compacted before the process of hydration is complete.
Bitumen stabilised materials
A range of bituminous products (foamed bitumen, emulsions, etc.) can be used to stabilise a wide range of
pavement materials. They predominantly act as glue-like cohesion agents in granular materials and as
water-proofers. Bitumen stabilisation is generally used with granular materials rather than clayey materials
because mixing is easier and the required strength gains are not as large.
Recycled materials
A related form of pavement stabilisation involves the use of recycled materials such as concrete and byproducts such as fly ash, bottom ash and ground granulated blast furnace slag. Fly ash, for example, is a byproduct of the burning of coal. It usually consists of fine siliceous or aluminous products and can react with
other materials in the presence of water to form cementing compounds. As it reacts particularly well with lime
it has the economic potential to replace cement in certain applications. Its use is generally limited by how far
it needs to be transported to a site and associated cost considerations.
Various blends such as slag/lime and bitumen/cement are now frequently used to rehabilitate pavements,
usually through an in situ stabilisation process.
4.3.2
Asphalt
Asphalt is a mixture of bituminous binder and several, typically, single-sized aggregate fractions. It is spread
and compacted while hot to form a pavement layer. While the binder is usually a conventional bitumen, for
special applications it may be modified by the addition of specific polymers to the bitumen.
Open graded asphalt is used as a skid resistant surfacing and also to reduce tyre/road noise. The drainage
provided by this surface also reduces the spray hazard. These safety and environmental factors are
becoming increasingly important with the trend of social values and expectations.
The steady introduction of polymer modified binders is extending the use of asphalt as there is considerable
potential for improving fatigue and rutting properties. However, as their properties often vary from those of
conventional asphalt mixes, some of the traditional asphalt mix design procedures may not always be
applicable and a great deal of research has been conducted in recent times aimed at characterising these
mixes in the laboratory and demonstrating their superior performance in the field.
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Guide to Guide to Pavement Technology Part 1: Introduction to Pavement Technology
The strength/stiffness of asphalt is derived from friction between the aggregate particles, the viscosity of the
bituminous binder under operating conditions and the cohesion within the mass resulting from the binder
itself, and the adhesion between the binder and the aggregate. The most common modes of distress for
asphalt layers are: (1) rutting and shoving due to insufficient resistance to permanent deformation, and (2)
cracking, either due to fatigue under applied loading or environmental factors (oxidation).
The recycling of asphalt (which has reached the end of its service life) by incorporating it with virgin asphalt
during the asphalt production process is a relatively recent – but rapidly expanding – industry. The resulting
product commonly contains 10‒20% recycled material. To compensate for the hardening of the bitumen that
has occurred throughout the service life of the asphalt, binders which lower the viscosity of the hardened
bitumen may be incorporated in the mix.
4.3.3
Concrete
Concrete refers to a homogeneous mixture of hydraulic cement, fine and coarse aggregate, water and
chemical admixtures. The cementitious portion of concrete may be Portland cement or blended cement,
which consists of Portland cement mixed with binders such as ground granulated blast furnace slag and/or
pulverised fly ash. Chemical admixtures may be used for set retardation and air entrainment. Concrete can
be used as a subbase in flexible pavements and a base or subbase in rigid pavements.
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5.
Pavement Types in Use Today
5.1
Unbound Granular Pavements
The design of unbound pavements with thin bituminous surfacings is empirically based, and Australian
practice (Austroads 2004a) has not changed much from the procedures used over 50 years ago (Hanson
1935; MacLean 1954). Structurally, the granular pavement material spreads the load to the foundation
through its interparticle friction and shear strength.
The provision of sound, low cost pavements is less technically demanding under permanently dry conditions.
However, while much of Australia has an arid climate, for many of its heavily-trafficked roads the question of
moisture in pavements is of primary importance in both Australia and New Zealand. The problem is not one
of drainage alone, though both surface and subsurface drainage are essential elements of moisture control.
Capillary forces, or soil suction, can maintain the saturated condition in many fine grained soils irrespective
of drainage. In this case evaporation is the only natural drying agent, and it may not be sufficiently available
in the road pavement to balance moisture infiltration. Conservative design therefore will assume the
saturated subgrade condition in the wetter coastal areas of Australia and in most of New Zealand.
However, for many thousands of kilometres of sealed pavement in inland areas of Australia the
evapotranspiration balance is such that the subgrade is never fully saturated. In this situation advantage can
be taken of the unsaturated strength, and a thinner pavement built, provided due care is taken with edge
conditions and drainage. This is true even in regions composed of highly reactive clays. In these areas
moisture movement causes longitudinal edge cracking of pavements, which can be confined to an edge
effect by the use of wide impermeable shoulders and prompt sealing of any cracks which do occur. Loss of
shape (surface profile) can also be a problem in these areas.
Specifications for unbound base material have been gradually developed since the advent of mechanised
construction techniques in the 1920s. Before that time little compactive effort was used on macadam bases.
However, the demand for smoother, dust free pavements to cater for higher speed pneumatic-tyred vehicles,
and mechanised construction, led to the development of the ‘maximum density’ grading where a range of
stone sizes was used to pack together into a dense, tight mass. The need was also recognised for adequate
compaction of the pavement before trafficking, to achieve a stable surface shape 2.
5.2
Asphalt Pavements
As for all pavement materials, the use of asphalt must be appropriate to its engineering properties to be
effective in the long term. Asphalt has a relatively low tensile strength for a bound pavement material – about
one-fifth that of concrete – but it has a high strain capacity, about double that of concrete. These and other
engineering properties can be used in a mechanistic design process, to produce more effective pavement
designs than the empirically based designs of the recent past.
The bitumen binder in asphalt gives it its viscoelastic properties which are dependent on temperature and
duration of loading. The performance of an asphalt surfacing can therefore be greatly influenced by the local
climatic temperature regime, the day/night distribution of heavy vehicles and traffic speed. For example,
when the traffic loading is heavy at night in an area where night temperatures can be quite low, this imposes
a significant constraint on the structural design against fatigue failure of the thin asphalt surfacing.
2
Initially any compaction was applied by the traffic but rollers were gradually introduced from about the mid-1800s. They were
commonly 1 metre long cast iron drums carrying rock-filled trays and drawn, initially, by teams of horses. They typically applied about 10
tonne per metre width. Lay (1984) reports that it was estimated that the original voids of 50% in macadam pavements were reduced to
about 30% using this procedure.
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Flexural fatigue life improves rapidly as the asphalt layer thickness either increases from about 100 mm or
decreases from about 50 mm. However, for thicknesses below 40 mm there is a higher degree of uncertainty
regarding the reliability of fatigue life predictions. With thick layers, the use of a stiffer binder can improve
both the fatigue life and the rutting properties. In a warm climate, rutting of the asphalt usually governs
design, particularly as the layer thickness increases. On the other hand, the viscous properties of the asphalt
provide a beneficial capacity to deform and creep without cracking. These properties are extremely useful in
the construction process, using higher temperatures to provide workability and a smooth riding surface, with
minimal traffic disruption.
The asphalt properties are also time dependent, through ageing of the bitumen and perhaps through
stripping of the binder in a wet environment. These factors tend to limit the justifiable design life using
ordinary bitumen binder. At this stage pavement design procedures usually do not take account of the
ageing of asphalt, or the strains induced by temperature gradients. The maximum horizontal tensile strain is
predicted at the bottom of an asphalt layer, but there is clear evidence that in thick asphalt surfacings
transverse load-induced cracking can also initiate at the surface. This may be due to oxidation hardening of
bitumen at the surface combined with a low surface temperature.
5.3
Rigid Pavements
As discussed earlier, rigid (concrete) pavements made their debut in Australia prior to 1930 and some of
these pavements have remained serviceable for up to 50 years, although maintenance has been
considerable and riding quality poor for old pavements. These pavements did not have structural subbase
layers or subsurface drainage, and joint spaces were wide, unlike modern concrete pavements which
appeared in Australia in the late 1970s. The first of these was continuously reinforced, the best early
example being at Clybucca Flat, near Kempsey, NSW, on a very soft subgrade (Leask et al. 1979).
The plain (unreinforced) undowelled pavement did not reappear until 1983. This form of concrete pavement
has become prevalent for new work on major highways in NSW because of its ease of construction using
slipform pavers, and consequent economy. Much of the recent works on the Hume Highway in NSW consists
of this type of pavement.
About 2% of the Australian network has concrete pavement and these applications tend to be confined to
heavy duty applications such as National Highways, particularly in New South Wales. In these types of
applications, they have a very important role to play in the overall performance of the network. There is very
little use of concrete pavements in New Zealand.
Figure 5.1 to Figure 5.4 show basic details of the four types of concrete pavement (Austroads 2004c). More
detailed information about the use of these concrete pavements are presented in relevant parts of the Guide
to Pavement Technology.
Figure 5.1: Typical longitudinal section of plain concrete pavement (PCP) steel fibre reinforced concrete is
sometimes used for PCP
Source: Austroads (2004c).
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Figure 5.2:
Typical longitudinal section of jointed reinforced concrete pavement (JRCP)
Source: Austroads (2004c).
Figure 5.3:
Typical longitudinal section of continuously reinforced concrete pavement
Source: Austroads (2004c).
Figure 5.4: Typical cross-section of dowelled plain concrete pavement (PCP-D) steel fibre reinforced concrete
is sometimes used for PCP-D
Source: Austroads (2004c).
In concrete pavements, shrinkage cracking is largely controlled to limit crack openings and hence maintain
load transfer across cracks and/or moisture ingress. At longitudinal joints, tie bars hold the joint together
while allowing slab warping to occur with temperature changes. If used, continuous reinforcement constrains
the concrete shrinkage so that transverse cracks are closely spaced and therefore fine, ensuring durability.
For plain concrete pavement, transverse cracking is induced by saw cutting to form joints, which are sealed
but free to move with temperature changes.
With undowelled transverse joints, the degree of shrinkage must be controlled to provide for some load
transfer by grain interlock at the joints; a concrete subbase is required to compensate for the discontinuity.
Concrete shrinkage and strength are both critical for pavement performance, but may be to a degree
contradictory attributes for production. It is not only the ultimate values of these properties which are
important, but also their relative rates of increase.
Concrete strength and base thickness are very sensitive design parameters, as a 10% decrease in thickness
or strength can result in a 90% reduction in pavement life (DMR, NSW 1986). Concrete pavement
technology is therefore relatively rigorous and requires strict quality control during construction.
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5.4
Pavement Strengthening Treatments
5.4.1
Pavement Overlays
Thin bituminous overlays, such as slurry seals, sand asphalt or microsurfacing, are regarded as nonstructural overlays, while structural overlays involve the use of either granular material or asphalt at least 40
mm thick. A non-structural overlay is used to address deficiencies in the functional performance of a
pavement (shape, ride quality, surface texture, etc.) whilst a structural overlay is generally used to address
distress and structural deficiencies, in which case any functional deficiencies are also corrected.
Current Australasian thickness design procedures allow for the following four overlay types:
• granular overlays on flexible pavements
• asphalt overlays on flexible pavements
• asphalt overlays on rigid pavements
• concrete overlays on flexible or rigid pavements.
For flexible pavements, which do not include stabilised materials, the chart-based structural overlay design
procedures are based on determining the characteristic deflection and curvature of the existing pavement
and the appropriate deflection properties of the pavement after overlay. Due to seasonal moisture variations,
deflections may need to be adjusted to represent the condition of the pavement in its weakest condition. For
asphalt overlays on asphalt-surfaced granular pavements, a further correction is usually required because
pavement temperature influences the stiffness of the asphalt layers and hence its response to load. In New
Zealand, the past traffic is used to calibrate models for determining the required granular overlay thickness.
The design and selection of pavement rehabilitation treatments is addressed in Part 5 of the Guide to
Pavement Technology.
5.4.2
In situ Stabilisation
Stabilisation is defined as the ‘process of improving a material to achieve a long term increase in its load
bearing properties’. Stabilisation by modification of a material is preferred when the quality of the material,
not its thickness, is deficient.
The main methods of stabilisation are as follows:
• granular (mechanical) stabilisation
• cementitious stabilisation
• lime stabilisation
• bitumen stabilisation
• other chemical stabilising binders such as dry powdered polymers.
Deep lift in situ stabilisation involves the recycling of the existing pavement material through its incorporation
with binders such as bitumen/cement and slag/lime. The formation, once compacted, forms a bound
pavement layer of higher strength.
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5.5
Unsealed Roads
Approximately two-thirds of Australia’s roads, and 40% of New Zealand’s roads, are unsealed. They play an
important role in the Australasian road network in terms of providing access to rural communities, the
movement of primary products, haulage roads for the mining and timber industries, recreational and tourist
activities and movement within State forests and defence training areas.
The design and selection of pavement rehabilitation treatments is addressed in Part 5 of the Guide to
Pavement Technology.
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6.
Pavement Behaviour Under Load
The basic function of a pavement is to support the applied traffic loading within acceptable limits of riding
quality and deterioration over its design life. To do this, the pavement structure must spread the concentrated
wheel loads to the foundation (subgrade material) such that, under peak and accumulated (e.g. fatigue)
traffic loads:
• the pavement materials and subgrade do not deform excessively
• the pavement courses do not crack excessively.
To achieve these objectives, the pavement structure must be protected from the effects of environment. The
first two requirements are addressed using the pavement layer thickness and stiffness to disperse the
concentrated surface load to stress levels acceptable for the various materials. As mentioned earlier, the
load-spreading effect of unbound granular materials is essentially through inter-particle friction and shear
strength, which depend on the presence of horizontal confining stresses (Figure 6.1). On the other hand,
bound layers tend to spread the load through slab action, as significant horizontal tensile stresses can be
sustained at the bottom of the layer.
The ability of a material to withstand repeated cycles of vertical stress without excessive deformation being
induced is called the ‘bearing capacity’. As a result, the higher quality, or stiffer, materials were traditionally
used in the top layers of the pavement. A contemporary alternative option, however, is the ‘upside down’
pavement, which consists of a relatively thick and stiff (stabilised) subbase and an unbound granular
basecourse. These pavements can be used in situations where shrinkage cracking of a stabilised
basecourse layer – and the resultant reflection cracking through the surface – is an issue.
Figure 6.1:
Dispersion of surface load through a granular pavement structure
Because a flexible pavement deforms (bends and deflects) under load, horizontal tensile strains are
produced (Figure 6.2a). The vertical compressive strains in the pavement and subgrade produce the
deformations in unbound layers and asphalt which lead to rutting, whereas the horizontal tensile strains can
induce cracking in bound layers. Loading applied to relatively stiff rigid pavements, on the other hand, results
in a relatively uniform distribution of strain on the subgrade (Figure 6.2b).
The two modes may be used in one application. For example, flexible subbases can be used under concrete
bases to provide a drainage layer, absorb subgrade volume changes and provide a working platform though
pumping of fines through the joints of a concrete base layer can be a problem for heavily-trafficked roads.
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Figure 6.2:
Responses of different bound pavement types to load
6.1
Structural Analysis
6.1.1
Flexible Pavements
The purpose of structural analysis is to quantify the critical strains and/or stresses which are induced by the
traffic loading in the trial pavement configuration.
In structural analysis, it is usual to represent pavements as a series of layers of different thicknesses and
elastic properties (e.g. modulus). The pavement layers may be considered to be fully elastic or viscoelastic,
uniform in lateral extent, or variable, and with full friction, or no friction, between the layers. These variations
have been used in an attempt to obtain theoretical estimates which agree with observed reactions to traffic
loading.
The traffic loadings which can be analysed vary from a single vertical load having a uniform tyre-pavement
contact stress to multiple loads with multi-directional components and non-uniform stress distribution. The
rate of loading will also vary with traffic speed.
Care must be taken to ensure that the sophistication of the analysis method is compatible with the quality of
the input data. If not, then so many assumptions must be made to fill the gaps that the results of the analysis
can be misleading, if not worthless.
The method of structural analysis presented in the Austroads (2004a) Pavement Design Guide is consistent
with the extent of knowledge of pavement materials and their performance which exists within the Austroads
member authorities and industry. Information required as input to the analysis method can already be
obtained with some reliability or is currently being developed. The results obtained provide predictions of
pavement performance which are in reasonable agreement with Australasian experience of pavement
performance.
The results of the structural analysis are used to estimate the allowable loading of the pavement
configuration. Most of the performance criteria which are assigned to pavement materials, and to the
subgrade, are in the form of relationships between the level of strain induced by the single application of a
standard single axle load and the number of such applications which will result in the condition of the
material, or the pavement, reaching a tolerable limit.
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6.1.2
Rigid Pavements
The purpose of structural analysis is to quantify the critical stresses and joint displacements which are
induced by the traffic loading in the trial pavement configuration.
The design thickness of the base is a function of the traffic loading, material properties, thermal effects and
the cumulative stiffness of the subbase and subgrade. Many concrete pavement failures have been
attributed to uneven support conditions that may occur over large underground services, culverts or at the
transition of the cut and fill zones. Hence, the concrete base layer should be longitudinally and laterally
uniformly supported by the subbase and subgrade layers.
Over the last ten years, experience has shown that heavy duty concrete pavements in Australia are being
subjected to numerous overloaded trucks with axle loads exceeding the legal limit. Unusual forms of
pavement distress are also being observed that appear to be mainly related to environmental loading.
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7.
Pavement Life Cycle Costing
In assessing alternative pavement types, alternative maintenance and rehabilitation strategies or
combinations of these, it is important to consider the relative economic values of the different options. This
comparison is most correctly made using Life Cycle Costing (LCC) or Whole of Life Costing (WOLC)
techniques, which use discounting equations to calculate the values of one or more truly comparable
measures of all costs occurring over the life of each alternative.
It is appropriate to elaborate on some aspects of this statement.
• The life of a road pavement for pavement design purposes is usually taken to be the time from its initial
construction to its first reconstruction, which can be considered to be the start of a new life. During this
life, the serviceability of the pavement is maintained by undertaking maintenance activities in response to
deterioration due to time, environment and traffic loading. For the purposes of economic evaluation a set
analysis period (e.g. 40 years) is chosen regardless of the life of the road pavement, and all costs and
benefits occurring over this analysis period are considered. Ideally, the analysis period for any alternative
will be an integer multiple of the life for that alternative.
• When the objective of an economic assessment is to compare only different pavement types and/or
maintenance strategies, the vehicle operating cost savings from travel time savings in relation to
parameters such as route, geometric design and traffic capacity are assumed to be the same for all
options. The comparison can therefore be made on the basis of the costs of provision of each pavement
option and the effects of vehicle operating costs due to travel delays from lane closures required for future
pavement maintenance and rehabilitation.
• The present value of pavement life cycle costs occurring over the analysis period that must be estimated
to enable the evaluation of each alternative includes:
– the initial cost of construction of the pavement
– the costs of maintenance, rehabilitation and reconstruction activities carried out over the analysis
period and the time at which each activity occurs
– the vehicle operating costs due to travel delays from lane closures required for future pavement
maintenance and rehabilitation
– the salvage value (which may be negative or positive) at the end of the analysis period.
• Discounting is the process of bringing monetary payments or receipts that occur at different points in time
to equivalent values at one point in time. It reflects the ‘value in use’ of money, that is, the fact that if
money is available at an earlier time, it can be used to produce returns that lead to an increased value at
a later time. Because of this, a given amount of money available now is equivalent to a greater amount at
a future time and, conversely, a given amount available at a future time is equivalent to a lesser amount
available now. ‘Value in use’ has nothing to do with inflation – it exists even if the inflation rate is zero.
• The discount rate is the basic parameter used in discounting. It often is qualified as the real or inflationfree discount rate, to indicate that it represents the true, ‘value in use’ return on money, excluding any
apparent increase due to inflation. A discount rate is typically stated as a percentage per annum (e.g. 4%
p.a.) but is used in calculations as an absolute proportion per annum (e.g. 0.04 p.a.).
• Because the effects of inflation are excluded from the economic analysis, all future costs should be
estimated in present day dollars (i.e. as what the cost would be today).
• A truly comparable measure of the life cycle costs of a number of options is a measure that fairly
compares the economic worth of the different options. The two most commonly used measures that meet
this criterion, and the conditions under which they do so, are as follows:
– The Present Value of Costs (PVC) is a truly comparable measure provided that all the options are
evaluated over the same analysis period, and that period is either a whole number of lives for each
option or is a very long period (e.g. 50 years or more, depending on the discount rate).
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– The Equivalent Annual Cost (EAC) is a truly comparable measure even if the analysis period is
different for different options, provided that the analysis period for each option is an integer multiple
(usually 1 is convenient) of the life of that option.
While LCC (or WOLC) is used extensively in Australia, engineers have struggled with the determination of
appropriate values for maintenance, rehabilitation and reconstruction costs. This is especially so for
pavement types which have not been widely used until recent times, so that there is a lack of historical data.
It is possible, however, to develop maintenance strategies that are appropriate for each of a range of
pavement types, for the purposes of undertaking LCC comparisons. Where previous records are not
available to assist this development, guidance can be obtained from Chapter 10 of Austroads (2004b)
Pavement Rehabilitation Guide (and Part 5 of the Guide to Pavement Technology), from evaluation systems
published by a number of state road agencies and from various publications of industry organisations such
as the Australian Asphalt Pavement Association and the Cement Concrete and Aggregates Australia.
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8.
Brief Description of each part of Guide to Pavement
Technology
8.1
Part 2: Pavement Structural Design
This part addresses those considerations associated with:
• the design of flexible pavements for conventional highway traffic
– flexible pavements consisting of unbound granular materials
– flexible pavements that contain one or more bound layers
• the development of design charts for flexible pavements for specific conditions as required by the user
• the design of rigid pavements for conventional highway traffic.
Brief descriptions of a number of topics listed below are provided, whilst explanatory notes on these topics
are provided in the commentaries at the end of the document:
• Pavement design systems (empirical and mechanistic)
• Construction and maintenance considerations
• Environment (moisture, temperature) considerations
• Subgrade evaluation
• Characterisation of pavement materials to be input into the design process
• Determination of design traffic
• Design of new flexible pavements, including low volume roads and bikeways
• Design of new rigid pavements
• Economic comparison of designs
• Implementation of the design and the importance of obtaining feedback on performance.
Detailed descriptions of methods and procedures, including example design charts, are contained in a series
of appendices which are available as separate documents.
An integral part of the pavement design process is an assessment by the designer of how well the outcome
of the design – the constructed pavement – will perform. Because of the many factors which must be
evaluated to design pavements, there is no absolute certainty that the desired performance will be achieved.
Guidance is provided on how to design projects to a desired reliability of outlasting the design traffic.
It is assumed that pavements are constructed to the usual quality standards specified by Austroads member
authorities.
The design and selection of pavement rehabilitation treatments is addressed in Part 5 of the guide. The
design of unsealed pavements is addressed in Part 6 of the guide. Issues such as structural detailing or
design detailing are not addressed in this guide.
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8.2
Part 3: Pavement Surfacings
The selection of the most appropriate pavement surfacing requires balancing the needs of road asset
managers, road users and the community at large. In addition to evaluating the characteristics of a surfacing,
the selection of the most appropriate surfacing requires a consideration of a number of other issues including
drainage, traffic levels, workplace and public safety, opportunities for stage construction, whole of life costing
and environmental issues such as noise levels.
The purpose of this part of the guide is to identify the significant factors, their inter-relationship and the
rationale for assessing the suitability of various types of pavement surfacing. The final solution needs to be
the best compromise between risk assessment and whole of life cost considerations.
The Australasian sealed road network is characterised by substantial lengths of unbound granular
pavements with thin bituminous surfacings. Whilst this is an effective, low cost treatment, it has limitations,
especially in its ability to cope with high shear stresses generated by heavy vehicles, especially on grades
and around small-radius curves. On more heavily-trafficked pavements, particularly in urban areas, asphalt
and rigid (concrete) pavements are often used as they are most resistant to the stresses applied by heavy
vehicles. Unlike thin bituminous seals, they also act as a structural layer in a pavement.
The structural design of surfacing layers is addressed in Part 2 (Pavement Structural Design) and Part 5
(Pavement Evaluation and Treatment Design) of this guide.
Brief descriptions of a number of topics listed below are provided, whilst explanatory notes on these topics
are provided in the commentaries at the end of the document:
• surfacing types
• performance characteristics which may influence the choice of pavement surfacing type
• investigation levels for determining the performance characteristics of pavement surfacings
• measures for determining the required level of service of pavement surfacings
• the selection of the most appropriate surfacing for new pavements
• identifying and correcting deficiencies in existing road surfacings
• the selection of surfacings for retreatments.
8.3
Part 4: Pavement Materials
8.3.1
Unbound Granular Materials
This part summarises practice in the selection and testing of granular materials and aggregates for pavement
construction. These include:
• Naturally occurring granular materials (natural gravels/sand-clay/soft and fissile rock), which do not
require costly extraction or crushing processes. They are an important source of material used in the
pavement (base and subbase) and shoulder construction of flexible pavements in Australia.
• Crushed rock produced by the crushing and screening of hard source rock (igneous, metamorphic or
sedimentary rock), which would typically need to be excavated by the use of explosives, and river
gravels. They are used in the pavement (base and subbase) and shoulder construction of flexible
pavements.
• Aggregates produced by controllable manufacturing processes (i.e. blasting, crushing and screening, or
by screening alone) from natural sources (river gravels, weathered conglomerates, talus deposits, sand
deposits or massive rock deposits) or from slags derived from metallurgical processes. They are
designed and manufactured to have the required characteristics for surface layer construction such as
bituminous seal, asphalt and concrete.
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• Recycled construction and demolition wastes, and industrial by-products.
Issues addressed include:
• the factors influencing the performance of granular materials (i.e. their ability to support the prevailing
load and environmental conditions) and those properties which are important in determining the suitability
of materials for their intended purposes within the pavement structure
• the procedures for the location and field evaluation of deposits of granular materials potentially suitable
for pavement construction, including those procedures suitable for surface deposits to the technically
more complex requirements for large, permanent quarry sites
• the preparation of, or development of, specifications for the selection/production of:
– natural gravel, sand clay, or soft and fissile rock for use in pavement and shoulder construction, or to
evaluate potential sources of such materials
– crushed rock for use in base and subbase construction
– aggregates for use in bituminous seals, asphalt or concrete
– recycled materials for pavement construction
• the basic properties for quality assessment and the significance of variability and sampling risks in terms
of specifications and the assessment of quality.
8.3.2
Modified Granular Materials
Modified granular materials are granular materials to which small amounts of stabilising binder have been
added to correct deficiencies in properties (e.g. by reducing plasticity) without causing a significant increase
in tensile capacity (i.e. producing a bound material). Modified granular materials are considered to behave as
unbound granular materials, i.e. they do not develop tensile strain under load.
8.3.3
Bound Materials
Stabilised materials
Stabilisation through the use of binders such as lime, Portland cement or bitumen can result in large
enhancements to the ability of the material to perform, including the addition of lime and cement to clay soils
which have a high potential to swell.
This section of the guide provides practical advice and direction for the stabilisation of road pavements and
subgrades to assist asset managers and practitioners in pavement design, construction and maintenance
operations to optimise the benefits stabilisation technology has to offer when applied to:
• the enhancement of construction and performance attributes of pavement materials and subgrades
• mix design to determine the appropriate binder and application rate
• the structural rehabilitation of existing pavements by recycling in situ pavement material
• the incorporation of stabilised pavement layers into new pavements.
Guidance is limited to the application of stabilisation of road pavements and does not include other
geotechnical applications such as soil and rock slope stability, retaining structures or land reclamation etc.
Cemented materials may be described as a combination of a cementitious binder, water and granular
material which are mixed together and compacted in the early stages of the hydration process to form a
pavement layer which is subsequently cured. The cementitious binder may consist of Portland cement,
blended cement, lime, or other pozzolanic materials such as fly ash or ground granulated blast furnace slag.
The binder should be added in sufficient quantity to produce a bound layer with significant tensile strength.
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Issues addressed include:
• the factors affecting modulus of stabilised materials, including mix composition, density and moisture, and
aging and curing
• the determination of design modulus, i.e. an estimate of the in situ flexural modulus after 28 days' curing
in the road bed
• the factors affecting the fatigue life of stabilised materials
• means of determining the fatigue characteristics of stabilised materials.
Asphalt
Asphalt is widely used in the construction and surfacing of roads in Australia. The properties of asphalt are
complex and its performance requirements vary considerably with the application. Engineers responsible for
the design of works incorporating asphalt have a responsibility to acquire an adequate understanding of the
properties of asphalt and appropriate usage as well as an understanding of the application of specifications
and construction requirements.
The purpose of this part of the guide is to provide an overview of the principal types of asphalt, selection of
asphalt mix type, selection of component materials, asphalt mix design, performance characterisation, and
manufacture and placing. Specific details, supporting the topics discussed in this document, are provided by
other parts in this guide.
Brief descriptions of a number of topics listed below are provided, whilst explanatory notes on these topics
are provided in the commentaries at the end of the document:
• asphalt mix types
• selection of component materials
• asphalt mix design
• performance characterisation
• asphalt manufacture
• asphalt paving.
Concrete
Relevant issues related to the use of concrete as a base layer as well as a subbase layer are addressed,
including the determination of elastic parameters and performance characteristics.
Part 4 includes:
• Part 4A: Granular Base and Subbase Materials
This part contains advice on the selection, testing and specification of crushed rock and naturally
occurring granular materials for use in pavement base and subbase construction
• Part 4B: Asphalt
This part describes the nature of asphalt as a material and its application in road pavements. It overviews
the principal types of asphalt, selection of asphalt mix type, selection of component materials, asphalt mix
design, performance characterisation, and manufacture and placement.
• Part 4C: Materials for Concrete Road Pavements
This part summarises Australian and New Zealand practice including base concrete and lean mix
concrete subbase, concrete curing compounds, steel reinforcement such as tie bars and dowel bars, and
joint sealants and fillers.
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• Part 4D: Stabilised Materials
This part discusses the types of stabilisation undertaken to improve pavement materials and subgrades,
the types of binders used in stabilisation, the materials suited to particular binders, the laboratory
determination of the type and quantity of binder required to achieve a particular mix design.
• Part 4E: Recycled Materials
This part deals with the specification, manufacture and application of recycled products from the building
industry, reclaimed asphalt pavement from maintenance and rehabilitation activities, and reclaimed glass
from the glass disposal industry. A process is presented by which other sources of wastes may be
assessed for suitability for use in pavements, e.g. industrial slags from the ore extraction industry.
• Part 4F: Bituminous Binders
This part advises on selection of a bituminous binder type for a particular application as well as covering
some of the properties and composition of bituminous materials. The principal tests used for the
assessment of bituminous materials are also covered.
• Part 4G: Geotextiles and Geogrids
This part advises on selection of geotextiles and geogrids for use in construction and maintenance of
roads including embankments and subsoil drainage. It provides information on the properties and
functions of geotextiles, applications and testing.
• Part 4H: Test Methods
This part provides a listing of Austroads test methods and details the technical bodies that oversee the
content of the test methods.
• Part 4I: Earthworks Materials
This part outlines requirements for earthworks materials and the characteristics of material types used in
a range of applications. It also discusses desirable properties, test methods, stabilisation of earthworks
materials and provides direction on borrow pit selection and design.
• Part 4J: Aggregate and Source Rock
This part provides guidance on classification and description of source rocks, properties of source rock
materials that need to be specified to ensure a durable end product, aggregate properties requiring
specification, and quality assurance testing.
• Part 4K: Seals
This part guides selection and design of thin bituminous surfacings such as seals and reseals, slurry
surfacings, primes and primerseals and geotextile seals. The binders include conventional bitumens,
polymer modified binders and emulsions.
• Part 4L: Stabilising Binders
This part describes binders most commonly used in manufacture of stabilised pavement materials either
by in situ construction practices or plant-mixed operations. The types of binders described are lime,
cement, cementitious pozzolans, bitumen, chemical and synthetic polymers.
8.4
Part 5: Pavement Evaluation and Treatment Design
The purpose of this part is to give the practitioner an overview of the issues involved in the management of
individual pavements, specifically through the identification of distress observed on the surface, the analysis
of the distress and mechanisms causing it and the design of treatments aimed at restoring the pavement to a
good condition.
Brief descriptions of topics listed below are provided, whilst explanatory notes on these topics are provided in
the commentaries at the end of the document:
• causes and modes of pavement distress
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• inspection and testing, but restricted to forensic, or project level, assessments
• evaluation of pavement defects and test results
• selection of maintenance treatments
• thickness design of pavement structural treatments
• economic consideration of design options
• assessment and analysis of special vehicles and loads.
Detailed descriptions of methods and procedures, as well as distress types, are contained in a series of
appendices which are available as separate documents.
The subject area is often considered part of the broader area of asset management, but for the purposes of
the Austroads Guides, a distinction has been made between pavement management at the network level
and project level pavement management. This distinction is described in greater detail in Section 2 of this
document. The reader is referred to the Austroads Guide to Asset Management for information on network
level pavement management.
8.5
Part 6: Unsealed Pavements
In terms of length of road, unsealed pavements comprise about two-thirds and 40% of Australia’s and New
Zealand’s road networks respectively. On the other hand, between 20-25% of the total amount spent on the
construction and maintenance of roads each year is spent on unsealed roads, so small efficiency gains can
result in significant benefits. The unsealed road network is predominantly composed of formed and gravelled
roads; other forms include formed and unformed roads. They provide an important role in terms of servicing
rural communities, the movement of primary produce to markets and the servicing of access to tourist
facilities.
Unsealed roads are susceptible to rapid deterioration as a result of loss of wearing course material and
damage from water. The severity and frequency of defects - such as corrugations, potholes, rutting and loss
of shape - combined with the levels of service commensurate with available resources, sets the maintenance
requirements for the unsealed road network.
Brief descriptions of topics listed below are provided, whilst explanatory notes on these topics are provided in
the commentaries at the end of the document:
• maintenance practices
• materials selection
• pavement design
• pavement construction considerations
• performance management.
8.6
Part 7: Pavement Maintenance
This part is intended to give the practitioner an overview of current routine maintenance practices for sealed
pavements suitable for use by both supervisory and field staff.
It outlines the general aspects involved in pavement maintenance. The information outlined has been
adapted from the practices of Australian road authorities but owing to differences in geology, topography,
climatic conditions and traffic volumes, it may vary according to local conditions.
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This publication should be read in conjunction with Part 5: Pavement Evaluation and Treatment Design
(Austroads 2008), which covers periodic maintenance and pavement rehabilitation. The maintenance of
unsealed pavements is addressed in Part 6: Unsealed Pavements (Austroads 2009f).
Roads are designed to varying standards and built from natural or processed materials to meet the needs of
the communities they serve. Like all other structures they are subject to deterioration which commences as
each part of a road is completed. If the facility is to give the standard of service for which it was designed,
maintenance must begin as soon as construction ends.
Ideally, maintenance would ensure that the road always functioned as efficiently as when it was first
constructed, but in planning maintenance, due regard must be paid to limitations of available labour, plant
and funds. For these reasons maintenance programs are adjusted to control the rate of deterioration and to
ensure that the road serviceability does not fall below some minimum level, depending upon the resources
and policy of the road authority concerned.
The guide contains descriptions of the topics listed below:
• maintenance of drainage elements
• maintenance of flexible pavements
• maintenance of rigid pavements
• maintenance of shoulders
• other maintenance activities.
8.7
Part 8: Pavement Construction
This part addresses those issues related to quality control and quality assurance in road construction
including the data that needs to be collected, how it is collected and how it is analysed, including statistical
analysis techniques. The part does not cover procurement processes and competencies because these
issues are addressed in the Guide to Project Delivery.
8.8
Part 9: Pavement Work Practices
The intention of this part is to present a ‘compendium of experience’ gained by road authorities and industry
in terms of optimum pavement work practices. Relevant material already available (viz. Work Tips, etc.) is
presented.
8.9
Part 10: Subsurface Drainage
This part describes types of pavement subsurface drainage systems and procedures to design these
systems, materials used for pavement subsurface drainage and construction, and maintenance
considerations for these systems.
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Development of Road Pavements in Australasia
An excellent review of the history of the development of road pavements in Australasia is contained in Lay
(1984) and subsequent publications (e.g. Lay 1998). Some of his material is taken from Coane et al. (1915).
Another excellent source reference is the report submitted by Australia to the Eighth PIARC Congress, the
Hague, in June 1938 3. In terms of New Zealand chip sealing practice (see Footnote 1), readers are referred
to Chapter 1 of Transit New Zealand, Road Controlling Authorities and Roading NZ (2005).
The earliest Australian pavement types were based on the method adopted by the French engineer,
Trèsaguet, in which large (200 mm) pieces of stone were placed on the natural formation, very much in the
way of a road paved with large paving stones. Smaller stones were then hammered into the gaps and also
placed on top of the large stones to provide a running surface (see Figure C1 1).
Figure C1 1: Early practice – Trèsaguet pavement
Source: Lay (1998).
By the mid-1850s, the Telford method was being used. Whilst this was based on the early French method,
the use of large stones was avoided, but the use of prepared cubical stone of equal size carefully placed on
the existing ground was retained. Drainage was provided in the form of a trench (Figure C1 2). Telfords’s
other major contribution to road making was to emphasise that the layout of new roads must take account of
the capabilities of the vehicles intended to use it.
The macadam pavement was introduced in 1822. The term is a corruption of the designer's name – McAdam
– and is contemporary jargon for any open graded, including single-sized, crushed rock material. McAdam
used only small, angular broken stone (less than 35 mm) spread on the natural formation to a thickness of
about 200 mm (Figure C1 3). The method relied heavily on interlock between the stone pieces.
3
The report prepared by the Australian States Organising Committee for the Eighth PIARC Congress in 1938 had the following five
sections.
1. Introduction
2. Progress Made Between 1934 and 1938 in the Use of Cement for the Construction of Carriageways
3. Road Construction by the Heat Treatment of Surface Soils
4. Progress Made Between 1934 and 1938 in the Use of:
a. Tar for the Construction and Maintenance of Carriageways
b. Bitumen for the Construction and Maintenance of Carriageways
c. Emulsions for the Construction and Maintenance of Carriageways
5. Examination of Subsoils
a. Determination of the Properties of Subsoils – Methods of Testing and Testing Apparatus
b. Influence of the Properties of Subsoils Upon the Construction of Roads (Foundations and Surfaces) and their Maintenance
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Figure C1 2: Telford pavement
Source: Lay (1998).
The rocks were originally broken by hand and placed in piles prior to spreading on the road. The process
was eventually replaced by steam-powered crushing plant which had been introduced by 1865. Unlike the
earlier methods, where the stone was usually placed in a water collecting trench, McAdam’s broken stone
was often placed at or above the natural surface level, resulting in greatly improved natural drainage.
Figure C1 3: McAdam pavement
Source: Lay (1998).
The demand for smoother, dust free roads to cater for higher-speed pneumatic-tyred vehicles, and
mechanised construction, led to the use of smaller stone sizes and hence the development of a ‘maximum
density’ grading where a range of stone sizes was used to pack together into a dense, tight mass.
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Figure C1 4: Construction of Princes Highway in 1924
Source: Lay (1984).
As a result, densely graded fine crushed rock began to replace the larger open graded materials because
they were more workable, cheaper, and easier to compact. Also, macadam performed poorly under moist
conditions and heavy axle loads.
Figure C1 4 shows the construction of the Princes Highway near Kromelite, South Australia, in 1924 (the first
road construction funded by the Federal Government under the Main Roads Development Act).
C1.1 Surfacings
In terms of pavement surfacings, during the 1880s there was much debate as to the best surface to adopt,
particularly in urban areas. Although macadam was by this time being widely used in rural areas, there were
problems associated with its use in urban areas, particularly if inferior quality source rock was used. The
narrow cast iron wheels of horse-drawn carriages tended to pulverise the material, creating dust and, after
rainfall, a very muddy (and slippery and smelly) surface. As a result, there was strong pressure to develop
less permeable and more easily cleaned surfaces.
Coal tar and natural asphalt had been used in Europe and the USA since the 1830s and, by the 1870s, a
form of coated macadam, using gasworks or other coal tars, was being used in Australia to produce a 40 mm
thick wearing course. Tar was also used in Sydney and Melbourne in the 1880s and 1890s to fill the
macadam interstices: this became known as ‘penetration macadam’.
Solid blocks of compressed Swiss natural asphalt, about 50 mm thick, were used in trials in Sydney in 1880
but were considered too slippery when wet and too prone to wear. Powdered bitumen was also trialled.
Natural Trinidad bitumen was first used in Melbourne in 1894. However, the use of bituminous binders did
not become widespread until after the introduction of the automobile and the pneumatic tyre and the
increasing demand for smooth, dust-free surfacings. Trials to assess the performance of asphalt as a
pavement surface had commenced by 1920.
The major alternative pavement form involved the use of wooden cube setts, often red gum. Lay (1984 and
1998) reports that the first pavement composed of wooden blocks was trialled in King St Sydney (between
George Street and Pitt Street) in 1880, closely followed by a trial in Melbourne on the corner of Swanston
and Collins Streets. The blocks were pre-dipped in boiling tar and the joints were filled with tar. By 1894,
about 20 km of road in Sydney was surfaced with wooden blocks. Whilst they were more expensive than tarAustroads 2009 | page 33
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macadam, they remained the most desirable and dominant urban paving material until the Second World
War. Applications can still be seen today, for example between tram tracks in some parts of inner Melbourne.
Figure C1 5: Corduroy and plank roads (vertical scale exaggerated)
Source: Lay (1984).
Timber was also used in rural applications. For example, the corduroy road comprised a close packed
sequence of logs, normally placed transverse to the direction of trafficking (Figure C1 5). It was commonly
used over sandy or swampy ground and first came into use when the Telford pavement was found to be
unsatisfactory in these types of applications. Lay (1984) reported that a length of corduroy road was still in
existence near Halbury, South Australia, as late as the early 1980s.
The plank road used a more elaborate technique in which a longitudinal bed of logs was covered by
transverse planks (Figure C1 5).
Stone setts had limited application because they were considered too expensive, slippery and noisy. The
use of concrete and clay paving blocks was regenerated in the late 1970s, particularly in local road
applications. This was related to the development of processes which allowed for the manufacture of
products of high strength to very accurate dimensional tolerances and in a range of ‘interlocking’ shapes as
well as the traditional rectangular shape. The best known arterial road application of interlocking concrete
paving blocks is King William Road in Adelaide which was constructed in the early 1980s.
New Zealand
From about 1880 coal tar from local gasworks was sprayed over roads and covered with locally-sourced
chips to make a dustproof and waterproof surfacing. Coal tar was the only binder used in New Zealand until
about 1910, when bitumen for roading use first became available. Bitumen was imported until 1964, when
the New Zealand Refinery opened at Marsden Point, near Whangarei, and took over supply almost totally,
with distribution to a total of nine ports around New Zealand.
During the early 1930s, testing and experimenting with aggregates and bitumen commenced in an effort to
develop more quantitative techniques less dependent on the skill of the on-site manager. Hanson’s (1935)
paper to the Conference of the New Zealand Society of Civil Engineers was the first step towards quantifying
the chip seal concept. The concept was that the rate of application of the binder should be designed to be
2/3rd up the height of the stone chips, leaving a non-skid, non-glare surface capable of withstanding the
stresses applied by traffic. Hanson’s principles relating to the theory of surface sealing were summarised by
the National Roads Board in 1968. Although the principles that Hanson promoted are still current, refinement
to the values of voids has been made as more information has been collected.
In terms of urban applications, surfacings in the early 1900s included stone block paving in high stress areas,
stone penetrated by, or mixed with, coal tar (tar macadam), and birch blocks bedded on mass concrete
surfaced with 10 mm of sand sheet asphalt to produce a quiet surface (for the most important
thoroughfares).
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C1.1.1 Seal Coats
As already discussed, the need for a low cost surface treatment was highlighted during the 1920s as the use
of pneumatic-tyred vehicles became more widespread. The seal coat, or sprayed bituminous seal, was
developed in response to these needs and is the major Australasian contribution to international road making
practice. Lay (1984 and 1998) reports that the technique developed as a form of penetration macadam to
upgrade existing macadam roads subjected to high speed motor vehicles. Lay also reports that trials of
bitumen as an alternative to tar were conducted in Glenelg as early as 1919. Early field experiments soon
pointed to the need to top-dress the surface with rolled-in screenings.
Loder et al. (1938) reported that, by the mid-1930s, in order to meet the requirements of increasing volumes
and speeds of traffic, the practice of surfacing earth, gravel and waterbound pavements with bituminous
surfacings had greatly increased and that the treatment of main roads in this way was proceeding as rapidly
as funding allowed.
This in turn necessitated the development of mobile construction plants for these operations. The
establishment, commencing in the 1920s, of central road authorities (now state road authorities) greatly
enhanced this process which previously had been the responsibility of the municipalities which lacked the
resources of these centralised authorities. For example, in the spraying season 1936-37, the total length of
road sprayed by the CRB was 850 miles (1,360 km) but the average length per job was only 3 km.
Loder et al. reported that the aggregate used was generally crushed stone or gravel graded between ¾ inch
and 1/8 inch. The binder used was generally fluxed bitumen cut back with a volatile oil (generally kerosene).
The construction of asphalt pavements commenced in about 1920 with the laying of a single-coated asphalt
mix on reconditioned and consolidated macadam foundations or, in a few cases, Portland cement concrete
foundations. This practice continued for about 10 years and was confined to the larger cities. It consisted
mainly of coarse graded asphalt with the surface coat about 50 mm thick either laid in one course or sealed
with a sand carpet mixture resulting in a total thickness of about 50-60 mm.
Loder et al. reported that a study conducted at this time indicated that this type of pavement would not be
adequate to meet the needs of traffic and that a stronger pavement was required. This led to the gradual
introduction of the two-coat construction, consisting of a 37.5 mm thick sand carpet wearing surface and a
37.5 mm thick layer of binder course.
By this time the process known as ‘road mix’ sealing had been developed to produce a true-riding pavement
as well as a sealed surface. Using this process, the binder and aggregate, after being applied to the road
surface, is ‘mixed by the passage of specially-designed machines, working on the principles of the road
planer, and spread in such a manner as to fill in slight depressions and thus leave the material with an even
surface’.
Loder et al. also noted that coloured asphalt had been introduced by this time on footways through the
addition of 4% synthetic iron oxide.
The development of surfacing practice in New Zealand is described in Transit New Zealand, Road
Controlling Authorities and Roading New Zealand (2005). It is similar to the development in Australia.
C1.1.2 Concrete
Lay (1984) reports that the first documented use of concrete pavements in Australia was in Melbourne in
1870, where it was used as a base for stone setts. Cement was first produced in Australia in 1882 and
cement and lime mortars were also used for filling macadam interstices. An example of this application is the
use of cement grout poured into a macadam base. This type of pavement was quite common in the 1920s
and examples can still be seen in streets in the inner suburbs of Melbourne and Sydney.
It was reported in the report to the 1938 PIARC Congress that concrete pavements had been constructed in
Australia since 1916. Toyer et al. (1938) reported that cement-concrete was being used at that time as both
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a basecourse under thin bituminous wearing courses and largely without a wearing course. These early
pavements were generally laid by municipal authorities to specification that ‘would be regarded as obsolete
in the light of present day knowledge’. Many developed extensive cracking and had to be overlaid with
asphalt though one pavement laid in 1918 by the North Sydney Municipal Council and carrying all classes of
traffic to a shopping centre was still in service 20 years later without requiring a surface coat.
General practice was to proportion by volume with an allowance for bulking of moist sand. The standard mix
adopted at the time was 1:2:3 (sand:cement:aggregate) for very heavily-trafficked roads (this was not
defined) near capital cities with a 1:2:3½ mix adopted for other applications. Toyer et al. (1938) reported that
tests of 28 day old cylinders removed from the road showed compressive strengths of about 28 MPa up to
values as high as 42 MPa.
Slabs were normally reinforced with two half-inch (12.6 mm) diameter edge bars. Mesh reinforcement was
used when the subsoil was poor, on embankments over 2 feet (0.6 m) high or on roads carrying extremely
heavy traffic. General practice was to thicken the outside 30 inches (760 mm) of the pavement. A typical
pavement for ‘heavy traffic (i.e. 800 tons per day per foot width of traffic) was 9 inches (225 mm) in the
centre and 12 inches (300 mm) at the edges. On main roads the thicknesses were 6 inches (150 mm) and 9
inches (225 mm). The typical mix on main roads was 1:2:4 (sand:cement:aggregate) unreinforced. However,
it was reported that cracking occurred when this mix was adopted and that it should only be used when the
subgrade conditions were suitable and traffic was relatively light.
Toyer et al. (1938) also reported that the major recent research effort had been geared towards reducing
costs through the adoption of methods that would ensure premixed concrete pavements of adequate
strength with the use of rich mixes used in standard practice at that time. This was achieved through the use
of a much higher proportion of aggregates to cement. These pavements were described as ‘roller
consolidated concrete’.
The first experimental work in Australia involving such a harsh mix that consolidation using ordinary methods
was impossible was by the Country Roads Board in 1929. In March 1930, a short section of a State highway
was widened using rolled concrete slabs 3 feet (1 m) wide using a 1:1¾:8 mix. In 1932, the CRB constructed
another trial section on the Hume Highway at Balmattum, the mixes being 1:2:8, 1:2:10 and 1:2½:10. An
early example of an application of the latter mix was Beach Road, Melbourne.
In 1934 the Department of Main Roads NSW (DMR) constructed some sections using a 1:2¼:9 and 1:2½:9
mixes and the Sydney City Council also trialled mixes of 1:2:7 up to 1:2½:10. The DMR found that the
harshness of the mix that could be used depended to a large extent on the rigidity of the side forms and the
firmness of the road bed. A mix of 1:2½:14½ was successfully used in one application.
The materials used for concrete pavements were generally considered suitable for this class or road,
although rapid hardening cement had been successfully trialled in NSW.
In terms of construction, for mixes of 1:2¼:9, using crushed stone as the coarse aggregate, a water-cement
ratio of 0.9 was generally used whilst, for mixes of 1:2½:9 using uncrushed rounded gravel as the gravel a
ratio of 0.75 was used. Compaction was conducted using a three-axle steel-wheeled roller. Light rollers (6
ton) were used on most work in Victoria although 12 ton rollers were also used. It was found that there was
little difference between the two rollers because the differences in operating speed compensated for the
differences in weight. After rolling, tampers were used to remove minor irregularities and excess mortar
swept off to give the desired surface finish.
Roller compacted concrete pavements are now not commonly used in Australia. In NSW it is used as a
subbase layer in composite pavements that require quick construction solutions. A recent example of an
application in Melbourne was the trial section constructed in Wells Road, Seaford, in 1988 (Jameson, Sharp
& Rollings 1993).
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C1.1.3 Stabilisation
According to Ingles and Metcalf (1972), the earliest applications of stabilisation in road construction in
Australia were in NSW and Queensland in 1930. In NSW calcium chloride was trialled to alleviate dust and
wear on unsealed roads and in Queensland stabilisation of heavy clay by heating was trialled. In 1937
bituminous stabilisation was introduced, followed by the introduction of cement in NSW and Victoria. Grouted
and lean mix cemented gravels or macadams had been used in the 1920s and by about 1950 most forms of
stabilisation (predominantly cement, lime, bitumen emulsion) had been used with varying success.
Ingles and Metcalf also reported the results of a 1967 survey which indicated that the use of stabilisation had
quadrupled over the previous ten years and road stabilisation formed over 75% of all stabilisation
undertaken, with 60% use for roads and car parks, 13% in floodways and 6% in airfields.
Foamed bitumen was developed during the 1960s followed in the 1970s by supplementary binders such as
slag and fly ash. Later they were combined with cement or lime to produce the now commercially available
slow-setting binders.
In the area of chemical stabilisation, ligno sulphonates and ionic bonding compounds and other by-products
became available as stabilisers during the 1970s but they were principally marketed as dust suppressants.
During the 1990s polymer compounds for use as stabilisers on sealed and unsealed roads were developed.
Other historical evidence of the development of road stabilisation in Australia is documented in RTA NSW
(2004).
In New Zealand, cement treatment of basecourses was first utilised in Wellington City in the late 1950s. The
first recorded extensive use of in situ cement stabilisation was in Tauranga and Rotorua in the early 1960s.
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References
Austroads 2000, RoadFacts 2000: An Overview of the Australian and the New Zealand Road Systems, APG18/00, Austroads, Sydney, NSW.
Austroads 2004a, Pavement Design: A Guide to the Structural Design of Road Pavements, AP-G17/04,
Austroads, Sydney, NSW.
Austroads 2004b, Pavement Rehabilitation Guide, AP-T15/02, Austroads, Sydney, NSW.
Austroads 2004c, 2003 Austroads Guide to the Structural Design of Road Pavements: Technical Criteria to
Chapter 9: Design of New Rigid Pavements, by G Vorobieff, APRG Document APRG 01/06(PD),
Austroads, Sydney, NSW.
Cassimatis, P 1988, A concise introduction to engineering economics, Unwin Hyman, Boston USA.
Coane, JM, Coane, HE & Coane, JM 1915, Australasian roads, 2nd edn, George Robinson & Co., Melbourne,
Vic.
Department of Main Roads 1986, Concrete pavement contract control, circular M&R 86/2, Department of
Main Roads, Sydney, NSW.
Hanson, FM 1935, ‘Bituminous surface treatment of rural highways’, New Zealand Society of Civil Engineers
conference, New Zealand Society of Civil Engineers, vol. 21, pp. 88-179.
Ingles, OG & Metcalf, JB 1972, Soil stabilisation: principles and practice, Butterworth, London.
Jameson, GW, Sharp, KG & Rollings, RS 1993, ‘An investigation of the use of roller compacted concrete in a
heavily-trafficked, high-speed application in Australia’, International conference on concrete pavement
design and rehabilitation, 5th, Purdue University, Indiana, Purdue University, School of Civil Engineering,
West Lafayette, Indiana.
Lay, MG 1984, History of Australian roads, report SR 29, Australian Road Research Board, Vermont South,
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Lay, MG 1998, Handbook of road technology, 3rd edn, vols. 1 & 2, Gordon and Breach Science, New York.
Leask, A, Penn, HG, Haber, EW & Scala, AJ 1979, ‘Continuously reinforced concrete pavements across
Clybucca Flat’, ARRB conference, 9th, 1978, Brisbane, Queensland, Australian Road Research Board,
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Loder, LF, Garnsey, AH, Hicks, RJ & Luker, SL 1938, ‘Report by Australia on progress made since the
Congress at Munich with the use of bitumen for the construction and maintenance of carriageways’,
PIARC congress, 8th, The Hague, Netherlands, PIARC, Paris.
Mincad Systems 2004, CIRCLY 5 users’ manual, Mincad Systems, Richmond, Vic.
MacLean, DJ 1954, ‘The application of soil mechanics to road and engineering foundations’, Journal of the
Institute of Municipal Engineering, vol. 81. no. 7, pp. 323-39.
New Zealand National Roads Board 1968, Manual of sealing and paving practice, National Roads Board,
Wellington, NZ.
PIARC 1938, Reports submitted by Australia to the eighth PIARC congress, The Hague, Netherlands,
Australian States Organising Committee, Sydney, NSW.
Roads and Traffic Authority NSW 2004, Oral history on pavement recycling and stabilisation, RTA NSW,
Sydney, NSW, CD-ROM.
Samson, DA (ed) 1995, Management for engineers, 2nd edn, Longman Cheshire, Melbourne, Vic.
Toyer, AE, Gilchrist, EF, Hinder, RB, Mathieson, J & Sutherland, GBH 1938, ‘Report by Australia on
progress made since the Congress at Munich with the use of cement for the construction of
carriageways’, PIARC congress, 8th, The Hague, Netherlands, PIARC, Paris.
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Transit New Zealand, Road Controlling Authorities & Roading New Zealand 2005, Chip sealing in New
Zealand, Transit New Zealand, Wellington, NZ.
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