7/29/2019 The Last 20 Years - Australian Pavement Research

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Australian Pavement Research - the last 20 years

byGeoffYoudale

Past-Chairman, Austroads Pavement Research Group

Over the past 20 years with Australia, there have been substantial improvements in theunderstanding of how pavements perform, how to design them correctly and how to properlyutilise the vast range of materials now available for their construction, rehabilitation andmaintenance.

 Australia has a vast road network consisting of over 900,000 km of roads, 70% forming the ruralnetwork and 30% the urban network. The replacement value of the road pavement part of thisasset is in the order of $A50 billion. The relatively small population of Australia means there is asmall funding base for roadworks compared to other developed nations. For example, the lengthof road per capita is about 280m in USA, 130m in Great Britain and 90m in Japan compared toabout 450m in Australia.

This has necessarily meant that the Australian road network has been built in an environment of 

restrained funding which has emphasised the need to innovate wherever possible to providemaximum value for the limited funds available. However, Australians are innovative by nature,probably as a result of our heritage, we are outward looking by nature and quick to adopt or adapt others’ solutions to our problems if they are appropriate. The solutions adopted to

 Australian pavement problems have therefore been a mixture of overseas technology and Australian innovation.

Over the past 20 years there have been a number of significant changes that have made thechallenge for pavement engineers a difficult one.

These include:-

• The amount of freight carried on the road network (in truck tonne-km) has more than tripled.•

 Allowable truck vehicle mass has been increasing at about 10% each decade.• Truck tyre pressures have increased from about 550 Kpa to over 700 Kpa with the changefrom cross-ply to radial tyres.

These changes have put to the test the concepts of pavement design that were current in the1970s. At that time, flexible pavements were generally designed using empirical procedures.These had been developed on the basis of classifying and indexing the materials available interms of properties such as grading, plasticity and compaction characteristics and thencomparing them to similar materials of known performance. Little, if any, strength testing wascarried out.

The disadvantages of this method were that it could not cope with novel materials or pavementcompositions (such as bound layers within the pavement) and was a bit like driving a car by onlylooking in the rear vision mirror, you could only be sure where you had been, but not where youwere going.

 At this time there was a realisation that there was a need to control the deflections of pavementsunder load, particularly pavements containing asphalt or bound layers and the importance of thestiffness of pavement materials in controlling flexural failure was recognised.

The importance of adequate stiffness in pavement structures for heavily trafficked roads, meantthat the use of stabilised layers began to gain favour instead of the use of unbound granular materials. This is almost uniformly the case across Australia in the 1990s with the exception of 

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Victoria where heavy duty unbound pavements are still successfully constructed. This is largelybecause of high quality crushed rock materials available there, heavy compaction and very goodquality control.

The increased use of cemented layers was not without cost in terms of cracking problems andpumping problems which required research into pavement design, materials design andconstruction practices to rectify.

The 1970s also saw the commencement of the modern era of rigid pavements. Improved designprocedures, the advent of high volume slip-form pavers and the acceptance of life cycle costingallowed the cost effective construction of long lengths of concrete pavement for conditions of heavy traffic and poor subgrade, particularly in NSW, since the 1970s. The adaptation of the bestoverseas design technology, from both the USA and Europe, by the use of bound subbases, tiedshoulders and checks for erosion at joints has meant Australian concrete pavement technology isnow world class.

Up until the National Association of Australian State Road Authorities (NAASRA) Interim Guide toPavement Thickness Design was produced in 1979, State Road Authorities had their individualmethods for pavement design. The NAASRA Guide was the first attempt to provide a systematicnational approach to pavement design which advocated assessment of all the criteria such as :-

• Design traffic• Subgrade evaluation• Materials characterisation• Construction & maintenance influences• Environment

The guide also contained design procedures for flexible pavements, rigid pavement andpavement overlays. It represented a major step forward both in pavement design and nationaluniformity.

However, the 1970s also brought with it the personal computer and the availability of computingpower meant that the use of so-called mechanistic pavement design procedures could be

pursued. Mechanistic design considers the pavement to act as a mechanism and analyses itusing a computerised model in a similar way as used in the structural design of buildings.

The advantages of such a mechanistic procedure, compared to an empirical procedure are:-

• The ability to take into account many more variables and test these for sensitivity. This isparticularly useful in the analysis of pavement failures.

• The ability to rationally assess the likely performance of novel materials and loadingconditions. (i.e. by using the previous analogy - driving by looking forward through thewindscreen)

Mechanistic design procedures using linear elastic analysis were introduced in Australia in the1987 NAASRA Guide to the Structural Design of Road Pavements which was further revised in

1992 to become the AUSTROADS Guide to the Structural Design of Road Pavements.

Pavement research in Australia until the early 1980s was carried out in a relatively unco-ordinated way by the State Road Authorities and the Australian Road Research Board.

The publishing of the NAASRA Interim Pavement Design Guide and the decision by NAASRA toconstruct and operate an Accelerated Loading Facility (ALF) formed the catalyst for theintroduction of a more co-ordinated approach to pavement research at a National level.

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The NAASRA working group which was put together under the chairmanship of Trevor Parminter from the Queensland Department of Transport to oversee the operation of the ALF programwhich commenced in 1984, also commenced work on a National Pavement Research Strategywhich was published in 1987.

This strategy, which has been revised and republished in 1992 and 1996 by AUSTROADS, hasbeen the cornerstone for the national co-ordination of pavement research, both withingovernment and industry. The management of the strategy, which is the responsibility of the

 AUSTROADS Pavement Research Group, has enabled a holistic approach to be taken topavement research and has, through its project teams, provided an effective framework for communication and co-operation of all stakeholders and ensured that efforts are concentrated inareas of greatest potential benefit. It has also had the major benefit of making best use of thelimited expertise that is available within Australia.

Two focal points within the AUSTROADS Pavement Research Strategy, have been the Australian ALF Program and the Guide to the Structural Design Of Road Pavements.

The Australian ALF program which has been running continuously since 1984, has been a major success, both Nationally and internationally. ALF applies rolling wheel loads which can be variedin 10 Kn increments between 40 and 80 kn at a constant speed of 20 km/hr and has performed

tests in 4 Australian states. The ALF was designed by the Roads and Traffic Authority NSW andis owned and operated by ARRB Transport Research Ltd.

The Australian ALF Program is by far the most productive accelerated loading program in theworld. ALF’s have been sold to the USA (3) and the Peoples’ Republic of China (1).

The Australian ALF has carried out tests in 4 Australian states and has lead to a substantialacceleration in the introduction of improved pavement technology.

Some examples includes:-

• Refinement of construction procedures for layered cement treated pavements to eliminatepumping problems.

• Ranking and acceptance of polymer modified binder asphalts• Development of mix design procedures and test procedures to control rutting in asphalt• The use of innovative blast furnace slag in road pavements• The development of geotextile reinforced seals on expansive clay pavements as a cost-

effective treatment for lightly trafficked remote rural roads.• Validation of deep lift recycling of granular pavements using cementitious binders.• Validation of the use of stabilised power station flyash as a pavement material.

The ability of the ALF to look at a specific pavement problem in a relatively short period of timeprovides a major boost to the confidence of practitioners and researchers alike in the adoption of new technology. The need for researchers and practitioners to work together during the tests andthe high profile of ALF have also provided benefits in terms of rapid and effective technologytransfer.

The 1980s also brought the beginning of closer ties with overseas organisations carrying outpavement research. Closer ties with the OECD Road Transport Research Program, the USStrategic Highway Research Program and the Permanent International Association of RoadCongresses (PIARC) have improved communication, accelerated the recognition of usefuloverseas research and also enabled Australian research to be successfully showcased andbenchmarked.

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 Also, the 1980s also brought with it an increasing concern on matters environmental which wasreflected in the AUSTROADS Pavement Research Strategy. Considerable emphasis was givento development of environmentally friendly materials and processes which has lead toconsiderable progress with the use of recycled materials (blast furnace and steel slag, flyash,recycled concrete, recycled asphalt) in road construction and rehabilitation.

The arrival of new equipment has allowed the insitu recycling of asphalt wearing surfaces to becarried out successfully using both hot and cold technologies.

Of particular significance, has been the development within Australia of deep lift recyclingtechniques for granular pavements using cementitious binders. This technology is now in routineuse in rural areas and can recycle to a depth of about 400mm at a cost saving in the order of 20 -40% compared to conventional rehabilitation treatments. It required the use of specialisedstabilisation equipment, the development of new, slow setting binders and represents anoutstanding example of co-operation between government agencies, contractors and materialssuppliers.

Looking back over the achievements in pavement research in Australia over the past 20 years, itis evident that a lot has been achieved. Of particular note is the improvement in TechnologyTransfer that has taken place so that much more of the results of the successful research is now

reaching the practitioner. There is a large array of well-written, easy to understand guides andmanuals of which the recently released C&CA Guide to Concrete Construction is a goodexample.

We also seemed to have moved from an empirical age to a more systematic, knowledge basedage with research being better organised over a more comprehensive range of needs andorganised nationally. Australia has a competitive advantage in this regard compared to say theUSA and Europe. All the states and territories in Australia, have a common language and cultureand because there is only 6 states and 2 territories, it is relatively easy to act nationally. This hasmajor benefits in terms of avoiding duplication of effort and utilising available resources andshould continue to be vigorously pursued.