In 2024, NTRO will celebrate the 40th anniversary of the Accelerated Loading Facility, affectionately known as 'ALF'. To celebrate and reflect on the significant legacy ALF has contributed to engineering, academia, and Australian pavement standards, NTRO has developed a three-part editorial highlighting the ALF's journey and accomplishments across an illustrious forty years of operation.
ALF on the forecourt of the Sydney Opera House, 1983
Part 1: The Early Years - Paving the Way for Pavement Research
Roads are vital arteries of our society, connecting people, businesses, and communities. However, constructing and maintaining these roads can be a significant investment. Since its formation in 1960, the Australian Road Research Board (ARRB, now NTRO) has aimed to ensure that essential assets provide long-lasting benefits. It has, therefore, been of crucial importance for the industry to understand how various pavement designs, materials, and traffic loads will affect the long-term performance of pavements.
In 1978, the Principal Technical Committee of the National Association of Australian State Road Authorities (NAASRA) commissioned a review of ARRB and State Road Authority pavement research to identify future research needs. Waiting decades to determine the effectiveness and long-term performance of innovative materials and construction methods was deemed impractical and slowed the adoption of superior technologies in the nation's critical infrastructure.
As Australia's population and communities grew, a new solution was needed to address the current and future demands placed on road pavements by the increasing number and heavier vehicle loads. To meet these challenges, NAASRA established a Working Group to develop and implement proposals for Australia's first full-scale pavement test facilities. These facilities intended to research the factors causing premature distress, cracking and rutting of heavily trafficked pavements and the limits of the performance of unbound granular pavements that comprised most of Australia's sealed road network.
By 1982, informed by recommendations of the working group, NAASRA commissioned The Department of Main Roads NSW (DMR) to design and construct the Accelerated Loading Facility (ALF). This machine, with its ability to test a 12-meter pavement length with a half-axle load capacity of 9 tonnes, and its energy conservation-focused design, was a practical and efficient solution. The test wheels, driven by electric motors, and the assembly's lifting mechanism for energy conversion, made the design remarkably energy-efficient. The ALF's portability, achieved by hitching it to a prime-mover tractor unit, further enhanced its practicality, providing a reliable and versatile tool for pavement testing.
Under Deputy Director John Metcalf's leadership, ownership and operational responsibility for ALF were transferred to ARRB in July 1984, immediately and significantly impacting pavement research. The first trial of its kind in Australia took place in July 1984 on the existing heavy-duty unbound pavement of the Sydney-Newcastle Freeway to evaluate the operation of ALF as a pavement testing facility, its associated instrumentation, and data processing. Further early trials focused on evaluating the performance of pavements under heavy traffic conditions, providing valuable insights into the factors contributing to pavement failure.
Over its 40-year operation, ALF has had six Program Managers, with John McLean, Dr Peter Kadar, Kieran Sharp, Dr Richard Yeo, Dr Michael Moffatt, and Dr Jaspreet Pooni sequentially assuming these roles. Under each stewardship, ALF has continually adopted new technologies, including the acquisition of a Falling Weight Deflectometer in the late 1980s to assess changes in pavement strength and the introduction of portable computers and mobile phones to facilitate operational efficiency, facilitating on-site in-service highway and purpose-built off-road site trials in Victoria, Queensland, New South Wales, and South Australia.
During the 1980s, the ALF was used to address three broad issues:
- Proof testing of in-service pavements: This included validating that well-constructed granular pavements with sprayed seals could withstand heavy-duty trafficking on the Benalla Bypass on the Hume Highway.
- Design and construction practices: The observation of de-bonding of separately placed cemented base layers during ALF trafficking in Beerburrum, Queensland, which led to significant findings and changes in construction practice. This finding led to a re-evaluation of the construction process, resulting in improved methods and ultimately, more durable pavements.
- Alternative materials and practices: Testing of pavement bases consisting of blast furnace slag in Prospect, NSW, which found that both unbound and stabilised slag could be used instead of unbound and stabilised crushed rock, provided they were protected from excessive tensile strains by an adequate subgrade and an adequate wearing course, preferably asphalt, was used to prevent surface wear.
By the end of the 1980s, projects involving the ALF also began to examine the relationships between observed fatigue and deformation performance of asphalt in the field with the properties of materials determined in the laboratory. Between July 1988 and October 1989, a range of asphalt mixes was tested at a site in Callington, SA. The high sensitivity of the asphalt failure mode to the temperature regime was demonstrated. It was concluded that pavement design and traffic characterisation methods needed to address this phenomenon more rationally if there was to be greater confidence in predicting asphalt surfacing performance. It was also found that deformation at high temperature was confined predominantly to the upper asphalt layer, indicating that a more rut-resistant product was necessary to effectively repair temperature-related deformation problems.
International Application
During this period, the success of ALF attracted the attention of other research institutions worldwide. The US Department of Transportation and Federal Highway Administration commissioned two ALFs, manufactured under license, at the Turner Fairbank Highway Research Centre, McLean, Virginia. The Louisiana Transportation Research Centre (sponsored by the Louisiana Department of Transport and the Louisiana State University), where John Metcalf lectured following his tenure as Deputy Director of ARRB, also owns an ALF. The Ministry of Communications Research Institute of Highways (RIOH) operates an ALF in the People's Republic of China, manufactured by the original system designers and manufacturers. This global interest in ALF's success is a testament to its significant impact on the transportation and pavement industry worldwide.
By March 1987, AIDAB endorsed a technical assistance package encompassing data acquisition systems, training, and research and analysis counsel to aid China in developing its road research facilities. Consequently, ARRB formulated an equipment package, inclusive of a road roughness vehicle equipped with RRDAS, VDDAS, TTDAS, CULWAY, and some materials testing equipment, in conjunction with training and support. The success of these early works led to the resolution of RIOH to enlist the then DMR NSW to fabricate an ALF for importation to China. The ALF was dispensed in 1987 and remains operational to this day.
ALF in the People's Republic of China
The success of the Australian ALF led to the global adoption of a truly innovative machine. Across the global transport industry, ALF has addressed a wide range of pavement research questions, contributing to advancements in pavement technology and design. Key Achievements from this period included proof testing of in-service pavements as the ALF was used to validate the performance of existing pavements, ensuring that they could withstand heavy traffic demands. Additionally, the ALF helped identify potential problems with pavement design and construction methods, leading to improvements in industry standards. Further, the ALF was used to evaluate the performance of new materials, such as recycled materials and alternative binders, for use in pavement construction.
The ALF's Legacy
The ALF has played a crucial role in advancing pavement research and ensuring the long-term sustainability of Australia's road network. The ALF has enabled researchers to develop more durable and cost-effective pavement designs by providing a controlled environment for accelerated testing. As the demand for reliable and efficient transportation infrastructure continues to grow, the ALF will remain an essential tool for ensuring the future of our roads.
Part two of this three-part series will be released in November.
Acknowledgement and thanks to Kieran Sharp, Ray Brindle, Max Lay, John Metcalf, Ian Johnston, and Dave Jones, who wrote ARRB: The First Fifty Years (book), from which this series has referenced.
Sharp, K & Lay, M 2011, ARRB: the first fifty years, ARRB Group, Vermont South, Vic.