Greg White

The strength of all registered airport runways is managed through a system referred to as ACN-PCN. The International Civil Aviation Organisation is replacing ACN-PCN with a new system, known as ACR-PCR. The transition from runway PCN values to PCR values requires airports to consider the basis of the current runway PCN, the thickness, composition, and associated strength of their runway pavement. Many of the regional airports do not have adequate resources to transition from PCN to PCR in a robust manner. These regional airports require practical support and a theoretical method for estimating a PCR, from the current PCN. This research developed a theoretical method for estimating PCR from published PCN values, based on a correlation between aircraft ACN and ACR values, for aircraft applicable to regional Australian airports. The correlation between regional aircraft ACN values and ACR values provides a reasonable basis for the transition, without the need for expensive pavement testing. It was concluded that although a first-principles approach to the transition from ACN-PCN to ACR-PCR is preferred, the use of the developed, regional airport specific, correlation is better that not transitioning at all, and it comes at no financial burden to regional airports.

Runway microtexture is a key parameter governing pavement friction. In recent years, several microtexture assessment methods have been developed; however, understanding of microtexture evolution under operational conditions, as well as the effects of maintenance techniques, remains limited. In this study, a runway at an Australian airport was investigated using laser profilometry. Measurements were conducted across multiple transverse sections, including aircraft touchdown and mid-runway zones. Microtexture deterioration rates were evaluated based on the estimated number of tire–pavement contacts, and aggregate polishing was assessed at different locations. Measurements were also performed after rubber contamination removal and rejuvenation treatments. The results indicate that approximately 25% of total microtexture reduction can be attributed to surface polishing, with a lower contribution in touchdown zones due to the protective effect of rubber deposits. A non-linear degradation trend was observed in touchdown zones, where approximately 1100 tire contacts reduced average microtexture roughness from 18 μm to 11 μm. Rubber removal effectively restored microtexture close to its original levels across the runway width. A rejuvenation treatment with a covering of fine sand initially improved microtexture; however, rapid deterioration occurred due to loss of the sand coating. These findings improve the understanding of microtexture evolution under operational runway conditions, albeit only at a case study level, and support more effective runway maintenance planning and intervention strategies.

Runway friction is a critical factor for aircraft operational safety, yet the role of adhesion in wet friction remains insufficiently understood, especially in areas where tyre rubber contaminates the surface. This study evaluated approximate adhesive contribution for representative common runway surfaces, using contact angle measurements and British pendulum tester friction tests. The results show that approximate adhesion influence varies strongly with surface type: negligible on cement concrete, 16% to 19% on rubber-contaminated asphalt, and up to 49% on roughened rubber. A linear correlation between friction and contact angle confirmed that wetting behaviour governs adhesion-driven friction. Friction tests at different temperatures also confirmed the adhesive nature of the temperature influence on friction. The analysis further indicates that material properties and greater effective surface area correlate with stronger adhesive contributions, explaining material-specific differences in friction performance. These findings may provide a conceptual basis for interpreting variability in continuous friction measurements and suggest the importance of considering adhesion effects in runway surface characterisation and maintenance systems.

The contraction joints within paver runs are important for the design and construction of rigid aircraft pavements. These joints are typically un-doweled and sawn into the pavement to induce a crack. The joints control shrinkage cracking during curing, allow for thermal expansion and contraction, and provide load transfer through aggregate interlock joint stiffness between adjacent slabs. Aggregate interlock joint stiffness is typically modeled by assigning a spring element between two slabs that is indicative of the stiffness of the joint. However, that simplification may not accurately represent the complex interaction of irregularly shaped concrete faces and joint openings. Consequently, previous researchers have recommended modelling aggregate interlock stiffness based on physical crack shape. This research uses a novel approach to characterize crack shape through an idealized two-dimensional sinusoidal shape. Once the crack shape was defined, finite element methods were used to determine the significance of load, sublayer, and crack shape factors on load transfer values. It was determined that joint opening was the most significant factor for aggregate interlock load transfer. Future research is recommended to further validate the model against a larger data set, to confirm if the two-dimensional idealization of crack shape is an appropriate estimation of field conditions.

With the growing trend of incorporating waste and industrial by-products in infrastructure, airport pavements built with sustainable materials are of increasing interest. This research developed six theoretical concrete mixtures for airport pavement and evaluated their financial, social and environmental cost within a stochastic triple bottom line framework. A Monte Carlo simulation was used to capture uncertainty in key parameters, particularly material transport distances, embodied carbon, and cost variability, allowing a probabilistic comparison of conventional and sustainable mixtures. The results showed that mixtures incorporating supplementary cementitious materials, recycled concrete aggregate and geopolymer cement consistently outperformed the ordinary Portland cement benchmark across all triple bottom line dimensions. Geopolymer concrete offered the greatest overall benefit, while the mixture containing blast furnace slag aggregate demonstrated how long haulage distances can significantly erode sustainability gains, highlighting the importance of locally available materials to sustainability. Overall, the findings provide quantitative evidence that substantial triple bottom line cost reductions are achievable within current airport pavement specifications, and even greater benefits are possible if specifications are expanded to include emerging low-carbon technologies such as geopolymer cement. These outcomes reinforce the need for performance-based specifications that permit the use of recycled materials and industrial by-products in pursuit of sustainable airport pavement practice.

Runway friction is a critical factor in aircraft safety, affecting braking performance during landing and take-off. This study evaluates friction measurement variability and runway life-cycle dynamics at four typical Australian airports, using GripTester data from calibration strips and operational runways. The results show that friction measurements are influenced by seasonal effects, random errors, and testing equipment tire wear, with greater variability at lower speed (65 km/h) than at higher speed (95 km/h). Analysis of runway friction decay indicates that friction reduction rates are higher in touchdown zones and decelerating rate gradually decrease as friction declines, while regular rubber removal significantly restores friction, sometimes exceeding post-construction levels. Current internationally recommended friction testing intervals may not adequately ensure safety, with a sufficient probability of friction dropping below maintenance planning levels between tests. Based on observed reduction rates, updated intervals of approximately 3000 to 4000 landings are proposed to achieve 90% confidence in maintaining safe friction levels. The findings provide practical guidance for friction management and maintenance scheduling as part of an optimized airport pavement management system.

Crumb rubber modification of bituminous binders for asphalt concrete mixture production has been shown to provide significant environmental benefits, in terms of reduced embodied carbon, as well as improvement in the mechanical performance properties of asphalt mixtures. Furthermore, even at low dosages of crumb rubber, significant anti-ageing benefits have been reported, in terms of oxidation and ultra-violet light exposure. However, the effect of low dosage crumb rubber modification on the mechanical properties of asphalt mixtures must be understood. This research compared otherwise nominally identical dense-graded asphalt mixtures produced with crumb rubber modified binder at 5%, 10%, and 15% (by weight of the bitumen) and, using short digestion (reflecting field blending) and long digestion (reflecting terminal blending), to two control asphalt mixtures across a range of mechanical properties indicative of stiffness, rutting resistance, fatigue cracking resistance, cold fracture resistance, and moisture damage resistance. It was concluded that 10% was the optimum crumb rubber content and that crumb rubber modification generally improved the mechanical properties of asphalt mixtures, particularly the deformation resistance and the fatigue cracking resistance, which were both improved significantly. However, the effect of crumb rubber content and digestion times was variable. Consequently, the decision to field blend (short duration) or terminal blend (long duration) should be based on logistics, and not on asphalt mechanical properties and the associated mixture performance.

Runway skid resistance is crucial for the safety of aircrafts. Despite being internationally regulated, investigation reports published by the Australian Transport Safety Bureau and the US National Transportation Safety Board indicate that 4.9–22% of runway excursion accidents are related to insufficient friction, or to friction overestimation. Consequently, based on this review of friction physics, aircraft accident reports, international runway surface regulation, and aircraft braking performance regulation, it was concluded that significant improvement in the management of runway surface characteristics can be achieved. Areas for potential improvement in the current systems for aircraft skid resistance include gaps in the operational reporting of prevailing runway contamination, as well as friction and surface texture measurement and interpretation protocols. Furthermore, aircraft braking performance regulations are not related to actual runway surface friction levels, resulting in reportedly good runways being found to provide inadequate aircraft skid resistance in certain conditions. Recommendations include improvements in the management of runway friction and texture measurement and analysis during pavement design, and through the service life of the pavement surfaces. Finally, the basis of an improved international runway surface engineering design and management system is outlined. Recommendations can reduce the risk of aircraft skidding accidents in the future.

The aviation industry is under increasing pressure to reduce its environmental impact while maintaining safety and performance standards. One promising area for improvement lies in the use of sustainable materials in airport infrastructure. One of the issues preventing uptake of emerging sustainable technologies is the lack of guidance relating to the opportunities, potential benefits, associated risks and an implementation plan specific to airport pavements. This research reviewed opportunities to incorporate waste materials into rigid airport pavements, focusing on concrete base slabs. Commonly used supplementary cementitious materials (SCMs), such as fly ash and ground granulated blast furnace slag (GGBFS) were considered, as well as recycled aggregates, including recycled concrete aggregate (RCA), recycled crushed glass (RCG), and blast furnace slag (BFS). Environmental Product Declarations (EPDs) were also used to quantify the potential for environmental benefit associated with various concrete mixtures, with findings showing 23% to 50% reductions in embodied carbon are possible for selected theoretical concrete mixtures that incorporate waste materials. With considered evaluation and structured implementation, the integration of waste materials into rigid airport pavements offers a practical and effective route to improve environmental outcomes in aviation infrastructure. It was concluded that a Triple Bottom Line (TBL) framework—assessing financial, environmental, and social factors—guides material selection and can support sustainable decision-making, as does performance-based specifications that enable sustainable technologies to be incorporated into airport pavement. The study also proposed a consequence-based implementation hierarchy to facilitate responsible adoption of waste materials in airside pavements. The outcomes of this review will assist airport managers and pavement designers to implement practical changes to achieve more sustainable rigid airport pavements in the future.

International waste policy promotes the reduction and re-use of waste materials, and in some cases, specifically calls for the use of recycled materials in pavements. In countries like Australia, most of the aircraft pavement network is constructed of flexible pavements. Consequently, understanding the opportunities for recycled materials in flexible aircraft pavements is paramount to increasing the technology uptake. This paper reviews opportunities for the incorporation of recycled materials in flexible airport pavement construction, specifically, their application to particle substitution in unbound and asphaltic layers, use in stabilization treatments, and use as a bitumen modifier. Additionally, environmental product declarations are reviewed to provide a range of typical environmental costs for each recycled material when considering material processing for incorporation into flexible pavements. These materials are compared to virgin material environmental costs to determine which recycled materials provide the highest environmental benefit potential. It was concluded that particle replacement in unbound layers with waste materials had a similar environmental cost to using virgin materials. However, the requirement to dispose of waste material to the landfill can be significantly reduced. For asphaltic layers, recycled asphalt pavement as an asphalt mixture replacement, fly ash as a hydrated lime replacement, and waste plastic and crumbed rubber as a virgin polymer replacement all are effective in reducing the environmental cost. To further increase the technology uptake, a risk-based approach for the implementation of waste materials in airport flexible pavements is recommended, which considers performance testing, the depth of the pavement layer, and the pavement functional area.