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.

Foamed asphalt stabilized base course is a bound but flexible material, with beneficial stiffness, strength, and moisture resistance properties. When the granular material being stabilized is an existing airport pavement base, foamed asphalt stabilization is also highly sustainable and provides a more resilient pavement structure. Despite these advantages, to gain acceptance as a mature technology, a material specification and a clear basis for characterization in thickness determination software are required. A specification was published in 2024, and this research aimed to provide a basis for material characterization in layered elastic design methods. Based on a review of the nature of the materials and field performance of various airport pavements containing foamed asphalt stabilized base, it was concluded that the elastic modulus should be varied broadly from 1,000 MPa to 3,500 MPa, depending on the climatic conditions and the time until critical aircraft trafficking is expected. It was also concluded that a fatigue performance model, such as that associated with asphalt concrete or cementitiously stabilized materials, is unlikely to be applicable to foamed asphalt stabilization in airport pavements.

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.

Low traffic local roads are often comprised of a marginal gravel base course with a thin bituminous surfacing. These pavements commonly require rehabilitation at the end of their life. The economic (financial) and environmental (embodied carbon) cost of three typical pavement rehabilitation designs were estimated and objectively compared. The rehabilitation treatments included full depth granular reconstruction with new material, an insitu cementitious stabilisation of the existing pavement to form a lightly bound gravel base, and an insitu foamed bitumen stabilised existing gravel base, each with a sprayed seal surface. The full depth reconstruction with new granular materials had the highest economic and environmental costs, by a significant margin. It is recommended that stabilisation be the preferred rehabilitation option for local roads, and that pavement reconstruction using new materials only be considered when stabilisation of the existing pavement is determined to be unviable.

The airport pavements at Merimbula airport (Australia) required strengthening to support larger aircraft. Four structurally equivalent pavement designs were developed, using standard pavement materials, except for an option to use of foamed bitumen to stabilise the existing granular pavement material, prior to surfacing with an asphalt wearing course. The sustainability and resiliency of the four pavement designs were considered and scores assigned. The sustainability score was based on the embodied carbon in the rehabilitated pavements, while the resiliency score was subjectively assigned based on the resistance of the pavement to moisture ingress. It was found that the new rigid pavement and the foamed bitumen stabilised flexible pavement were the most resilient, reflecting the bound nature of these materials. Furthermore, the foamed bitumen stabilised pavement and the structural asphalt overlay of the existing pavement were preferred in terms of sustainability. Because of its high scores in both sustainability and resiliency, the foamed bitumen stabilised pavement was preferred. It is recommended that other airports consider the potential for stabilisation of existing pavements, for sustainable and resilient pavement rehabilitation, whenever the existing pavement materials are suitable.

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.