Greg White

Many local roads in Australia are comprised of a thin marginal granular material base courses with a thin bituminous surface. When these pavements require rehabilitation, new granular reconstruction is the standard historical approach. However, in recent times, stabilisation of the existing pavement has also become popular. This research calculated seven structurally equivalent pavement rehabilitations, including a new granular and two stabilised pavement options, each with sprayed seal and asphalt surface options, as well as a full depth asphalt pavement. The social, financial and environmental cost of each was estimated, and a triple bottom line value was calculated. It was concluded that stabilisation of the existing pavement structure consistently provided the lowest cost solution, whereas new granular pavement reconstruction was consistently the most expensive option. It is recommended that existing pavement stabilisation be the preferred existing pavement rehabilitation for local roads, except where other factors render stabilisation unviable.

The phenomenon of aggregate loss from the surface layer, known as fretting (minor) and ravelling (severe) is considered one of the distresses that trigger pavement resurfacing in airport pavements, even in absence of other distresses. Most of the laboratory tests developed for the prediction of fretting and ravelling are abrasion based, but in airport pavements, fretting and ravelling is reported along the full width and length of pavement, much of which is untrafficked. The main objective of this study was to determine the relative contribution of aircraft traffic loading to asphalt mastic erosion and fretting/ravelling by comparing the macro-texture of otherwise identical trafficked and untrafficked airport asphalt surfaces. Three airports in South East Queensland, each with a surface age between 9 and 12 years, were selected for the study and a laser texture meter was used to measure the volumetric macro-texture of runway and taxiway surfaces. Statistical analysis of the macro-texture measurements showed that there was no significant difference between the trafficked and untrafficked portions of both the runway and taxiway surfaces. This means, at least for the investigated airports, that fretting and ravelling had occurred equally in and out of aircraft wheel path. It is therefore concluded that fretting and ravelling in airport pavements is primarily caused by environmental factors, such as oxidative ageing, ultraviolet radiation and exposure to rainfall. Although the investigated airports are typical of airports in many parts of Australia, these finding should be generalized by extending the investigation to airport pavement surfaces with different aircraft traffic and volumes, as well as in different climates. Moreover, accelerated weathering should become the focus of fretting and ravelling research for airport pavement surfaces and a standard for accelerated laboratory airport asphalt ageing requires development in the future.

Flexible airport pavements in Australia have traditionally been surfaced with Marshall-designed dense graded asphalt (DGA). Grooving is undertaken on runways to avoid aircraft skidding incidents during wet weather conditions, as well as satisfying regulatory skid resistance requirements. Closure of the grooves is a common distress experienced at airports surfaced with DGA in Australia and has led to the investigation of stone mastic asphalt (SMA) as an alternate runway surfacing. Due to the gap-graded nature of SMA, and therefore increased surface texture, grooving can be avoided. This paper summarises the research to validate SMA as an alternate runway surface for Australian airports, including laboratory performance testing and a subsequent field trial. A performance-based specification for SMA has now been developed and will undergo validation in the Australian airport context.

The construction and maintenance costs, as well as the residual value, were calculatedfor structurally equivalent rigid and flexible airfield pavements for a range of typicalcommercial aircraft and a range for typical subgrade conditions. Whole of life cyclecost analysis was performed for a range of analysis periods, from 40 years to 100 years.For the standard 40-year analysis period and a residual value based on rigid pavementreconstruction, the rigid pavements had a 40-105% higher whole of life cost thanequivalent flexible pavements. However, longer analysis periods had a significantimpact on the relative whole of life cost, although the rigid pavements always had ahigher cost than the flexible pavements. The assumed condition of the rigid pavementat the end of the design life was the most influential factor, with a 60-year service liferesulting in the rigid pavements having a lower whole of life cost than the flexiblepavements, but assuming a requirement for full expedient reconstruction resulted in therigid pavements costing approximately 4-6 times the flexible pavements over the 40-year analysis period.

The privatised ownership of many airports has resulted in an increased desire to incorporate environmental sustainability into the construction of airport pavements and surfaces. However, more demanding aircraft and less reliable supplies of bituminous binder have combined with risk-averse airport managers to limit the use of available technologies. Incorporation of recycled asphalt, as well as other recycled construction materials and industrial by-products, reduces the environmental impact of airport asphalt surfaces. As does extending the period between resurfacing by use of rejuvenators, enrichments and surface filling treatments. Increased use of more environmentally sustainable airport asphalt surfaces is expected in the future, as confidence in new technologies increases.