Greg White

The desire to develop more sustainable infrastructure, including pavement structures and materials, is ever increasing. Using recycled plastics in asphalt concrete has gained significant attention in recent years, despite having been trialed and offered by various companies since the 1980s. Although some solutions are as simple as shredding up milk containers, bottles or crates and adding them to the asphalt concrete production plant, MR6 and MR10 are commercially available recycled plastic products that have been produced under a quality assurance system since 2016. These products have been tested using various asphalt binder and mixture tests commonly specified in the United Kingdom, the United States and Australia. Comparisons to unmodified asphalt binders were performed using a range of dense graded and stone mastic asphalt concrete mixtures, as well as various grades and unmodified asphalt binder. MR6 and MR10 generally increased the resistance of asphalt binder to flow and the resistance of the asphalt concrete mixtures to deformation. Significant asphalt binder ductility and elasticity was introduced, but the effect on asphalt concrete crack resistance was either moderate or not significant. There was no significant change to asphalt concrete moisture damage resistance, but the stiffness of various asphalt concrete mixtures increased two- to three-fold. Overall, the general effects of MR6 and MR10 were found to be similar to the effects associated with conventional polymer modification of asphalt binders and asphalt concrete mixtures, particularly those associated with the plastomeric polymer EVA

There are currently two established approaches to the accelerated ageing of asphalt mixture and bituminous binder samples in the laboratory. The first is to expose a film of the bituminous binder to heat and air, under controlled conditions. Different protocols are intended to represent the ageing associated with asphalt mixture production, as well as the long-term field ageing of an asphalt surface. The second approach is to expose the asphalt mixture to elevated temperature in an oven, intended to represent long-term field ageing. The current protocols for ageing bituminous binder samples do not take into account the interactions between the binder and the aggregate. The binder ageing protocols do not include UV irradiation and do not use representative binder film thicknesses. Furthermore, the current protocols for ageing asphalt mixture samples do not include UV irradiation, and the heat is applied equally to all sides of the sample, which is not representative of field conditions. The limitations associated with the current protocols for the accelerated ageing of asphalt binder and mixture samples in the laboratory is a significant issue. Any research into the effect of incorporating recycled waste materials in asphalt mixtures relies on a robust accelerated ageing protocol. Similarly, research on asphalt rejuvenation and preservation treatments also requires reliable accelerated ageing protocols, to avoid the need for 10 or more years of field ageing to measure the benefits. Therefore, more reliable accelerated asphalt ageing protocols are critical to better pavement surfacing technology. This paper explains the limitations of the current asphalt binder and mixture laboratory ageing protocols and summarises efforts to develop a more reliable approach. The proposed approach incorporates UV and heat exposure, which is more representative of field conditions. Examples demonstrate that the proposed approach results in more realistically aged asphalt surfaces and the preferred indicators of sample age are described.

With the increased focus on recycling of waste materials in infrastructure construction and maintenance, there is an ever-increasing interest in the recycling of waste plastic in the production of asphalt mixtures for road and other pavement surfacing. However, there are many types of plastic and only some are compatible with asphalt production. Some compatible plastics are capable of extending the mineral aggregate in asphalt mixtures, while others can also improve the mixture properties, by increasing the resistance to rutting and cracking. However, the most valuable plastics can extend and improve the bituminous binder in the asphalt mixture, effectively replacing the synthesized polymers that are commonly used to improve moisture resistance, temperature susceptibility, crack resistance and deformation resistance. Despite these potential benefits, there are many challenges associated with the categorization of different plastics and their associated effects, as well as the sourcing of a consistent and uncontaminated plastic supply. Other challenges include the digestion and stability of plastic in the bituminous binder phase when the wet mixing process is used. It is also essential to confirm and demonstrate that asphalt mixtures containing recycled plastic do not increase fume generation during construction, or chemical leachate of road surfaces during service. These challenges must be resolved if the potential for recycling plastic in road and other pavement asphalt layers is to be fully maximised in the future. This paper summarises the potential benefits of waste plastic as an asphalt binder modifier and explores the challenges associated with the implementation of waste plastic as a mature technology in asphalt binder and mixture production. The potential to overcome those challenges is also considered.

Increased access to the polar regions requires increased infrastructure. Design and construction of this infrastructure can only be achieved by accurately estimating surface bearing capacity. We reviewed contemporary methods for determining bearing capacity in soils and applied these to data obtained from almost 100 cone penetration tests conducted in Antarctica. Numerous direct and indirect methods exist to enable estimation of surface bearing capacity in polar snow, but the preferred method is the rate-controllable, friction-sleeve equipped, cone penetration test (CPT). Application of this and similar techniques is essential to ensure the correct design and construction of infrastructure in ever-more trafficked polar regions.

When rutting and fatigue cracking distresses are avoided, surface fretting and ravelling due to age-related erosion of the bituminous mastic is the usual trigger for asphalt surface replacement in flexible pavement structures. This is particularly the case for lightly trafficked pavements, such as local roads, as well as for aircraft pavements, where the majority of the pavement surface is rarely trafficked. The age-related erosion of bituminous mastic is complicated and is affected by many factors, although the chemical aging of the bituminous binder is the most significant. Researchers and practitioners have many established tests for the mechanical properties of asphalt mixtures, including fatigue, fracture and deformation resistance, along with stiffness/modulus and moisture damage resistance. However, the protocols for accelerated laboratory aging are less clear. Most current accelerated laboratory aging protocols for asphalt mixtures are based on placing loose or compacted asphalt samples in a dry oven, typically at 70-90°C, for a pre-determined period, typically a few days or weeks. The combination of oven temperature and exposure time is intended to result in oxidative binder aging that is equivalent to a lifecycle of aging in a typical real-world pavement surface. The benchmarks used for setting equivalent aging are usually either the modulus of asphalt samples cored from a real pavement, or the viscosity of the binder extracted from a core of asphalt. These existing protocols do not reflect the temperature gradients or cycles that are known to exist in real pavement surfaces, nor do they expose the asphalt samples to ultraviolet radiation or moisture. Because of the importance of accelerated laboratory aging to the assessment of surface durability of asphalt mixtures containing recycled or waste materials, as well as the efficacy of surface preservation treatments, a more realistic accelerated laboratory aging protocol for asphalt samples is of great interest to researchers and practitioners alike. This paper explains the need for a more realistic accelerated asphalt aging protocol, the use of a commercially available weathering chamber for this purpose and the hypothetical results of asphalt aging trials. The conclusions address the preliminary protocol developed to date, the need for further research in this area and the benefits associated with such a protocol once it is finalized.

During construction, the compaction of asphalt layers is critically important to the life-cycle performance and durability of the pavement surface, particularly for aircraft pavements. As a result, there is a strong focus on achieving a high level of compaction during airport surfacing projects, with specification limits for the density of the paved construction joints (the joints), as well as the area of contiguously paved surface between the paving joints (the mat). In recognition of the greater difficulty in achieving high density at the joints, there is usually a relaxed requirement for joint density, compared to the mat. Furthermore, there is usually different treatments of the joints depending on their temperature at the time the adjacent paving lane is performed, with ‘hot’, ‘warm’ and ‘cold’ joint categories commonly defined. To allow ‘warm’ joints to be treated as ‘hot’ joints during construction, joint heaters are often used to reheat the asphalt along the joint, immediately prior to the adjacent lane of asphalt being paved. Although there are different forms of reheating equipment, infrared gas burners are most common and avoid the direct application of a naked flame to the asphalt mixture or surface. This research quantified the benefit of a typical asphalt paving joint heater for better joint density and finish, during a runway resurfacing project. The temperature of the joints and the mat was monitored over seven days, three of which used the joint heater and four of which did not. Furthermore, the density of the joints and mat were compared, and the effect of the prevailing weather conditions was considered. It was clear that the joint heater significantly increased the joint temperature and significantly improved the joint density and finish. Recommendations include mandating the use of joint heaters for runway resurfacing and the potential to remove ‘warm’ joints from specifications, meaning all joints would be considered to be ‘cold’ or would be reheated to ensure they are ‘hot’.

The compaction of airport asphalt is critical for the good performance of airport pavement surfaces. Traditionally, airport asphalt compaction was assessed using destructive cores recovered from the surface during each work period, resulting in 200-500 cores being taken along the length of a typical runway, each creating a weak point in the surface. In recent times, non-destructive testing of asphalt density has come to the interest of practitioners and researchers alike, including nuclear and non-nuclear gauges for density testing. The benefits include faster testing, which otherwise allows more locations to be tested, and the avoidance of introduced weak points in the surface, which allow moisture ingress over the life of the surface. However, physical testing of recovered cores is the gold standard of asphalt density testing and some practitioners and researchers question the reliability of gauge-based estimates of air voids and relative density. To evaluate the efficacy of common non-destructive density gauges, field evaluations of both nuclear and non-nuclear devices have been performed, in parallel with destructive coring, during six airport resurfacing projects. This research compares the destructive core test results to the gauge-based results, both on the joints between paving runs and in between the paving joints. It was concluded that following a mixture-specific calibration, the gauges were just as effective at measuring asphalt density as destructive coring. It was also found that the nuclear gauge was prone to occasional low density estimates of the joints, and when coupled with the simpler logistical restrictions associated with non-nuclear gauges, the non-nuclear gauge was concluded to be preferred.

Coarse and fine aggregate constitutes approximately 93% of dense graded airport asphalt and the aggregate properties can affect asphalt surface performance. Despite a general trend towards performance-related specification of asphalt mixtures, prescriptive aggregate properties are generally still retained. This primarily reflects the absence of reliable performance-based laboratory test methods for determining the effect of aggregates on asphalt weathering and erosion. Historical airport asphalt specifications included a broad range of aggregate durability properties and the aggregate supply industry has questioned whether coarse aggregate durability testing can be simplified to combinations of just two properties. To determine whether a reduction in aggregate durability testing is appropriate for Australian airport asphalt, eight sources of aggregate were tested for wet strength, wet-dry strength variation, Los Angeles abrasion, sodium sulphate soundness and water absorption. The different tests were associated with different levels of variability and the correlation between the various tests results was generally low, except for Los Angeles abrasion and wet strength. The industry recommended combinations of aggregate durability testing were found to be inconsistent and ineffective. Consequently, the current range of aggregate durability tests must be retained. The only exception was the potential to omit Los Angeles abrasion when the wet strength is high. Furthermore, there was no significant difference between the results associated with the various coarse aggregate fraction sizes, indicating it may be appropriate to allow only one sized fraction per quarry source to be tested. Further work is required to correlate the various aggregate durability tests to asphalt field performance.

Foamed bitumen stabilization is a useful and well established method for improving crushed rock and natural gravel materials for pavement construction. Like most pavements, those with a foamed bitumen base course (FBB) are usually designed using layered elastic softwares in which the FBB layer is characterized by an elastic modulus and a Poisson’s ratio, with the modulus having a significant influence on pavement thickness. In Australia, FBB characterization is based on the saturated indirect tensile modulus after three days of accelerated curing of samples produced in a laboratory mixer. It is well established that this approach to FBB characterization is not representative of field production and in-pavement curing conditions. To determine the effect of FBB production and curing on FBB modulus, pavement thickness and predicted pavement life, the same FBB was produced using a laboratory mixer, an exsitu pugmil and an insitu stabilizer. Material was sampled and the uncured, cured and saturated modulus was measured after various periods of accelerated laboratory curing. The exsitu produced FBB was also cured using simulated in-pavement conditions. The various FBB modulus values were then used to determine the required thickness and predicted life of a typical aircraft pavement including a 300 mm thick FBB layer. It was found that field produced FBB modulus increased significantly during the first 90 days after production and that laboratory production and curing protocols were not representative of field production and in-pavement curing conditions. Layered elastic pavement modelling showed that more than 80% of the predicted pavement damage occurred in the first 20 days after FBB production. It is therefore recommended that FBB remains untrafficked for 7–12 days after production, wherever possible, and thinner pavements are likely to perform adequately in situations where the FBB is protected from traffic loading for more than 14 days following production.

Concrete pavements are commonly used infrastructural assets that require various types of materials. There are many technologies and materials to improve the engineering properties and sustainability of concrete pavements. One such technology that opens new horizons in civil engineering involves nanomaterials. Use of nanomaterials increases structural strength and durability against aggressive chemical compounds and elements that extend the effective service life of the concrete pavement. Furthermore, nanomaterials can enhance environmental stewardships of concrete pavements through the reduction of demand for raw materials for maintenance and rehabilitation. Therefore, nanomaterials play a pivotal role in the development of high-strength and low-energy concrete pavements, especially for heavy-duty applications. In this chapter, various types of nanomaterials and pertinent performance mechanisms on the structural response of concrete pavements are discussed. In addition, the results of laboratory and field studies on the environmental burdens of nano-concrete pavements are analyzed in detail. In conclusion, the challenges of nano-concrete pavements as resilient infrastructure are discussed.