Rapid economic and industrial growth has increased Australia’s waste production. In an attempt to manage these wastes and reduce their impact on the environment, different research projects have been conducted at Curtin University, Western Australia. These projects were focused on using waste materials to improve the building materials industry [1
]. Results from these projects have shown the significance of utilising waste materials in building work and, in particular, improving geotechnical solutions and asphalt pavement reinforcement.
On the 1 January 2018, China enforced a ban on importing plastic waste, followed by similar prohibitions in other countries, such as India and Malaysia. These bans have had a significant impact on Australia’s waste recycling industry [4
]. The report stated that during 2018, the annual consumption of plastic was over three million tonnes, with only 9% recycled. It can be seen that during the last 17 years, Australia faced an extraordinary increase in waste materials as a result of people’s daily lifestyle demands [4
]. The consequent plastic waste produced has increased hazards and pollution [4
]. As a result, the recycling of plastic waste in an environmentally friendly method is of great interest.
Using waste materials instead of new materials in the construction of roads has two significant benefits: substantially reduced costs and reduced waste going to landfill. Along with the importance of these benefits, the future development of using waste plastic in bitumen modification must consider how it enhances the properties of the mixture [6
]. The current paper and another published paper [9
] both belong one big project of using domestic waste plastic in the improvement of roads in WA, Australia. The published paper is different from the current submitted paper, because it only focused on binder properties in short- and long-term aging using the pressure aging vessel (PAV) method. Plastic has long been used in the asphalt industry showing competitive properties with commercial elastomer polymers in terms of improving engineering properties, such as rutting resistance and stiffness properties [10
However, the addition of waste inclusions like PET would possibly lead to heterogeneous binders with brittle characteristics and low resistance to thermal and fatigue cracking. Previous studies focus on virgin plastic polymers and pay less attention to recycled plastics. Other studies [14
] have displayed positive results using plastic in asphalt modification; nevertheless, few argue the use of a significant amount of plastics, such as PET and high-density polyethylene (HDPE), for improving the mechanical properties and durability of modified asphalt. Durability is the ability to resist deformation in the long-term service of asphalt life. Of interest, these studies [11
] reported that adding plastic polymers could notably improve rutting resistance [15
]. Studies also confirmed that adding plastic enhanced the workability and stability of the mixture [13
]. Further studies have indicated that using waste plastic also results in improved rutting resistance of asphalt mixtures [16
According to previous studies [12
], a waste plastic content of 4% is suggested as the ideal in asphalt to achieve good properties in term of strength, stability, stiffness, better durability and rutting resistance. On the other hand, studies by [21
] suggested 6% waste plastic content is essential for an enhanced modifier that could increase the fatigue life and cracking resistance of asphalt. The application of recycled plastic to improve pavements’ properties has been carried out and evaluated in several countries, such as in the United Kingdom, Canada, India, the Netherlands and New Zealand, over the last seven years. In 2012, the city of Vancouver, Canada, used plastic waste as an alternative additive for reinforcing warm-mix asphalt [25
]. As reported, three trail sections in Vancouver used local waste plastic in a 19 mm Superpave surface course warm-mix asphalt, thus helping to reduce the impact of greenhouse gases and improve air quality with 20% savings in energy used during mixing. Another example of the significance of utilising waste plastic in the pavement industry comes from the Netherlands in 2015 [26
]. According to the construction company, a road fashioned out of recycled plastic would be able to resist low temperatures of −40 °C and up to highs of 80 °C, and be anti-corrosion and long-lasting for up to 50 years after construction [26
According to investigations’ reports [26
], one of the effective ways of modifying asphalt is waste plastic, which would also be a way of supporting the environment and ecosystems. In addition, utilizing plastic polymers in asphalt potentially enhances the bitumen’s temperature susceptibility and stiffness; this enhancement of bitumen results in an enhancement in the rutting and fatigue cracking resistance of asphalt pavement.
Lately, a valuable application of plastic waste has been tested in New Zealand to modify asphalt mixes [34
]. According to their report, a large-scale trial of asphalt made with recycled plastic was conducted using 250 tonnes of plastic containers that would otherwise have been sent to landfill. Despite a few field trials in Brisbane, Melbourne and Sydney, since 2019 [35
] no documented investigation has been reported in Australia. An earlier study by [35
] was conducted using UK commercial plastic waste products added to C320 bitumen. Although some performance indicators were tested, the study [35
] did not investigate the effect of local waste PET plastic on the elasticity and engineering properties of C320 asphalt using the wet-mix method. Consequently, there is a vital need to examine the performance of PET plastic-modified asphalt. This study aims to investigate and evaluate the impact of waste plastic in improving the engineering properties of asphalt mixes. The study will examine and evaluate the impact of waste plastic-modified asphalt on the enhancement of ageing stiffness performance and rutting resistance of the mixtures.