Engineering properties, microplastics and emissions assessment of recycled plastic modified asphalt mixtures.

The use of recycled plastic in asphalt is raising interest since contributing to increase the sustainability of roads pavements. The engineering performance of such roads are commonly assessed but scarcely correlated to the environmental impacts of incorporating recycled plastic in asphalt. This research encompasses an evaluation of the mechanical behaviour and environmental impact of introducing low melting point recycled plastics, low density polyethylene and commingled polyethylene/polypropylene, to conventional hot mix asphalt. While this investigation reveals a reduction in moisture resistance between 5 and 22 % contingent on the plastic content, the benefits include a significant 150 % enhancement in fatigue resistance and 85 % improvement in rutting resistance when compared with conventional hot mix asphalt (HMA). From an environmental perspective, high-temperature asphalt production with higher plastic content resulted in decreased gaseous emissions for both types of recycled plastics up to 21 %. Further comparison studies indicate that microplastic generation from recycled plastic-modified asphalt is comparable to that from commercial polymer-modified asphalt products, long employed by the industry. Overall, the use of low melting point recycled plastics as an asphalt modifier is promising since offering both engineering and environmental benefits when compared to conventional asphalt.

Analysis of possible carcinogenic compounds in recycled plastic modified asphalt.

The incorporation of recycled plastics in asphalt mixtures is getting a growing interest, however, exposing recycled plastics to the high working temperatures of asphalt has posed health and safety concerns. Few studies have paid attention to assessing health and environmental risks concerning recycled plastic-modified asphalt. This study investigates the release of 6 carcinogenic compounds from asphalt modified with recycled plastics, 4 volatile organic compounds (VOCs) and 2 polycyclic aromatic hydrocarbons (PAHs). The concentration of each compound was quantified by GC-MS. Human health risk assessments were conducted using probabilistic methods to assess the risk for an average Australian construction worker to get non-carcinogenic and carcinogenic health issues when exposed to conventional and plastic-modified asphalt fumes. Results showed that non-carcinogenic and carcinogenic risks related to VOC carcinogens (benzene, trichloroethylene, tetrachloroethylene and styrene) are negligible while PAHs (benzo[a]pyrene and dibenz[a,h]anthracene) constitute a possible non-carcinogenic risk and low carcinogenic risk for workers exposed to asphalt fumes. Overall the incorporation of recycled plastic in asphalt reduced the risk for workers to get non-carcinogenic and carcinogenic health issues compared to conventional asphalt mixes. ENVIRONMENTAL IMPLICATION: With increasing trends of using recycled plastics as road materials, concerns about the exposure of workers to carcinogenic gaseous emissions have been raised. This study demonstrates a non-carcinogenic and carcinogenic risk assessment on exposure to recycled plastic modified asphalt fumes. The findings suggest that recycled plastics decrease non-carcinogenic and carcinogenic risks compared to conventional asphalt.

Recycled plastic modified bitumen: Evaluation of VOCs and PAHs from laboratory generated fumes.

A key aspect when investigating the use of recycled plastics in bitumen relates considerably to the issues relating to occupational, health and safety for humans and the environment from a fuming and emissions perspective. This research investigates laboratory-generated fumes in the forms of volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs) generated from producing polymer modified bitumen using five different types of recycled plastics. A comparative analysis of recycled plastic modified bitumen fumes was conducted based on a series of optimized parameters, including working temperatures (160 °C, 180 °C and 200 °C) and polymer contents (1%, 2%, 4% and 6% by weight of bitumen) against neat bitumen and polymer-modified bitumen. Forty-eight volatile organic compounds (VOCs) and sixteen polycyclic aromatic hydrocarbons (PAHs) were quantified using gas chromatography-mass spectrometry (GC-MS). The results from the comparative analysis revealed that the incorporation of recycled plastics could reduce overall emissions from both VOCs and PAHs perspectives. The reduction in emissions can be attributed to the enhancement in thermal stability of the bitumen blend when recycled plastics are added. The reduction rate is heavily dependent on the type and source of recycled plastics used in the blending process. Furthermore, a specific compound concentration analysis of the top-four weighted compounds emitted reveals that the total concentration of emissions can be deceiving as specific compounds can spike when adding recycled plastics in bitumen despite a reduction trend for the overall concentration.

Selection of recycled waste plastic for incorporation in sustainable asphalt pavements: A novel multi-criteria screening tool based on 31 sources of plastic.

This study investigated the suitability of 31 recycled waste plastic samples obtained from 15 major recycling companies across Australia and New Zealand to be used as bitumen/asphalt modifiers. The plastics have been selected to be representative of recycled waste plastic around Australia and New Zealand. The recycled waste plastics belonged to either the post-industrial or post-consumer collection scheme. A new classification scheme was developed to rank each recycled waste plastic based on their chemical and physical properties against those of bitumen/asphalt. Specifically, density, polarity, melting point, solubility and melt flow index of the samples as well as the presence of contaminants, fillers and additives were analyzed for each recycled waste plastic material and their virgin counterpart. These 8 properties were used to rank various sources of recycled low-density poly(ethylene), linear low-density poly(ethylene), high density poly(ethylene) and poly(propylene) in addition to commingled plastics based on their suitability for bitumen modification (wet method). The modification of asphalt via replacement of virgin quarry aggregate with plastic aggregate (dry method) by recycled acrylonitrile butadiene styrene and poly(ethylene terephthalate) was also assessed by considering four criteria of purity, polarity, recycling contamination and hazardous additives. This new multi-criterion ranking approach revealed that low-density and linear low-density poly(ethylene) and acrylonitrile butadiene styrene and poly(ethylene terephthalate) should be preferentially used as bitumen/asphalt modifiers. This tool has been developed for recycling companies and bitumen/asphalt contractors to determine the suitability of recycled waste plastics within asphalt roads by a series of experimental techniques.

Sustainable Polymers from Recycled Waste Plastics and Their Virgin Counterparts as Bitumen Modifiers: A Comprehensive Review.

The failure of bituminous pavements takes place due to heavy traffic loads and weather-related conditions, such as moisture, temperature, and UV radiation. To overcome or minimize such failures, a great effort has been put in recent years to enhance the material properties of bitumen, ultimately improving field performance and increasing the pavement service life. Polymer modification is considered one of the most suitable and by far the most popular approach. Elastomers, chemically functionalised thermoplastics and plastomers * (* Note: notwithstanding the fact that in Polymer Science the word 'plastomer' indicates a polymer with the simultaneous behaviour of an elastomer and plastics (thermoplastics), this paper uses the term 'plastomer' to indicate a thermoplastic polymer as it is more commonly found in Civil and Pavement Engineering.) are the most commonly used polymers for bitumen modification. Plastomers provide several advantages and are commonly acknowledged to improve high-temperature stiffness, although some of them are more prone to phase separation and consequent storage instability. Nowadays, due to the recent push for recycling, many road authorities are looking at the use of recycled plastics in roads. Hence, some of the available plastomers-in pellet, flakes, or powder form-are coming from materials recycling facilities rather than chemical companies. This review article describes the details of using plastomers as bitumen modifiers-with a specific focus on recycled plastics-and how these can potentially be used to enhance bitumen performance and the road durability. Chemical modifiers for improving the compatibility between plastomers and bitumen are also addressed in this review. Plastomers, either individual or in combination of two or three polymers, are found to offer great stiffness at high temperature. Different polymers including HDPE, LDPE, LLDPE, MDPE, PP, PS, PET, EMA, and EVA have been successfully employed for bitumen modification. However, each of them has its own merit and demerit as thoroughly discussed in the paper. The recent push in using recycled materials in roads has brought new light to the use of virgin and recycled plastomers for bitumen modification as a low-cost and somehow environmental beneficial solution for roads and pavements.