Use of plastic waste in sidewalks
An article, currently in pre-proof for publication in cleaner materialsstudied the use of plastic waste as a modifier in bituminous mixtures for flexible pavements.
Study: A mini-assessment on the use of plastic waste as an asphalt modifier for flexible pavement. Image Credit: tcharts/Shutterstock.com
Plastic waste is a growing problem due to population growth, rapid urbanization and industrial activities. The recovery of plastic waste is crucial to reducing the environmental damage caused by human activities, and one potential recovery route is to use plastic waste as a material in pavements.
Recovering plastic waste for commercial products
The growth of cities and world population has resulted in massive environmental damage. Products needed by society and industry are usually produced in a linear process, where they use virgin resources that are discarded at the end of their useful life, and in the process valuable materials are lost. Plastic production is incredibly damaging to the environment, causing greenhouse gas emissions and pollution.
Circular diagram of plastic waste locations. Image Credit: Noor, A & Rheman, MAU, Cleaner Materials
Valuing plastic waste to produce commercially viable products is a cornerstone of the circular economy concept and a key strategy to reduce environmental damage and achieve net-zero carbon emissions in line with international commitments such as the Paris Agreement.
The use of recovered plastic waste has been widely explored in sectors such as construction to reduce the need for raw, non-renewable building materials such as concrete. Not only does this reduce the number of virgin materials that are mined, it also reduces carbon emissions from manufacturing, and polymers can impart desirable mechanical and physicochemical properties to building materials.
With the rapid growth of urban areas and infrastructure, there is a need for road surfaces that can withstand repeated use. Many road surfaces are made up of multi-layer flexible pavements using different materials. These are the surface, base, subbase, and subsoil layers.
Pavement performance can be influenced by the thickness of each layer. For example, increasing the thickness of the bituminous layer reduces the compressive stress on the sub-base, which is the compacted soil used to support the entire pavement.
Flexible pavements can fail due to several factors including potholes, stripping, overweight vehicles, and fatigue cracks are some of those influential factors. Maintaining them requires a large number of resources and repair methods can be costly and time-consuming, leading to traffic disruptions and increased travel times.
The parameters that influence the thickness of each layer are the load that the pavement will have to support, the materials used in each layer and the conditions of the area in which the pavement will be built.
Many studies have been carried out over the years to investigate the optimum thickness of each layer and the materials to be used as bituminous additives for the surface layer of flexible pavements. The research aimed to improve the overall mechanical properties of flexible pavements, increase their lifespan and reduce the need for maintenance and unsustainable use of resources. Many materials have been explored as bituminous additives, including waste plastics, to improve the properties of the surface layers of flexible pavements.
Flexible pavement layers. Image Credit: Noor, A & Rheman, MAU, Cleaner Materials
A mini-review on the use of waste plastics as bituminous modifiers for flexible pavements
In recent years, emphasis has been placed on the recovery of waste as bituminous additives. Plastic waste is an interesting modifier because its use reduces the environmental impact of the plastics industry and imparts improved mechanical properties to flexible pavements. A mini-review of current perspectives and research has been done by Pakistani authors, currently in pre-evidence in cleaner materials.
The authors noted the challenges associated with the use of bitumen, the most commonly used binder material in the construction of flexible pavements, including carbon emissions, high temperature softening and gassing during heating, as well as the loss flexibility and increased brittleness at low temperatures. Studies have shown that polyethylene and polystyrene waste can improve the properties of bituminous materials and have good adhesion properties.
Wet process. Image Credit: Noor, A & Rheman, MAU, Cleaner Materials
Some researchers have used virgin plastics for modification purposes. The authors noted the use of plastic waste from tire production and recycling as modifiers in flexible pavements. Virgin and recycled plastics improve surface layer properties and performance. The use of plastic for this purpose is not new: the first use was reported in 1843. Recent research has been carried out to optimize modification parameters as well as to study economic and environmental aspects.
Processing techniques such as wet processing, dry processing, and modified processes have been explored in the mini-review. Among plastic wastes, PET bottles, recycled LDPE from greenhouses, waste PE, PVC and HDPE pipes and waste plastic bags have been extensively explored in the current literature for use as bituminous modifiers for flexible pavements. Using different waste plastics as modifiers improves different properties in various ways.
In conclusion, the authors asserted that plastic waste improves the chemical stability and mechanical strength of bituminous materials to create robust and durable flexible pavements. In addition, the use of plastic waste reduces both environmental impacts and manufacturing and maintenance costs. The recovery of plastic waste as bituminous modifiers in flexible pavements deserves to be widely implemented.
Noor, A & Rheman, MAU (2022) A mini-assessment on the use of plastic waste as an asphalt modifier for flexible pavement [online] cleaner materials 2022 100059 | sciencedirect.com. Available at: https://www.sciencedirect.com/science/article/pii/S2772397622000193
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