Turning Plastic Trash into Tarmac Treasure
In the relentless pursuit of sustainable solutions to manage plastic waste, the successful incorporation of polymers into road construction has emerged as a technical marvel having the potential to facilitate the seamless transition towards a circular economy. This strategic repurposing of polymeric waste not only tackles the global plastic pollution crisis head-on but also establishes a robust foundation for creating a resilient, environment-friendly infrastructure. In this blog post, we look into the intricacies behind the success of polymeric waste in plastic roads, along with some of the characteristics and the parameters involved that exhibit its profound impact on both the environment and civil engineering practices.
To appreciate the scale of the problem, it is imperative to grasp the magnitude of plastic waste globally in numbers. According to the World Bank, approximately 242 million tons of plastic waste were generated worldwide in 2016. Furthermore, according to the UN’s website, the world currently is producing 430 million tonnes of plastic per year on average – two thirds of which are only used for a short period of time. This staggering figure underscores the urgency of finding effective and sustainable solutions to manage plastic waste.
Plastic Waste to Infrastructural Wonder
Picture Credits: https://datatopics.worldbank.org/what-a-waste/tackling_increasing_plastic_waste.html, https://www.prakati.in/use-of-plastic-for-road-construction-in-india/
One of the ways that can lead the change in which the post-consumer waste gets treated lies in its usage in formulating polymer-modified bitumen, a key component in asphalt used for road construction. The inclusion of polymeric waste in bitumen enhances the structural performance of roads, significantly extending their service life. The properties of the mixture of polymer-modified bitumen used in plastic roads contribute to its success in terms of durability, flexibility, and environmental sustainability. Let's delve into some key properties that make this mixture a superior choice for road construction:
• Enhanced Durability: The addition of polymer waste to bitumen significantly enhances the durability of the road surface. Polymers improve the binding properties of bitumen, creating a more robust matrix that resists wear and tear over time. Laboratory tests, such as the Marshall Stability Test and the Indirect Tensile Strength Test, consistently demonstrate higher values for polymer-modified bitumen. These metrics indicate improved resistance to deformation and cracking, particularly under heavy traffic loads.
Mashall Flow Test on Bitumen (Picture Credits: https://theconstructor.org/practical-guide/marshall-stability-test-flow-test/2640/)
• Flexibility and Elasticity: Polymers introduce a higher degree of flexibility and elasticity to the road surface. This property is crucial in areas with temperature variations, as the road can expand and contract without developing cracks. The Dynamic Shear Rheometer study reveals a superior elastic response of polymer-modified bitumen, indicating its ability to withstand repeated loading and stress without permanent deformation.
Setup of Dynamic Shear Viscometer for plastic modified bitumen testing
(Picture Credits: Singleton, T. M., Airey, G. D., Collop, A. C., & Widyatmoko, I. (2000). Residual bitumen characteristics following dry process rubber-bitumen interaction. In Asphalt Rubber 2000 Conference, Vilamoura, Portugal (pp. 463-482)).
• Improved Fatigue Resistance: The fatigue life of roads, a measure of their ability to withstand repeated loading cycles, is significantly improved with the use of polymer-modified bitumen. This is particularly important in high-traffic areas where fatigue failure can lead to premature road deterioration. Statistical analyses, including the Fatigue Life Prediction Model, demonstrate a notable extension in the fatigue life of roads constructed with polymer-modified bitumen compared to conventional asphalt.
• Resistance to Rutting and Permanent Deformation: Polymer modification imparts a high resistance to rutting, the formation of depressions in the road caused by repetitive traffic loads. The evidence from Accelerated Pavement Testing programs showcase a substantial reduction in rut depth for roads utilizing polymer-modified bitumen. The Superpave Gyratory Compactor tests further support these findings, indicating superior resistance to permanent deformation and rutting.
Superpave gyratory compaction: (a) SGC test and (b) diagram of SGC. (Picture Credits: https://www.mdpi.com/2073-4360/11/6/1006)
• Environmental Sustainability: The incorporation of polymer waste in road construction aligns with environmental sustainability goals. Plastic roads are made up of 6–8% plastic and 92–94% bitumen. Although these numbers may not sound promising, the current total length of just Indian national highways stands at a staggering 1,45,240 km, a 59% rise in the last 10-year period. The polymer-modified bitumen mixture reduces the demand for virgin materials and diverts plastic waste from landfills, making it an environmentally friendly alternative. Lifecycle assessments, considering factors such as energy consumption and carbon emissions, consistently demonstrate the eco-friendly profile of roads constructed with polymer-modified bitumen.
• Adhesion and Cohesion: Polymers enhance the adhesion between bitumen and aggregates, improving the overall cohesion of the asphalt mixture. This results in better resistance to moisture damage and increased stability of the road surface. Peel and shear tests, measuring the adhesive properties of polymer-modified bitumen, reveal higher adhesion strengths compared to traditional asphalt.
Studies comparing the durability of traditional asphalt to polymer-modified bitumen highlight compelling statistical evidence. Roads constructed with polymer-modified bitumen exhibit a 20-30% increase in resistance to rutting and a remarkable 15-25% reduction in cracking, according to data compiled by the American Society of Civil Engineers. These metrics underscore the superior performance of polymer-infused roads under heavy traffic loads and adverse weather conditions. The environmental benefits are equally quantifiable. By diverting plastic waste from landfills, polymer-modified bitumen reduces greenhouse gas emissions associated with traditional disposal methods. The data from Ellen MacArthur Foundation suggest that every kilogram of plastic waste repurposed in road construction results in a net reduction of 6 kilograms of CO2 emissions compared to conventional disposal methods. Furthermore, from an economic standpoint, the success of polymer waste in plastic roads translates into substantial cost savings. Lifecycle cost analyses conducted by the Federal Highway Administration indicate that the initial investment in polymer-modified bitumen is offset by a reduction in maintenance costs, yielding a net economic benefit over the lifespan of the road.
Since the construction of the first road in Chennai in 2002 by Dr. Rajagopalan Vasudevan, India has made substantial strides in leveraging discarded plastic for road development. Over the years, the country has successfully built 1 lakh kilometres of roads across at least 11 states using this innovative approach. Impressively, a tenth of the total materials employed in the construction of national highways have been derived from plastic waste. Furthermore, the global acceptance of polymer-modified bitumen in road construction is gaining considerable momentum. According to a report by the European Asphalt Pavement Association, this innovative method has been embraced by over 30 countries, showcasing an annual growth rate exceeding 8%. These statistics underscore the international acknowledgment of polymer waste as a valuable resource for the creation of sustainable, high-performance road infrastructure.
The technical triumph of polymer waste in plastic roads, not only addresses the complex challenge of plastic pollution but also propels the construction industry towards a more sustainable future. The properties of the polymer-modified bitumen mixture, backed by rigorous laboratory testing and statistical analyses, highlight its superiority in terms of durability, flexibility, and environmental sustainability. As these properties continue to prove their worth in real-world applications, the adoption of polymer waste in plastic roads is poised to revolutionize the landscape of sustainable infrastructure development. As the numbers continue to reinforce the efficacy of polymer-modified bitumen, it becomes clear that this innovative approach is not merely a solution to plastic waste; it is a pioneering leap towards environmentally conscious and economically efficient road construction practices on a global scale.
If you have any other questions or would like to suggest topics for us to write about, please feel free to contact us at prashant.gupta@polymerupdateacademy.com
Author
Dr. Prashant Gupta
Faculty, Polymerupdate Academy
