Recycled Plastic in Construction : Sahadat Hossain: "With plastic roads we can pave the way for a more sustainable future."

What inspired you to explore the use of recycled and unrecycled plastic waste in road construction?

For over 20 years, I have dedicated myself to advancing sustainable waste management through the reuse of recycled plastic. The 2018 ban on importing plastic waste by China triggered a global recycling crisis, leading many nations to struggle with the proper disposal and management of plastic waste as many countries did not create a local market for reusing recycled plastic waste. Unfortunately, this resulted in recycled plastic being either sent back to landfills or mismanaged through open burning, posing severe environmental and public health risks as microplastics infiltrate our food chain.

Amidst these challenges, leveraging recycled plastic for transportation infrastructure emerged as a transformative solution. By incorporating recycled plastic into pavement construction, we not only address the plastic waste crisis but also enhance the longevity of roads. This innovative approach not only establishes a local market for recycled plastics but also fosters a circular economy, promoting sustainability at its core.

My passion for mitigating environmental harm and safeguarding public health has been the driving force behind my exploration of plastic repurposing in road construction. By embracing plastic roads, we take a significant step towards minimising environmental impact, creating cleaner, safer, and healthier urban and rural landscapes. Together, we can pave the way for a more sustainable future.

Can you describe how plastic roads compare to traditional asphalt roads in terms of durability, cost, and environmental impact?

Plastic roads are more durable, less expensive, and better for the environment than traditional asphalt roads. By incorporating up to 10% recycled plastic, these roads become more resistant to cracks and potholes, reducing damage by up to 75% and potentially extending the lifespan of plastic roads significantly. Plastic roads benefit the environment by reducing the carbon footprint as they use recycled plastic waste. 

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What challenges did you encounter during the research and development phase of this project?

Major challenges during the plastic road project's research and development phase: 

• Material Selection 
• Optimisation of Mix Design 
• Evaluating Asphalt Plant’s Mixing Capability 
• Performance evaluation.

Achieving the desired mechanical properties without compromising durability involved extensive laboratory testing to identify the plastic grade and proportion of recycled plastics. Adjustments in temperature and mixing time were crucial during the mixing process due to varying melting points and bitumen compatibility, ensuring a homogeneous blend.

Maintaining the softening temperature of plastics below the threshold during plant mix was critical to prevent the release of dioxin and uphold environmental safety standards. Performance tests, including rutting, cracking, and moisture susceptibility analyses, were essential but time-consuming, necessitating specialised equipment for accurate evaluation. 

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Are there any specific types of plastics that work best for this application?

Based on an extensive experimental program and performance evaluation, Low-Density Polyethylene (LDPE) (including one-time used plastic bags), High-Density Polyethylene (HDPE), and Polypropylene (PP), were found to be most suitable for plastic roads. Interestingly, one-time use plastic bags are considered non-recyclable, and we used them for plastic road construction. 

Is the road material itself recyclable?

Yes, the road material made from recycled plastics is recyclable. Plastic-modified asphalt, like traditional asphalt, can be milled and reused in new road construction projects as reclaimed asphalt pavement (RAP). This process saves raw materials, reduces energy consumption, and lowers greenhouse gas emissions associated with the production of new asphalt.

How does the plastic road material work to fill surface cracks and reduce rutting?

Extensive experiments were conducted to evaluate plastic roads performance against cracks: (1) Thermogravimetric Analysis (TGA), (2) Derivative Thermogravimetry (DTG), and (3) Dynamic Vapor Sorption (DVS) analyses. TGA results show improved thermal stability, with higher decomposition temperatures allowing the asphalt to withstand elevated temperatures without softening, reducing rutting and allowing the surface to resist cracks. DTG analysis reveals a slower decomposition rate, indicating better bonding between plastic and bitumen, improving the material's ability to absorb stresses and prevent crack propagation. This is also backed up by the results from the Texas Overlay Tester (TOT), where plastic road mix showed significant improvement from the control mix regarding thermal and reflective cracking. Furthermore, DVS analysis reveals lower moisture affinity of the plastic-coated aggregates, which reduces water-induced damage such as stripping and pothole formation while maintaining the asphalt's consistency and flexibility.

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How does weather, such as Texas heat, affect the performance of plastic roads?

Based on the performance evaluation of plastic roads at the University of Texas at Arlington (UTA) campus, the extreme heat in Texas has an insignificant effect on the performance of plastic roads, as no signs of thermal distress were observed during the last 20 months of performance evaluation. Similar performance was observed for the plastic road constructed in Dhaka, Bangladesh. During the hottest summer (in the last 50 years) in April 2024, many traditional asphalt roads in Bangladesh began to soften and melt due to extreme heat, whereas the plastic road section had no visible distress and showed heat resilience. The superior thermal performance and durability of plastic roads is making them a dependable and sustainable solution for regions with extreme weather conditions.

How did you select the area for the first implementation project?

Jennifer Cowley, President of the University of Texas at Arlington (UTA), wanted to build the first plastic road in Texas on the campus so that the plastic road can be used for demonstration of sustainable practices at UTA Campus. That’s how we choose the location to build the first plastic road at UTA campus in Texas. 

Are there more areas where your plastic roads have already been built?

In addition to plastic roads at the University of Texas at Arlington (UTA) campus, plastic roads have been successfully constructed at two districts in Bangladesh. Bangladesh Roads and Highway Department (RHD) helped us build the first plastic road section in Dhaka, Bangladesh. As Dhaka, capital of Bangladesh, is easily accessible for policymakers and government officials to visit the site, Dhaka was selected for the first plastic road section in Bangladesh. The second site, just outside Dhaka (Cumilla) is more susceptible to flooding and was constructed to evaluate the performance of a plastic road under flooding conditions. 

How responsive is the industry to new ideas like that?

The pavement industry is becoming more interested in plastic roads as the emphasis on sustainability, cost-efficiency, and durability is getting more focus. With growing pressure to reduce carbon footprints and manage plastic waste, industry stakeholders such as government agencies, private contractors, and transportation departments are more willing to adopt innovative technologies that align with green infrastructure goals.

However, while pilot projects and research initiatives have gained traction, widespread adoption remains dependent on the development of standardised guidelines, demonstrated large-scale performance, and economic feasibility assessments. Before widely adopting new materials, conducting a feasibility study of plastic roads considering local conditions is a vital component for the successful implementation of plastic roads globally. 

What long-term benefits do you foresee for Texas and beyond if plastic roads become widely adopted?

The widespread use of plastic roads in Texas and elsewhere would result in numerous long-term benefits, including economic, environmental, and infrastructure advantages. The major advantages of plastic roads are:

• Reduce failure risks and maintenance costs of pavement and transportation infrastructure under extreme weather conditions (extremely elevated temperature, heavy rainfall, cold and icy conditions),
• Tackle climate change (reduction of greenhouse gas emission) by using recycled Plastic waste instead of virgin construction materials and convert plastic pollution into a sustainable solution,
• Promote circular economy,
• Create a local market for recycled Plastic and green jobs and elevate the quality of life,
• Align developing countries with the Global SDG strategic goal of Climate and Sustainability through climate change adaptation.

The increased durability of plastic roads would result in remarkable cost savings by reducing the need for frequent repairs and maintenance. This has the potential to reduce the Texas Department of Transportation (TxDOT’s) road maintenance budget and to fund other critical infrastructure projects. By using recycled plastics in road construction, Texas could address its plastic waste management issues while also lowering greenhouse gas emissions associated with new asphalt production, in line with climate action goals.

Furthermore, plastic roads can withstand extreme weather conditions found in Texas, such as elevated temperatures, reducing the occurrence of cracks, potholes, and rutting. Their adoption would result in increased road safety, better driving conditions, and fewer traffic disruptions caused by maintenance work.

Are there any regulatory or logistical hurdles that need to be addressed before widespread adoption?

The widespread use of plastic roads faces a few regulatory and logistical challenges that must be addressed to ensure successful implementation. The lack of standardized guidelines for plastic-modified asphalt, including plastic content, volumetric and performance criteria, is a significant barrier. Solid Waste Institute for Sustainability (SWIS) at UTA is working with local transportation agencies to develop guidelines for plastic road design and construction in Texas, which can be used nationally.  

Establishing a dependable supply chain for collecting, processing, and transporting suitable plastic materials (such as LDPE, HDPE, and PP) is critical. 

Overcoming these barriers will necessitate collaborative efforts from regulatory bodies, industry stakeholders, and research institutions to develop standardised protocols, improve recycling infrastructure, and conduct large-scale pilot projects, paving the way for the long-term and cost-effective integration of plastic roads into modern infrastructure.

What are the challenges for a large-scale production?

The major challenges for large-scale production and implementation of plastic roads are developing construction guidelines and enforcement of including plastic waste in pavement construction by regulators and policymakers. The absence of standardised guidelines for plastic content, mixing processes, and performance benchmarks makes acceptance by the government agencies and the private sector quite difficult. Training asphalt plant workers is necessary for the success of the new idea and technology.

How does this initiative contribute to a circular and green economy?

The use of recycled plastics in road construction makes a significant contribution to the circular and green economy by encouraging sustainable waste management, resource efficiency, and environmental protection. This approach converts plastic waste, which would otherwise end up in landfills and pollute the environment, into a valuable resource for infrastructure development. Incorporating plastics such as LDPE, HDPE, and PP into asphalt mixtures reduces the demand for virgin petroleum-based materials, lowering the carbon footprint of road construction. Furthermore, plastic-modified asphalt improves road durability and lifespan, requiring fewer repairs and using fewer resources for maintenance activities. This results in lower energy consumption and greenhouse gas emissions throughout the pavement's lifecycle. The process also promotes energy efficiency by melting the plastics at controlled temperatures below dioxin emission levels, ensuring environmentally safe practices. On a larger scale, widespread use of plastic roads would promote a circular economy by creating new markets for recycled materials and stimulating green job growth in the recycling and road construction industries.

What role do you see plastic roads playing in developing countries, and what came out of your discussions with the World Bank?

In future, plastic roads will be part of the transportation infrastructure in most developing countries, both in rural and urban areas. This will create green jobs and promote a circular economy for those countries. Based on the performance evaluation results and a recently completed workshop on plastic road for the World Bank, Dhaka, WB is interested in plastic road projects and may consider doing pilot projects in several South Asian countries. 

Beyond road construction, what are some other infrastructure applications for recycled plastics?

Beyond road construction, recycled plastics have a wide range of applications in infrastructure, providing sustainable, long-lasting, and cost-effective solutions. One notable application is the use of recycled plastic pins (RPP) alternative to traditional soil and slope stabilisation methods. These pins, made from recycled plastic waste, help to reduce waste and promote a circular economy by reusing materials that would otherwise end up in landfills or oceans. They are known for being lightweight, durable, and corrosion-resistant, making them ideal for use in geotechnical engineering construction. Because of their ability to withstand harsh environmental conditions without degrading and capable of excellent load-bearing capabilities, RPPs are being widely used in construction for soil and slope stabilisation in Texas.

Another impressive innovation is plastic bricks and pavers, which are lightweight, weather-resistant, and long-lasting, making them ideal for footpaths, driveways, and housing projects, especially in low-income neighbourhoods. Plastic lumber, made from recycled plastics, is an environmentally friendly alternative to wood for fencing, decking, and park benches, offering rot-resistant and low-maintenance options.

In drainage and piping systems, recycled plastics are used to make corrugated pipes that are corrosion-resistant and last longer than traditional materials. Recycled plastics are also used to make railway sleepers, which are more durable, termite-resistant, and require less maintenance than traditional wooden or concrete sleepers. Plastics are lightweight, durable, and effective noise-reducing materials for highway sound barriers.

Are there any drawbacks or potential concerns with using plastic in road materials?

While plastic roads have significant advantages, a major concern is the potential release of microplastics from the pavement surface. However, based on our research on samples collected at the laboratory and from the field, microplastic release from plastic roads is not significant and below the threshold risk characterisation ratio.  The lack of standardised guidelines for plastic-modified asphalt, including plastic content, volumetric and performance criteria, is a significant barrier. Solid Waste Institute for Sustainability (SWIS) at UTA is working with local transportation agencies to develop guidelines for plastic road design and construction in Texas, which can be used nationally and globally.