Plastics in the Infrastructure Conversation
BY Ben Scott, Ph.D.
Pundits anticipate state departments of transportation (DOTs) should see their first round of funds from the historic Bipartisan Infrastructure Bill (BIL), which became law in November, by third quarter this year. (See the article “Infrastructure Law Presents Construction Opportunity” in the February 2022 issue.)
Let us consider the opportunities the bill provides to advance new technologies that will allow us to build a more sustainable and resilient infrastructure, while also addressing rapidly emerging climate and sustainability challenges. Now is the moment we can set our sights on vetting and implementing sustainable infrastructure solutions, such as the use of recycled plastic waste in asphalt, as funding is dispersed.
The use of recycled waste plastic products in asphalt mixes has recently captured the attention of the Federal Highway Administration (FHWA) as well as many state DOTs. Climate-conscious agencies and asphalt professionals are exploring the use of a range of recycled plastic waste products to serve as additives in asphalt formulations. GreenMantra, like other recycled plastic waste product manufacturers, understands that demonstrating beneficial use in asphalt is key. Testing to demonstrate performance of products and blending methods is at varying stages today. However, if GreenMantra’s early testing success is any indication, the future for the use of recycled plastic waste in asphalt is bright.
As a “newer” product to asphalt roadways, GreenMantra had the benefit of being used in asphalt shingles for years. Given the known performance of recycled plastic waste products in asphalt shingles, making the leap to exploring roadways seemed like a logical next step. GreenMantra began performing asphalt roadway testing of its CERANOVUS® product about eight years ago but, in the last two years or so, has ramped up studies both internally and by working with the National Center for Asphalt Technology (NCAT).
The first tests performed by NCAT were focused on storage stability, showing CERANOVUS polyethylene specialty waxes are 100% compatible with, and miscible in, the liquid asphalt binder. NCAT conducted the standard 48-hour static conditioning per ASTM D7173 to determine the stability with dosages up to 3%.
Additional testing showed uniform distribution at dosages up to 4%. Once CERANOVUS waxes are incorporated, they remain stable in the binder, with minimal separation tendencies. This was confirmed via internal extended storage stability studies using the standard 48-hour static conditioning and softening point testing per ASTM D7173 and ASTM D36, with results shown in Figures 1 and 2 below.
It is important to settle concerns over microplastics within the use of recycled plastic modified (RPM) asphalt. In the wet blending process, the goal is that all additives, including recycled plastic waste products, maintain uniform dispersion in the binder. Over time, undispersed plastic particles may phase-separate and agglomerate near the surface, creating a potential for performance problems as well as allowing for small plastics to break away.
In laboratory testing, GreenMantra’s CERANOVUS A115 product maintained dispersion and created a homogenous mixture with the liquid asphalt binder, with no phase separation occurring. This was demonstrated by Fluorescence Microscopy (FM) testing. FM is a scientific method that uses UV light to analyze the miscibility of components. It is widely used to analyze polymer distribution and miscibility in asphalt binders. Dispersed materials are largely unseen, while undispersed agglomerated particles appear as light green in the dark binder.
FM tests were performed by NCAT using a Ziess Axiovert 200 Inverted Fluorescence Microscope. Figure 3 shows the FM analysis of 3% unmodified recycled polyethylene plastic in a PG64-22 binder, demonstrating a high level of undispersed, agglomerated plastic particles. In contrast, Figure 4 shows the complete homogeneity of 3% CERANOVUS A115 wax in a PG64-22 binder. These findings indicate that recycled plastic waste alone may need an additional additive to help maintain dispersion, whereas waxes can be easily dispersed and do not phase separate.
The benefits for recycled plastic wastes and additives are being tested, from enhancing asphalt product performance, improving the sustainability profile, and in some cases, providing lower energy consumption through cold temperature processing. Using recycled plastic waste products also results in a reduced consumption of fossil fuel-based products and diversion of plastic waste from landfills and our environment. Since the initial testing two years ago, GreenMantra has continued to build data on asphalt performance, carrying out lab-scale tests necessary to move to large-scale demonstration.
Proving and Advancing
As mentioned, the performance and evaluation of RPM is in varying stages for different products and blending methods. The industry would benefit from a coordinated approach to testing. Beyond lab testing, a series of demonstration projects are taking place around the United States. GreenMantra has worked with partners in North America—such as the City of Vancouver, Shell Chemicals, Nova Chemicals, Chevron Phillips Chemical, the Pennsylvania DOT and others—to test and validate its products. While there is still much work to be done in North America to advance RPM asphalt, key stakeholders like NAPA and NCAT are leading an excellent initiative to educate the asphalt industry about the successes (and failures) from use cases so state and local decision makers can continue to innovate and expand the use of RPM asphalt.
There are currently materials being tested from mechanically recycled processes, and materials derived from advanced recycling technologies. Advanced recycling is a class of technology that is relatively new to the world. GreenMantra uses these technologies, employing a patented technology that transforms waste plastic into sustainable specialty polymer additives to enhance infrastructure products. Advanced recycling can overcome some of the technical limitations that exist with mechanically recycling plastics. This means communities will be able to create beneficial uses for plastics that were previously destined for the landfill or polluting our environments.
Over the course of 2020-2021, as part of the additive group phase 1 experiments, NCAT confirmed that GreenMantra’s recycled polyethylene waxes enhance asphalt performance, creating the potential for a 10% thinner asphalt pavement while delivering the optimum performance of a standard asphalt pavement. Results for these studies will be released soon and GreenMantra has entered into a multi-year service agreement with NCAT to complete ongoing testing that validates the long-term performance of GreenMantra’s CERANOVUS specialty waxes in asphalt.
With the new infrastructure and appropriations bills in place, we are at an exciting nexus of innovation and investment when it comes to advancing infrastructure in the United States. Transportation agencies are being given a unique opportunity to invest in new, sustainable technologies at an unprecedented scale. For the asphalt space, that means an opportunity to accelerate the use of sustainable asphalt products. Recognizing the innovative potential of RPM asphalt, state and local agencies will play a critical role in expanding the use of these formulations.
Together, we can go farther, be better, and do good.
Ben Scott, Ph.D., is the director of technology for GreenMantra Technologies, Brantford, Ontario.