MIX IT UP
Plastics in the Infrastructure Conversation BY BEN SCOTT, PH.D.
P
undits 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.
DEMONSTRATE PERFORMANCE
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. Green12 | JULY 2022
Figure 1. Storage Stability of 2-4% CERANOVUS A115 wax in PG64-22
Figure 2. Extended Storage Stability of 2% CERANOVUS A115 wax in PG64-22
All illustrations appear courtesy of GreenMantra
Mantra 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%.
RECOGNIZING THE INNOVATIVE POTENTIAL OF RPM ASPHALT, STATE AND LOCAL AGENCIES WILL PLAY A CRITICAL ROLE IN EXPANDING THE USE OF THESE FORMULATIONS.
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 above.
MICROPLASTICS
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,
