NRRA Flexible Team Field Tests Recycling Agents

During the 21st annual conference and workshop for the Association of Modified Asphalt Producers (AMAP), Michael Vrtis, Ph.D., of Minnesota Department of Transportation (MnDOT), shared with the audience two preservation research projects performed in the state.

This article shares information from the National Road Research Alliance (NRRA) Flexible Team’s recycling agent field study specifically.

The May issue of AsphaltPro included information in the article MnROAD Tests Cracking on 70th Street from cold recycling techniques performed on 70th Street. Vrtis presented both of these Feb. 13.

The two projects Vrtis discussed were done in unique partnerships with MnDOT and industry: one with the National Center for Asphalt Technology (NCAT) and Buzz Powell for the pavement preservation study; and one done with the National Road Research Alliance (NRRA). NRRA is comprised of 10 different state agencies. Eight state departments of transportation, the Illinois Tollway and the Minnesota Local Road Research Board make up this pooled fund, but it also includes 50+ industry and academia members. The point Vrtis found important to make is “We can’t and shouldn’t be building roads on our own. We need to be learning from our neighbors and we need all the stakeholders involved…At the end of the day, we’re all trying to make better roads and better products.”

All of the work done on this project was done under the NRRA’s Flexible Team. Agency and contractor members as well as industry and academia were on this team to take an existing project and turn it into a demonstration—or research—project to gather data in addition to preserving a roadway. The contractor performing the work was Anderson Brothers Construction, Brainerd, Minnesota, on a project in MnDOT District 3. Vrtis spoke highly of the contractor saying, “Anderson Brothers really made this project possible.” The project began in winter 2019 with a callout for asphalt rejuvenator—or recycling agent—suppliers to participate if they wished. Anderson Brothers calculated the cost of performing the changes to the job and those costs were split evenly among the seven rejuvenator suppliers who elected to participate.

Vrtis’ colleagues recognized that the use of recycling agents is an emerging technology in HMA used to increase recycled asphalt content in mixes, but especially at the DOT, they’ve seen a lot of producers, sources and salespeople coming to them wanting to get various products incorporated into recycle jobs. Vrtis pointed out: “There’s a lot of research going on with rejuvenators, but a lot of that is primarily laboratory-based.” The researchers wished to add field performance testing to the knowledge base.

“We used a lot of the tools that we used to monitor performance at MnROAD to monitor progress here.” It was the intent to blend inline each rejuvenator at the hot-mix asphalt (HMA) plant as that was the easiest process to handle the logistics of having seven different products, but one product was best handled by blending at the terminal.

The NRRA Flexible Team wanted to answer:

1. Can mix rejuvenator be incorporated into the HMA plant and construction process?
2. How well do these products perform in real world construction?
3. What are rejuvenators doing to our asphalt and how long does it last?

Along trunk highway 6 (TH6), the 13-mile project stretched from south of Emily to Outing, Minnesota. The contractor performed 2 inches of mill and fill, then placed 1.5 inches wearing course overlay with rejuvenators dosing mixes that included 40 percent reclaimed asphalt pavement (RAP). All the research sections were placed in the southbound lanes.

The mix testing was done with the state agencies, but the binder testing and comparison of how the rejuvenators perform long-term will be part of a $100,000 research findings contract let in February. At this time, from the 300+ buckets of mix collected during construction, states are performing the following tests:

• MnDOT: DCT and Hamburg
• Illinois: I-FIT
• Missouri: TSR
• Wisconsin: IDEAL CT
• And more to come

Vrtis made it clear that this project is “not a direct comparison or ranking of product performance, but a comparison of each product to the control section. In reality, with the location, what we’re expecting, field wise, is more of a mix durability type of assessment.” They expect reflective cracking to occur and want to learn how well the mix “holds together” over the years.

“We had seven different products there; we had pine-based products, corn-based products, soy products,” Vrtis said. “Anderson Brothers did a good job of knowing their plant; each one of these has a slightly different viscosity, a slightly different dosing rate. The contractor was able to keep each supplier and producer happy. Anderson worked great dialing it in and then calling us to let us know it was dialed in.”

Bob Kluttz from Kraton Polymers concurred, saying, “They did an excellent job of monitoring. They had an ammeter on the pump. They were monitoring the levels of drop in each of the totes. When they did ours, their calculated dose rate was within a tenth of a percent of what we asked for.”

Even though the project took place in northern Minnesota, the binder specified for the original project was a PG58S-28 unmodified. “LTTP Bind tells you that you need -34 and -40 for this location, but for Minnesota, we used a -28 on this job. We’re expecting it to have reflective cracking no matter what binder we put in.”

“We had a lot of discussion on what the target dosage of rejuvenator would be.” They settled on a -34 low temperature grade based off of what would be collected from plant-produced pressure aging vessel (PAV) samples. “The feedback we got from producers was that’s higher than typical dosage; the feedback we got from academia was that producers tend to under-dose these.” Because the team started with a “pretty good, pretty soft RAP,” they anticipated—and experienced—having some extra rejuvenator in the mixes. They considered that a bonus.

Construction took place at the end of August 2019 and Vrtis reported there were no major issues during construction. The crew reported no unpleasant smells, stating one section had a touch of a “piney” scent, but even that wasn’t overwhelming. Rolling patterns remained consistent. “All suppliers were happy with their test sections,” he said.

Since construction, initial testing with Gmm has already occurred and ride has been measured twice in the fall of 2019 with the digital inspection vehicle. “We cored sections six weeks after construction for future binder testing.” The RFP for binder testing and long-term evaluation closed in February.

When Vrtis traveled to the project site to get pictures in January 2020, he was pleased by the smoothness of the drive. “Driving into the project at 60 miles an hour, it was very smooth. It looked perfect.” When he turned around to drive the shoulder of the project at a much slower speed, he became aware of “sporadic reflective cracking in each of the test sections and control sections. My takeaway is, we drove in, and couldn’t feel any cracks.”

Participants:

Section 6001 includes Cargill Anova 1815 Rejuvenator
Section 6002 includes Poet JIVE
Section 6003 includes U.S. Soybean Board’s Sub Epoxidized Soybean Oil (SESO)
Section 6004 includes Ingevity’s WMA Evoflex CA-17
Section 6005 includes Kraton Polymers US LLC’s SYLVAROAD™ RP1000 Performance Additive
Section 6006 includes Asphalt and Wax Innovations’ PAVSAV
Section 6007 includes Georgia Pacific’s TUFFTREK 4002 Renewable Oil Technology (this was terminally blended with a different binder source)
Section 6010 control section using 30 percent RAP
Section 6011 control section using 40 percent RAP on day 1
Section 6012 control section using 40 percent RAP on day 2

Source: Michael Vrtis, Ph.D., is a research project engineer with Minnesota Department of Transportation (MnDOT) Office of Materials and Road Research (OMRR). For more information, contact him at Michael.vrtis@state.mn.us.