MIX IT UP
GTR in SMA Makes Missouri Job Special
Here the N.B. West crew has closed down one ramp for nighttime mill and fill work on I-44 going over the Meramec River Bridge. Photo courtesy of N.B. West personnel BY SANDY LENDER
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or a single-lift, mill and fill project on Interstate 44 (I-44) during 2020, the team at N.B. West Contracting, Pacific, Missouri, made great use of the Missouri Department of Transportation’s (MoDOT) performance job special provision (JSP). The state didn’t exactly have a balanced mix design (BMD) spec, per se, at the time, but used the performance JSP to allow contractors to influence multiple facets of a mix—achieving cracking and rut-resistance characteristics and meeting volumetric specs during design and production. To share their process and success incorporating ground tire rubber (GTR) in a stone mastic asphalt (SMA) design, Quality Control Manager Joe Schroer, P.E., and General Manager Steve Jackson, P.E., discussed the project. Schroer had worked with recycled materials in roadways at MoDOT before joining the N.B. West team in 2014, thus he is wellversed in the department’s design process and performance goals. He spoke of the JSP allowing GTR for the I-44 project bringing new technology to the table, which is in accordance with the Federal Highway Administration’s (FHWA) Every Day Counts program. N.B. West incorporated Elastiko® ECR, an engineered crumb rubber product from Asphalt Plus, Barrington, Illinois. 10 | JANUARY 2022
“I had suggested the idea of using a GTR process to enhance the performance of the SMA after visiting the Asphalt Plus and Liberty Tire booths at the 2019 World of Asphalt,” Schroer explained. “I was interested in the dry process of adding the GTR due to ease of adding the product and it not requiring the blending tank and agitation generally associated with GTR use in the past. Plus, only one binder grade would be required to fill multiple roles at the plant.” The dry process removes terminal blending and multiple liquid storage tanks from the equation. The Asphalt Plus blog explains that a chemically-engineered crumb rubber product is fed into the plant—like a fine aggregate—at the production stage. The heated AC then reacts with the crumb rubber product during mixing, storage and transport to the paving site.
They produced the mix at their new Astec portable Double Barrel™ with V-pack™ at its St. Clair location. Damon Feldman was the plant operator who executed production while implementing a performance job special provision. The team ran Hamburg Wheel Tracker tests and
