VAA Virginia Asphalt Fall/Winter 2019

18 FALL/WINTER 2019 David T. Lee, P.E., Vice President of Engineering, Virginia Asphalt Association FINDING THE RIGHT BALANCE Balanced Mix Design Pilot Program Virginia continues to help lead the national effort towards Balanced Mix Design (BMD). As part of Virginia’s journey, the Virginia Department of Transportation (VDOT), the Virginia Transportation Research Council (VTRC), and the Virginia Asphalt Association (VAA) embarked on a pilot program in 2019. As a largely voluntary effort, a num- ber of producers/contractors in Virginia stepped up to assist in this significant undertaking. In 2019, Superior Paving Corp, a producer in Gainsville, VA, and Boxley Asphalt, a producer in Lynchburg, VA, were the contractors who agreed to run the initial phase of the pilot. Virginia’s BMD focus has centered around three specific tests: the Ideal CT (ASTM 8225-19) for cracking, Cantabro (AAS- HTO TP-108) for durability, and Asphalt Pavement Analyzer, or APA (AASHTO T340-10), for rutting. The pilot program is also broken down into multiple elements. These include control mixes which are designed and produced in accordance with VDOT’s standard mix design and production requirements; pilot mixes designed and produced in accordance with VDOT’s mix design procedures with BMD testing; and pilot mixes that are designed, produced, and tested solely based on BMD optimization. The initial phase of this pilot focuses on the use of high recycled asphalt pavement (RAP) contents in asphalt mixtures. For purposes of this pilot, high RAP is defined as mixtures containing 40% or greater RAP. These higher RAP contents are typically accomplished in a number of ways. Meth- ods include the use of “rejuvenators” to reactivate the RAP binder (in conjunction with a typical PG64-22 base binder) and the use of softer base binders such as a PG58-22 or PG58-28. Superior Paving Corp Bull Run Pilot Effort Superior Paving Corp began the first BMD/high RAP pilot project in June of this year using both of the referenced methods. This effort utilized an SM-9.5A control mix with 30% RAP and PG64-22, a 40% RAP mix with a rejuvenator, a 40% RAP mix with PG58-28, a 40% RAP mix with PG64-22, and a 30% RAP mix with PG58-28. These mixtures were produced at their state of the art Bull Run facility in Chantilly, VA. Aside from the standard asphalt content, gradation, and volu- metric testing, all previously referenced specific BMD tests were performed. Both Superior and VDOT/VTRC are performing the referenced testing. So far, test results are favorable with both Ideal CT, Cantabro, and APA tests passing their preset targets. Superior’s initial test results indicate average Ideal CT results ranging from 99.1–183.2 (minimum is 70) and Cantabro results ranging from 3.2–4.4 (maximum is 7.0). Additionally, VDOT/VTRC so far report similar results with Ideal CT tests ranging from 101–136 and Cantabro tests ranging from 3.5–4.2. VTRC is also performing APA rut testing with as-designed results ranging from 4.8mm–5.2mm. Danny Poole, Superior Paving’s Director of Quality Assurance, shows reserved optimism following this initial phase of work, saying, “We are pleased with the initial results from our pilot work at the Bull Run plant. The fact that we are able to meet all of the preset targets with each of the mixes is encouraging.” Superior Paving Corp Powell Lane Pilot Effort The second phase of Superior Paving Corp’s effort moved to their Powell Lane Plant in Fredericksburg, VA. This time they focused primarily on the use of var- ious rejuvenators. This effort utilized an SM-9.5D control mix with 30% RAP, a 40% RAP mix with PG64-22, a 40% RAP with Rejuvenator A, a 40% RAP with Rejuvena- tor B, and a 40% RAP with Rejuvenator C. All mixes used a PG64-22 liquid asphalt. The mixtures were laboratory prepared and tested with no plant production to date. Aside from the standard asphalt con- tent, gradation, and volumetric testing, all previously referenced specific BMD tests were performed. It is noteworthy that all Ideal-CT tests failed to meet the minimum target of 70. Additionally, all but one of the mixes failed the Cantabro test. As with the other pilots, both Superior and VDOT/VTRC are performing the referenced continues on page 20 △ Superior Paving Corp - Bull Run Mix Ideal-CT Cantabro SM-9.5A Design Production Design Production 30% RAP Control 60.5 127.6 7.1 4.4 40%RAPw/Rejuvenator 104.6 110.7 4.0 3.4 40% RAP PG58-28 73.5 99.99 4.0 4.1 40% RAP PG64-22 111.0 99.1 5.5 4.6 30% RAP PG58-28 157.4 183.2 3.5 3.2