VAA Virginia Asphalt Spring/Summer 2021

VAASPHALT.ORG 31 packages that are being marketed nowa- days to alleviate the potential brittleness of asphalt mixtures, particularly those that might incorporate higher fractions of reclaimed asphalt pavement (RAP). Jhony, with help from VTRC field support, contractors, and Districts Materials staff, spent part of last season collecting raw material from typical Virginia sources (virgin aggregates, RAP, and conventional binder) for transport to Raleigh. Those materials are being blended with a spectrum of recycling agents (i.e., rejuve- nators and softeners) to create VDOT- representative mixtures that will be studied as a complete mixture, as well as indicative components (e.g., binder and mortar). Most of this year’s work will happen in laboratories in Raleigh and Charlottesville. With any luck, strong guidance on what types of recycling agents to accept/reject will emerge from this work as Virginia enters the initial implementation stages of BMD. Accelerated Testing of BMD Mixes Some of the most interesting BMD-related research is happening at the Virginia Smart Road in Blacksburg. VTRC is working with the Virginia Tech Transportation Institute (VTTI) to test a series of BMD mixtures under the Heavy Vehicle Simulator (HVS). Late last summer, Salem District worked with Boxley to place five experimental mixtures and a control section on the testbeds for the HVS. Loading started shortly thereafter, and we’ve already learned how easy it is to “over-juice” an asphalt mixture when trying to meet cracking performance, even one with 45 percent RAP. On the bright side, our performance tests (using the APA criteria) are showing good agreement with what actually happened under accelerated loading (Figure 4). Impact of Production Variability on BMD We’re also continuing to work with our old friend Ben Bowers (now at Auburn University) to understand how normal variation of mix properties during produc- tion ultimately impacts laboratory perfor- mance indicators. In the past two seasons, we’ve sampled, packaged, and shipped components from six Virginia mixtures to the laboratories at NCAT for Ben and his army of graduate students. Unfortunately, university campuses’ activity came to a screeching halt last spring, and testing to support that work is only now beginning to catch back up again. We expect consider- able progress this summer, and we’ll keep you posted. Reflective Crack Mitigation High Polymer (HP) Mixtures Beyond the work that directly supports the department’s move to BMD, we continue to develop more expertise with asphalt modifiers. A persistent application for high-performing (and modified) binders is mitigation of reflective cracking, especially over jointed concrete pavements. Among the tools that we’re studying are High Polymer (HP) and rubber modified binders. Numerous field trials for HP mixtures have been conducted in Virginia in recent years. Documentation of those trials, along with early-life in-service performance reviews and a wealth of related information from beyond Virginia, will be included in a report that we will release early this spring. Jhony Habbouche led this work with assistance from Ilker and Brian Diefenderfer. Rubber-Modified Mixtures Hari Nair and Shabbir Hossain are following two field trials with rubber-modified mixtures, both of which were placed in Richmond District in 2019. The first is a gap-graded rubber-modified mixture placed on southbound I-85 in Dinwiddie County over jointed concrete. This two-layer “wet” Figure 2: Recent VTRC Lab Upgrades—Bending Beam Rheometer (BBR), Rolling Thin Film Oven (RTFO), Pres- sure Aging Vessel (PAV), and Counter-Top Despatch Ovens VTRC PROGRAM OVERVIEW SPRING 2021 Figure 3: Assortment of Specimens Awaiting Testing continues on page 32 △