Emergency response?
Plans for this test section began well before 2011, and the site was originally used as part of an emergency paving demonstration for the Department of Homeland Security through Oak Ridge National Laboratory’s SERRI program. The purpose of originally building the full-scale test sections was to prove the concept that asphalt paving could be more effectively used in response to disasters such as hurricanes where power and infrastructure are often lost for a period of days to weeks over a widespread area. The original study utilized warm-mix technology (WMT) to show that haul distances easily exceeding six hours could facilitate producing asphalt far from the disaster where power and infrastructure were not damaged, and effectively using that material for paving the way into the disaster zone so that all other essential functions that make use of a functional path into the area can be less affected than in previous disasters. Once the emergency paving research and demonstration had successfully completed, the Figure 1 parking lot had been paved with 12 strips of asphalt with different WMTs, different haul times, and compacted to different air void levels.
Within days of completing the emergency paving demonstration, some participants began discussing the value of this as a longer-term aging site, especially since raw materials such as binder had been individually sampled during paving. These plans materialized quickly, and specimens began to be extracted from the parking lot (cores and slabs) for unaged assessments (November 2011). These unaged specimens have been evaluated relative to specimens aged over time at the test section, with most assessments being on specimens extracted from the section on a yearly recurring basis so they have received full yearly weather cycles (e.g., three years, four years; not 3.5 years or 4.6 years). Beginning in November 2012, gyratory-compacted specimens of a variety of additional mixtures began to be placed onto the test section in plastic sleeves.
Putting on the years
One of the major findings to date is the need to use combined effects damage mechanisms during laboratory conditioning to simulate longer-term aging in Mississippi. Table 1 shows several attempts to replicate the aging experienced in the field with laboratory protocols, and that the only manner that could consistently replicate longer lives was the one where oxidation (oven), moisture (64°C water) and expansion (freeze-thaw) mechanisms were present. Note that the first row of Table 1 is AASHTO R30, which is a current national standard method that did not simulate the duration of time claimed in the method (seven to 10 years).
Another major finding to date is that pressure-aging vessel (PAV) conditioning of binders via AASHTO R28 has used 20 hours of PAV time for several years under the premise that this would simulate five to 10 years of binder aging. Five combinations were evaluated in the field where corresponding raw binders were PAV-aged in the lab for up to 80 hours. The main finding was that only one of these five cases showed PAV conditioning for 20 hours actually simulating five years of field aging (less than five years was simulated in the remaining cases). When this finding is combined with Table 1, the overall assessment of the Columbus, Miss., experiment to date is that national laboratory conditioning protocols are not simulating as much field aging as one might expect at this location.
