VAA Virginia Asphalt Fall/Winter 2019

VAASPHALT.ORG 23 Have you ever wished you could use your standard state DOT asphalt mixes for more airport paving projects? As of December 2018, this might just be possible! The Federal Aviation Administration (FAA) recently issued revised standard specifications for the construction of airports. This new standard, designated by the Advisory Circular (AC) 150/5370-10H, contains significant changes from the previous version (-10G). These changes include several revisions, on items such as improved minimum lift thickness guidance and the new, more complex loaded wheel test (APA) requirement for mix design. This article breaks down just a few of these asphalt-related changes; however, it’s always recommended that each contractor review the 700-page AC document in detail. Loaded Wheel Test First, let’s discuss the most significant changes to P-401 mix design requirements. As many of you are aware, P-401 is the primary designation for asphalt mixes used on aviation projects. This new standard includes a number of adjustments. One of the most signif- icant is the inclusion of a new loaded wheel test requirement to mix design (401-3.3 Table 1). The loaded wheel test, otherwise known as the Asphalt Pavement Analyzer (APA), is used to determine the rut susceptibility of an asphalt mixture. As with previous iterations of the job mix development, the Job Mix Formula (JMF) must be prepared by an accredited laboratory. The APA results (< 10 mm rutting @ 4000 passes), tested in accordance with AASHTO T340, must be included with the design submittal. Given there are a lim- ited number of APA’s around the country, this will not only require substantially more lead time to complete the testing but may also require the use of a third-party testing laboratory. Gradation Bands One of the seemingly basic changes to the specification is the adjustment to the gradation bands for P-401 mixes (401-3.3 Table 2). These adjustments are necessary to bring the gradation bands for P-401 mixes and military aviation projects in line with one another. Certainly, this change offers the ability to minimize the number of mix designs a contractor needs to develop each year. However, it is noteworthy that nearly every gradation band has changed to some degree. As such, the mix designer needs to review the changes care- fully to ensure compliance. Required Grade Bump Table Mix design has also changed in respect to specifications related to liquid asphalt PG grade selection guidance. In particular, the “Required Grade Bump” table in 401.23 (1) now includes a section for “Pavement area with slow or stationary aircraft.” This table high- lights the required grade bump for three Aircraft Gross Weights. As with the previous guidance, the grade bump only applies to the high temperature, not the low temperature side of the grade. Mat Density Concurrent to mix design, specification changes place a great emphasis on contractor quality control requirements. A key change in the specifications is related to the determination of mat density. Past versions of this specification used the bulk specific gravity of laboratory specimens to determine in-place density (401-6.1 (4)). “Mat Density” of the revised specification now utilizes the AIRPORT PAVING