AASHTO PP78:17 (2020) StandardI Practice for Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in Asphalt Mixtures.
4. DESIGN CONSIDERATIONS WHEN USING RAS IN ASPHALT MIXTURES
4.1. The introduction of aggregate from RAS can have an effect on the gradation properties of the asphalt mixture. The designer must determine the particle size and percentage of shingle aggregate present and adjust the new aggregate composition accordingly.
4.2. The introduction of RAS may affect the asphalt hinder content requirements of a mixture. The designer must determine the new asphalt binder content of the asphalt mixture as part of the volumetric design procedure.
4.3. Although the amount of RAS in an asphalt mixture design is generally small, typically
3 to 5 percent by weight of aggregate, the non-asphalt components (aggregates and fibers) can have a significant effect on the mixture. Voids in the mineral aggregate (VMA) will generally increase due to the hard angular properties of the RAS granules as well as the presence of the fibers. Dust content of the RAS causes a reduction in VMA that is generally less than the increase from granules and fibers, resulting in a net VMA increase. Other properties influenced by the shingles include fine aggregate angularity and dust to binder ratio.
Note 2—The properties of RAS binder are much stiffer than paving asphalt binder. As a result. agencies typically limit the use of RAS to a maximum of 5 percent by weight of aggregate.
5. DETERMINING THE RAS AGGREGATE GRADATION AND SPECIFIC
GRAVITY
5.1. Collect a representative sample of RAS and proceed in accordance with T 164 or T 319 to extract the RAS asphalt binder or T 308 to ignite and remove the RAS asphalt binder and recover the RAS aggregate. The size of the sample should be such that the amount of RAS aggregate material recovered will meet the size requirements of the gradation procedure.
Note 3—Generally, 400 g of RAS is sufficient to provide the 300 g of aggregate needed for T 27. For T 3 19, extracting 400 g of RAS will meet the minimum sample size requirements. T 308 recommends a sample size of 1200g. however, the test should be run with 400 g of RAS. if the ignition oven ventilation system cannot handle the exhaust. the sample may need to be run in two parts and the results combined.
5.2. Determine the RAS aggregate specific gravity by determining the theoretical maximum specific gravity (G,,1,,,) of the RAS according to T 209 and calculating the effective specific gravity (Ga) of the aggregate according to Equation 1.AASHTO PP78 pdf download.