AASHTO PP 53:09(2012) Standard Practice for Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in New Hot Mix Asphalt (HMA)

AASHTO PP 53:09(2012) Standard Practice for Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in New Hot Mix Asphalt (HMA).
3. INTRODUCTION
3.1. Although RAS has been used as an additive in HMA in the United States for more than 15 years, it remains a relatively new application. As a result, there are design considerations that are not generally known to the specification user. Four separate areas are addressed by this recommended practice, with each elaborating on and providing recommendations relative to the following:
• Design Considerations When Using RAS in HMA;
• Determining the Shingle Aggregate Gradation and Specific Gravity;
• Estimating the Contribution of the Shingle Asphalt Binder to the Final Blended Binder in New HMA (Values ofF); and
• Determining the Performance Grade (PG) and Percentage of the Virgin Asphalt Binder in New HMA.
4. DESIGN CONSIDERATIONS WHEN USING RAS IN NEW HMA
4.1. The introduction of shingle aggregate from RAS will affect the gradation properties of the new HMA. The designer must determine the particle size and percentage of shingle aggregate present and adjust the virgin aggregate composition, if necessary. to ensure that the new 1-IMA meets the appropriate gradation requirements.
4.2. The introduction of RAS will affect virgin asphalt binder content requirements. The designer must determine the virgin asphalt binder content of the new HMA as part of the volumetric design procedure.
4.3. During the production of the new IIMA, shingle asphalt binder present in the RAS will mix with the virgin asphalt binder to produce a final blended binder. The properties of the shingle asphalt binder can be considerably different from those of virgin asphalt binder. If the quantity of virgin asphalt binder is less than 70 percent by mass of the total binder, the properties (PG) of the final blended binder may be measurably different from the design PG of the binder as specified by the local jurisdiction. In addition, the size of the RAS can be expected to affect the percentage of shingle asphalt binder that contributes to the final blended binder. For example, material that is ground to a size passing a 12.5-mm (0.5-in.) sieve can be expected to release lower levels of available shingle asphalt binder (20 to 40 percent) than RAS ground to a size passing a 4.75-mm (No. 4) sieve (as much as 95 percent available). The designer must be prepared to adjust the PG of the virgin asphalt binder to compensate for this effect.
4.4. The release of shingle asphalt binder into the virgin asphalt binder can result in reduced virgin asphalt binder requirements. It is unlikely, however, that all of the shingle asphalt binder will dissolve and blend with the virgin asphalt binder. Particles of undissolved shingle asphalt binder may act like aggregate particles that require more virgin asphalt binder to accomplish coating. Additionally, particles of shingle asphalt binder may absorb bituminous oils from the virgin asphalt binder. The location in an HMA plant where RAS is introduced into new HMA can also affect the binder blending process. This point of introduction must minimize damage to the RAS from excess heat and maximize the softening of shingle asphalt binder to facilitate the blending of the shingle asphalt binder with virgin asphalt binder.AASHTO PP 53 pdf download.