Asphalt in Depth’s RAP/RAS Session
Jun 24, 2011
The RAP/RAS session at NAPA's Asphalt in Depth conference included the following presenters; Kent Hansen with NAPA , Brad Bradford with R.K. Hall Construction, Joe Schroer with MoDOT and Scott Quire of the Frankfort Testing Laboratory.
Kent Hansen presented the NAPA Survey which is a collection of surveys on RAP/RAS/WMA use from contractors and asphalt paving associations in 48 states and provinces. From 2009 to 2010, there has been a 10% increase in RAP use and 57% increase in RAS use. The increase in RAP and RAS use has saved over 4 MT of binder. Of the WMA technologies used, 80% was foamed asphalt. There was an estimated 47.2 MT of WMA in 2010 compared to 2009 of 16.7 MT. That is a 180% increase in WMA!
Brad talked about R.K. Hall's practices for including RAP and RAS into a mix design. They use 75% effective RAS binder, a practice similar to NB West in Missouri. Scott Quire said there are a couple of different ways to calculate RAS binder into mix design. One of these methods was using the Availability Factor (AASHTO PP53).
Joe Schroer spoke about using Ground Tire Rubber (GTR). They use Transpolyoctenamer Rubber (TOR) to add a chemical link between the asphalt and GTR. He also went over the advantages and disadvantages of processing GTR at ambient vs. cryogenic temperatures. The ambient is harder to process but requires a lower percentage to reach the targeted PG grade. The cryogenic process is easier but requires a higher percentage to reach PG grade and it tends to fall out of suspension easier. He tested samples in a DSR with a 2mm gap and a 1 mm gap and the values were almost identical. There is a GTR section on the NCAT test track which has slightly less rutting than it’s SBS modified counterpart. The 2011 specification will require a chemical cross-link like TOR but they will evaluate other technologies.
Some of the other presentations were on best practices of constructing longitudinal joints, thin overlays, tack coats (and trackless tack), and the Every Day Counts Initiative.
Author: Jenna Michael