Monday, October 15, 2012

Superpave Pilot Project Changes III

Welcome to our third post on the upcoming changes to the Caltrans specifications that are coming about with the instituting of Superpave.  The first post, Changes I, focused on changes to the paperwork and paving procedures.  The second post, Changes II, focused on changes that affect the operations group at hot mix asphalt plants.  This post will focus on the changes that will affect you if you produce RAP and add it to hot mix asphalt.

RAP (Recycled Asphalt Pavement)
  • Where RAP is applicable, it will now be included in mix designs at 25 ± 1%.  In many jobs 25%, not up to 25% will be required.  This is a big change from Caltrans' previous maximum of 15%.  
  • During production, you will now only be able to vary the RAP content by 3%.  This may cause a problem from those of you who use your feeder settings as a way to regulate your gradations and oil contents.  It is another specification that Caltrans is instituting to encourage producers to regulate their mix BEFORE it hits the hot plant, IE during aggregate, or in this case RAP, production.
  • For surface courses, Caltrans will allow a 25% binder replacement and the contractor has the option to bump down the virgin binder grade.  In lower courses, Caltrans will allow up to 40% binder replacement but a bump down in virgin binder grade will be required.  Since the binder in RAP is weathered and oxidized from years exposed to the elements, the binder is stiffer than a virgin binder would normally be.  When a higher content of RAP is added to a hot mix, the mix itself gets stiffer due to the recycled binder. The bump down in virgin binder allows the mixture of recycled binder and virgin binder to retain a stiffness that is still workable and long lasting.  This is one area that your operation will want to examine costs on.  Although you are saving money on using RAP in the mix, depending on the cost of the softer binder, you may end up spending more money on a higher RAP content mix than a standard 25% RAP mix.   
  • RAP must now be fractionated into + #4 and - #4 piles.  You can no longer use one size RAP if it includes sizes from both + #4 and - #4.  You will now need two separate RAP piles and two separate RAP feeders.
  • There are now tighter variances on your RAP stockpile testing.  The binder can only vary  ±2% throughout the pile and the RICE Specific Gravity variance  is now Gmm±0.0600.  
  • Despite the new variances, you can still have live RAP piles but you will need to do frequent testing to verify the variances are within specifications.
There have already been some industry complaints regarding several of these RAP specifications.  I will mention again that if you feel that your plant will NOT be able to meet some of these specifications start recording data to prove it NOW.  Caltrans is open to adjusting these specifications but industry will have to prove its case.  Step up and do so. 

We've started a forum for discussing the upcoming changes here: Superpave Discussion Forum.  Please feel free to post any of your questions, opinions, and concerns.  Utilize this area to discuss your findings and work with other companies to make the changes you feel are needed. 

Our next Superpave post will focus on the changes that are coming to Mix Designs and Verifications.  Stay tuned!

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