Tuesday, March 6, 2012

Caltrans Revises CT 207 Again... March 2012 Changes

Many of us have expressed concerns with the new version of CT 207-Method of Test for Determining Specific Gravity and Absorption of Fine Aggregate that was released in September 2011. Specifically in regards to the major change in the test method where you would now need to wash the sample before testing. After a couple months it seems that Caltrans has now determined that this may actually be an issue. In recent communication, Joe Peterson, Caltrans' Chief of Roadway Materials Testing says:

"Our concern is that washing the fines produces an artificially low fine SPG and absorption value. Per AASHTO T 84 washing the fines over a #200 sieve can change the SPG value as much as 0.13 , depending on the percentage of P200's present. This in turn has a dramatic effect on the VMA of the mixture, driving the VMA value up 1-3 points. As a result of this we are starting to see a few JMF's that have adjusted their binder content down so their HMA meets minimum VMA requirements. This is producing an overly dry mix that could be subject to early age cracking, oxidation and premature failure. If the washing of the fines replicated production these would be valid values. To my knowledge most producers of HMA do not wash their fines prior to production."

Because of this, Caltrans has decided to change to using a hybrid version of the March 2000 test method and September 2011 test method of CT 207 for the immediate future while a task group reviews the test method and determines what changes would work best for California's roads.

The following changes can be seen between the September 2011 and March 2012 versions:
  • The mold sizes have returned to metric measurements although they are the same size molds.
  • The material is no longer washed over a #200 sieve before testing.
  • The material is now supposed to be soaked in water for a minimum of 15 hours (overnight) instead of 24hr±4 hrs. (The original wording from the Mach 2000 version)
  • After pouring off the free water, you can now dry the sample by spreading it on a smooth porous surface. In the Sept2011 version you were to spread it on a nonabsorbent surface. (The original wording from the Mach 2000 version)
  • The method for tamping is less strict. (The original wording from the Mach 2000 version)
  • The calculation for the bulk specific gravity reverted back to the original calculation that was used in the March 2000 version.
  • The rest of the test method has remained the same from the September 2011 version. 
You might be asking what you should do with all of the mix designs and tests you performed using the September 2011 version. For any projects that advertised during the period between September 2011 and February 2012 you will use the September 2011 version of CT 207. For any projects advertised starting in March 2012 you will use the March 2012 version.

This version is the March 2012 version and can be found on the Caltrans website and here.

*This entry was updated 8/22/12


  1. First off I would like to say that I enjoy your blog very much. It is very informative and well written. With that being said I would like to say that it is funny that CalTrans changed their minds so quickly. At the lab where I work, we had a training session on the "new" test method, and a lot of debate took place on whether or not the method was any good. Then a couple of weeks after that training, we got an email from our boss stating that the test method had changed. We now joke around calling the tests the "new-old" method and the "old-new" method.

  2. Thanks for reading! From the sounds of it, this test method change was out of the ordinary. The quick change may have been due to conversations with industry representatives. I'm not sure that Caltrans had a full handle on the effects that a major change to this test method would have throughout the state when they released it and caught many laboratories off guard.

  3. Just wanted to point out that the calculation for bulk specific gravity reverted back to what it was before 2011.

  4. Good catch Leif, thank you!!!