Friday, November 4, 2011

Caltrans' progress with Warm Mix and Hamburg Test

I was able to attend the California Asphalt Pavement Conference last Thursday in Sacramento and it was filled with useful and productive presentations for the quality control community.

The 3rd speaker of the day, Joe Peterson, Caltrans' Chief of Roadway Materials Testing spoke about the implementation of Warm Mix Paving Specifications.  Caltrans has already completed 26 projects with warm mix asphalt and there are 14 projects currently in construction now.  What was impressive to hear was not only the amount of jobs that warm mix asphalt is being used on, but that they have already laid down 1,310,000 tons of it.

As we speak, Caltrans specifications are being drafted in two forms: permissive and required.  The "permissive" specifications will give contractors the option to use warm mix at the contractor's expense.  Caltrans is planning on releasing this specification in January of 2012 so keep your eyes open.  The "required" specifications will require contractors to use warm mix on the job and the contractor will be compensated for the additional cost of warm mix which is pretty much the cost of the additive.  They did not mention an exact date for the release of this specification but they are shooting for next year sometime.  Both specifications will have the same quality standards as the new section 39 hot mix asphalt products for the standard and qc/qa jobs.  Even the method specification is remaining the same, including temperatures.  This is a little bit of a disappointment because one of the perks for the producers is the fuel savings from producing the mix at lower temperatures.

As of July 7, 2011 there are currently only four warm mix technologies that have been approved by Caltrans: Advera, Rediset WMX, Evotherm DAT, and Sasobit.  These processes all use a chemical additive of some sort and can be used on any Caltrans warm mix job with either a permissive spec or required spec.  I'm sure you're wondering, but what about the water injection system?  At this time the water injection system has not been unconditionally approved by Caltrans because they are still doing a few studies on it.  Peterson believed that a decision will be made in the next year about whether to add certain water injection systems to the approved warm mix technologies list.  The list of Caltrans approved products can be found at: Approved Products.  I encourage you to visit it frequently over the next year because I have a feeling that at least three or four new technologies could be added to this list soon. In the mean time, you still have the chance to use the water injection systems and any other warm mix technology not currently on the approved list by submitting your choice of warm mix technology to the Caltrans approval process.  The full approval process can be found at the same link that I mentioned before.  Basically you will submit a brief summary of the technology, results of laboratory and field testing, and evidence that the WMA can perform equal or better than conventional HMA.  You must also specify how the warm mix additive is added to the hot mix in production and provide the Caltrans laboratory with samples in order for them to recreate the process in the lab and run their own tests.

One of the tests that will need to be run on warm mix asphalt is the Hamburg Wheel -Track Test (AASHTO T 324).  This test is being written into the specifications as a requirement at production start-up and once every 10,000 tons.  I'm still examining the test method but will hopefully be posting on the test soon.  On non-warm mix jobs, Caltrans is also looking at the Hamburg test as a replacement for the TSR test.  The machine costs from $40-60k.  The concerning part of the day was when we were told that Caltrans is not planning on putting the machine in each district laboratory.  Although they are 98% sure that this test will be used to measure stability, resistance to raveling, and potentially some moisture sensitivity, they are still not 100% and they don't want to spend the money to put them in all of the laboratories just to find out that there is a new improved test that might be better.  They have one machine in the north part of the state and one in the south part of the state currently.  This is concerning for the producers and private laboratories who may be considering buying this machine.  Up until this point Caltrans seemed very gung-ho about taking this test on permanently but personally I'll be wanting to hold off on buying this very expensive machine until Caltrans can commit to it among their own labs.                          

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