Friday, November 11, 2011

Caltrans and Superpave

At the CalAPA meeting on 10/27/11 there was also discussion about Caltrans' movement towards Superpave specifications.  Caltrans plans to have 6 pilot projects with Superpave specifications across the state in 2012 and even more in 2013.  As of right now Joe Peterson (Caltrans Chief of Roadway Materials Testing) is 99% sure that all new Caltrans specifications will be Superpave starting in 2014.

The Superpave specifications are very similar to the specifications that recently came out that we lovingly refer to as new Section 39.  The major difference is that in Superpave specifications, mix designs are creating using a gyratory compactor instead of a kneading compactor.  Here is a video that shows the gyratory compactor in action.

Caltrans has announced the purchase of 12 Pine Instruments Corp. gyratory compactors; one for each of their district labs.  The Pine Instruments website is here.  Although Caltrans will be using the Pine Instruments Corp. compactors there are several companies who make a gyratory compactor that can be used for Superpave mix designs.  The cost per unit is roughly $50-60k.

In other terms of the specifications, most of what we will be doing in Superpave overlaps with the new Section 39 requirements.  The Superpave mix designs are based on the same metrics as new Section 39 where attention will be paid to, not only gradation and oil content, but VMA, VFA, and Air Voids.  The construction and testing specifications for method, standard, and qc/qa jobs will also be the same, though a few of the test value specifications may change slightly due to the new compaction method.

Superpave has been around for quite a long time and has been used in Europe as well as most of the rest of the country for decades.  Although I acknowledge that is is frustrating that we are switching to yet another set of specifications so soon after adapting the new Section 39 specifications, the Superpave mix designs do seem to have good performance records.  It should also be recognized that, despite being behind the times or even in our own world in terms of test methods for quite a few years, Caltrans is finally making an effort to join the rest of the country, something I'm extremely happy about.  The difficult part for suppliers will be that many of the other entities like cities and counties may not switch over to Superpave leaving the suppliers having to produce Medium, Coarse, HMA, and new Superpave designs.  But if we didn't have these types of changes, the job wouldn't be so fun right?

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