Superpave vs Marshall

[BigH]

Ron, et. al.

Was curious from a practical point of view: Has switching from the Marshall methods of asphalt pavement design to Superpave actually resulted in better and more durable pavement at less cost - or has it really just been a cash cow for those who pushed it?

Have we actually seen a better pavement today than, say, 20 years ago?

 

[Ron]

A big, resounding NO!! In particular, the SuperPave mixes have tended to be a bit more rich (more costly), exhibit more flushing or bleeding, and deform more.

When I was with my old firm, we had these big-deal internal meetings about gearing up for SuperPave (early to mid-90's). They hired on a few "experts" (interesting that these guys were experts even before the first mix hit production!), who went around to the branch offices who had asphalt testing and consulting experience, to tout the panacea of SuperPave. My job as Chief Engineer was to keep my people grounded in the technical aspects, so I asked one of these "experts" in one of our meetings what they hoped to achieve through SuperPave that couldn't be or hadn't been done through Marshall or Hveem methods. After all, the constituents were the same...asphalt cement, graded aggregates, mineral filler...no change to that. To my shock (not really) he had no good answer for that, other than to say that the projected performance was better. As it has turned out, I see little or no difference in performance, and in some cases, worse performance.

One result was that only the suppliers could afford to gear up with appropriate mix design equipment and the testing labs could only do minimal checking with the newly required NCAT ovens instead of solvent extraction and gradations. Granted, most suppliers have typically done their own mix designs, but at least under the Marshall or Hveem methods, they could be checked in parallel by an independent source.

I think that over the last 15 years or so, the Departments of Transportation have learned to adapt and have been able to achieve results of a nature similar to the older methods, but I just don't see that we've improved greatly. I'm sure others will disagree!

 

[SlideRuleEra]

A contributing problem is the decline in the quality of available asphalt. Asphalt is literally the bottom of the crude oil barrel; as the price of oil has climbed (over the past 40 years) petroleum refiners have economic incentive to extract more valuable products from crude oil stock. The result is that the extra gasoline, diesel fuel, lubricating oil, etc. comes from the "best" hydrocarbons that used to be included in asphalt.

Here is a short article that mentions this problem:

http://www.asphaltandsourcingallian...ew Case for Bitumen Modifiers & Additives.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[emmgjld]

With all the changes, things remain the same.

Back in the Slide Rule Era, I had returned from Viet Nam (early '72), listened to my Father and his Chief Materials Tech talking about the recent changes in AC designations, the refineries removing a few more 'goodies' & the attempts to explain that all would be the same or better.

The next AASHTO design method slightly improved but the Regional Factor was nearly a waste of effort.

We saw things start to improve with AASHTO '86 & I thought the HVEEM criteria for design was some improvement. However, it still seemed that a good tech & Engineer did better field control with the Marshal methods.

I agree with Ron, the SuperPave seemed almost like a scam. I do appreciate some of the new equipment.
I cry at how Voids Acceptance has been used to beat up on the contractors.
I laugh at the actual field performance.

 

[BigH]

So - the question begs, why did the change come about? Researchers and Government types needing a new "technology" to keep their jobs? or to show they are "relevant.:?

Is this why we have gone to LRFD for geotechs? (and still correlating the LRFD to the old way anyway?

 

[Ron]

BigH...the changes primarily came about with a few US government programs initially bounded by pavement management. Money was available to research and "improve" the present standards (as of the late 1980's).

As with many gov't programs, there needed to be the illusion of need, the improvision of technology to respond to the illusion of need, the positive formation of a result, a plan for implementation, and buzzwords/acronyms aplenty to establish the technical mystique. Thus we have.....Superpave (SUperior PERforming Asphalt PAVEments), Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA (Ice-Tea)), etc.

I suppose another word for it would be "boondoggle"...but on the positive side, it provided jobs for a lot of researchers!

 

[emmgjld]

I remember an old (now deceased) paving engineer stating --- there always seemed to be some embarrassment that a 1930's method (Marshall) in the hands of good people, consistently produced pavements as good as the newer Hveem and the up & coming Superpave.
But, of course, he was old fashioned & known to express his opinion, usually embarrassing local & regional government specifiers.

But if you want to journey into a morass, get into airport pavements.