SUPERPAVE Digest 254
Topics covered in this issue include:
1) Phosphorous Acid Testing
by "Kenneth Hobson" <>
· To: <>
· Subject: Phosphorous Acid Testing
· From: "Kenneth Hobson" <>
· Date: Fri, 15 Oct 1999 19:45:30 -0600
· Cc: <>
Is anyone doing tests for phosporous acid in asphalt binders?
Oklahoma has a moisture susceptibility (retained strength) test similar to
AASHTO T 283. In the past it was rare to add anti-strip additives to the
asphalt binder to meet the requirement. We implemented the PG grading
system in 1998 and did not see a problem in this area. Now, we seldom have
a mix that does not require an anti-strip additive. In some cases the
normal 0.5% is not sufficient. Up to 1% has been needed in some cases. I
am talking about the design phase. During production the retained strength
used to increase. Now it decreases on the average.
It was speculated that phosphorous acid was the problem. If there are any
anti-strip additive producers reading this please add any input you can
provide.
I will post this question to
http://www.telepath.com/khobson/odot/ubb/ubbcgi/Ultimate.cgi?action=intro as
well.
Kenneth Hobson
Bituminous Branch Manager (Acting)
OK DOT
SUPERPAVE Digest 257
Topics covered in this issue include:
5) RE: Phosphorous Acid Testing
by "Dempsey, Steve (SPDE)" <>
7) Re: Phosphorous Acid Testing
by "Kenneth Hobson" <>
· To: "''" <>, "McAuley, Joe (JHMC)" <>, "Hiddemen, Joseph C (JHID)" <>, "Miller, Denise (DDIR)" <>
· Subject: RE: Phosphorous Acid Testing
· From: "Dempsey, Steve (SPDE)" <>
· Date: Mon, 18 Oct 1999 11:50:50 -0700
· Cc: "Jennings, Doug (DCJE)" <>, "Tolonen, Bill (WTOL)" <>
Bob look at this comment in regard to the Dupont catalyzed Elvaloy. Didn't
Judd have a similar problem with Phosphoric acid Industrials?
· To: <>
· Subject: Re: Phosphorous Acid Testing
· From: "Kenneth Hobson" <>
· Date: Mon, 18 Oct 1999 19:19:19 -0600
As with many problems it was just an initial theory. Because of the
chemical properties between aggregate, asphalt cement and anti-strip
addtives it was theorized that the phosphorous acid could be the problem.
It was my understanding that an anti-strip additive producer put forth this
theory.
Obviously, sulfuric acid could also cause moisture susceptibility problems.
I imagine concentrations of these acids would play a key role.
By using more acids and other modifiers one can achieve the PG binder
specifications but perhaps it is a tradeoff at times. I suspect that better
anti-strip additives may need to be designed with the new PG binders if they
continue to be modified in such a way as to cause this failure mechanism.
Lime as an anti-strip additive has not worked for us.
Moisture damage is a big problem in Oklahoma so this issue needs to be
resolved if we are to achieve asphalt pavements that perform well.
This problem is being seen with our conventional Hveem designs. With
superpave designs to date we have only had one mix design that has this
problem as shown by failing AASHTO T 283 tests. This superpave design has
dust proportion problems as well. I suspect field control of dust and
asphalt cement are the more critical items on this job.
I have not tested how much asphalt content affects AASHTO T 283 results. I
suspect that as the design approaches the dust proportion limit there would
be failures.