A national workshop on Polyphosphoric Acid (PPA) Modification of Asphalt Binders was conducted in Minneapolis, MN on April 7-8, 2009. The workshop was jointly sponsored by the Transportation Research Board (TRB), Federal Highway Administration, Minnesota Department of Transportation, TERRA, Association of Modified Asphalt Producers, Innophos, ICL Performance Products, and the Asphalt Institute (AI).
AI has a publication on the subject of PPA called IS-220, Polyphosphoric Acid Modification of Asphalt. TRB also plans on publishing a circular of papers from the workshop. And all the speaker presentations from the workshop (both slides and webcast videos) are now available online.