Field Test of a Polyphosphoric Acid (PPA) Modified Asphalt Binder on Rt. 1 in Perry: Final Report

US Transportation Collection2013PDFTech ReportThompson, BillMaine. Dept. of Transportation. Transportation Research DivisionMaine. Department of TransportationMaineSuperpaveHot mix asphaltBindersPhosphoric acidTemperatureField testsTest sectionsRutting13-03The Maine Department of Transportation (MaineDOT) uses the Superpave hot mix asphalt process and specifies asphalt binder grades using the Performance Grade criteria. The Department mainly uses asphalt binder grade PG 64-28. This is an asphalt binder material that passes the performance tests for high temperatures (rutting potential) at 64 degrees Celsius and passes tests for low temperatures (thermal cracking) at -28 degrees Celsius. In order to create the properties of PG binder, polyphosphoric acid is sometimes added to the asphalt. It is widely recognized in the industry that the addition of polyphosphoric acid to asphalt can increase the high temperature PG grade to the next higher grade. However, there are concerns among transportation agencies that this PPA could alter the long term performance of the asphalt binder. One of the major asphalt suppliers to MaineDOT paving projects uses PPA to alter their PG58-28 neat asphalt binder into a PG64-28. An explanation of the specification and development of Superpave Performance Grade (PG) binder specification has been described in an FHWA TechBrief . \u201cIn the PG system the high and low temperature performance range is specified i.e., PG 64-22. The 64 represents the expected high temperature range of the binder and the -22 is the expected low temperature range. The difference between the high and low temperature range of the binder is call the useful temperature interval (UTI). All asphalt binders refined from crude oil have a specific UTI\u2026.Changes in the refining process can shift the UTI up or down, but in general they cannot change the UTI\u2026.To change the UTI of an asphalt binder it would have to be blended with an asphalt binder which has a different UTI or modified with some type of additive\u2026The use of the Superpave binder specification has encouraged agencies to specify stretch grades. These are grades that go beyond the UTI of most neat asphalts\u2026.To meet the requirements for these grades some type of modification is needed. In many cases this would be a polymer. Polymers do quite well in increasing the high temperature properties of a binder. However, polymer modification can also affect the intermediate temperature properties of some asphalt binders. The use of PPA in combination with the polymer will minimize the increase in stiffness \u2026. The amount of PPA needed will vary based on the crude source and polymer being used\u2026.\u201d.1 PPA is a hydrophilic material, however, and easily absorbs water\u2026.[and] it has been demonstrated that binders modified with PPA content above 1%, have a tendency to absorb water and lose strength\u201d.2 The potential for increased moisture damage and reduced pavement performance has therefore been a concern when PPA modified binder is used.125