Asphalt modification with polyphosphoric acid

Abstract

The properties of neat asphalt and mixes can be significantly improved by the addition of polyphosphoric acid at relatively low concentrations. This approach is increasingly being used in North America to meet the high performance requirements for binders in SuperpaveTM applications. This paper discusses the effect of polyphosphoric acid in various neat asphalt binders and mixes with aggregates. Conventional rheological measurements and Superpave parameters were used to evaluate the properties of various asphalts. It was found that polyphosphoric acid increased the high-temperature Performance Grade (PG) of the neat binders with no loss of low-temperature properties. Further, moisture sensitivity testing has demonstrated superior adherence of the binders to aggregates and a dramatic reduction in the level of rutting. No adverse adhesion effects were found by the use of the polyphosphoric acid together with commercially available anti-strip agents. Another significant finding is that binders treated with polyphosphoric acid show increased resistance to oxidative aging, as measured by the pressure-aging vessel. The results demonstrate that a level of polyphosphoric acid near 0.5 percent works well for most binders.