Comparison of Polyphosphoric Acid-Modified Asphalt Binders with Straight and Polymer-Modified Materials

Abstract

This paper discusses the effects of polyphosphoric acid (PPA) modification on asphalt binders. Findings are compared with those for straight and polymer-modified materials of similar grades. The effect of PPA modification was investigated by means of conventional protocols as well as three new binder tests developed in Ontario, Canada. The compact tension test and the extended bending beam rheometer protocol were used to investigate low-temperature performance properties. The double edge-notched tension test was used to study the resistance to ductile failure. The brittle state fracture properties and the reversible aging processes were largely unaffected by PPA modification. However, changes in the low-temperature grade were considerable in some instances. While the essential work of fracture increases with the addition of PPA, the yield stress increases more rapidly in most binders and thus results in an overall drop in strain tolerance in the ductile state. Recent field experience in Ontario suggests that the use of PPA may either prevent or contribute to wheelpath cracking, depending on the formulation and concurrent use of polymer.