PPA Modified Binders and Mixtures: Aggregate and Binder Interactions, Rutting and Moisture Sensitivity of Mixtures

Almost simultaneously with the onset of PPA usage concerns were raised by a cross section of individuals, organizations and agencies associated with the asphalt production and supply, bituminous paving and governmental sectors. These concerns were manifested by fears of mixture stripping because of the hygroscopic nature of PPA, fears of accelerated aging and adverse effects on low temperature properties of both binders and their mixtures because of the well known use of phosphoric acids, PPA and phosphorus pentoxide to catalyze the production of roofing asphalt during the blowing process. There was also the often unstated but ever present belief that purchasers of PPA modified binders were being cheated because they were not receiving polymer when purchasing some premium PG grades. Some of these concerns were justified, many were not. The information in this study will endeavor to put some perspective around these concerns, to show where there might be cause for concern and where there is not. This document does not provide an answer to all questions and it raises a few questions that still need to be answered.