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Polyphosphoric acid (PPA) has been used in 3.5% to 14% of the asphalt placed in the United States over the past 5 years. This represents up to 400 million tons of hot mix. As with all other components of the mix, testing is required to demonstrate the performance of PPA with each formulation of asphalt and aggregate, together with polymer, antistrip agents, and other additives that may be used. Results of the following tests are presented: dynamic shear rheometer, Hamburg, Lottman, and multiple stress creep and recovery tests on a matrix of a common asphalt with aggregate, three antistrip agents, two types of polymers, and PPA. Laboratory data for the materials tested show that the performance of PPA-modified asphalt can be improved with the addition of antistrip agents such as a phosphate ester, a particular polyamine compound, and hydrated lime. These findings hold true for cases where modification includes the use of polymers: styrene–butadiene–styrene and Elvaloy.

The use of vacuum distilled residues from the re-refining of used motor oils as blend stock in paving grade bitumen has occurred in isolated markets in North America for more than 30 years. Recently in the United States the increasing need for low stiffness bitumen for use in high binder replacement mixtures, coupled with economic considerations, has led to an expanding market for these products. Little in-depth investigation into the long-term impact of these additives on mixture performance has taken place until recently. Conflicting studies from researchers in Canada and private organizations have been published. Here, we review the eight-year performance of four virgin mixture test sections placed on a county highway Minnesota. Three test sections used PG 58-28 bitumens from different crude sources, one of which contained approximately 8% of the re-refined engine oil residuum. The fourth utilized PG 58-34 polymer-modified bitumen. Pavement distress surveys were conducted over the eight year period. Tests of the original bitumen following extended laboratory aging were conducted. Properties of the recovered bitumen from eight-year-old field cores were correlated to pavement distress. Double Edge Notched Tension (DENT) tests were conducted on 20-and 40-hour PAV residues of the original bitumen. Iatroscan and extensive rheological testing were conducted on laboratory aged bitumen and on bitumen recovered from laboratory aged mixtures and field cores to determine the colloidal index, rheological index and the extent to which laboratory aged and recovered bitumen materials were m-controlled. Also evaluated were three test sections constructed at the Minnesota DOT MnROAD test site. A comparative study of and PG 58-40 (PMA +re-refined engine oil bottoms) were evaluated over eight years. Bitumen used on the projects was tested as described above. The PG 58-40 exhibited the worst performance. The results of binder evaluations correlated to the fatigue cracking observed in the field with the test sections containing the re-refined engine oil residuum exhibiting the most extensive fatigue cracking. Based on this investigation we provide recommendations for test criteria to identify bitumens that could increase an asphalt mixture's likelihood to exhibit poor durability and fatigue cracking performance.

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