AASHTO TP 78-09 (2013) PDF

This qualitative test method can be used to identify the presence of polyphosphoric acid (PPA) in asphalt binder or residue. If PPA is present in the binder, a blue color is developed in approximately 5 min. The test method is not quantitative, but it can detect PPA at concentrations as low as 0.1 percent. The test method can only determine the presence of phosphorus. It is not specific for the presence of PPA. A positive test result assumes that the phosphorus is from PPA. Any additive that contains phosphorus will give a false positive for the presence of PPA.