Polyphosphoric Acid Modification of Asphalt

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.