Polyphosphoric acid compositions having a reduced viscosity compared to neat polyphosphoric acid. The viscosity of the polyphosphoric acid is reduced by combining the polyphosphoric acid with an additive that reduces the viscosity of the polyphosphoric acid composition. In one embodiment, additives that can cause solvation and/or partial neutralization of the polyphosphoric acid without the addition of water may be used. The reduced viscosity polyphosphoric acid may be used, for example, as an additive in asphalts used in road pavements.