Polyphosphoric-acid modification of asphalt binders - Impact on rheological and thermal properties

Three compositionally different binders were modified (1.5 wt%) by the addition of polyphosphoric acid (105%). The rheological and thermodynamic properties of the unmodified and acid-modified binders are compared. These same properties for the unaged and aged binders are also compared in the report. Acid modification increases the complex modulus at 58 degrees C and the increase is persistent in the aged, modified binders. The impact of acid modification on the thermodynamic properties of the binders is variable, with binder AAM-1, which contains microcrystalline wax and has a substantially higher average molecular weight, being the exception. In all cases, the glass transition temperature is reduced and, in general, the height of the transition is reduced, while the width is increased. These thermodynamic results indicate that the changes for binders ABD and AAD-1 are consistent with the conversion of some of the maltenes to asphaltenes and for AAM-1 the results are consistent with a conversion of some asphaltenes to maltenes.