achieved through an oxidation process, in which air was blown into the binder at high temperatures. This enhanced the performance of the binder at high temperatures, but severely damaged its low temperature properties. In fact, this procedure is believed to elevate the glass transition temperature . On the contrary, adding PPA alters standard refinery-binders to binders with higher resistance to rutting while still meeting the low temperature requirements. This is the case for example of binder grade AC-30 to which PPA is added to enhance its viscosity to that of AC-40 without shifting the binder’s penetration. In the last decades, PPA has been used to modify asphalt binders by is increasing the range of the binder’s PG without adversely affecting its low temperature limit. For example, through this technology, the service temperature range of asphalt with PG 64-22 can be raised to PG 70-22. Thus, higher stiffness, improved elasticity, lower temperature susceptibility, and increased viscosity are observed in PPA modified binders compared to the plain. Several researcher, among which Bishara, et al.,, Ho, et al., , and Maldonado, et al., have documented the mechanisms of PPA modification. The strength of the effect may vary from binder to binder, but it is generally agreed that the higher service temperature limit PG increases almost linearly with the amount of added PPA . Further, Giavarini, et al., and Arnold et al., have observed that the capacity of upgrading a binder by using PPA depend, not only on the type of the base asphalt binder subjected to modification, but also on the colloidal properties of the asphaltene fraction contained in the binder. The researchers performed in-depth rheological and physiochemical analysis, including binder fractionation. The effects of adding PPA were investigated on both binder and on the asphaltene and resin fractions of the binder. An increase of asphaltene to resin ratio due the addition of PPA was observed. The resulting product exhibits high colloidal stability. Arnold, et al., also noted that when the asphaltene to resin ratio increase
Kodrat, I., Sohn, D. and Hesp, S. A.M. “Comparison of polyphosphoric acid-modified asphalt binders with straight and polymer-modified materials” Transportation Research Record: Journal of the Transportation Reasearch Board (2007); Vol. 1998, pp. 47-55. Li, X. and Marasteanu, M.O. “Evaluation of the Low Temperature Fracture Resistance of Asphalt Mixtures Using the Semi Circular Bend Test.” Journal of the Association of Asphalt Paving Technologists ( 2004); No. 73, pp. 401-426. Maldonado R.,Falkiewicz M., Bazi G. “Asphalt Modification with Polyphosphoric Acid”. Proc., Canadian Technical Asphalt Association (2006); Vol. 51. - pp. 163-178. Marasteanu, M.O. et al. “Investigation of Low Temperature Cracking in Asphalt Pavements – A Transportation Pooled Fund Study”, Minnesota Department of Transportation, Final Report MN/RC 2007-43 (2007). Turos, M., Moon, K. H., and Marasteanu, M.O. Air Voids Testing for MnROAD Cells, Minnesota Department of Transportation, Final Report MN/RC 2010-28 ( 2010). Table . Description of Asphalt Mixtures used MnROAD Test Cell Construction date Binder Grade Asphalt modifiers Innovalt W Liquid Antistrip 33 September 2007 PG 58-34 0.75% PPA 0.5% 34 September 2007 PG 58-34 1.0% SBS + 0.3%PPA 0.5% 35 September 2007 PG 58-34 2.0% SBS None 77 September 2007 PG 58-34 1.1% Elvaloy + 0.3% PPA 0.5%