Acid Modification of Asphalt Binders

Phosphoric acid has been used for some thirty years to stiffen asphalt for paving applications. More recently it has been used to stiffen asphalts that may be marginal on the Superpave RTFOT test. This has been particularly so in the case of polymer modified binders. It was found more cost effective to add a small amount of acid, which could readily be dispersed in the binder rather than mill in additional quantities of more expensive polymer. It was then found that by adding polyphosphoric acid the amount of polymer could be reduced thereby saving cost for the contractor. The use of polyphosphoric acid has proliferated to such an extent that Colorado DOT found they were supplied with polymer modified binder which actually contained no binder at all, the modifier was just phosphoric acid. Colorado DOT has banned the use of phosphoric acid until more test data is available. Other state agencies have similar problems, phosphoric acid is being widely used but nobody knows if it is good or bad, which of the many grades of phosphoric acid can and cannot be used, how it is affected by other asphalt additives and what are the long-term effects of acid modification as it relates to pavement performance. Studies attribute both harmful and beneficial properties associated with the acid modification of asphalt binders. Polyphosphoric acid suppliers claim their product, used in optimal amounts (0.3 to 0.7%), causes no harm to the HMA mixes and pavements. They also claim most of the adverse studies relate to the use of orthophosphoric or "green" acids. The objective of this project is to address the risks and benefits associated with the use of phosphoric acid as an asphalt modifier. To clearly identify which grades can and cannot be used and the pitfalls associated with the use of phosphoric acid with antistrip compounds, such as amines and lime as well as asphalt binders from differing sources. Not proceeding with this research leaves state agencies at risk of building less than optimum quality roads.


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    • Status: Active
    • Sponsor Organizations:

      Federal Highway Administration

      Office of Infrastructure
      1200 New Jersey Avenue, SE
      Washington, DC  United States  20590
    • Project Managers:

      SaLut, Terry

      Youtcheff, Jack

    • Principal Investigators:

      Rozario, Jenny

      SaLut, Terry

      Youtcheff, Jack

    • Start Date: 20041101
    • Expected Completion Date: 0
    • Actual Completion Date: 20071231
    • Source Data: RiP Project 11746

    Subject/Index Terms

    Filing Info

    • Accession Number: 01458453
    • Record Type: Research project
    • Source Agency: Federal Highway Administration
    • Files: RIP, USDOT
    • Created Date: Jan 3 2013 12:43PM