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Publication Number:  FHWA-HRT-14-086    Date:  November 2014
Publication Number: FHWA-HRT-14-086
Date: November 2014


The Use of Phosphoric Acid to Stiffen Hot Mix Asphalt Binders

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The Use of Phosphoric Acid to Stiffen Hot Mix Asphalt Binders provides guidelines for the use of the different commercially available grades of phosphoric acid to enhance the high temperature performance grade of asphalt binders derived from different crude oil sources for use in hot mix paving applications. The expected effect on pavement life, in terms of oxidative aging, moisture resistance, fatigue, rutting, and use with different types of aggregates are presented. Analytical procedures for detecting the presence of phosphoric acid using X-ray fluorescence spectroscopy as well as a simple rapid test method are included. 

The guidelines presented in this report will be useful to producers of asphalt binders, hot mix paving contractors, State departments of transportation, and local highway agencies.

Jorge E. Pagán-Ortiz
Director, Office of Infrastructure
Research and Development


This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.


Technical Report Documentation Page

1. Report No.


2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

The Use of Phosphoric Acid to Stiffen Hot Mix Asphalt Binders

5. Report Date

November 2014

6. Performing Organization Code
7. Author(s)

Terence Stanley Arnold CChem FRIC

8. Performing Organization Report No.


9. Performing Organization Name and Address

Federal Highway Administration
Pavement Materials Team (HRDI-10)
6300 Georgetown Pike
McLean, VA 22101-2296

10. Work Unit No. (TRAIS)

11. Contract or Grant No.
12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered


14. Sponsoring Agency Code


15. Supplementary Notes
16. Abstract

This document offers guidelines for the use of phosphoric acid to stiffen asphalt binders for hot mix paving applications. Data are presented on the likely effect on pavement life, moisture resistance, and use with limestone aggregates and liquid amine antistrip additives. Analytical methods for the detection of phosphoric acid in asphalt binders are also presented. Asphalt producers, hot-mix paving contractors, and State departments of transportation are the main audiences.

17. Key Words

Asphalt, aggregate, phosphoric acid, superphosphoric acid, polyphosphoric acid, lime, antistrip additives, X-ray fluorescence spectroscopy

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.

19. Security Classification
(of this report)


20. Security Classification
(of this page)


21. No. of Pages


22. Price
Form DOT F 1700.7 Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors





AASHTOAmerican Association of State Highway and Transportation Officials
BBRBending Beam Rhometer
DSRDynamic Shear Rheometer
FIDFlame Ionized Detection
HDPEHigh Density Polyethylene
HMAHot Mix Asphalt
NMRNuclear Magnetic Resonance
NYSDOTNew York State Department of Transportation
PAVPressure Aging Vessel
PGPerformance Grade
PPAPolyphosphoric Acid
RHRelative Humidity
RTFOTRolling Thin Film Oven Test
SARASaturate, Aromatic, Resin, and Asphaltene
SHRPStrategic Highway Research Program
TFHRCTurner Fairbank Highway Research Center
XRFX-Ray Fluorescence Spectroscopy


Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101