GRADING ASPHALT CEMENTS BY PENETRATION OR VISCOSITY AT 77 F

ANY ATTEMPT TO MODIFY CURRENT SPECIFICATIONS FOR ASPHALT CEMENTS SHOULD EMPHASIZE TWO MAJOR OBJECTIVES: (1) IT SHOULD FACILITATE HIGH-TEMPERATURE CONSTRUCTION OPERATIONS, AND 275 F IS A REPRESENTATIVE TEMPERATURE FOR THE HIGH-TEMPERATURE CONSTRUCTION TASKS OF MIXING, SPREADING, AND BREAKDOWN ROLLING; AND (2) IT SHOULD IMPROVE LONG-TERM PAVEMENT PERFORMANCE, PARTICULARLY UNDER THE LOW WINTER TEMPERATURES THAT OCCUR IN AT LEAST HALF OF THE UNITED STATES AND IN ALL OF CANADA, AND 77 F IS A REASONABLY AVERAGE PAVEMENT SERVICE TEMPERATURE IN MUCH OF NORTH AMERICA. NEITHER OF THESE TWO OBJECTIVES IS ACHIEVED BY THE AASHO SPECIFICATION BASED ON GRADING ASPHALT BY VISCOSITY AT 140 F. THE CHARACTERISTICS OF ASPHALTIC CEMENTS ARE DISCUSSED, AND THE RELATIONSHIPS OF TRANSVERSE CRACKING TO VARIOUS VISCOSITIES AND PENETRATIONS ARE GRAPHED. IT IS NOTED THAT THE OILY CONSTITUENT PART OF ASPHALTS IS HIGHLY DESIRABLE AS CAT-CRACKER FEED STOCK AT REFINERIES, WHERE IT IS CONVERTED INTO GASOLINE AND OTHER LIGHT DISTILLATES. CURRENTLY, THE OILY CONSTITUENTS ARE MORE VALUABLE AS CAT-CRACKER FEED STOCK THAN WHEN SOLD IN THE FORM OF ASPHALT. APART FROM THE INCREASED HARDNESS THAT RESULTS, THERE IS NO REDUCTION OR DETERIORATION IN ASPHALT QUALITY BY THE REMOVAL OF OILY CONSTITUENTS. IN VIEW OF THIS. THE AASHO VISCOSITY-GRADED SPECIFICATIONS, WITH THEIR WIDE RANGE OF PENETRATION AT 77 F, ARE AN INVITATION OF PETROLEUM REFINERS TO PRODUCE THE HARDEST GRADE PERMITTED BY THE SPECIFICATION. THIS CAN HAVE A DAMAGING EFFECT ON LOW- TEMPERATURE PAVEMENT PERFORMANCE. WHEN WE GRADE ASPHALT CEMENTS BY VISCOSITY AT 140 F, WE ARE IMPLYING THAT PAVEMENT PERFORMANCE WILL BE THE SAME OVER A BROAD PENETRATION RANGE, AN ASSUMPTION THAT THE PETROLEUM REFINER IS OBLIGED TO RESPECT. ON THE OTHER HAND, WHEN ASPHALT CEMENTS ARE GRADED BY PENETRATION OR VISCOSITY AT 77 F, A PETROLEUM REFINER IS RESTRICTED WITH REGARD TO THE AMOUNT OF OILY CONSTITUENTS THAT HE CAN REMOVE BECAUSE HE MUST PROVIDE THE PENETRATION GRADE THAT HAS BEEN SPECIFIED. GRADING ASPHALT CEMENTS BY VISCOSITY AT 140 F WILL PROMOTE A PROLIFERATION OF SPECIFICATIONS FOR ASPHALT CEMENTS IN AN ATTEMPT TO AVOID THE VARIABLE PAVEMENT PERFORMANCE THAT WILL INEVITABLY RESULT FROM THE VERY WIDE RANGE OF PENETRATION AT 77 F, WHICH IS ASSOCIATED WITH EACH VISCOSITY GRADE. IT IS SUGGESTED THAT GRADING BY PENETRATION OR VISCOSITY AT 77 F, PREFERABLY WITH A VISCOSITY REQUIREMENT AT 275 F, COULD SERVE VERY ADEQUATELY AS A NATIONAL OR INTERNATIONAL SPECIFICATION FOR ASPHALT CEMENTS.

• Record URL:
  http://onlinepubs.trb.org/Onlinepubs/hrr/1972/404/404-010.pdf
• Supplemental Notes:
  • Sponsored by Committee on Characteristics of Bituminous Materials. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Authors:
  • McLeod, Norman W
• Conference:
  • 51st Annual Meeting of the Highway Research Board
  • Location: Washington District of Columbia, United States
  • Date: 1972-1-17 to 1972-1-21
• Publication Date: 1972

Media Info

• Media Type: Print
• Features: Figures;
• Pagination: pp 112-120
• Monograph Title: Asphalt mixture characterization and asphalt grading
• Serial:
  • Highway Research Record
  • Issue Number: 404
  • Publisher: Highway Research Board

Subject/Index Terms

• TRT Terms: Asphalt; Asphalt cement; Asphalt pavements; Grading (Earthwork); Pendulum tests; Temperature; Transverse cracking; Viscosity
• Uncontrolled Terms: Asphalt grading; Grading
• Subject Areas: Highways; Materials;

Filing Info

• Accession Number: 00211777
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Apr 17 1973 12:00AM