AIR PERMEABILITY OF ASPHALT CONCRETE

THE IMPORTANCE OF LOW AIR PERMEABILITY IN INCREASING THE DURABILITY OF ASPHALTIC CONCRETE HAS BEEN DISCUSSED BY MANY AUTHORS. ALSO, PERMEABILITY HAS BEEN SHOWN TO BE RELATED TO THE VOIDS CONTENT AND DENSITY OF A PARTICULAR MIX. THIS PAPER PRESENTS AN IMPROVED METHOD AND EQUIPMENT FOR DETERMINING RAPIDLY AND CONVENIENTLY THE IN-PLACE AIR-FLOW RATE THROUGH PAVEMENTS. FIELD TESTS ARE REVIEWED SHOWING THE APPLICATION OF THIS EQUIPMENT TO MEASUREMENTS ON PAVEMENTS IN PLACE. THE RELATION BETWEEN IN-PLACE MEASUREMENTS AND THE DENSITY OF CORES IS ESTABLISHED FOR A PARTICULAR MIX. ALSO SHOWN IS THE VARIABILITY OF FIELD PERMEABILITIES. THIS VARIATION IS PRESUMED TO BE DUE TO MIX SEGREGATION DURING CONSTRUCTION. EXTENSIVE PNEUMATIC ROLLING REDUCES PERMEABILITY OF SOME MIXES, BUT WHERE SEGREGATION HAS OCCURRED THE EFFECT DIFFERS, DEPENDING ON THE INITIAL CONDITION OF THE MIX. MIX-DESIGN STUDIES SHOW THAT PERMEABILITY, WHEN INFLUENCED BY GRADATION CHANGES, IS NOT ALWAYS PROPORTIONAL TO VOIDS CONTENT. THIS FINDING IS CONTRARY TO CUSTOMARY CONCEPTIONS. IT SUGGESTS WAYS IN WHICH HIGHLY STABLE, LOW-PERMEABILITY MIXES CAN BE DESIGNED. THUS, PERMEABILITY MEASUREMENT IS SUGGESTED AS AN ESSENTIAL PART OF ROUTINE MIX-DESIGN STUDIES. MEASUREMENTS ON PAVEMENTS AT HIGH TEMPERATURE ARE MADE POSSIBLE WITH THE NEW TECHNIQUE. SYSTEMATIC CHANGE OF AIR-FLOW RATE WITH TEMPERATURE IS SHOWN. HIGH-TEMPERATURE AIR-FLOW RATES ARE RELATED TO THE AMBIENT TEMPERATURE PERMEABILITIES OF CORES. THUS, THE CONCEPT AND PROCEDURE SUGGEST HOW FUTURE MIX DESIGNS CAN INCLUDE HIGH-TEMPERATURE PERMEABILITIES ON THE OPTIMUM MIX AT SEVERAL TEMPERATURES AND LABORATORY COMPACTIVE EFFORTS. THIS PROCEDURE PERMITS A DENSITY OR PERMEABILITY SPECIFICATION IN TERMS OF A NONDESTRUCTIVE TEST. FURTHERMORE, A HIGH-TEMPERATURE AIR-FLOW MEASUREMENT MIGHT BE SPECIFIED TO PERMIT ADDITIONAL ROLLING WHILE THE MIX IS STILL HOT ENOUGH TO BE COMPACTED OR TO PREVENT UNECONOMICAL EXCESSIVE ROLLING.

  • Supplemental Notes:
    • No 309, P 49
  • Authors:
    • Hein, T C
    • Schmidt, R J
  • Publication Date: 1961

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  • Accession Number: 00210961
  • Record Type: Publication
  • Source Agency: Highway Research Board Bibliography
  • Files: TRIS
  • Created Date: Jun 3 1994 12:00AM