PROPERTIES OF ASPHALTIC BITUMEN IN RELATION TO ITS USE IN ROAD CONSTRUCTION

THE PRINCIPAL PROPERTIES OF BITUMEN OF INTEREST TO THE ROADMAKER ARE ITS RHEOLOGICAL CHARACTERISTICS, ADHESIVE PROPERTIES, AND DURABILITY. THE TWO PROPERTIES OF BITUMINOUS ROAD SURFACINGS THAT ARE AFFECTED BY THE RHEOLOGICAL PROPERTIES OF THE BITUMEN BINDER ARE THE TENDENCY TO DEFORMATION OR FLOW, PARTICULARLY UNDER HEAVY TRAFFIC AT HIGH ROAD TEMPERATURES, AND THE POSSIBILITY OF FRACTURE AT LOW TEMPERATURES. BITUMEN MACADAM IS NOT GENERALLY LIABLE TO DEFORMATION BECAUSE, WHEN WELL COMPACTED, THE INTERNAL FRICTION DUE TO STONE-TO-STONE CONTACT IS ADEQUATE FOR RESISTING MOST TRAFFIC STRESSES. WITH DENSE MIXTURES, HOWEVER, INTERNAL FRICTION IS REDUCED AND SO THE PREPARATION OF A DURABLE DENSE SURFACING MATERIAL GIVES RISE TO THE RISK OF DEFORMATION. DEFORMATION OF A DENSE ASPHALT DEPENDS TO A CONSIDERABLE DEGREE ON THE AMOUNT AND VISCOSITY OF BITUMEN IN THE MIXTURE. THE HIGH TEMPERATURE COEFFICIENT OF VISCOSITY OF BITUMINOUS BINDERS EXPLAINS WHY DEFORMATION CAN BE A SERIOUS PROBLEM AT HIGH ROAD TEMPERATURES. FRACTURE OF AN ASPHALT ALSO DEPENDS TO A MAJOR DEGREE ON THE VISCOSITY OF THE BITUMEN USED. WHEN A BITUMINOUS BINDER IS SUBJECTED TO A CONSTANT TENSILE STRESS, DEFORMATION TAKES PLACE, THE STRAIN INCREASING WITH TIME, BUT NOT NECESSARILY AT A UNIFORM RATE. THE STIFFNESS OF THE BINDER IS DEFINED BY VAN DER POEL AS THE RATIO BETWEEN THE TENSILE STRESS AND THE TOTAL AMOUNT OF STRAIN WHICH OCCURS. THIS RATIO DEPENDS ON THE TIME FOR WHICH THE STRESS ACTS BECAUSE STIFFNESS IS A DECREASING FUNCTION OF TIME. WHEN STIFFNESS IS PLOTTED AS A FUNCTION OF TIME, DIFFERENCES IN HARDNESS OR IN TEMPERATURE RESULT FOR BITUMENS OF THE SAME PENETRATION INDEX IN CURVES OF THE SAME SHAPE, DISPLACED IN A DIRECTION PARALLEL TO TIME-AXIS IN CONFORMITY WITH A GIVEN RELATIONSHIP. WHEN BITUMEN IS USED IN A DENSE MIXTURE, THE STIFFNESS OF THE MIXTURE IS DEPENDENT ONLY ON THE STIFFNESS OF THE BITUMEN AND ITS VOLUME CONCENTRATION. IT IS INDEPENDENT OF THE GRADING OF THE AGGREGATE. RUPTURE IN AN ASPHALT IS OF TWO DISTINCT TYPES: A BRITTLE FRACTURE UNDER HIGH RATES OF STRAIN AT LOW ROAD TEMPERATURES, OR A DILATANT FRACTURE UNDER LOW RATES OF STRAIN, USUALLY AT HIGHER ROAD TEMPERATURES. THE ADHESION ATTRIBUTES OF BITUMEN ARE DISCUSSED. PREPARATION, TREATMENT AND TESTS OF BITUMEN AS A SURFACE DRESSING ARE DESCRIBED.

  • Supplemental Notes:
    • Vol 12, No 1, PP 34-38
  • Corporate Authors:

    N/A

    ,   United States 
  • Authors:
    • Lee, A R
    • NICHOLAS, J H
  • Publication Date: 1958

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  • Accession Number: 00211000
  • Record Type: Publication
  • Source Agency: Highway Research Board Bibliography
  • Files: TRIS
  • Created Date: Aug 5 2003 12:00AM