AN APPRAISAL OF FAILURE IN BITUMINOUS PAVEMENTS

FAILURE IN BITUMINOUS PAVEMENTS CONSISTS IN GENERAL IN THE FORMATION OF CRACKS WHICH RESULT FROM EXTERNAL FORCES BEING LARGER THAN THE COHESIVE FORCES OF ASPHALTS. BASED PARTLY ON EXPERIMENTAL EVIDENCE, IT HAS BECOME CUSTOMARY TO RELATE LOSS IN COHESIVE FORCES OF WEATHERED ASPHALTS WITH AN INCREASE IN CONSISTENCY AS DETERMINED BY VISCOSITY, PENETRATION AND DUCTILITY TESTS. WEATHERED ASPHALTS HAVE AT CONSTANT TEMPERATURE FLOW PROPERTIES WHICH VARY WITH THE MAGNITUDE OF THE SHEARING STRESS. AT LOW STRESSES UP TO A CERTAIN LIMIT, THE VISCOSITY IS CONSTANT AND THE SHEAR STRESS IS PROPORTIONAL TO THE SHEAR RATE. BEYOND THIS STRESS LIMIT, THE FLOW IS NON-NEWTONIAN AND THE SHEAR STRESS IS PROPORTIONAL TO THE SHEAR RATE RAISED TO THE POWER OF B. IT REQUIRES THEREFORE THREE CONSTANTS TO CHARACTERIZE THE FLOW PROPERTIES OF NON-NEWTONIAN ASPHALTS IN THE DESCRIBED STRESS RANGE. IT HAS BEEN SUGGESTED TO COMPARE THE VISCOSITIES AT A GIVEN SHEAR RATE OF AN ASPHALT BEFORE AND AFTER WEATHERING AS A MEASURE OF DURABILITY WITHOUT TAKING THE FLOW PROPERTIES INTO CONSIDERATION. IT IS SHOWN THAT THIS DISREGARD CAN LEAD TO WRONG INTERPRETATIONS OF THE TESTS AND CAN LEAD UNDER CERTAIN CIRCUMSTANCES TO LOWER VISCOSITIES AND HIGHER PENETRATIONS OF THE WEATHERED ASPHALTS THAN THOSE OF THE ORIGINALS. FLOW PROPERTIES AT LOW STRESSES ARE DIFFICULT TO MEASURE, BUT BASED ON THE BEHAVIOR OF ASPHALTS IN PAVEMENTS, A LARGE AMOUNT OF WEATHERING IS ACCOMPANIED BY A LARGE DECREASE IN THE VALUE OF THE PARAMETER B WHICH CAN BE EASILY OBTAINED FROM VISCOSITY AS WELL AS PENETRATION MEASUREMENTS. THE SIGNIFICANCE OF DUCTILITY IS DISCUSSED IN THE LIGHT OF PRESENT KNOWLEDGE AND IT IS SHOWN THAT A DECREASE IN DUCTILITY OF AN ASPHALT AFTER WEATHERING IS ALSO ACCOMPANIED BY A DECREASE IN THE VALUE OF THE PARAMETER B. A GREAT CHANGE IN THE FLOW PROPERTIES OF A WEATHERED ASPHALT IS NOT THE CAUSE BUT THE EFFECT OF FAILURE IN A PAVEMENT. FAILURE IS DUE TO THE PRESENCE OF LARGE RESIDUAL STRESSES IN THE ASPHALT FILM WHICH ARE MAINLY CAUSED BY THE CONSIDERABLE DIFFERENCE IN THE COEFFICIENTS OF EXPANSION OF MINERAL AGGREGATE AND ASPHALT. THIS PHASE IS DISCUSSED ON THE BASIS OF THE TOTAL ENERGY PRESENT. IT IS DEONSTRATED THAT RESIDUAL STRESSES CAN BE REDUCED AND THE DURABILITY OF THE PAVEMENT IMPROVED BY PROPER SELECTION OF THE MINERAL AGGREGATE. /AUTHOR/

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Filing Info

  • Accession Number: 00210813
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 6 1970 12:00AM