TENSILE BEHAVIOR AND FAILURE CHARACTERISTICS OF ASPHALT CEMENTS IN THIN FILMS

THE REPORTED STUDY WAS CONDUCTED TO EXTEND THE KNOWLEDGE OF THE BEHAVIOR OF ASPHALT CEMENT IN THIN FILM SUBJECTED TO TENSILE STRESSES. THE TENSILE BEHAVIOR AND FAILURE CHARACTERISTICS OF 11 ASPHALT CEMENTS IN THIN FILMS WERE STUDIED. VARIABLES IN THE STUDY INCLUDED: (1) FILM THICKNESS, (2) RATE OF DEFORMATION, (3) TEMPERATURE, (4) CONSISTENCY, AND (5) SOURCE OF THE BITUMINOUS MATERIAL. A DEFINITE RELATIONSHIP WAS FOUND TO EXIST BETWEEN THE TENSILE PROPERTIES OF A GIVEN ASPHALT CEMENT AND THE FILM THICKNESS OF THE SPECIMEN. THE TENSILE STRENGTH OF ASPHALT CEMENTS IN THIN FILMS IS SIGNIFICANTLY INFLUENCED BY THE TEST RATE OF DEFORMATION AND/OR THE TEST TEMPERATURE. THE CONSISTENCY OF THE ASPHALT CEMENT HAS A SIGNIFICANT INFLUENCE ON TENSILE STRENGTH. THE SOURCE OF THE ASPHALT CEMENT MAY INFLUENCE THE TENSILE STRENGTH OF THE MATERIALS. IT APPEARS THAT THE ASPHALTENE CONTENT OF ASPHALT CEMENTS OBTAINED FROM A GIVEN SOURCE MAY HAVE A SIGNIFICANT INFLUENCE ON THE CONSISTENCY OF THE MATERIALS AND THUS, ON THE TENSILE STRENGTH. THREE MODES OF FAILURES WERE OBSERVED IN THE ASPHALT SPECIMENS. THE RANGE OF FILM THICKNESS EXHIBITING EACH FAILURE MODE WAS DEPENDENT UPON SPECIFIC COMBINATIONS OF: (1) ASPHALT SOURCE AND CONSISTENCY, (2) RATE OF DEFORMATION, AND (3) TEMPERATURE. THE OBSERVED MODES OF FAILURE WERE REFERRED TO AS: BRITTLE FRACTURE, FLOW FAILURE AND INTERMEDIATE FAILURE OR TENSILE RUPTURE. SPECIMENS WHICH EXHIBITED THE BRITTLE MODE HAD FAILURE SURFACES WHICH WERE SMOOTH AND GLASSY IN APPEARANCE. SPECIMENS WHICH EXHIBITED FLOW FAILURE USUALLY EXHIBITED A FAILURE SURFACE FORMED BY EXCESSIVE NECKING AND INTERNAL FLOW OF THE SPECIMEN. THE INTERMEDIATE MODE FAILURE SURFACE EXHIBITED A COMBINATION OF MULTIPLE DEPRESSIONS AND MULTIPLE RIDGES. THE LIMIT OF BRITTLE FRACTURE AND THE LIMIT OF FLOW FAILURE ARE: FUNCTION OF TEMPERATURE, RATE OF DEFORMATION, AND ASPHALT CONSISTENCY. THE TYPE OF FAILURE THAT OCCURS IN THIN FILMS OF BITUMINOUS MATERIAL SUBJECTED TO TENSILE STRESSES CAN GENERALLY BE CLASSIFIED AS A COHESIVE FAILURE RATHER THAN AN ADHESIVE FAILURE. A CONSTANT RATE OF LOADING TEST APPEARS TO BE A MORE DESIRABLE TEST METHOD THAN A CONSTANT RATE OF DEFORMATION TEST FOR DETERMINING ASPHALT CEMENT BEHAVIOR CHARACTERISTICS. BITUMINOUS MATERIALS IN THIN FILMS WHEN SUBJECTED TO TENSILE STRESSES EXHIBIT A CAVITATION PHENOMENA AND THE VOLUME OF THE SPECIMEN APPEARS TO INCREASE. THE AMOUNT OF DEFORMATION TO FAILURE APPEARS TO BE PARTIALLY DEPENDENT UPON FILM THICKNESS.