PROPERTIES OF CONCRETE CHANGE WHEN MICROCRACKING OCCURS

THE STRESS/STRAIN PROPERTIES AND THE FRACTURE OF PLAIN CONCRETE ARE STUDIED UNDER BIAXIAL TENSILE AND COMPRESSIVE STRESS. EXPERIMENTS WERE PERFORMED BY SUBJECTING TUBULAR SPECIMENS OF PLAIN CONCRETE TO COMBINED TORSION AND AXIAL LOADING. MEASUREMENTS WERE MADE OF THE APPLIED LOADS AND OF THE DEFORMATIONS OF THE CYLINDER. FROM THESE, THE MAGNITUDES AND DIRECTIONS OF PRINCIPAL STRESSES PC AND PT AND STRAINS EC AND ET IN THE CYLINDER WALL WERE OBTAINED. PREVIOUS WORK SHOWS THAT THE PROCESS OF FRACTURE IN CONCRETE UNDER UNIAXIAL TENSILE OR UNIAXIAL COMPRESSIVE STRESS BEGINS WITH THE SPREADING OF MICROCRACKS, MOST OF WHICH ORIGINATE IN THE COARSE-AGGREGATE/MORTAR INTERFACE. THE PRESENT EXPERIMENT DEFINES THE INCEPTION OF MICROCRACKING, OR "DISCONTINUITY," AS THE PROPORTIONAL LIMIT IN THE TORQUE/TWIST RELATION OF EACH CYLINDER. THE STRENGTH OF EACH CYLINDER IS DEFINED AS THE COMBINED MAXIMUM STRESSES. TWO BASIC TYPES OF EXPERMENTS WERE PERFORMED. ONE TYPE INVOLVED LOADING VIRGIN SPECIMENS UP TO MAXIMUM STRESS; PROPORTIONAL LOADING, IN WHICH THE RATIO OF PRINCIPAL STRESSES IS HELD FIXED, WAS APPLIED TO MOST SPECIMENS, BUT COMPRESSION FOLLOWED BY TORSION WAS APPLIED TO A FEW OTHERS. A SECOND TYPE OF EXPERIMENT INVOLVED APPLYING A SECOND LOADING TO SPECIMENS WHICH HAD PREVIOUSLY BEEN LOADED AND IN WHICH SEVERE MICROCRACKING EXISTED AT THE TIME OF SECOND LOADING. THE TWO TYPES OF EXPERIMENTS AIMED FIRST TO DEFINE THE STRESS/STRAIN PROPERTIES, STRENGTH, AND MODES OF FRACTURE OF VIRGIN SPECIMENS AND THEN TO FIND WHETHER THESE PROPERTIES ALTER WHEN MICROCRACKING OCCURS. THE PRINCIPAL TENSILE-STRESS/STRAIN RELATIONS WERE STRONGLY INFLUENCED BY THE RATIO PC/PT; THE INITIAL SLOPE OF THE PT/ET CURVE COULD BE PREDICTED FROM YOUNG'S MODULUS, POISSON'S RATIO AND THE STRESS RATIO. THE PRINCIPAL COMPRESSIVE-STRESS/STRAIN RELATIONS WERE INFLUENCED LESS BY THE STRESS RATIO. THE PRINCIPAL DIRECTIONS OF STRESS AND STRAIN COINCIDED VERY NEARLY, INDICATING THAT THE SPECIMENS WERE NEARLY ISOTROPIC; SLIGHT EVIDENCE OF ANISOTROPY WAS NOTICED, HOWEVER. THE STRENGTH OF THE SPECIMENS ALSO DEPENDED ON STRESS RATIO.

  • Corporate Authors:

    American Concrete Institute (ACI)

    38800 Country Club Drive
    Farmington Hills, MI  United States  48331
  • Authors:
    • Isenberg, J
  • Publication Date: 1968

Subject/Index Terms

Filing Info

  • Accession Number: 00213805
  • Record Type: Publication
  • Source Agency: Am Concrete Inst Journal & Proceedings
  • Report/Paper Numbers: Title No Sp 20-2
  • Files: TRIS
  • Created Date: Sep 28 1970 12:00AM