CRACKING AND FRACTURE OF CONCRETE AND CEMENT PASTE

CRACK FORMATION AND PROPAGATION WERE STUDIED EXPERIMENTALLY AND THEORETICALLY FOR CONCRETE SUBMITTED TO STATIC COMPRESSIVE LOAD, TO SUSTAINED LOAD, AND TO PULSATING LOAD. SPECIMENS 7.5 BY 7.5 CM IN CROSS SECTION AND 40 CM LONG WERE PREPARED FROM CONCRETE HAVING A WATER-CEMENT RATIO OF 0.52, 325 KG STANDARD PORTLAND CEMENT PER CU M, AND 16 MM MAX. SIZE GRANITE GRAVEL AGGREGATE. THE SPECIMENS WERE SLICED IN SECTIONS, 7.5 BY 7.5 BY 2.5 CM. THE CUT SURFACES, DISPLAYING CROSS SECTION THROUGH THE MATERIAL STRUCTURE, WERE POLISHED AND THE SPECIMENS WERE DRIED IN THE LABORATORY FOR SEVERAL YEARS BEFORE BEING LOADED. MICROSCOPIC AND SONIC OBSERVATION METHODS WERE USED TO STUDY THE FORMATION AND PROPAGATION OF CRACKS IN THE MATERIAL STRUCTURE WHILE THE SPECIMENS WERE LOADED: (1) SHRINKAGE CRACKS WERE NOT OBSERVED IN SPECIMENS WHICH HAD BEEN DRIED FOR SEVERAL YEARS. (2) WHEN THE SPECIMENS WERE LOADED INSTANEOUSLY IN COMPRESSION, THE FIRST CRACK DEVELOPED AT 45 TO 55 PERCENT OF THE COMPRESSIVE STRENGTH. (3) THE CRACK ALWAYS DEVELOPED IN THE BOND PHASE BETWEEN THE CEMENT MORTAR MATRIX AND ONE OF THE LARGER AGGREGATE PARTICLES, AND EXTENDED IN THE DIRECTION OF APPLIED LOAD. (4) WHEN LOAD WAS INCREASED, THE CRACK WIDENED AND PROPAGATED IN THE DIRECTION OF APPLIED LOAD.(5) COMPRESSIVE FAILURE OF CONCRETE IS NOT CAUSED BY GRADUAL DETERIORATION OF THE MATERIAL STRUCTURE DUE TO PROGRESSIVE CRACKING, BUT IS INITIATED BY THE SPLITTING OF CONCRETE SPECIMENS INTO COLUMNS IN THE DIRECTION OF APPLIED LOAD. (6) A THEORETICAL ANALYSIS OF THE STRESS DISTRIBUTION AROUND DENSE AGGREGATE PARTICLES WITH HIGH MODULUS OF ELASTICITY INDICATES WHY CRACKS ALWAYS DEVELOP IN THE BOND PHASE OF CONCRETE MADE WITH SUCH AGGREGATE MATERIAL. (7) WHEN SPECIMENS ARE SUBMITTED TO SUSTAINED LOADING, THE CRACKS ARE INITIALLY UNSTABLE. (8) WHEN CONCRETE IS SUBMITTED TO PULSATING LOAD, CRACKS ONCE FORMED, NEVER STABILIZE BUT CONTINUE TO GROW UNTIL ULTIMATE FAILURE OCCURS. AND (9) FRACTURE OF CEMENT PASTE MAY BE INITIATED BY FLAWS IN THE BOND PHASE BETWEEN UNHYDRATED CEMENT GRAINS AND HYDRATED CEMENT GEL.

  • Corporate Authors:

    American Concrete Institute (ACI)

    38800 Country Club Drive
    Farmington Hills, MI  United States  48331
  • Authors:
    • Hansen, T C
  • Publication Date: 1968

Subject/Index Terms

Filing Info

  • Accession Number: 00213806
  • Record Type: Publication
  • Source Agency: Am Concrete Inst Journal & Proceedings
  • Report/Paper Numbers: Title No Sp 20-3
  • Files: TRIS
  • Created Date: Sep 28 1970 12:00AM