STP678

    Fracture and Multiple Cracking of Cementitious Composites

    Published: Jan 1979


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    Abstract

    Cementitious composites consist essentially of a Portland cement paste, mortar or concrete matrix reinforced with steel (primarily) or mineral fibers. Compared to fiber reinforced polymeric and metallic matrices they form in a way a different class of composites. Their primary characteristics are: (1) that the ultimate tensile strain of the matrix is much lower than the yield or ultimate tensile strain of the fibers, and (2) the bond strength at the fiber matrix interface is relatively small (there is little adhesion in the chemical sense).

    Attempts have been made to calculate some fracture properties of these composites, using linear elastic fracture mechanics approach, by testing notched beam specimens, notched tension specimens, or cleavage type specimens. The results have been only partly successful because these composites may not show a brittle type of failure depending upon the relative dimensions of the specimen and the length of the critical crack (in the Griffith's sense). Tests on double cantilever type cleavage specimens of Portland cement mortar reinforced with steel fibers showed that a pseudo-plastic zone develops in front of an advancing crack. In this zone the matrix is cracked but the fibers are in a state of pull-out. If the plastic zone is larger than the specimen cross section, then instead of a rapid crack propagation, multiple cracking and ductile failure may occur. The length of the pseudo-plastic zone can be determined from the results of the cleavage tests and depends on: (a) the length, aspect ratio, volume fraction, spatial distribution, and the pull-out behavior of the fibers, and (b) the properties of the matrix.

    It is concluded that for cementitious composites for which no fracture testing standards exist, specific experimental techniques to measure fracture properties and analytical approaches to interpret their values, must be developed.

    Keywords:

    concrete, fiber concrete, fracture strength, crack propagation, notched beams, double cantilever beams, notched tensile prisms, multiple cracking, surface energy, size effects, fracture mechanics, reinforced concrete, fracture (materials)


    Author Information:

    Naaman, AE
    Associate professor of structural design and professor of civil engineering, University of Illinois at Chicago Circle, Chicago, Ill.

    Shah, SP
    Associate professor of structural design and professor of civil engineering, University of Illinois at Chicago Circle, Chicago, Ill.


    Paper ID: STP36637S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP36637S


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