Fracture and Stress-Strain Relationship of Concrete under Triaxial Compression

Specimens of paste, mortar, and concrete were tested to failure when subjected to different amounts of lateral confining pressure. Two distinct modes of behavior were observed. Under low confining pressures, failure was accompanied by splitting, by large axial compressive and lateral tensile strains, significant internal microcracking and by a reduction in pulse velocity. For high lateral pressures, the axial strains at failure were smaller, lateral strains were compressive, and very little cracking and reduction in pulse velocity occurred at failure. This transition in behavior is explained in terms of the relative values of maximum deviatoric and hydrostatic components of failure stress, and the strengths of porous matrix and sliding interfaces. A stress-strain relationship includes two basic material constraints: bulk modulus and Poisson's ratio. These material properties are considered functions of invariants of stresses; the appropriate functions are derived from test results.