TRIAXIAL CHARACTERIZATION OF HIGH-STRENGTH PORTLAND CEMENT CONCRETE
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Triaxial characterization tests were conducted on a high-strength portland cement concrete proportioned from readily available materials. The objective was to develop mechanical response data for this high-strength concrete along selected stress and strain paths in multiaxial stress space. The concrete chosen for testing had a water-cement ratio of 0.23 and an unconfined compressive strength at 56 days of 105 MPa. The triaxial test specimens were 50-mm nominal diameter right circular cylinders. All tests were performed in a 276-MPa-capacity cylindrical triaxial cell in conjunction with a 1340 kN-capacity servohydraulic materials testing system. Confining pressure was generated by an external 600-MPa-capacity, air driven hydraulic pumping system. Active measurements attempted for each test included vertical and horizontal strain, testing machine displacement, axial load, and confining pressure. Triaxial shear tests were conducted at confining pressures of 50, 100, 150, and 200 MPa, and uniaxial strain tests were conducted to a principal stress difference of 350 MPa. These stress-strain data were plotted, and a failure envelope was developed. The test data show that high-strength portland cement concrete is capable of large plastic strains and ductile flow under states of high confinement. The material exhibited strain-softening behavior at the 50-MPa level; thus, it appears that the brittle-ductile transition for the material lies between the 50- and 100-MPa confining stress levels. At confining stresses of 100 MPa and greater, the material behavior is characterized by a strain-hardening ductile behavior to axial strains of 10% or greater.