Seventy-nine 10 x 10 x 55-cm prisms for triaxial compression-compression-tension specimens were tested. The tests were taken in a special device containing 2 compression testing apparatus to exert lateral compressive loadings and an ordinary universal material-testing machine to exert longitudinal tensile loading. One 3 mm fluorine-based resin sheet (Teflon) was used as a friction-reducing pad. Test results of strength and stress-strain relationships are analyzed, and formulas of concrete strength are suggested. Failure modes of specimens are also described.