Abstract: The mechanical behavior of concrete specimens (cube, L=100 mm) subjected to a mixed path of stress and strain loading was investigated. The specimens were statically loaded into a true triaxial apparatus. First, the stresses in all three directions were simultaneously increased to a specified value p. Then, the strain in Y axis was increased monotonically while maintaining a constant Z-axial stress and a constant strain rate ratio between Y and X axes. The experimental results show that the compressive strengths of the concrete increase with the minimum principal stress, and decrease linearly with the increase in the strain rate ratio, which are higher than uniaxial compressive strength, and the maximum value is 3.4 times of the uniaxial compressive strength. The hydrostatic pressure does not affect the initial shear modulus when the concrete specimens experience only monotonic increase in hydrostatic pressure, and a coinciding part is found in the curves of shear stress versus shear strsin for different experimental groups. The peak value of volumetric strain increases with the minimum principal stress and the strain rate ratio. The volume of the concrete specimen decreases first and then increases, volumetric dilatancy phenomenon occurs. The peak strength and peak volumetric strain appear at the same time when the minimum principal stress is 10 MPa. Then as the minimum principal stress increases the time interval between the peak strength and peak volumetric strain increases, and the peak volumetric strain appears latter.

Key words: civil engineering, composite material, concrete, mixed load path of both stress and strain, true triaxial, volumetric strain