抄録
The results of the present study are summarized as follows : 1) A new type of stiff compressive testing machine was developed. The strain rate is controlled by wedge action of steel blocks installed in parallel with a specimen. The machine has a high stiffness (about 310t/mm) and is capable of carrying out cyclic loading. As its production cost is relatively cheap, it is a very practical testing machine to obtain complete stress-strain curves of strain-softening materials, such as rock and concrete. 2) The stress-strain curve of concretes made with various aggregates was measured by using the stiff testing machine. The complete stress-strain behavior is closely related to the degree of mechanical heterogeneity of concrete which is dependent on the relative mechanical properties of coarse aggregate and mortar matrix, and the degree of geometrical heterogeneity of concrete which is dependent on the volume fraction and shape of coarse aggregate and the relative size of coarse aggregate and specimen, etc. Compressive strength, strain at the compressive strength and the maximum negative slope of stress-strain curve increase, but the ductility and absorbed energy of concrete decrease with the decrease of heterogeneity.
