Abstract: Previous researches on the stress-strain curve of plastic concrete are focused on the curve in the absence of preloading. In this paper, compressive strength and elastic modulus tests were conducted on cylinder and prismoid concrete specimens poured with different mix proportions. The characteristics of the stress-strain curve,the stress-strain curves in the presence of preloading and in the absence of preloading and under cyclic loading were respectively analyzed. Moreover, the stress-strain curves with preloading and no preloading were compared. Through analysis on the slope of the curves, micropores were proved to exist in the concrete, and how the number of cycles during preloading affecting the curves was obtained. The results show that the rise stage of stress-strain curves of plastic concrete is significantly different from that of normal concrete, and the slope of stress-strain curves of preloading stage firstly increases then decreases, whereas the slope of stress-strain curves always increases at none-preloading stage. At the same time, we can macroscopically understand the existence of inner micro pores in the specimens, and the number of preloading cycles has a little effect on stress-strain curves.The results show that the rise of stress-strain curves of plastic concrete is significantly different than those of normal, the slope of stress-strain curves of preloading firstly increases then decreases, and the slope of stress-strain curves of no preloading has been increased. At the same time, we can understand the macro of the specimens, and number of preloading has no effect on stress-strain curves. The results have reference significance to the scientific and engineering applications.The results can be referenced for the scientific research and engineering applications of plastic concrete.

Key words: plastic concrete, cyclic loading, elastic modulus, stress-strain curve, peak stress