中文摘要：

利用大型液压伺服试验机研究了不同加载速率下饱和混凝土与干燥混凝土的劈拉强度变化情况，试验研究表明：在准静态加载时，与干燥的混凝土相比饱和混凝土的劈拉强度有所降低，随着加载速率的升高，饱和混凝土的的动态劈拉强度有较大的提高。通过对干、湿混凝土强度变化的比较表明：孔隙及裂缝中的自由水对混凝土强度有所影响。根据细观层次上、不同加载速率下裂纹中孔隙水压力的作用形式（即低加载率时孔隙水的“楔入”作用和高加载率时的“Stefan效应”），利用断裂力学来探讨不同加载速率下饱和混凝土劈拉强度的变化机理。结果表明：提出的机理可以较好地解释饱和混凝土强度的变化情况。

英文摘要：

The tensile strengths of saturated and dry concrete under different loading rates were studied by splitting tensile tests. The experimental results show that the tensile strength of saturated concrete was lower than that of the dry concrete under low loading rate but was larger under high loading rate. The comparison between dry and saturated concretes indicates that the free water in the pores and cracks affects the mechanical properties of concrete. The mechanisms of these changes are analyzed in terms of the acting modes of pore water on the saturated concrete under different loading rates. The free water in the cracks acts as a wedge, which decreases the strength of saturated concrete under quasi-static loading, but it acts as opposite force, which increases the strength of saturated concrete under high loading rate according to the Stefan effect in physics. The fracture mechanics based on these mechanisms are used to discuss these changes and the results show that these mechanisms can explain the mechanical properties of saturated concrete well.