The mixed mode I-II crack propagation process in concrete subjected to quasi-static conditions has been extensively investigated. However, in engineering practice, many concrete structures are subjected to various loading rates. The rupture process is closely related to the loading rate. Therefore, the knowledge of loading rate effect on the mixed mode I-II crack propagation process in concrete is of significant application value. The purpose of this study is to predict the crack propagation in concrete under different loading rates and to evaluate the effect of loading rate on the characteristics of crack propagation in concrete by laboratory tests and numerical analyses. A total of 60 four-point shear concrete specimens with four different initial crack locations are investigated in the study. The mixed mode I-II crack propagation process in concrete is evaluated for loading rates of 0.012, 0.12, 1.2, 12 and 120 mm/min. The main parameters, such as the tensile strength, elastic modulus, Poisson’s ratio, mode I initial fracture toughness and fracture energy of concrete, are measured. The initial fracture toughness is used as a parameter of the crack propagation criterion. The finite element method (FEM) is used to simulate the load-crack mouth shear displacement (P-CMSD) curves and crack propagation paths for each loading rate, and the numerical simulation results are compared with the test results. It is shown that the tensile strength, elastic modulus, mode I initial fracture toughness and fracture energy all increase significantly with loading rate. The P-CMSD curves and crack propagation paths of four-point shear specimens under each loading rate agree well with the test results. It is also shown that the mixed mode I-II fracture process zone length of concrete at a given load increases with loading rate.

准静态条件下混凝土的混合模式I-II裂纹扩展过程已得到广泛研究。但是，在工程实践中，许多混凝土结构要承受各种载荷率。破裂过程与加载速率密切相关。因此，了解加载速率对混凝土中I-II混合裂纹扩展过程的影响具有重要的应用价值。这项研究的目的是通过不同的实验室测试和数值分析来预测不同加载速率下混凝土的裂纹扩展，并评估加载速率对混凝土裂纹扩展特性的影响。本研究共研究了60个具有四个不同初始裂纹位置的四点剪切混凝土试样。评估混凝土在混合模式I-II裂纹扩展过程中的加载速率为0.012、0.12、1.2、12和120 mm / min。测量了混凝土的抗拉强度，弹性模量，泊松比，I型初始断裂韧度和断裂能等主要参数。初始断裂韧性用作裂纹扩展标准的参数。有限元方法（FEM）用于模拟载荷裂纹口的剪力位移（P-CMSD）曲线和裂纹扩展路径的每个加载速率，并将数值模拟结果与测试结果进行比较。结果表明，拉伸强度，弹性模量，I型初始断裂韧度和断裂能均随加载速率的增加而显着增加。各加载速率下四点剪切试件的P-CMSD曲线和裂纹扩展路径与试验结果吻合良好。还表明，在给定载荷下，混凝土的混合模式I-II断裂过程带长度随载荷速率的增加而增加。