Time-dependent fracture of concrete

Concrete generally exhibits time-dependent fracture behavior. In practical applications, such time-dependent characteristics of concrete can cause extraordinary deformations and stress corrosions, and thus affect the safety of a structure. If the time-dependent behavior of concrete is not thoroughly understood, an improper design (i.e., unsafe or uneconomical) may result. In this study, time-dependent tensile fracture behavior such as tensile creep rupture was investigated for better understanding of this phenomenon. Experimental program, theoretical modeling, and numerical analysis were included in this research.; In the experimental program, cylinder splitting test, tensile creep rupture test, and quasi-static loading test were performed. The tensile creep rupture behavior and the effect of loading rate on fracture behavior of concrete were observed through these tests.; Two time-dependent fracture mechanics models, the viscoelastic beam model (VBM) and the elastic beam model (EBM), were proposed to characterize the time-dependent behavior of concrete. Both of the proposed models were based on the concept of cohesive crack model. Concrete was assumed to behave in a viscoelastic manner in the viscoelastic beam model. An effective modulus of elasticity was proposed in the viscoelastic beam model to control the time-dependent deformation inside the fracture process zone. On the other hand, elastic behavior was assumed for concrete in the elastic beam model. A rate-dependent fracture energy was proposed in the elastic beam model to control crack propagation inside the process zone. A rate-sensitive elastic beam model (RSEBM) was further extended from the elastic beam model to characterize the loading rate effect on fracture behavior of concrete.; The proposed models were applied to simulate tensile creep rupture behavior through numerical analyses. The theoretical predictions were demonstrated to closely predict the creep rupture time and the time history of crack mouth opening displacements (CMOD). Parametric studies showed that the proposed models were able to give predictions consistent with commonly observed experimental results. In the meantime, the loading rate effect on fracture behavior of concrete predicted by the rate-sensitive elastic beam model was also considered reasonable in comparison with experimental findings.