Abstract
Tensile strength and fracture toughness are two essential material parameters for the study of concrete fracture. The experimental procedures to measure these two fracture parameters might be complicated due to their dependence on the specimen size or test method. Alternatively, based on the fracture test results only, size and boundary effect models can determine both parameters simultaneously. In this study, different versions of boundary effect models developed by Hu et al. were summarized, and a modified Hu-Guan’s boundary effect model with a more appropriate equivalent crack length definition is proposed. The proposed model can correctly combine the contributions of material strength and linear elastic fracture mechanics on the failure of concrete material with any maximum aggregate size. Another size and boundary model developed based on the local energy concept is also introduced, and its capability to predict the fracture parameters from the fracture test results of wedge-splitting and compact tension specimens is first validated. In addition, the classical Bažant’s Type 2 size effect law is transformed to its boundary effect shape with the same equivalent crack length as Koval-Gao’s size and boundary effect model. This improvement could extend the applicability of the model to infer the material parameters from the test results of different types of specimens, including the geometrically similar specimens with constant crack-length-to-height ratios and specimens with different initial crack-length-to-height ratios. The test results of different types of specimens are adopted to verify the applicability of different size and boundary effect models for the determination of fracture toughness and tensile strength of concrete material. The quality of the extrapolated fracture parameters of the different models are compared and discussed in detail, and the corresponding recommendations for predicting the fracture parameters for dam concrete are proposed.
Highlights
At present, several super-high arch dams have been constructed or are under construction in Southwest China [1,2,3]
Koval-Gao’s size and boundary effect model is less flexible than the other two models, because the liner fit is unique for one set of the test results, and one can calculate the tensile strength from the intercept and fracture toughness from the slope, respectively
Hu-Guan’s boundary effect model proposed in this study, the Koval-Gao’s size and boundary model, and Bažant’s Type 2 size effect law are all able to capture the effects of crack length and sample size on the fracture behavior of wedge-splitting and compact tension specimens
Summary
Several super-high arch dams have been constructed or are under construction in Southwest China [1,2,3]. The proposed modified Hu-Guan’s boundary effect model considers the effect of maximum aggregate size on the equivalent crack length, changes the contributions of strength of material and linear elastic fracture mechanics (LEFM) on the specimen failure This improvement is anticipated to be important when the maximum aggregate size of concrete getting larger. The test results of geometrically similar wedge-splitting and compact tension specimens with constant crack-length-to-height ratios [28,29,30] and specimens with different initial crack-length-to-height ratios [31,32,33] are adopted, to verify the applicability of the different boundary effect models on the determination of fracture toughness and tensile strength for concrete material
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