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The tension-softening parameters for different concrete-concrete interfaces are determined using the bimaterial cracked hinge model. Beams of different sizes having a jointed interface between two different strengths of concrete are tested under three-point bending (TPB). The load versus crack mouth opening displacement (CMOD) results are used to o...
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... tension-softening relation (stress versus crack opening s -w) is obtained for all the specimens using the parameters f t , a 1 , a 2 , and b 2 obtained from the inverse analysis. Figures 9 through 11 show the tension-softening relations for small-, medium-, and large-sized specimens, respectively, for the different types of interfaces considered in this study. It can be seen from the tension-softening diagrams that the intact specimens (Beam AI) of all sizes have a higher crack-resisting stress than interface specimens (Beams AA, AB, AC, and AD). ...
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Citations
... Currently, there are some tests for the shear strength of a layer, such as the direct shear test [16][17][18], Z-type specimen test [19], semicircular bend (SCB) specimen test [20], and double-edge notched plate test [21]. The tension fracture properties can be investigated using a three-point bending test [22], wedge splitting test [15,23], Brazilian disc test [24], and SCB specimen test [20]. Among these methods, the SCB specimen type could be adapted to research the shear and tension fracture properties of interfaces with less materials usage and a simpler manufacturing process. ...
Interfaces of cementitious layers have widely existed in construction projects, and they are the weakest part of the whole building. In this article, laser scanning and ultrasonic pulse, splitting tensile, and semi-disc fracture tests were carried out to study the bonding performance of cementitious layers. Different performance metrics, such as splitting tensile bond strength, ultrasonic pulse velocity, and attenuation of first arrival, were used to evaluate the bonding characteristics of the concrete layers. The results revealed that the parameters of the interface curve decreased, and the mechanical properties of the interface became weaker with an increase of the interval time. The amplitude of the first wave was more sensitive to the presence of the interface than the ultrasonic pulse velocity. Finally, the relationships between the performance metrics were analyzed. The fracture toughness of model I and mode II was highly correlated with the parameters of the micromorphology of the layered concrete, and the correlation coefficient is not less than 0.9511. The fracture toughness of mode I was strongly related to the splitting tensile strength, with a correlation coefficient of not less than 0.9744. This study was useful for the future study of the mode I and I fracture performance, the morphology, and other physical properties of cementitious layers.
... These repair methods entail the application of new materials onto the existing structures, thereby enhancing their strength and extending their operational lifespan. Although these repair techniques are widely utilised and highly developed, it is crucial to exercise caution to ensure optimal compatibility between the new and existing materials, as crack propagation at the interface is rather complex and it is weaker than the materials present on either side of the interface [1]. ...
... Concrete structures built on rock foundation, such as gravity dams, piers, and other offshore structures, are prone to fatigue or cyclic loading caused by periodic changes in temperature or cyclic waves and wind loads. Under the fatigue loading, damage will gradually accumulate to form microcracks along the interface between the concrete and rock, which is weaker than the matrices on both sides (Shah et al. 2011). Research studies have confirmed that the stability of microcracks subjected to fatigue loading is strongly dependent on the loading amplitude (Breitenbücher and Ibuk 2006). ...
... Here, f t denotes the uniaxial tensile strength of concrete. Shah and Kishen (2010) and Shah et al. (2011) experimentally investigated the concrete-to-concrete interface fracture, the tension softening, and nonlinear fracture properties between different strengths of concrete. However, in cases of a rock-concrete interface, to the best of the authors' knowledge, no formulized tensionsoftening relationship based on experimental results has been reported. ...
To investigate the interface mechanics and fracture properties and establish an interface tension-softening constitutive law between concrete and rock for analyzing fracture failure of rock-concrete structures, uniaxial tension and three-point bending tests are conducted on rock-concrete composite specimens with artificial grooving or natural interfaces. Tensile strength, fracture energy, and initial fracture toughness of a rock-concrete interface are obtained from experimentation. Based on the load-displacement curves measured in the three-point bending test, the energy dissipation at a rock-concrete interface is derived using the modified J-integral method. In addition, through enforcing a balance between energy dissipation and energy generated by fictitious cohesive forces acting on the fracture process zone (FPZ), the tension-softening constitutive law of a rock-concrete interface is established, which takes into account the effects of fracture energy and tensile strength of an interface. For the sake of practical applications, the tension-softening constitutive expression is simplified as a bilinear function. Finally, the crack propagation process of a series of concrete-rock composite beams is simulated numerically based on a nonlinear fracture mechanics theory by introducing a crack-propagation criterion. The predicted load versus crack mouth opening displacement (P-CMOD) curves show a reasonable agreement with the experimental ones, verifying the tension-softening constitutive law for the rock-concrete interface derived in this study.
The construction industry is experiencing a significant increase in hybrid concrete structures due to the need for repairing/strengthening of existing structures and the development of novel hybrid structures. The crack development and the ultimate capacity of hybrid concrete structures may significantly be governed by the properties of interface between the two concretes, making the quantification of inter-face properties essential. A large number of bond tests have been reported in literature but most of them do not result in a failure directly/entirely at the interface (unless the interface is very weak), resulting in only a lower bound estimate of the interfacial strength. Furthermore, the reported interfacial properties are only determined from small-scale bond tests where structural effects (like shrinkage) are limitedly taken into account. In the current study, the most commonly used bond tests are critically assessed in terms of the stress distribution caused by their inherent boundary conditions. Furthermore a testing procedure is then discussed which can allow for the quantification of the interfacial properties. A possible structural test is also designed which forces the failure to localize at the interface and allows to determine interface properties considering structural effects.
Most of the substrate-repair bond tests available are of limited practicality and comparability since results are intrinsically affected by the specific stress condition applied, specimen and interface geometry, and disturbed stress flows around the interface. A new experimental procedure is suggested, based on modification of the slant shear test, commonly adopted as a low-cost and easy-to-perform test. Specimen design, preparation, and testing are discussed. Cohesion and friction are extrapolated from experimental data. These two key-parameters can be employed to design and optimize repair bond strength and failure mechanisms under various interfacial stress states and for different application requirements.
