Abstract
With the recent development of 3D printing technology, concrete materials are sometimes used in 3D printing. Concrete structures based on 3D printing have been characterized to have the form of multiple layer build-up. Unlike general concrete structures, therefore, the 3D-printed concrete can be regarded as an orthotropic material. The material property of the 3D-printed concrete’s interface between layers is expected to be far different from that of general concrete bodies since there are no aggregate interlocks and weak chemical bonding. Such a difference finally affects the structural performance of concrete structures even though the interfaces are formed before initial setting of the concrete. The current study mainly reviewed the changes in fracture energy (toughness) with respect to various environmental conditions of such interface. Changes in fracture energies of interfaces between concrete layers were measured using low-speed Crack Mouth Opening Displacement (CMOD) closed loop concrete fracture test. The experimental results indicated reduction in fracture energy as well as tensile strengths. To improve the tensile strength of interfaces, the use of bridging materials is suggested. Since it was assumed that reduction in fracture energy could be a cause of shear strength, to evaluate the reduced structural performance of concrete structure constructed with multiple interfaces by 3D printing technology, the shear strength of RC beam by 3D printing technology was predicted and compared with that of plain RC beam. Based on the fracture energy measured in this study, Modified Compression Field Theory (MCFT) theory-applied Vector 2 program was employed to predict the degree of reduction in shear strength without considering stirrups. Reduction factors were presented based on the obtained results to predict the reduction in shear strength due to interfaces before initial setting of the concrete.
Highlights
In recent years, 3D printing technology has gained large attention and has become important in many engineering applications
GraphTest nearand point of 2.0 mm Crack Mouth Opening Displacement (CMOD), as shown in Figure 5, where WF is total work of fracture, Nmm; WFM is measured work of fracture, Nmm; A is Experimental procedure to estimate the fracture energy of interface formed by using 3D printing far tail constant, N-mm2 ; δR is load-point at the end of test, mm; and δA is CMOD at zero P1 for the technology was implemented by following the draft ASTM test standard (ACI 446 2009) for the raising part of curve, mm
Beam, cracks were formed at fracture energy energy affected beam, thethe cracks were formed at the the interfaces
Summary
3D (three dimensional) printing technology has gained large attention and has become important in many engineering applications. In this technology, powdered forms of materials such as resin and metals are processed to produce 3D shapes very precisely based on design data. The draft ASTM (2009) instructs to perform the experiments according to the constant certain upward force from the dead load. To offset such an upward force generated by self-weight rate of CMOD increase in the lower central notch of three-point bending test [11]. CMOD rate is not compensation, the whole graph must be offset upon test termination as in Figure 5 to make the load 0
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