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Mechanical Properties of DFRCC


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[Reference]
Fiber Reinforced Concrete (FRC)
Concrete is brittle material for tensile force. Concrete structures consist of merits of steel reinforcement, which is ductile material. There is a possibility of a new type of structure if tensile capacity can be expected in cementitious composites. Fiber reinforced concrete (FRC), in which tensile ductility is expected, has been studied.
DFRCC
In late years, the ductile fiber-reinforced cementitious composite (DFRCC), in which tensile ductility can be expected, has been developed. High strength organic fiber such as PVA, polyethylene fiber is mixed in mortar based materials. Though crack strain of normal concrete is several hundred micro strain, DFRCC has tensile ductility with several percent strain.
Uniaxial tension test for DFRCC
Currently, evaluation method for tensile ductility of DFRCC is not established. "Dog-bone type" specimens are introduced to obtain reliable data under pure tensile stress. Uniaxial tensile test has been performed.
Bending test for DFRCC
The uniaxial tension test is not so easy to manufacture the specimens and to perform. Bending test is also conducted to evaluate the fracture energy of DFRCC.
Pullout test of single fiber
Tensile ductility of DFRCC is controlled under the bridging performance of fiber between matrix. The bridging performance of fiber is provided by pullout characteristics of a single fiber from matrix. The pullout characteristics are influenced by bond behavior between fiber and matrix, and snubbing effect characterized by orientation angle of fiber. The fundamental pullout characteristics of fiber can be evaluated by the pullout test of single fiber.
Pullout test result
From the pullout test results, it is recognized that the maximum pullout load increases as the thickness of matrix (bond length) and orientation angle increases.
Calculation of bridging law
Calculation of tensile stress vs. crack width curve (bridging law) can be performed by numerical calculation in which the pullout loads of fibers in matrix are all added up under modeling of pullout behavior.
(Program for calculation of bridging law is available here.)

Orientation vizualization of the fibers
There is a possibility to not show the expected tensile performance if the fibers do not have a orientation to be effective for the subjected force. High viscosity of mortar matrix influences the flow of the fibers. The vizualization experiment using liquid glass is performed to evaluate the fiber orientation in DFRCC.
Vizualization method
The sets of the coordinates of the target fibers are obtained by the image processing. The fiber orientation angle is calculated and the influence of matrix flow is investigated. In other words, we can control the fiber orientation in DFRCC.