Yes / As a type of excellent reinforcing filler, super-fine stainless wire (SSW) can form widely distributed network in reactive powder concrete (RPC) to transfer crack tip stresses as well as inhibit the initiation and propagation of cracks, leading to significant improvement of flexural toughness of RPC. In this paper, the flexural toughness of RPC beams and plates reinforced with 1% and 1.5% by vol. of SSWs was investigated, and its calculation model was established according to the composite material theory. Experimental results showed that the flexural toughness of unnotched beams fabricated with RPC containing 1.5% SSWs is 146.5% higher than that of control RPC without SSWs according to load-deflection relationships. The equivalent flexural strength of notched RPC beams is enhanced by 80.0% as SSW content increases from 1% to 1.5%. The limitation ability of SSWs on crack mouth opening can be used to evaluate the flexural toughness of composites. An addition of 1.5% SSWs leads to 201.9% increase of flexural toughness of RPC plates in accordance with load-deflection relationships. The calculation model based on the composite material theory can accurately describe the toughening effect of SSWs on RPC beams and plates. The enhancement of flexural toughness of RPC caused by SSWs is beneficial for improving the safety of structures as well as broadening the engineering applications of composites. / National Key Research and Development Program of China (2018YFC0705601) and China Postdoctoral Science Fundation (2019M651116).

Concrete structures may be subjected to dynamic loading during their service life. Understanding the dynamic properties of concrete structures is becoming critical because of the increased concern about the dynamic loading of both civilian and military structures, and especially, the recent increase in terrorist attacks on structures. Fiber reinforced concrete (FRC) is known to exhibit superior performance in its post-peak energy absorption capacity, (i.e., toughness) under flexural and tensile loading. However, the behavior of fiber reinforced concrete under compressive impact has not previously been investigated. In the present research, the response of fiber reinforced concrete was investigated over the full strain rate regime, from static loading to high strain rate loading, and finally to impact loading. The compressive toughness of FRC under static loading was studied using an existing Japanese standard (JSCE SF-5). Then, a test method for FRC under compressive impact loading was developed, involving the use of a high speed video camera system to measure the deformation of FRC cylinders under compressive impact. The strain rate sensitivity of FRC in both flexure and compression was also fully investigated. FRC was found to have higher strengths under impact loading (both flexural and compressive) than under static loading. The compressive toughness under impact loading increased due to the high peak load and the high strain capacity. FRC under flexural impact loading showed a greater strength improvement than under static flexure. FRC displays a much higher Dynamic Improvement Factor (DIF) under flexural impact than under compressive impact. It gave an overall higher performance under impact than under static loading. It also exhibited a higher strain rate sensitivity than plain concrete in both compression and flexure. Damage analysis, in terms of loss of strain energy, was carried out based on damage mechanics principles. Damage was found to increase with increasing strain rate. A new constitutive model was proposed to account for the relationship between DIF (Comp) and strain rate and the data derived from the model were found to be consistent with the experimental results.

Concrete structures may be subjected to dynamic loading during their service life. Understanding the dynamic properties of concrete structures is becoming critical because of the increased concern about the dynamic loading of both civilian and military structures, and especially, the recent increase in terrorist attacks on structures. Fiber reinforced concrete (FRC) is known to exhibit superior performance in its post-peak energy absorption capacity, (i.e., toughness) under flexural and tensile loading. However, the behavior of fiber reinforced concrete under compressive impact has not previously been investigated. In the present research, the response of fiber reinforced concrete was investigated over the full strain rate regime, from static loading to high strain rate loading, and finally to impact loading. The compressive toughness of FRC under static loading was studied using an existing Japanese standard (JSCE SF-5). Then, a test method for FRC under compressive impact loading was developed, involving the use of a high speed video camera system to measure the deformation of FRC cylinders under compressive impact. The strain rate sensitivity of FRC in both flexure and compression was also fully investigated. FRC was found to have higher strengths under impact loading (both flexural and compressive) than under static loading. The compressive toughness under impact loading increased due to the high peak load and the high strain capacity. FRC under flexural impact loading showed a greater strength improvement than under static flexure. FRC displays a much higher Dynamic Improvement Factor (DIF) under flexural impact than under compressive impact. It gave an overall higher performance under impact than under static loading. It also exhibited a higher strain rate sensitivity than plain concrete in both compression and flexure. Damage analysis, in terms of loss of strain energy, was carried out based on damage mechanics principles. Damage was found to increase with increasing strain rate. A new constitutive model was proposed to account for the relationship between DIF (Comp) and strain rate and the data derived from the model were found to be consistent with the experimental results.

Concrete structures may be subjected to dynamic loading during their service life. Understanding the dynamic properties of concrete structures is becoming critical because of the increased concern about the dynamic loading of both civilian and military structures, and especially, the recent increase in terrorist attacks on structures. Fiber reinforced concrete (FRC) is known to exhibit superior performance in its post-peak energy absorption capacity, (i.e., toughness) under flexural and tensile loading. However, the behavior of fiber reinforced concrete under compressive impact has not previously been investigated. In the present research, the response of fiber reinforced concrete was investigated over the full strain rate regime, from static loading to high strain rate loading, and finally to impact loading. The compressive toughness of FRC under static loading was studied using an existing Japanese standard (JSCE SF-5). Then, a test method for FRC under compressive impact loading was developed, involving the use of a high speed video camera system to measure the deformation of FRC cylinders under compressive impact. The strain rate sensitivity of FRC in both flexure and compression was also fully investigated. FRC was found to have higher strengths under impact loading (both flexural and compressive) than under static loading. The compressive toughness under impact loading increased due to the high peak load and the high strain capacity. FRC under flexural impact loading showed a greater strength improvement than under static flexure. FRC displays a much higher Dynamic Improvement Factor (DIF) under flexural impact than under compressive impact. It gave an overall higher performance under impact than under static loading. It also exhibited a higher strain rate sensitivity than plain concrete in both compression and flexure. Damage analysis, in terms of loss of strain energy, was carried out based on damage mechanics principles. Damage was found to increase with increasing strain rate. A new constitutive model was proposed to account for the relationship between DIF (Comp) and strain rate and the data derived from the model were found to be consistent with the experimental results. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

In this study, the mechanical properties of a fiber-reinforced cementitious composite (FRCC) were derived for specimens fabricated using two different methods of casting: conventional cast construction and pump-driven extrusion. Through the extrusion process, fibers are more likely to be oriented along the length of the member being cast and will therefore be more efficient since they are aligned parallel to the tensile stresses produced in flexure testing. The FRCC employed 0.5% and 1% polyvinyl alcohol (PVA) fiber reinforcement by volume. The flexural properties of FRCC were determined using four-point bend tests according to a modified ASTM C1609. Calculations included the modulus of rupture (MOR) and flexural toughness based on load-deflection curves. The fracture properties of FRCC were determined by using three-point bend tests on the same design but having notched beams using the two-parameter fracture model (TPFM). Calculations included the Mode I critical stress intensity factor (KIC), the critical crack tip opening displacement (CTODc), the strain energy release rate (GIC), and the total fracture energy (GF). The results show that enhanced ductility and post-peak behavior are achieved in concrete to which fibers have been added, as has been demonstrated in other studies, although this study further demonstrated how preferential fiber alignment produced via an extrusion can enhance fracture and flexural properties of cementitious composites. / Master of Science / Fiber-reinforced cementitious composite (FRCC) is a type of cementitious composite that contains fibers that are added to the mixture to improve its strength, durability, and ductility. One of the key factors of FRCC that affects its mechanical properties is the fiber alignment. Extrusion can be used as a method to preferentially align the fibers in order to maximize the benefit of fibers. Extruded FRCC can be pumped through a nozzle, making fiber alignment a convenient option for construction projects where traditional concrete placement methods would be difficult. One of the main benefits of aligning fibers in pump-extruded FRCC is that it can improve cementitious composites' fracture and flexural toughness. Fracture toughness refers to the ability of a material to resist crack propagation, while flexural toughness refers to its ability to withstand bending. By adding fibers to the mixture, the fibers act as reinforcement and help to distribute stress more evenly throughout the material, leading to increased strength and ductility. Furthermore, the alignment of fibers within the mixture also plays a critical role in the fracture and flexural strength of the material. Research has shown that when fibers are aligned in a specific direction, they can improve the tensile strength of the concrete and decrease the likelihood of crack propagation. This can be especially useful in structures that are exposed to seismic activity or long-lasting heavy loads. Overall, the use of pump extrusion-based method as a fiber alignment for FRCC can significantly improve the fracture and flexural strength of concrete. This makes it an attractive option for construction projects that require strong and durable members.

During the last four decades, fiber reinforced concrete has been increasingly used in structural applications. It is generally accepted that addition of steel fibers significantly increases tensile toughness and ductility, also slightly enhances the compressive strength. Although several studies have reported previously the favorable attributes of steel fiber reinforced concrete (SFRC), little general data is related to performance modeling. There are studies on the effect of fibers on compression, tension and shear behavior of concrete. As models proposed so far can, at best, describe only a few aspect of SFRC with a given type and amount of fibers, establishing simple and accurate generalized equations to describe the behavior of SFRC in tension, compression and shear that take into account the fiber type and content is essential. Therefore, a comprehensive experimental research on SFRC is conducted in University of Canterbury to develop generalized equations to represent the characteristics of SFRC. In this research, standard material tests of SFRC are carried out in tension, compression and shear to enable the parametric characterization and modeling of SFRC to be conducted. The tests are conducted using two different propriety fiber types (NovotexTM and DramixTM) with volumetric ratios ranging from 0 to 2 percent of the Novotex fibers and with 1 percent Dramix fibers. Compression tests are conducted on small and large cylinders. For characterization of tensile behavior, several different test methods are used including: direct tension of SFRC alone; SFRC with tension applied to an embedded longitudinal rebar; and flexural bending test. Similarly direct shear tests are conducted to investigate the additional shear resistance contributed by steel fibers. Variations in the results of different specimens are reconciled through normalization of stress and strain parameters. Based on the experimental results, empirical relations are derived for modeling and analysis of SFRC.