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).

Yes / To study the flexural behavior of Steel-FRP (Fiber-Reinforced Polymer) Composite Bars (SFCBs) reinforced Reactive Powder Concrete (RPC) frame beams, the flexural behavior of six frame beams with different types of concrete and reinforcement was simulated and analyzed using the finite element software ABAQUS. The strain behavior of concrete and reinforcement was simulated using real strain models, and the simulation results matched well with the experimental results. Based on the validated model, the effect of mechanical properties of concrete and SFCB, reinforcement ratio, and the dimensions of frame beam on the flexural behavior of frame beams was parametrically analyzed. The results showed that, compared with the steel-reinforced ordinary concrete (OC) frame beam, the ultimate deflection of SFCB-OC frame beam increased by 5%. Compared with the SFCB-OC frame beam, the bearing capacity and ultimate deflection of the SFCB-RPC frame beam increased by 16% and 22%, respectively. Improving the steel content of SFCB reduced the ultimate load and deformation of SFCB-RPC frame beam. The yield strength of SFCB core steel had a significant influence on the yield load of frame beam, but a small influence on the ultimate load and deformation. Enhancing the elastic modulus of SFCB out-wrapped FRP reduced the ultimate deformation of the frame beam. Improving the reinforcement ratio of SFCB increased the bearing capacity and reduced the deformation. When reinforced concrete frame beams had similar bearing capacity, the cross-sectional dimensions of steel-RPC frame beam, FRP-RPC frame beam, and SFCB-RPC frame beam are 90.1%, 61.5%, and 72.7%, respectively, of those of their corresponding respective reinforced OC frame beams. All reinforced RPC frame beams exhibited high bearing capacity, good deformation, ductility, and energy dissipation performance. This research can provide a reference for the design of SFCB-RPC frame beams. / High-End Foreign Experts Project of Ministry of Science and Technology, China (G2022014054L), the Science and Technology Project of Gansu Construction System (JK2021-19), the Science and Technology Project of Jiangsu Construction System (2018ZD047, 2021ZD06, 2023ZD104, 2023ZD105), the Science and Technology Cooperation Fund Project of Yangzhou City and Yangzhou University (YZ2022194), the Yangzhou Construction System Science and Technology Project (202309, 202312), the Research Project of Jiangsu Civil Engineering and Architecture Society (the Second Half of 2022).

Yes / To investigate the bending behavior of Steel-FRP Composite Bars (SFCBs) reinforced Reactive Powder Concrete (RPC) frame beams, both experimental and theoretical study were conducted on five concrete frame beams with different reinforcement ratio, types of concrete and reinforcement. The results indicate that the bending behavior of SFCBs-RPC frame beams progresses through three distinct stages: from loading to the cracking of tensile RPC, from cracking to the yielding of tensile SFCBs, and from yielding to failure. Compared with steel-reinforced RPC frames, the load of SFCBs-RPC frame beam continues to increase with the increase of deformation after the yielding of SFCBs, demonstrating good bearing capacity and ductility. Furthermore, the deformation and crack width of RPC frame beams are obviously lower than those of ordinary concrete frame beams, indicating the excellent deformation control and crack resistance ability of RPC beams. In addition, formulae for flexural stiffness at each stage were derived using the effective moment of inertia method. Taking the design code of reinforced concrete structure for reference and the tensile contribution of steel fibers and the mechanical performance of SFCBs into consideration, and the formulae for crack width of SFCBs-RPC flexural beam were developed. Formulae for the bearing capacity of SFCBs-RPC frame beams were also proposed on the base of simplified materials constitutive models and reasonable basic assumptions. The values predicted by these proposed formulae aligned well with the results tested. The research provides a theoretical support for the design and application of SFCBs-RPC frame beams.

Submitted by Vanessa Nunes (vnunes) on 2015-03-31T13:19:31Z No. of bitstreams: 1 RobertoChrist.pdf: 9317574 bytes, checksum: 23b19b5dd98381b184ffb8f3c20b2951 (MD5) / Made available in DSpace on 2015-03-31T13:19:31Z (GMT). No. of bitstreams: 1 RobertoChrist.pdf: 9317574 bytes, checksum: 23b19b5dd98381b184ffb8f3c20b2951 (MD5) Previous issue date: 2014-02-20 / itt Performance - Instituto Tecnológico em Desempenho da Construção Civil / O desenvolvimento de novos concretos vem sendo ampliado ao longo dos anos, o que ocorre paralelamente ao aprimoramento dos cálculos estruturais e ao maior conhecimento sobre as propriedades dos materiais, o que conduz os projetistas ao desenvolvimento de estruturas que necessitam ter características específicas. Com isso surge a necessidade de se desenvolver concretos especiais, que apresentam elevada resistência mecânica e durabilidade. O concreto de pós reativos, também chamado de CPR, é um exemplo destes materiais. Trata-se de um concreto de ultra alto desempenho, com elevada resistência mecânica, extremamente dúctil e de baixa porosidade. Este tipo de concreto apresenta propriedades mecânicas superiores em comparação aos concretos de alta resistência, chegando a resistências à compressão de 200 MPa, à tração de 45MPa e módulo de elasticidade superior a 50 GPa. O consumo de cimento neste tipo de concreto pode atingir 800 kg/m3, além de incorporar elevado volume de sílica ativa. A otimização granular dos constituintes, realizada através de métodos de empacotamento de partículas, faz com que seja possível obter um material com o mínimo de vazios e elevada densidade. As fibras introduzidas no composto proporcionam elevada ductilidade. Neste trabalho, parte do cimento Portland foi substituído por cinza volante, para desenvolver um CPR com baixo consumo de aglomerantes. Também foi estudada a incorporação de dois tipos de fibras, ou hibridização, para uma matriz de CPR com menor consumo de cimento. A introdução de dois tipos distintos de fibras proporciona ao material maior sinergia, diminuindo a formação e a propagação de fissuras durante o carregamento. Os resultados obtidos nesta pesquisa mostram que a substituição parcial do cimento por cinza volante apresentou melhor desempenho mecânico, atingindo resistência à compressão de aproximadamente 190 MPa com 30% de adição. A incorporação de dois tipos distintos de fibras, aço e polipropileno em teores de 80% e 20% respectivamente, proporcionou ao material elevada resistência à tração na flexão e tenacidade. Portanto, é possível dosar CPR com menores consumos de cimento e uso de dois tipos de fibras, melhorando as propriedades da mistura e obtendo um compósito com reduzido impacto ambiental. / The development of new concretes is being expanded over the years, withal the improvements in structural design, along the increased knowledge of materials properties, which leads the designers to develop structures with specific requirements. It arises the need of the development of special concretes, with have enhanced mechanical strength and durability. Reactive powder concrete, also called RPC, is an example of these materials. This is an ultra-high-performance concrete with high mechanical strength, extremely ductile and low porosity. This type of concrete has superior mechanical properties compared to high strength concrete, reaching compressive strengths of 200 MPa, tensile strengths of 45 MPa and modulus higher than 50 GPa. The cement consumption in this type of concrete may reach 800 kg/m3, while incorporating high volumes of silica fume. The optimization of granular constituents accomplished by particle packing methods provides a material with a minimum of voids and also high density. The fiber introduced into the material compound provides high ductility. On this report, fly ash was used to replace some part of the cement, aiming the development of a RPC with low agglomerate consumption. It was also studied the use of two types of fiber, or hybridization, to a RPC matrix array of CPR with less consumption of cement. The introduction of two distinct types of fibers gives the material improved synergy, decreasing the formation and propagation of cracks during the charging. The results obtained in this study show that the partial replacement of cement by fly ash gives better mechanical performance, reaching the compressive strength of approximately 190 MPa with 30% addition. The incorporation of two different types of fibers, steel and polypropylene at levels of 80% and 20% respectively, provided the materials high tensile strength and toughness. Therefore, it is possible to compose an RPC with lower cement consumption and use of two types of fibers, improving the properties of the mixture and obtaining a composite with reduced environmental impact.

Civil engineering development is connected with the application of new construction methods and the development of new building materials. Concrete, as one of the basic building materials, is part of this development. A major turning point in the development of concrete and its properties occurred with the use of new, more efficient plasticizing additives. This allowed to produce concrete with lower water cement ratio, while increasing the strength of concrete. Gradually, the compressive strength of concrete boundary has moved by several levels, when there are currently commonly used concrete with strength of about 100 N/mm2 and with the special methods of concrete production strength range from 250 to 300 N/mm2. A negative aspect of the development of (ultra) high-strength concrete is their energy and economic demands. A characteristic feature of high-strength concrete is a high content of cement and very fine admixtures, especially silica fume. One way to improve the economics of these types of concrete is the application of cheaper admixture based on industrial waste. The content of this work is the observation and description of the properties of high-strength concrete and reactive powder concrete, in which the admixtures were based on industrial waste were applied. Part of this work is the comparison of economic parameters for individual types of concrete.