Les Bétons de Poudre Réactive (BPR) sont connus pour leur résistance très élevée et leur bonne durabilité, mais aussi pour leur prix élevé. L’objectif de cette étude concerne la mise au point d’une formulation de BPR extrudable (BPR). Des essais préliminaires d’écoulement au mini cône d’Abrams ont été réalisés avec des teneurs variées en superplastifiant et en substituant partiellement la fumée de silice par du quartz broyé. Cinq mélanges ont été retenus et caractérisés de façon systématique au microscope électronique à balayage et en diffraction des Rayons X. Une étude complète de retrait au jeune âge, de résistance mécanique et de durabilité face à l’azote et aux ions chlorure a été menée. Un montage expérimental d’extrusion a été mis au point. Un mélange incorporant du quartz broyé en remplacement d’une fraction de la fumée de silice et une composition optimisée en superplastifiant montre des propriétés intéressantes : extrudabilité, très bonne durabilité, performances mécaniques améliorées et retrait diminué. Sur cette composition, l’étude microstructurale met en évidence le rôle que joue le superplastifiant sur la chimie d’hydratation avec une forte consommation en bélite. Ce mélange permet ainsi de diminuer le coût de fabrication pour un BPR en permettant d’économiser la fumée de silice coûteuse et en ne nécessitant aucun traitement thermique. / Reactive Powder Concrete (RPC) is well known for ultra-high mechanical performances and very good durability as well as for a high cost. The aim of this study is to find an extrudable RPC. Abrams cone preliminary tests were made with various contents of superplasticizer and a partial substitution of silica fume by crushed quartz. Then, fives concrete samples were chosen and systematically characterized by scanning electron microscopy and X-ray diffraction. Then, a complete study was made including early-age shrinkage, mechanical strength, gas permeability and chloride diffusion measurements. An experimental extruder was build. Among the five compositions, one of them, where crushed quartz replaces a part of silica fume, exhibits very good properties: good extrudability, very good durability, and better mechanical strength with an improvement of shrinkage. The microstructural study of this composition highlights the effect of the superplasticizer on hydration, with high belite consumption. This composition allows a lower cost of RPC with a decreasing of silica fume content, without thermal treatment.

This thesis presents an experimental and theoretical study of the material and structural behaviour of a Steel-Fibre reinforced Reactive Powder Concrete (SF-RPC). The experimental program consisted of three phases. Phase 1 involved the development of a design mix for use throughout the remainder of the study. Phase 2 consisted of an in-depth investigation into the material properties of the mix. The final phase of the experimental component was the testing of 16 plain and prestressed SF-RPC beams. Twelve beams were tested under short-term loading to determine their cracking and ultimate moment capacity. The remaining 4 beams were used to investigate the time-dependent flexural behaviour of prestressed SF-RPC slabs. The material properties were measured using a range of short-term tests and included the compressive and flexural behaviour, static chord modulus of elasticity and crack mouth opening. In addition to the short-term tests, investigation into the time-dependent material behaviour was undertaken and included the creep and shrinkage characteristics of the material. The response of the material to various curing conditions was also investigated. The structural behaviour investigated included the short-term flexural moment-curvature response and load-deflection behaviour of beams and slabs along with the crack patterns of both plain and prestressed SF-RPC members. In addition to the investigations into the short-term flexural behaviour, a study into the time-dependent flexural behaviour was also undertaken. There are currently 2 available models for predicting the flexural response of plain and prestressed RPC cross-sections. The analytical phase of this investigation involved an evaluation of these models. Based on the experimental findings and analysis, a modified model was proposed for calculating the short-term flexural behaviour of plain and prestressed SF-RPC beams. The applicability of an age-adjusted effective modulus method for calculating the time-dependent deformations of prestressed SF-RPC slabs under various levels of sustained loads was also evaluated and found to be adequate with minor refinements.

Yes / Reactive Powder Concrete (RPC) is a new type of cementitious materials with a complex hydration mechanism, and active admixtures greatly influence the hydration reaction, formation of hydration products, and evolution of microstructure. In order to comprehensively study the quantitative effects of active admixtures contents, namely silica fume, slag and fly ash, on hydration characteristics, hydration products, and microstructure of RPCs, tests of workability, setting time, electrical conductivity, bound water and mechanical properties were conducted. Furthermore, a series of properties including morphology and micro-structure characteristics of RPCs were analyzed by thermogravimetric (TG) analysis, X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), mercury intrusion porosimetry (MIP), Brunauer-Emmet-Teller (BET), and scanning electron microscope (SEM). The results indicate that the initial hydration reaction rate of RPCs is reduced by partly replacing cement with active admixtures. The pozzolanic effect created by the active admixtures enhances hydration and improves RPC's compressive and flexural strength. RPCs made of cement-silica fume mixture exhibit the best macroscopic properties. The adoption of silica fume promotes the production of C-S-H gel during hydration and exerts pozzolanic and crystal nucleation effects to promote cement hydration. RPCs made of pure cement exhibit 15.3% porosity after 28 days of hydration, with the largest proportion of less harmful pores in the microstructure. The porosity is reduced to 5.2% when cement is partially replaced with silica fume, and the microstructure is dominated by harmless pores. When replacement of silica fume is kept at 25%, using slag powder or fly ash substitute part of cement also reduces the number of less harmful pores. It is beneficial to add slag powder to increase the number of gel pores, whereas fly ash reduces the number of gel pores. The investigation presented in this paper would contribute to the production of low cost and environmentally-friendly RPCs, and accelerate the wider applications of ultra-high performance concrete (UHPC) in engineering structures.

A tecnologia dos materiais a base de cimento Portland vem se desenvolvendo rapidamente, onde a melhoria das propriedades mecânicas vem sendo alcançada, eliminando os agregados graúdos e estudando a composição granulométrica da mistura, procurando preencher os vazios utilizando materiais finos e ultrafinos, como pó de quartzo e a sílica ativa. Esta pesquisa tem como objetivos: desenvolver concreto de pós reativos com resistência à compressão próxima de 200 MPa e módulo de elasticidade acima de 45 GPa; propor uma relação constitutiva para o material, considerando o volume de fibras; especificar as deformações máximas na tração e na compressão; e verificar a influência das fibras nas resistências à compressão e à tração na flexão. Para isso, foi utilizado o método de empacotamento das partículas sólidas, com o intuito de definir composições granulométricas, e desenvolveu-se técnicas necessárias para a moldagem, adensamento e cura térmica. A análise experimental compreendeu o estudo das seguintes propriedades: resistência à compressão, módulo de elasticidade, resistência à tração na flexão, deformações e ductilidade. As fibras metálicas melhoraram as propriedades mecânicas e aumentaram a ductilidade do concreto. A temperatura de cura e o tempo de submissão ao tratamento térmico, tornou o material mais resistente. A deformação específica máxima na compressão foi definida experimentalmente como 4,3%. O limite elástico para as deformações de tração ficou em 0,28%. Foi proposta uma relação constitutiva para tensões de compressão, que pode ser utilizada para concretos de pós reativos, com resistência à compressão próxima de 200 MPa e taxa de fibras até 4% em volume. Os resultados obtidos indicam que o concreto de pós reativos desenvolvido apresentou altas resistências à compressão e à tração na flexão, onde a microestrutura do material mostrou-se com baixíssima porosidade e interface pasta - agregado praticamente suprimida. A tecnologia desenvolvida nesta pesquisa pode ser considerada um grande avanço na tecnologia de materiais a base de cimento Portland que, com maiores aperfeiçoamentos, espera-se a aplicação desse material em situações que tirem proveito das excelentes propriedades mecânicas e durabilidade / The technology of Portland cement materials has developed quickly, where the improvement of the mechanical properties has been reached, eliminating the coarse aggregates and studying the granular mixture, in order to fill the emptiness with fine and ultra-fine materials, like crushed quartz and silica fume. The present paper aimed: develop reactive powder concrete with compressive strength close to 200 MPa and module of elasticity above 45 GPa; propose a strength x strain relationship in compression for the material considering the volume of fibers; specify the maximum strain in the traction and in the compression; and to verify the influence of the fibers in the compression strength and in the bending strength. It went using the method of packing of the solid particles to define the grain size distribution, and necessary techniques were developed for the preparation and thermal cure. The experimental analysis understood the study of the following properties: compression strength, module of elasticity, bending strength, strain and ductility. The metallic fibers improved the mechanical properties and they increased the ductility of the concrete. The cure temperature and the time of submission to the thermal treatment, improved the compression strength. The maximum strain in the compression was defined experimentally as 4,3%. The elastic limit for the traction strain was 0,28%. A strength x strain relationship in compression was proposed, and can be used in reactive powders concrete, with compression strength of around 200 MPa and rate of fibers of up to 4% of volume. The results indicate that the reactive powders concrete developed presented excellent compression strength and bending strength, and the material presented a microestrutura with low porosity. The technology developed in this research can be considered a great progress in the technology of materials with Portland cement, and the application of that material is expected in situations that use advantage of the excellent mechanical properties and durability

A tecnologia dos materiais a base de cimento Portland vem se desenvolvendo rapidamente, onde a melhoria das propriedades mecânicas vem sendo alcançada, eliminando os agregados graúdos e estudando a composição granulométrica da mistura, procurando preencher os vazios utilizando materiais finos e ultrafinos, como pó de quartzo e a sílica ativa. Esta pesquisa tem como objetivos: desenvolver concreto de pós reativos com resistência à compressão próxima de 200 MPa e módulo de elasticidade acima de 45 GPa; propor uma relação constitutiva para o material, considerando o volume de fibras; especificar as deformações máximas na tração e na compressão; e verificar a influência das fibras nas resistências à compressão e à tração na flexão. Para isso, foi utilizado o método de empacotamento das partículas sólidas, com o intuito de definir composições granulométricas, e desenvolveu-se técnicas necessárias para a moldagem, adensamento e cura térmica. A análise experimental compreendeu o estudo das seguintes propriedades: resistência à compressão, módulo de elasticidade, resistência à tração na flexão, deformações e ductilidade. As fibras metálicas melhoraram as propriedades mecânicas e aumentaram a ductilidade do concreto. A temperatura de cura e o tempo de submissão ao tratamento térmico, tornou o material mais resistente. A deformação específica máxima na compressão foi definida experimentalmente como 4,3%. O limite elástico para as deformações de tração ficou em 0,28%. Foi proposta uma relação constitutiva para tensões de compressão, que pode ser utilizada para concretos de pós reativos, com resistência à compressão próxima de 200 MPa e taxa de fibras até 4% em volume. Os resultados obtidos indicam que o concreto de pós reativos desenvolvido apresentou altas resistências à compressão e à tração na flexão, onde a microestrutura do material mostrou-se com baixíssima porosidade e interface pasta - agregado praticamente suprimida. A tecnologia desenvolvida nesta pesquisa pode ser considerada um grande avanço na tecnologia de materiais a base de cimento Portland que, com maiores aperfeiçoamentos, espera-se a aplicação desse material em situações que tirem proveito das excelentes propriedades mecânicas e durabilidade / The technology of Portland cement materials has developed quickly, where the improvement of the mechanical properties has been reached, eliminating the coarse aggregates and studying the granular mixture, in order to fill the emptiness with fine and ultra-fine materials, like crushed quartz and silica fume. The present paper aimed: develop reactive powder concrete with compressive strength close to 200 MPa and module of elasticity above 45 GPa; propose a strength x strain relationship in compression for the material considering the volume of fibers; specify the maximum strain in the traction and in the compression; and to verify the influence of the fibers in the compression strength and in the bending strength. It went using the method of packing of the solid particles to define the grain size distribution, and necessary techniques were developed for the preparation and thermal cure. The experimental analysis understood the study of the following properties: compression strength, module of elasticity, bending strength, strain and ductility. The metallic fibers improved the mechanical properties and they increased the ductility of the concrete. The cure temperature and the time of submission to the thermal treatment, improved the compression strength. The maximum strain in the compression was defined experimentally as 4,3%. The elastic limit for the traction strain was 0,28%. A strength x strain relationship in compression was proposed, and can be used in reactive powders concrete, with compression strength of around 200 MPa and rate of fibers of up to 4% of volume. The results indicate that the reactive powders concrete developed presented excellent compression strength and bending strength, and the material presented a microestrutura with low porosity. The technology developed in this research can be considered a great progress in the technology of materials with Portland cement, and the application of that material is expected in situations that use advantage of the excellent mechanical properties and durability

Concrete is the most broadly used material in construction worldwide and Reactive Powder Concrete (RPC, a type of ultra high performance concrete) is a relatively new member of the concrete family. In this work the critical parameters of RPC mix design are investigated and the mix design is explored through a program of concrete casting and testing. Owing to the enhanced microstructure of RPC, porosity and permeability can be significantly decreased in the concrete matrix. This benefits the durability characteristics of RPC elements resulting in a longer service life with less maintenance costs than conventional concrete. It has been used for high integrity radiation waste material containers because of its low permeability and durability. Fibre reinforced RPC is also ideal for use in long span and thin shell structural elements without traditional reinforcement because of its advantageous flexural strength. Moreover, due to improved impact resistance, RPC can be widely employed in piers of bridges, military construction and blast protection. There is no standard approach to assessing the impact resistance of concrete. This investigation utilises relatively well accepted impact equipment to evaluate the mechanical properties of RPC under dynamic loading. The compressive and flexural tensile strengths of plain and fibre reinforced RPC are investigated using a variety of specimens and apparatus. The dynamic increase factor (DIF) is evaluated to indicate the strain rate sensitivity of the compressive and flexural strength.

Yes / In this study, the enhancement of stainless steel wires (SSWs) to the flexural fatigue performance of reactive powder concrete (RPC) including fatigue life and fatigue stress-strain hysteresis relationship as well as fatigue damage were investigated, and the underlying mechanisms were explored through microstructure observation and characteristic analyses of hydration products. The average flexural fatigue life of RPC is increased by 636.6%, 558.3% and 1010.7% at the maximum stress levels of 0.7, 0.8 and 0.9 when 1.5 vol.% SSWs are incorporated. The method of moments and method of maximum likelihood are employed to calculate the scale and shape parameters for fatigue life subscribed to Weibull distribution. The calculated ratio of flexural fatigue endurance limit to static flexural strength for SSWs reinforced RPC reaches up to 0.64. The incorporation of SSWs decreases the flexural failure damage of RPC by 41.5% and converts the long and link-up micro cracks into emission cracks centered on SSWs. Benefited from the large specific surface area of SSWs, abound of silica fume with pozzolanic activity absorbs on the surface of SSWs and continues to hydrate, reducing the surrounding water-binder ratio to form a microstructure enhancement zone with SSWs as the core and improve the homogeneity of RPC. This can be confirmed by the decrease of porosity, Ca(OH)2 crystal orientation index and molar ratio of CaO to SiO2 for calcium silicate hydrate gels. SSWs can also enhance the fatigue performance of RPC by transmitting hydration heat, inhibiting the initiation and propagation of micro cracks especially at the initial stage of fatigue load, bridging cracks and being pulled-off. The excellent flexural fatigue properties and homogeneous microstructures of SSWs reinforced RPC make it particularly suitable for large-span and ultra-thin elements in extreme service environments.

Yes / Super-fine stainless wire (SSW) can not only form widely distributed enhancing, toughening and conductive network in reactive powder concrete (RPC) at low dosage level, but also improve weak interface area and refine cracks due to its micron scale diameter and large specific surface. In addition, the crack resistance zone generated by SSWs and RPC matrix together has potential to further enhance the fracture properties of composites. Therefore, fracture and self-sensing characteristics of SSW reinforced RPC composites were investigated in this paper. Experimental results indicated that adding 1.5 vol. % of SSW leads to 183.1% increase in the initial cracking load of RPC specimens under three-point bending load. Based on two parameter fracture model calculations, an increase of 203.4% in fracture toughness as well as an increase of 113.3% in crack tip opening displacement of the composites reinforced with 1.5% SSWs are achieved. According to double-K fracture model calculations, the initiation fracture toughness and unstable fracture toughness of the composites are enhanced by 185.2% and 179.2%, respectively. The increment for fracture energy of the composites reaches up to 1017.1% because of the emergence of blunt and tortuous cracks. The mixed mode Ⅰ-Ⅱ fracture toughness of the composites is increased by 177.1% under four-point shearing load. The initial angle of mixed mode Ⅰ-Ⅱ cracks of the composites decreases with the increase of SSW content. The initiation and propagation of cracks in the composites can be monitored by their change in electrical resistivity. The excellent fracture toughness of the composites is of great significance for the improvement of structure safety in serviceability limit states, and the self-sensing ability of the composites can also provide early warning for the degradation of structure safety. / National Key Research and Development Program of China (2018YFC0705601), the National Science Foundation of China (51578110), China Postdoctoral Science Fundation (2019M651116) and the Fundamental Research Funds for the Central Universities in China (DUT18GJ203).

No / Nickel coated multi-walled carbon nanotubes (Ni-MWCNTs) having exceptional mechanical properties, thermal conductivity and dispersibility can effectively overlap in cementitious matrix, thus forming an enhanced and thermal conductive network. They are therefore a promising nanofiller for modifying cement and concrete materials. This paper studies the compressive properties of reactive powder concrete (RPC) filled with different aspect ratios of Ni-MWCNTs, including strength, toughness, Young's modulus and Poisson's ratio. It is concluded that the incorporation of 0.06 vol.% Ni-MWCNTs with an aspect ratio of 1500 maximally increases the compressive strength and toughness of RPC by 20.24%/20.39 MPa and 43.89%/56.35 (N·m), respectively. However, Young's modulus and Poisson's ratio of Ni-MWCNTs modified composites do not significantly be improved. Besides, a constitutive model of Ni-MWCNTs reinforced RPC under uniaxial compression is established based on the continuum damage mechanics theory, reasonably predicting the relationship between compressive strength and deformation of composites. The modification mechanism of Ni-MWCNTs is also investigated through the temperature distribution monitoring inside composites, Scanning Electron Microscope (SEM) observation and energy dispersive x-ray spectrometry (EDS) analysis of Ni-MWCNTs reinforced RPC. The thermal conductive network formed by Ni-MWCNTs in matrix reduces the temperature difference and improves the temperature uniformity inside composites, thereby decreasing thermal stresses, primary cracks and defects of composites. Furthermore, the incorporation of Ni-MWCNTs makes the RPC microstructures dense, decreases the average CaO to SiO2 ratio, and inhibits the development of cracks inside RPC, thus achieving effective enhancement to RPC. / National Science Foundation of China (52178188, 51978127 and 51908103), and the Fundamental Research Funds for the Central Universities (DUT21RC(3)039).

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).