Papers by Keyword: Concrete

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Authors: Tze Yang Darren Lim, Bahador Sabet Divsholi, Susanto Teng
Abstract: In today’s rapid construction, a reliable method for quick evaluation of concrete quality during construction is very important. The compressive strength of concrete has been used to evaluate the mechanical properties of concrete; however compressive strength may not represent the durability of concrete. Rapid Chloride Migration Test (RCMT) and electrical resistivity can be used to evaluate the durability of concrete. Obtaining the coefficient of chloride diffusivity from RCMT usually requires a testing duration of 24 hours or less for normal strength concrete. With the inclusion of supplementary cementitious materials and lower water/cementitious ratio to achieve a higher strength and more durable concrete, testing of the concrete becomes an elaborate affair which might takes at least four to five days of testing. Electrical resistivity technique has been used to evaluate the quality of normal strength concrete. However the suggested classification of concrete quality is not applicable to ultra durable concrete. In this work, the effectiveness of using the concrete resistivity test results from electrical resistivity technique is studied. With the use of direct and four points Wenner probe methods, the concrete resistivity results were obtained and compared with the coefficient of chloride diffusivity from RCMT. Six mixes of three different grades with the inclusion of 30% granulated ground blast-furnace slag and 10% undensified silica fume were designed and tested; and high correlation coefficients (>0.94) for all the mixes were achieved. This represents the effectiveness of using the electrical resistivity technique to carry out fast and accurate in-situ test to determine the quality of the ultra durable concrete.
1989
Authors: Vladimír Křístek, Lukáš Kadlec
Abstract: Due to increase of requirements on accuracy of structural analyses, practically applicable computational tools for reliable determination of the real structural performance of bridges are needed. A method is proposed for the true full 3D analysis which can be applied to achieve the real spatial behaviour of concrete bridge structures taking into account rheological phenomena and changes of structural systems. Particularly, the effects of shear lag, shear performance of webs of box girders, warping torsion, warping of cross-sections, distortional effects, state of stresses in the singular regions, the real prestress loss, etc., can be correctly determined. The method combines conventional approaches (based on the elementary beamtype assumptions) for calculating the time development of the internal forces due to rheological phenomena and changes in the structural system during construction and routine commercial FEM software intended for calculating spatial shell structures. The method is capable to give the true 3D prediction of structure behaviour by using only commercially available software. The primary advantage of the proposed method is its ease of application which allows the true 3D performance to be determined from simple calculations. The method offers the designers of concrete bridge girders an ideal design tool. The correct 3D simulation can lead to more efficient and economical designs.
69
Authors: Jun Hong, Li Guo, Ling Qiao, Xiao Ming Guo
Abstract: Since meso-structure of plain concrete can not be observed directly, numerical simulation is the main approach to obtain the model coincident with the real structure on statistics. By applying the discrete element method, we have developed the 3D dynamic simulation for random aggregate model of plain concrete. According to the real ration of mass, the spatial positions of aggregate have been obtained, which is more close-grained compared with the random-distributed models based on Monte Carlo method. Compared with the geometrical generating algorithm for 2D random polyhedral aggregate, the algorithm for 2D or 3D random polyhedral aggregate is simpler. The results are the foundation for further studying the interface fracture and chloride diffused channels.
56
Authors: Han Wang, Ming Hao Zhao, Ji Gao, Guang Yuan Wang
Abstract: Concrete is usually described as a three-phase material, where matrix, aggregate and interface zones are distinguished. The beam lattice model has been applied widely by many investigators to simulate fracture processes in concrete. Due to the extremely large computational effort, however, the beam lattice model faces practical difficulties. Moreover, real fracture processes are 3D and not 2D. In our investigation, a new 3D lattice called generalized beam (GB) lattice is developed to reduce computational effort. Numerical results obtained by the model are in agreement to what are observed in tests. The 3D effects of the particle content on the peak load and ductility are discussed as well as the 3D fracturing phenomenon.
1455
Authors: Le Sheng Hu, Shui Fu Chen
Abstract: This paper presents a numerical strategy for realistic modelling of the internal material configuration and cracking of concrete on mesoscale. Polyhedron shapes resembling crushed rocks are adopted to represent the aggregate. A packing approach in which the particles are heaped up layer by layer is proposed for 3-D condition. A cubic representative volume element (RVE) is generated using the method. The cohesive approach, in which zero thickness cohesive elements are inserted into the ordinary finite element mesh along the potential cracking path, is adopted to model the cracking developing process. The cracking behaviours of created RVE under uniaxial tension are well simulated using the current approach.
972
Authors: Jean-Marc Tulliani, Laura Montanaro, Alfredo Negro, Mario Collepardi
1847
Authors: Lin Xu, Chong Fang
Abstract: In order to solve the problems of one-sidedness of current researches in classification of fly ash, degree of fineness, vitreous body, ignition loss, K2O, SO3 and CaO are chosen as the index properties to analyze projection pursuit classification method after analyzing chemical constituents and physical properties that influence the quality of fly ash. Targeting on the activity characteristics, the thesis establishes a projection pursuit cluster analysis model and makes a program on the basis of MATLAB. Population migration algorithm is adopted to seek an optimal projection direction. Fly ash is classified in accordance with property index value of the projection. Researches have proved that the model overcomes the shortcomings of traditional classification methods and reflects the quality and performance of fly ash in a comprehensive way. The evaluation is simple with accurate results and provides a scientific basis for the comprehensive utilization of fly ash.
900
Authors: Osvaldo Vallati, Fabrizio Gara, Gianluca Ranzi, Graziano Leoni
Abstract: This paper presents a comparison of available numerical structural formulations for the short-and long-term analysis of composite beams with partial shear interaction. Four methods of analysis are considered and these include the finite difference method, the finite element method, the direct stiffness method and the exact analytical model. The results obtained using these formulations are compared qualitatively and their accuracy is estimated, adopting the exact analytical model as a benchmark reference with the objective of establishing the minimum spatial discretisations required to keep the error within an acceptable tolerance. These comparisons are carried out for two static configurations, i.e. simply-supported beams and propped cantilevers, from which the qualitative behaviour of these formulations in the modelling of continuous beams can also be deduced.
625
Authors: Lenka Scheinherrová, Anton Trník, Eva Vejmelková, Pavel Reiterman, Igor Medveď, Robert Černý
Abstract: In this paper, the effect of elevated temperatures (up to 1000 °C) on thermal properties of two similar types of high-performance concrete containing fine ceramic waste and clay shale, respectively are used as a partial replacement of the cement binder is investigated. Samples were prepared in the same manner and both types of concrete contained from 0 to 60 mass% of either replacement. Both replacements were used in our study as a pozzolana active material which can partially replace cement binder and can improve the final properties of concrete. The aim of this paper is to compare the influence of two different pozzolana active materials on selected thermal properties of high-performance concrete at high temperatures up to 1000 °C. The investigation was performed using the differential scanning calorimetry and these results were supplemented by measurement on horizontal dilatometer.
79
Authors: Liang Wu, Ze Li, Shang Huang
Abstract: The cohesive crack model and the crack band model are two convenient approaches in concrete fracture analysis. They can describe in full the fracture process by the different manner: The entire fracture process zone is lumped into the crack line and is characterized in the form of a stress-displacement law which exhibits softening; or the inelastic deformations in the fracture process zone are smeared over a band of a certain width, imagined to exist in front of the main crack. The correlation of the two models is developed based on a characteristic width of crack band. The analysis shows that they can yield about the same results if the crack opening displacement in the cohesive crack model is taken as the fracturing strain that is accumulated over the width of the crack band model. Some basic problems are also discussed in finite element analysis.
3375
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