Papers by Keyword: Aggregate

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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.
Authors: De Yu Kong, Jin Da Mao, Tong Yuan Ni, Jian Jun Zheng
Authors: Mohammad Reisi, Davood Mostofi Nejad
Abstract: It is nowadays very clear that the single most important parameter influencing the performance of concrete is the packing density of the aggregates. Among aggregate characteristics, grading of aggregates has the most significant effect on packing density (PD) of aggregates. In the current sstudy, packing density of five aggregates were measured by experimental tests and computer simulation base on discrete element method (DEM). Obtained results show that the performed computer simulation is very efficient method to predict packing density and optimization grading of aggregates.
Authors: Rong Lin Chen, Zhi Xing Zeng, Ke Min Zhou
Abstract: This paper is an overview of research about the concrete with expanded polystyrene beads as its aggregate in the past. First, a brief introduction to the expanded polystyrene beads concrete is given. Then, the researches of these years is presented and discussed, and the important studies are described in detail. Finally, the paper gives a summary of the research status and prospects of expanded polystyrene beads concrete.
Authors: Sarah Kayfetz Outzen, Cheng Chen
Abstract: Concrete has one of the highest carbon footprints of building materials in use, and is also one of the most often used building materials in modern construction. Polystyrene is a non-biodegradable polymer in continued use. This paper examines the feasibility of using polystyrene beads in structural concrete. Recycled polystyrene beads were used as a coarse aggregate in concrete mixtures to explore possible structural application. Two samples apiece of three experimental mixes of concrete as well as control concrete mixtures were tested in the laboratory for density and compressive strength at 14, 28, 56 and 70 days curing. The laboratory testing showed one experimental mixture was of comparable compressive strength to the control concrete mixture. The experimental results demonstrated that recycled polystyrene concrete in volumetric percentages below 18.75% could be a feasible green concrete mixture.
Authors: Mikhail D. Starostenkov, Nikolay Medvedev, Olga Pozhidaeva
Abstract: The formation of Frenckel pairs - vacancies and interstitial atoms takes place during external high energetical influence. The accumulation and aggregatization of point defects is noticed only at definite conditions. Vacancies form volume vacancy tetrahedrons and interstitial atoms form segregations. The conditions of the formation of point defects complexes on the basis of Frenckel pairs were studied by the methods of molecular dynamics in the dependence on temperature and intensity of external influence. Their possible role in the process of deformation and fracture of materials under study were evaluated. Comparison analysis of their stability was made for clusters of interstitial atoms. When the cluster had about 130 interstitial atoms, crowdion complexes were energetically profitable.
Authors: A. Fragata, R. Veiga
Abstract: Many historical buildings with renders based in air lime still exist in Portugal. These old mortars have proved to be durable and reliable materials. However, new lime mortars prepared nowadays to be used in conservation practice, often present low strength in comparison with cement mortars. This paper presents a study of the viability of improving the performance of lime mortars through the use of different nature aggregates (Tagus River siliceous sand and crushed calcareous sand) as well as different size distributions, varying the filler contents. For that purpose a set of mortars with volumetric proportion of 1:3 (lime:aggregate), using siliceous sand from Tagus river or calcareous sand and including different volume percentages of aggregate replacement by filler (0% of incorporation, 5% of incorporation, 10% of incorporation), were prepared. An evaluation of the main characteristics of this set of mortars was made in terms of: i) hygric behaviour (water absorption by capillarity), and ii) mechanical resistance (flexural and compressive strength and elastic modulus). This study aims to assess the viability and possible advantages of using calcareous aggregate in lime mortars and to evaluate the possibility of improving characteristics through a better compaction obtained by the incorporation of different ratios of filler.
Authors: António Santos Silva, Dora Soares, Lina Matos, Isabel Fernandes, Maria Manuela Salta
Abstract: The alkali-aggregate reaction (AAR) in concrete is a group of chemical reactions that involves the reaction of certain minerals present in the aggregates with alkali and hydroxyl ions in the interstitial solution of cement paste in concrete. These reactions form an alkaline hygroscopic gel that absorbs water and expands causing internal stresses with cracking [1]. The AAR mitigation measures oblige the correct evaluation of the alkali reactivity of the aggregates. This is normally assessed by petrographic, chemical or expansion test methods. Several studies regarding alkali reactivity of aggregates for concrete structures in Portugal, including bridges and dams, indicated that their field performance does not correspond to the previously performed evaluation. Presently, Portuguese methodology is based on the LNEC Specification E461-2007, which shows some limitations regarding rock types such as granitoids [2]. This situation motivated the development of a research project, involving medium and long term expansion tests in different conditions, under accelerated and natural exposure conditions, as well as petrographic evaluation of the main Portuguese aggregates used/to be used in concrete. This paper presents the preliminary results of this research.
Authors: Valeria Bennack, L.V.O. Dalla Valentina, Marilena Valadares Folgueras
Abstract: Economic and environmental issues are directly related to industrial processes which, not only employ natural resources but also generate by-products that may impact the environment. In order to achieve sustainable development, reducing the use of natural resources and lowering cost through adequate destination of waste becomes a crucial issue. The aim of this paper is to analyze the suitability of reusing waste (wood ash) resulting from the combustion process at wood product industries for manufacturing cement based materials used in civil engineering. The material assessed is ash from the combustion process of a wood product industry. In this study, physical and chemical properties such as grain size, mineral and chemical composition of this by-product were characterized. Thermal analysis and X-ray diffraction techniques were used for this purpose. Preliminary results show the suitability of using the waste (wood ash) for manufacturing cement based materials
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