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The Relation between Concrete, Mortar and Paste Scale Early Age Properties

MATERIALS 2021年第6期14卷 1569-1569页

作者： Klun, Martin Bosiljkov, Vlatko Bokan-Bosiljkov, Violeta Univ Ljubljana Fac Civil & Geodet Engn Jamova 2 SI-1000 Ljubljana Slovenia

microstructure development of concrete, mortar, and paste scale of cement-based material (CBM) during the early hydration stage has a significant impact on CBM's physical, mechanical, and durability characteristics at the high maturity state. The research was carried out using compositions with increased autogenous shrinkage and extended early age period, proposed within the RRT+ programme of the COST Action TU1404. The electrical conductivity method, used to follow the solidification process of CBM, is capable of determining the initial and final setting time, and the end of the solidification process acceleration stage for the paste and mortar scale. Simultaneous ultrasonic P- and S-wave transmission measurements revealed that the ratio of velocities V-P/V-S is highly dependent on the presence of aggregates-it is considerably higher for the paste scale compared to the mortar and concrete scale. The deviation from the otherwise roughly constant ratio V-P/V-S for each scale may indicate cracks in the material. The non-linear correlation between the dynamic and static elastic moduli valid over the three scales was confirmed. Additionally, it was found that the static E-modulus correlates very well with the square of the V-S and that the V-S is highly correlated to the cube compressive strength-but a separate trendline exists for each CBM scale.

关键词： concrete mortar and paste scale of cement-based material early hydration stage microstructure development electrical conductivity ultrasonic method standard tests

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Synthesis and characterization of bio-cement from conch shell waste

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CONSTRUCTION AND BUILDING MATERIALS 2019年 212卷 775-786页

作者： Chandrasiri, Chathurani Yehdego, Tesfamichael Peethamparan, Sulapha Clarkson Univ Dept Civil & Environm Engn 8 Clarkson Ave Potsdam NY 13699 USA

This paper demonstrates a laboratory-scale synthesis and analysis of cement using conch shell waste (CS bio-cement) similar in composition to Type I ordinary portland cement (OPC) by replacing calcite raw material with ground processed conch shell waste at varying levels (0-100%). The CS bio-cements were similar to Type I OPC in phase composition, hydration behavior, strength, and microstructure development up to 60% replacement. Higher conch shell substitution (60-100%) tends to incorporate more alumina and alkali in the clinker without compromising other properties significantly. CS bio-cement with above 60% conch shell exceeded the Na2O content limit for Type I OPC or low alkali cement. Nevertheless, those cements will be qualified as high alkali cements for appropriate construction use. The results suggest that CS bio-cement has potential for applications in concrete construction. However, the durability of the concrete containing CS bio-cement should be evaluated prior to real-world applications. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Conch shell waste Cement synthesis CO2 emission Phase composition Compressive strength Hydration kinetics microstructure development Reaction product composition

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Creep and Drying Shrinkage of Different Fly-Ash-Based Geopolymers

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ACI MATERIALS JOURNAL 2019年第1期116卷 39-49页

作者： Gunasekera, Chamila Setunge, Sujeeva Law, David W. RMIT Univ Sch Engn Melbourne Vic Australia RMIT Univ Civil & Infrastruct Engn Melbourne Vic Australia

Fly ash geopolymer concrete is a sustainable green construction material that has outstanding mechanical performance and is a low-energy material with a low carbon footprint. In this study, a detailed investigation of the long-term creep and drying shrinkage of three different 100% fry ash geopolymer concretes was carried out up to 1 year of age. Two geopolymers, producedfivm Gladstone and Pt. Augusta fly ashes, achieved approximately 700 microstrain at the end of 1 year-equivalent to the total creep strain displayed by portland cement (PC) concrete. Moreover;both geopolymer concretes displayed a lower creep coefficient than PC concrete. Hence, AS 3600 or the CEB-FIP model could be conservatively used to predict creep coefficient for two geopolymers. However, the Tatung fly ash geopolymer concrete differed signfficantly from the other geopolymers and achieved approximately 1900 microstrain after 1 year. The drying shrinkage of Gladstone and Pt. Augusta geopolymer concretes at 1 yearare 175 and 190 microstrain, respectively, while Throng geopolymer and PC concrete achieved 615 and 475 microstrain, respectively. All the fly ash geopolymer concrete showed lower drying shrinkage than the maximum permitted value recommended by AS3600. Incorporation of calcium-aluminasilicate-hydrate (C-A-S-H) gel with the sodium-alumina-silicatehydrate (N-A-S-H) geopolymeric gel was seen to positively affect the packing density of the gel phase. The degree of uniformity and compactness of aluminosilicate gel matrix together with the macroporosity in the 50 tint to 1 mu m range was identified as determining the long-term creep and drying shrinkage of the 100% low-calcium fly ash geopolymer concrete.

关键词： compressive strength creep drying shrinkage fly ash geopolymer concrete microstructure development porosity distribution

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Investigation about the reason of limited grain growth of Y-doped barium zirconate

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CERAMICS INTERNATIONAL 2019年第15期45卷 19120-19126页

作者： Wendler, L. P. Ramos, K. Souza, D. M. P. F. Univ Fed Sao Carlos Dept Mat Engn PPGCEM Grad Program Mat Sci & Engn Washington Luiz Rd Km 235 BR-13565905 Sao Carlos SP Brazil

Yttrium-doped Barium Zirconate is a protonic conductor that shows excellent chemical stability but low sinterability, demanding high sintering temperatures to achieve appropriate densification. However, even after sintering at high temperature, the grain size remains small, resulting in a low electrical conductivity due to the high grain boundary area. This behavior, according to literature, is associated with the high refractoriness. The first contribution of this work is the establishment of a suitable method to prepare the powder, following the fundamentals of conventional ceramic process, that allowed obtaining BZY20 samples with 98% of theoretical density after sintering at 1600 degrees C without sintering aid. The second contribution of this paper is to understand the parameters that limit the grain growth of BZY20, since high grain boundary area compromises the electrical conductivity. This understanding was constructed from SEM microstructure analysis associated with EDS of sintered samples.

关键词： Barium zirconate Conventional synthesis microstructure development

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Estimation of the Effect of Grain Boundary Diffusion on microstructure development in Magnetite Bi-crystal under Oxygen Chemical Potential Gradient at 823 K

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JOURNAL OF THE KOREAN CERAMIC SOCIETY 2012年第1期49卷 37-42页

作者： Ueda, Mitsutoshi Maruyama, Toshio Tokyo Inst Technol Grad Sch Sci & Engn Dept Met & Ceram Sci Meguro Ku 2-12-1-S8-11 Ookayama Tokyo 1528552 Japan

Mass transport near grain boundary in a magnetite bi-crystal has been estimated at 823 K by finite element method. Mass transport near grain boundary strongly depends on the diffusivities along grain boundary. If grain boundary diffusion has the same oxygen activity dependence as lattice diffusion, there is no mass transport between grains and grain boundary. On the other hand, mass transport between grains and grain boundary is observed in the case that grain boundary diffusion has different oxygen activity dependence.

关键词： microstructure development Grain boundary diffusion Mass transport Chemical potential distribution Divergence of the ionic flux

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microstructure tailoring of combustion-derived Ni-GDC and Ni-SDC composites as anode materials for intermediate temperature solid oxide fuel cells

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JOURNAL OF THE AUSTRALIAN CERAMIC SOCIETY 2019年第1期55卷 123-133页

作者： Skalar, Tina Zupan, Klementina Marinsek, Marjan Univ Ljubljana Fac Chem & Chem Technol Vecna Pot 113 Ljubljana 1000 Slovenia

The Ni-GDC and Ni-SDC cermets with tailored microstructures are potential candidates for anode materials in intermediate temperature SOFCs. In this work, a modified citrate-nitrate combustion synthesis was employed for the preparation of cermets. It was demonstrated that the preparation technique ensured randomly distributed phases of NiO and GDC or SDC on a nanometre scale. microstructure analysis revealed that during sintering under various conditions (from 1150 to 1400 A degrees C), the NiO phase grew faster than the GDC or SDC phases;however, phases remained well within the sub-micrometre range. In order to describe the overall relative electrical conductivity of the cermets, the sine-wave approximation of conductivity change for porous materials was used. Higher relative densities of the cermets resulted in improved electrical conductivity. The most appropriate sintering temperature, which ensured relatively small grains and at the same time sufficiently high electrical conductivity, for both materials was determined to be 1200 A degrees C.

关键词： Solid oxide fuel cell Combustion synthesis microstructure development Electrical properties

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Predicting final stage sintering grain growth affected by porosity

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APPLIED MATERIALS TODAY 2020年 20卷

作者： Kerbart, Gabriel Maniere, Charles Harnois, Christelle Marinel, Sylvain Normandie Univ ENSICAEN CNRS UNICAENCRISMAT F-14000 Caen France

Grain growth has a definitive impact on the quality of transparent sintered materials in areas such as ballistics, biomaterials, jewelry, etc. Controlling the sintering trajectory at the precise moment of final stage sintering is one of the main sintering challenges for obtaining high-performance, fully-dense nano ceramics. However, the final stage of sintering involves a very complex coupling between the rate of porosity elimination/grain growth and transition mechanisms. This complexity makes predicting the sintering trajectory very difficult, and most transparent material production escapes this problem by using expensive high-pressure methods such as hot isostatic pressing (HIP). In the quest for a pressureless transparent material process, this paper addresses the challenge of predicting grain growth in the transition domain from the grain growth onset (in a high porosity region) to full density for MgAl2O4 spinel. We present a comprehensive modeling approach linking theoretical models such as Zhao & Harmer's and Olevsky's equations to accurately predict the complex grain growth transition region of final stage sintering. This modeling approach opens up the possibility for numerical exploration of microstructure development via underlying kinetics experimental identification. (c) 2020 Elsevier Ltd. All rights reserved.

关键词： Grain growth Sintering microstructure development MgAl2O4 Mechanisms Modeling

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A development mechanism of graded microstructures in iron-containing SiC fibers revealed by electron microscopy

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MATERIALS CHARACTERIZATION 2020年第0期162卷 110177-000页

作者： Su, Xiaohui Luo, Zhishan Xiang, Congying Li, Yanwen Li, Siwei Yu, Zhiyang Xu, Qiang Gu, Hui Luo, Jian Xiamen Univ Minist Educ Key Lab High Performance Ceram Fibers Coll MatFujian Key Lab Adv Mat Xiamen 361005 Peoples R China Fuzhou Univ Coll Chem State Key Lab Photocatalysis Energy & Environm Fuzhou 350002 Peoples R China Xiamen Tungsten Co LTD Xiamen 361126 Peoples R China DENSsolutions Informat Laan 12 NL-2628 ZD Delft Netherlands Shanghai Univ Mat Genome Inst Sch Mat Sci & Engn Shanghai 200444 Peoples R China Univ Calif San Diego Dept NanoEngn Program Mat Sci & Engn San Diego CA 92093 USA

Transmission electron microscopy is utilized to investigate the microstructure development of iron-containing SiC fibers as a function of their annealing temperatures. Compositional and structural gradients along the radial directions start to form within SiC fibers fabricated at temperatures above 1200 degrees C. The graded microstructures are associated with the outward diffusion of iron-rich particles along the radial direction. In-situ heating TEM experiments suggest that the iron-rich particles within SiC fibers are highly mobile at elevated temperatures. Therefore, we propose that the graded microstructures along the radial directions are the synergetic effects of iron catalyzation and outgassing, namely, iron-rich particles are progressively driven to the surface of SiC fibers and in the trajectory of iron-rich particles, the decomposition of the amorphous SiCxOy phase is accelerated, promoting the growth of SiC grains. The current study emphasizes the important role of the outgassing process to the microstructure evolution of SiC fibers. Our proposed mechanism can be extended to understand the microstructural evolution of SiC fibers that use metallic additives as sintering aids.

关键词： Transmission electron microscopy In-situ electron microscopy microstructure development Polymer-derived SiC fibers Graded microstructure

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Cellular Automation Finite Element Modeling of the Evolution of the As-Cast microstructure of an Ultrasonically Treated Al-2Cu Alloy

Cellular Automation Finite Element Modeling of the Evolution...

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Light Metals Symposium at the 148th TMS Annual Meeting

作者： Wang, Gui Croaker, Paul Dargusch, Matthew McGuckin, Damian StJohn, David Univ Queensland DMTC St Lucia Qld 4072 Australia Univ Queensland Ctr Adv Mat Proc & Mfg St Lucia Qld 4072 Australia Univ New South Wales Sch Mech & Mfg Engn Kensington NSW 2033 Australia Pacific Engn Syst Int Glebe NSW 2037 Australia

ISBN: (纸本)9783030058647;9783030058630

Ultrasonic vibration characterised by high-intensity and low-amplitude is one of the physical (or mechanical) means that can effectively refine the as-cast grain structure without using inoculant particles [1-8]. Computational models that quantitatively describe hydrodynamic fields induced by ultrasonics and the resultant microstructure evolution are an invaluable way to understand and optimise ultrasonic treatment (UST) processes, and the development of these models is crucial in taking advantage of UST as part of a casting process [9-12]. The current work investigates the effect of acoustic streaming on the evolution of microstructure of an Al-2Cu alloy during the application of UST numerically. A computation model based on CAFE (Cellular Automation Finite Element) coupling fluid flow, heat transfer, nucleation and grain growth was developed and validated by comparing the results of numerical simulations against physical experiments.

关键词： Ultrasonic treatment Aluminium alloys Casting simulation Solidification microstructure development

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Performance of High-Volume Fly Ash Concrete Incorporating Lime Water

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ACI MATERIALS JOURNAL 2018年第2期115卷 289-297页

作者： Gunasekera, C. Ling, X. H. Setunge, S. Law, D. W. Patnaikuni, I RMIT Univ Sch Engn Melbourne Vic Australia VicRoads Mitcham Australia RMIT Univ Civil & Infrastruct Engn Melbourne Vic Australia

The use of concrete containing high-volume fly ash (HVFA) has recently gained popularity as a resource-efficient, durable, and sustainable option for a variety of concrete applications. The long-term creep and drying shrinkage of HVFA concrete containing 65% fly ash (HPFA-65) incorporating lime water has been investigated up to 1 year. Moreover, tensile strength and elastic modulus of HVFA-65 concrete have been examined in conjunction with microstructural development. The HVFA-65 concrete achieved similar to 200 microstrain of creep at the first 50 days;however, it only obtained approximately 100 microstrain between 50 and 365 days. This is equivalent to one-third of total creep strain displayed by portland-cement (PC) concrete, and also half of the predicted creep strain in accordance with AS 3600. Amalgamation of calcium-alumina-silicate-hydrate (C-A-S-H) gel with calcium-silicate-hydrate (C-S-H) gel was seen to positively affect the compactness and packing density of the gel matrix, which in turn influences the strength and elastic modulus development in HVFA-65 concrete. Early-age curing is also identified as significant in controlling drying shrinkage of the concrete.

关键词： creep drying shrinkage fly ash high-volume fly ash concrete mechanical properties microstructure development

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