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Dale P. Bentz - One of the best experts on this subject based on the ideXlab platform.
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Evaluating the hydration of high volume fly ash mixtures using chemically inert fillers
Construction and Building Materials, 2018Co-Authors: Igor De La Varga, Dale P. Bentz, Javier Castro, Franco Zunino, Jason WeissAbstract:Abstract Fly ash is frequently used as a replaCement for Cement in concrete. However, questions remain regarding the influence that fly ash has on the hydration of Cement. This paper examines physical aspects (e.g., surface nucleation, Cement Particle spacing) and chemical aspects (e.g., pozzolanic and hydraulic reactions) of the fly ash and Cement in mixtures containing high volumes of fly ash. In addition to using fly ash, a chemically inert filler was used consisting of a blend of fine silica sands with approximately the same Particle size distribution as that of the fly ash. The paper compares reactivity results from 1) Cement, 2) Cement-fly ash and 3) Cement-inert filler systems. Isothermal calorimetry measurements are used to quantitatively evaluate the role played by the fly ash in hydration of high volume fly ash mixtures. The results provide a decoupling of the physical and chemical effects of high volume fly ash on Cement hydration.
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influence of Particle size distributions on yield stress and viscosity of Cement fly ash pastes
Cement and Concrete Research, 2012Co-Authors: Dale P. Bentz, Chiara F Ferraris, Michael A Galler, Andrew S Hansen, John M GuynnAbstract:Abstract The rheological properties of blended Cement-based materials depend strongly on mixture proportions and the characteristics of the components. In this study, design of experiments is used to investigate the influence of three variables (Cement Particle size distribution (PSD), fly ash PSD, and ratio of fly ash to Cement) at each of four levels on the yield stress and viscosity of blended pastes. Both rheological parameters are seen to vary over several orders of magnitude for the evaluated design space. Physical characteristics of the powders, such as Cement and total Particle densities and total Particle surface area, are computed for each mixture. A percolation-type relationship is observed between yield stress and Cement Particle (number) density. While neither apparent nor plastic viscosities were particularly well described by the commonly employed Kreiger–Dougherty equation, plastic viscosities were found to be linear functions of either total (Cement + fly ash) Particle surface area or total Particle density.
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Critical observations for the evaluation of Cement hydration models
International Journal of Advances in Engineering Sciences and Applied Mathematics, 2010Co-Authors: Dale P. BentzAbstract:The development of computer models for Cement hydration and microstructure development, with an explicit consideration of microstructure, has accelerated in the past 25 years, creating a need for a set of critical experimental observations that can be used in evaluating the model predictions. During this same time period, there have been rapid advances in experimental techniques for quantifying both the hydration rates and the produced microstructures. This paper utilizes several of these techniques to elaborate a preliminary set of experimental observations concerning the influence of water-to-Cement ratio, Cement Particle size distribution, and curing conditions on hydration and microstructure development. Isothermal calorimetry provides a convenient measure of the ongoing hydration rates during the first 7 days of hydration, while low temperature calorimetry can be used to directly assess the percolation state of the capillary porosity and the quantity of freezable water in a hydrated Cement paste. Conventional measurements of setting times, such as Vicat needle penetration, are related to the ongoing percolation transitions of the solids within the three-dimensional microstructure. Finally, since concretes in the field rarely experience saturated curing conditions, the influence of sealed curing on resultant degree of hydration and microstructure is examined. The presented data sets should provide a first step in performing a critical evaluation of existing and future computer models.
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Mitigation strategies for autogenous shrinkage cracking
Cement and Concrete Composites, 2004Co-Authors: Dale P. Bentz, Ole Mejlhede JensenAbstract:Abstract As the use of high-performance concrete has increased, problems with early-age cracking have become prominent. The reduction in water-to-Cement ratio, the incorporation of silica fume, and the increase in binder content of high-performance concretes all contribute to this problem. In this paper, the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the Cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of the pore network, the visco-elastic response of the developing solid framework, and the kinetics of the Cementitious reactions. While the complexity of this phenomenon may hinder a quantitative interpretation of a specific Cement-based system, it also offers a wide variety of possible solutions to the problem of early-age cracking due to autogenous shrinkage. Mitigation strategies discussed in this paper include: the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the Cement Particle size distribution, modification of the mineralogical composition of the Cement, the addition of saturated lightweight fine aggregates, the use of controlled permeability formwork, and the new concept of “water-entrained” concrete. As with any remedy, new problems may be created by the application of each of these strategies. But, with careful attention to detail in the field, it should be possible to minimize cracking due to autogenous shrinkage via some combination of the presented approaches.
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the effect of statistical fluctuation finite size error and digital resolution on the phase percolation and transport properties of the nist Cement hydration model
Cement and Concrete Research, 2001Co-Authors: Edward J. Garboczi, Dale P. BentzAbstract:Abstract The National Institute of Standards and Technology (NIST) Cement hydration model starts with a three-dimensional digital image of Cement Particles, and then uses cellular automaton rules to simulate the reaction of Cement with water and the development of Cement paste microstructure. This stochastic model uses a digital image with a certain resolution to represent the reality of continuum shapes in a fairly small periodic unit cell. As such, it is potentially subject to statistical fluctuation, finite size error, and the effects of digital resolution. This paper evaluates the model in light of these potential sources of error, along with the effects of Cement Particle size distribution (PSD), water/Cement (w/c) ratio, and Cement chemistry, by focusing on the phase percolation and transport property predictions of the model. Statistical fluctuation and finite size error are shown to be of minor importance in the model. The effect of digital resolution is significant, however, but different from the case of a finite element or finite difference model. Unlike these cases, the “best” resolution is not necessarily the finest resolution, but must be chosen based on comparison with experiment and various physical length scales present in Cement paste.
Claus J. Haecker - One of the best experts on this subject based on the ideXlab platform.
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Influence of Cement Particle‐Size Distribution on Early Age Autogenous Strains and Stresses in Cement‐Based Materials
Journal of the American Ceramic Society, 2001Co-Authors: Dale P. Bentz, Ole Mejlhede Jensen, Kurt Kielsgaard Hansen, John Forbes Olesen, Henrik Stang, Claus J. HaeckerAbstract:The influence of Cement Particle-size distribution on autogenous strains and stresses in Cement pastes of identical waterto-Cement ratios is examined for Cement powders of four different finenesses. Experimental measurements include chemical shrinkage, to quantify degree of hydration; internal relative humidity development; autogenous deformation; and eigenstress development, using a novel embedded spherical stress sensor. Because the latter three measurements are conducted under sealed conditions, whereas chemicalshrinkage measurements are made under “saturated” conditions, the National Institute of Standards and Technology Cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those caused by the different initial spatial arrangement of the Cement Particles. The initial arrangement of the Cement Particles controls the initial pore-size distribution of the Cement paste, which, in turn, regulates the magnitude of the induced autogenous shrinkage stresses produced by the water/air menisci in the air-filled pores formed throughout the hydration process. The experimental results indicate that a small autogenous expansion (probably the result of ettringite formation), as opposed to a shrinkage, may be produced and early age cracking possibly avoided through the use of coarser Cements.
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influence of Cement Particle size distribution on early age autogenous strains and stresses in Cement based materials
Journal of the American Ceramic Society, 2001Co-Authors: Dale P. Bentz, Ole Mejlhede Jensen, Kurt Kielsgaard Hansen, John Forbes Olesen, Henrik Stang, Claus J. HaeckerAbstract:The influence of Cement Particle-size distribution on autogenous strains and stresses in Cement pastes of identical waterto-Cement ratios is examined for Cement powders of four different finenesses. Experimental measurements include chemical shrinkage, to quantify degree of hydration; internal relative humidity development; autogenous deformation; and eigenstress development, using a novel embedded spherical stress sensor. Because the latter three measurements are conducted under sealed conditions, whereas chemicalshrinkage measurements are made under “saturated” conditions, the National Institute of Standards and Technology Cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those caused by the different initial spatial arrangement of the Cement Particles. The initial arrangement of the Cement Particles controls the initial pore-size distribution of the Cement paste, which, in turn, regulates the magnitude of the induced autogenous shrinkage stresses produced by the water/air menisci in the air-filled pores formed throughout the hydration process. The experimental results indicate that a small autogenous expansion (probably the result of ettringite formation), as opposed to a shrinkage, may be produced and early age cracking possibly avoided through the use of coarser Cements.
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influence of Cement Particle size distribution on early age autogenous strains and stresses in Cement based materials
Journal of the American Ceramic Society, 2001Co-Authors: Dale P. Bentz, Ole Mejlhede Jensen, Kurt Kielsgaard Hansen, John Forbes Olesen, Henrik Stang, Claus J. HaeckerAbstract:The influence of Cement Particle-size distribution on autogenous strains and stresses in Cement pastes of identical waterto-Cement ratios is examined for Cement powders of four different finenesses. Experimental measurements include chemical shrinkage, to quantify degree of hydration; internal relative humidity development; autogenous deformation; and eigenstress development, using a novel embedded spherical stress sensor. Because the latter three measurements are conducted under sealed conditions, whereas chemicalshrinkage measurements are made under “saturated” conditions, the National Institute of Standards and Technology Cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those caused by the different initial spatial arrangement of the Cement Particles. The initial arrangement of the Cement Particles controls the initial pore-size distribution of the Cement paste, which, in turn, regulates the magnitude of the induced autogenous shrinkage stresses produced by the water/air menisci in the air-filled pores formed throughout the hydration process. The experimental results indicate that a small autogenous expansion (probably the result of ettringite formation), as opposed to a shrinkage, may be produced and early age cracking possibly avoided through the use of coarser Cements.
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Effects of Cement Particle size distribution on performance properties of Portland Cement-based materials
Cement and Concrete Research, 1999Co-Authors: Dale P. Bentz, Edward J. Garboczi, Claus J. Haecker, Ole Mejlhede JensenAbstract:The original size, spatial distribution, and composition of Portland Cement Particles have a large influence on hydration kinetics, microstructure development, and ultimate properties of Cement-based materials. In this paper, the effects of Cement Particle size distribution on a variety of performance properties are explored via computer simulation and a few experimental studies. Properties examined include setting time, heat release, capillary porosity percolation, diffusivity, chemical shrinkage, autogenous shrinkage, internal relative humidity evolution, and interfacial transition zone microstructure. The effects of flocculation and dispersion of the Cement Particles in the starting microstructures on resultant properties are also briefly evaluated. The computer simulations are conducted using two Cement Particle size distributions that bound those commonly in use today and three different water-to-Cement ratios: 0.5, 0.3, and 0.246. For lower water-to-Cement ratio systems, the use of coarser Cements may offer equivalent or superior performance, as well as reducing production costs for the manufacturer.
Ole Mejlhede Jensen - One of the best experts on this subject based on the ideXlab platform.
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Mitigation strategies for autogenous shrinkage cracking
Cement and Concrete Composites, 2004Co-Authors: Dale P. Bentz, Ole Mejlhede JensenAbstract:Abstract As the use of high-performance concrete has increased, problems with early-age cracking have become prominent. The reduction in water-to-Cement ratio, the incorporation of silica fume, and the increase in binder content of high-performance concretes all contribute to this problem. In this paper, the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the Cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of the pore network, the visco-elastic response of the developing solid framework, and the kinetics of the Cementitious reactions. While the complexity of this phenomenon may hinder a quantitative interpretation of a specific Cement-based system, it also offers a wide variety of possible solutions to the problem of early-age cracking due to autogenous shrinkage. Mitigation strategies discussed in this paper include: the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the Cement Particle size distribution, modification of the mineralogical composition of the Cement, the addition of saturated lightweight fine aggregates, the use of controlled permeability formwork, and the new concept of “water-entrained” concrete. As with any remedy, new problems may be created by the application of each of these strategies. But, with careful attention to detail in the field, it should be possible to minimize cracking due to autogenous shrinkage via some combination of the presented approaches.
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influence of Cement Particle size distribution on early age autogenous strains and stresses in Cement based materials
Journal of the American Ceramic Society, 2001Co-Authors: Dale P. Bentz, Ole Mejlhede Jensen, Kurt Kielsgaard Hansen, John Forbes Olesen, Henrik Stang, Claus J. HaeckerAbstract:The influence of Cement Particle-size distribution on autogenous strains and stresses in Cement pastes of identical waterto-Cement ratios is examined for Cement powders of four different finenesses. Experimental measurements include chemical shrinkage, to quantify degree of hydration; internal relative humidity development; autogenous deformation; and eigenstress development, using a novel embedded spherical stress sensor. Because the latter three measurements are conducted under sealed conditions, whereas chemicalshrinkage measurements are made under “saturated” conditions, the National Institute of Standards and Technology Cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those caused by the different initial spatial arrangement of the Cement Particles. The initial arrangement of the Cement Particles controls the initial pore-size distribution of the Cement paste, which, in turn, regulates the magnitude of the induced autogenous shrinkage stresses produced by the water/air menisci in the air-filled pores formed throughout the hydration process. The experimental results indicate that a small autogenous expansion (probably the result of ettringite formation), as opposed to a shrinkage, may be produced and early age cracking possibly avoided through the use of coarser Cements.
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Influence of Cement Particle‐Size Distribution on Early Age Autogenous Strains and Stresses in Cement‐Based Materials
Journal of the American Ceramic Society, 2001Co-Authors: Dale P. Bentz, Ole Mejlhede Jensen, Kurt Kielsgaard Hansen, John Forbes Olesen, Henrik Stang, Claus J. HaeckerAbstract:The influence of Cement Particle-size distribution on autogenous strains and stresses in Cement pastes of identical waterto-Cement ratios is examined for Cement powders of four different finenesses. Experimental measurements include chemical shrinkage, to quantify degree of hydration; internal relative humidity development; autogenous deformation; and eigenstress development, using a novel embedded spherical stress sensor. Because the latter three measurements are conducted under sealed conditions, whereas chemicalshrinkage measurements are made under “saturated” conditions, the National Institute of Standards and Technology Cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those caused by the different initial spatial arrangement of the Cement Particles. The initial arrangement of the Cement Particles controls the initial pore-size distribution of the Cement paste, which, in turn, regulates the magnitude of the induced autogenous shrinkage stresses produced by the water/air menisci in the air-filled pores formed throughout the hydration process. The experimental results indicate that a small autogenous expansion (probably the result of ettringite formation), as opposed to a shrinkage, may be produced and early age cracking possibly avoided through the use of coarser Cements.
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influence of Cement Particle size distribution on early age autogenous strains and stresses in Cement based materials
Journal of the American Ceramic Society, 2001Co-Authors: Dale P. Bentz, Ole Mejlhede Jensen, Kurt Kielsgaard Hansen, John Forbes Olesen, Henrik Stang, Claus J. HaeckerAbstract:The influence of Cement Particle-size distribution on autogenous strains and stresses in Cement pastes of identical waterto-Cement ratios is examined for Cement powders of four different finenesses. Experimental measurements include chemical shrinkage, to quantify degree of hydration; internal relative humidity development; autogenous deformation; and eigenstress development, using a novel embedded spherical stress sensor. Because the latter three measurements are conducted under sealed conditions, whereas chemicalshrinkage measurements are made under “saturated” conditions, the National Institute of Standards and Technology Cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those caused by the different initial spatial arrangement of the Cement Particles. The initial arrangement of the Cement Particles controls the initial pore-size distribution of the Cement paste, which, in turn, regulates the magnitude of the induced autogenous shrinkage stresses produced by the water/air menisci in the air-filled pores formed throughout the hydration process. The experimental results indicate that a small autogenous expansion (probably the result of ettringite formation), as opposed to a shrinkage, may be produced and early age cracking possibly avoided through the use of coarser Cements.
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Effects of Cement Particle size distribution on performance properties of Portland Cement-based materials
Cement and Concrete Research, 1999Co-Authors: Dale P. Bentz, Edward J. Garboczi, Claus J. Haecker, Ole Mejlhede JensenAbstract:The original size, spatial distribution, and composition of Portland Cement Particles have a large influence on hydration kinetics, microstructure development, and ultimate properties of Cement-based materials. In this paper, the effects of Cement Particle size distribution on a variety of performance properties are explored via computer simulation and a few experimental studies. Properties examined include setting time, heat release, capillary porosity percolation, diffusivity, chemical shrinkage, autogenous shrinkage, internal relative humidity evolution, and interfacial transition zone microstructure. The effects of flocculation and dispersion of the Cement Particles in the starting microstructures on resultant properties are also briefly evaluated. The computer simulations are conducted using two Cement Particle size distributions that bound those commonly in use today and three different water-to-Cement ratios: 0.5, 0.3, and 0.246. For lower water-to-Cement ratio systems, the use of coarser Cements may offer equivalent or superior performance, as well as reducing production costs for the manufacturer.
Wu Cheng-bao - One of the best experts on this subject based on the ideXlab platform.
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A Study on Characterization and Application of Particle Size Distributional Width of Cement Particle Group
Bulletin of the Chinese ceramic society, 2007Co-Authors: Wu Cheng-baoAbstract:The correctness and feasibility of using Particle size distribution fractal dimension to characterize the width of Particle size of Cement Particle group was proved by fractal theory.The Particle size mass cumulative frequency of 16 kinds of Cement Particle group was measured.At the log-log condition,the correlation between mass cumulative frequency and Particle size of Cement Particle group was linearly.That is,the Particle size distribution was fractal characterization and Particle size distributional width of Cement Particle group could be characterized by fractal dimension.The correlation between the voidage and Particle size distributional width of Cement Particle group had been investigated too.The result shows that the voidage of Cement Particle group decrease with the increase of the width of Particle size of Cement Particle group.They are negative interrelation.
Surendra P. Shah - One of the best experts on this subject based on the ideXlab platform.
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influence of Particle dispersion on the viscosity change in highly concentrated Cement suspensions an experimental correlation
Journal of Rheology, 2020Co-Authors: Jae Hong Kim, Hong Jae Yim, Surendra P. Shah, Byoung Il Choi, Tae Yong ShinAbstract:Fresh concrete is a concentrated suspension of Portland Cement and aggregates. Cement-based materials show a fluid-to-solid transition incorporating water, which allows us to cast and place a structure in field. Ease of construction requires a lower viscosity of Cement-based materials, and it could be achieved by Cement Particle dispersion in water. In this study, a laser backscattering measurement identifies the Cement dispersion in in situ samples, and their size distribution are parametrized using the occurrence rate of a Poisson process. The Cement dispersion is unaffected by external shearing intensity while the concentration (or water-to-Cement ratio) or the use of dispersant alters its degree. Finally, associating the dispersion measurement with the microstructural state determined by their viscosity curves makes it clear how the Cement viscosity decreases.
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Cement Particle flocculation and breakage monitoring under Couette flow
Cement and Concrete Research, 2013Co-Authors: Hong Jae Yim, Jae Hong Kim, Surendra P. ShahAbstract:Abstract Freshly mixed concrete is a suspension of Cement and aggregate Particles dispersed in water. To secure the desired quality of freshly mixed concrete, understanding its rheological behavior, which depends on its flow rate, is necessary. A number of chemical and physical factors influence the rheology of freshly mixed concrete, and the flocculation of Cement Particles is thought to cause thixotropy and shear thinning. This study proposes a rheometer coupled with a laser backscattering device, which allows us to simultaneously measure the viscosity and the size distribution of Cement clusters in Cement paste suspension. The laser backscattering instrument measures the cluster size distribution and monitors its growth or breakdown, while the parallel-plate rheometer measures its rheological properties. As a result, the change of Cement grains was continuously observed with the change of shear stress under specific strain rates of 1 s− 1, 10 s− 1, and 100 s− 1.