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2 pages, 179 KiB

Open AccessEditorial

Editorial for Special Issue “Advances in Experimental and Computational Rheology”

by Maria Teresa Cidade and João Miguel Nóbrega

Fluids 2019, 4(3), 131; https://doi.org/10.3390/fluids4030131 - 12 Jul 2019

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Abstract

Rheology, defined as the science of deformation and flow of matter, is a multidisciplinary scientific field, covering both fundamental and applied approaches [...] Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

Research

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18 pages, 625 KiB

Open AccessArticle

A 3D Numerical Study of Interface Effects Influencing Viscous Gravity Currents in a Parabolic Fissure, with Implications for Modeling with 1D Nonlinear Diffusion Equations

by Eden Furtak-Cole and Aleksey S. Telyakovskiy

Fluids 2019, 4(2), 97; https://doi.org/10.3390/fluids4020097 - 28 May 2019

Cited by 2 | Viewed by 4249

Abstract

Although one-dimensional non-linear diffusion equations are commonly used to model flow dynamics in aquifers and fissures, they disregard multiple effects of real-life flows. Similarity analysis may allow further analytical reduction of these equations, but it is often difficult to provide applicable initial and [...] Read more.

Although one-dimensional non-linear diffusion equations are commonly used to model flow dynamics in aquifers and fissures, they disregard multiple effects of real-life flows. Similarity analysis may allow further analytical reduction of these equations, but it is often difficult to provide applicable initial and boundary conditions in practice, or know the magnitude of effects neglected by the 1D model. Furthermore, when multiple simplifying assumptions are made, the sources of discrepancy between modeled and observed data are difficult to identify. We derive one such model of viscous flow in a parabolic fissure from first principals. The parabolic fissure is formed by extruding an upward opening parabola in a horizontal direction. In this setting, permeability is a power law function of height, resulting in a generalized Boussinesq equation. To gauge the effects neglected by this model, 3D Navier-Stokes multiphase flow simulations are conducted for the same geometry. Parameter variations are performed to assess the nature of errors induced by applying the 1D model to a realistic scenario, where the initial and boundary conditions can not be matched exactly. Numerical simulations reveal an undercutting effect observed in laboratory experiments, but not modeled when the Dupuit-Forchheimer assumption is applied. By selectively controlling the effects placed on the free surface in 3D simulations, we are able to demonstrate that free surface slope is the primary driver of the undercutting effect. A consistent lag and overshoot flow regime is observed in the 3D simulations as compared to the 1D model, based on the choice of initial condition. This implies that the undercutting effect is partially induced by the initial condition. Additionally, the presented numerical evidence shows that some of the flow behavior unaccounted for in the 1D model scales with the 1D model parameters. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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12 pages, 2892 KiB

Open AccessFeature PaperArticle

Assessment of Piezoelectric Sensors for the Acquisition of Steady Melt Pressures in Polymer Extrusion

by Sónia Costa, Paulo F. Teixeira, José A. Covas and Loic Hilliou

Fluids 2019, 4(2), 66; https://doi.org/10.3390/fluids4020066 - 3 Apr 2019

Cited by 6 | Viewed by 3226

Abstract

Piezoelectric sensors have made their way into polymer processing and rheometry applications, in particular when small pressure changes with very fast dynamics are to be measured. However, no validation of their use for steady shear rheometry is available in the literature. Here, a [...] Read more.

Piezoelectric sensors have made their way into polymer processing and rheometry applications, in particular when small pressure changes with very fast dynamics are to be measured. However, no validation of their use for steady shear rheometry is available in the literature. Here, a rheological slit die was designed and constructed to allow for the direct comparison of pressure data measured with conventional and piezoelectric transducers. The calibration of piezoelectric sensors is presented together with a methodology to correct the data from the inherent signal drift, which is shown to be temperature and pressure independent. Flow curves are measured for polymers showing different levels of viscoelasticity. Piezoelectric slit rheometry is validated and its advantage for the rheology of thermodegradable materials with viscosity below 100 Pa·s is highlighted. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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11 pages, 2652 KiB

Open AccessArticle

A Comprehensive Approach from Interfacial to Bulk Properties of Legume Protein-Stabilized Emulsions

by Manuel Félix, Alberto Romero, Cecilio Carrera-Sanchez and Antonio Guerrero

Fluids 2019, 4(2), 65; https://doi.org/10.3390/fluids4020065 - 3 Apr 2019

Cited by 9 | Viewed by 3358

Abstract

The correlation between interfacial properties and emulsion microstructure is a topic of special interest that has many industrial applications. This study deals with the comparison between the rheological properties of oil-water interfaces with adsorbed proteins from legumes (chickpea or faba bean) and the [...] Read more.

The correlation between interfacial properties and emulsion microstructure is a topic of special interest that has many industrial applications. This study deals with the comparison between the rheological properties of oil-water interfaces with adsorbed proteins from legumes (chickpea or faba bean) and the properties of the emulsions using them as the only emulsifier, both at microscopic (droplet size distribution) and macroscopic level (linear viscoelasticity). Two different pH values (2.5 and 7.5) were studied as a function of storage time. Interfaces were characterized by means of dilatational and interfacial shear rheology measurements. Subsequently, the microstructure of the final emulsions obtained was evaluated thorough droplet size distribution (DSD), light scattering and rheological measurements. Results obtained evidenced that pH value has a strong influence on interfacial properties and emulsion microstructure. The best interfacial results were obtained for the lower pH value using chickpea protein, which also corresponded to smaller droplet sizes, higher viscoelastic moduli, and higher emulsion stability. Thus, results put forward the relevance of the interfacial tension values, the adsorption kinetics, the viscoelastic properties of the interfacial film, and the electrostatic interactions among droplets, which depend on pH and the type of protein, on the microstructure, rheological properties, and stability of legume protein-stabilized emulsions. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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12 pages, 2118 KiB

Open AccessArticle

Saffman–Taylor Instability in Yield Stress Fluids: Theory–Experiment Comparison

by Oumar Abdoulaye Fadoul and Philippe Coussot

Fluids 2019, 4(1), 53; https://doi.org/10.3390/fluids4010053 - 16 Mar 2019

Cited by 14 | Viewed by 5739

Abstract

The Saffman–Taylor instability for yield stress fluids appears in various situations where two solid surfaces initially separated by such a material (paint, puree, concrete, yoghurt, glue, etc.) are moved away from each other. The theoretical treatment of this instability predicts fingering with a [...] Read more.

The Saffman–Taylor instability for yield stress fluids appears in various situations where two solid surfaces initially separated by such a material (paint, puree, concrete, yoghurt, glue, etc.) are moved away from each other. The theoretical treatment of this instability predicts fingering with a finite wavelength at vanishing velocity, and deposited materials behind the front advance, but the validity of this theory has been only partially tested so far. Here, after reviewing the basic results in that field, we propose a new series of experiments in traction to test the ability of this basic theory to predict data. We carried out tests with different initial volumes, distances and yield stresses of materials. It appears that the validity of the proposed instability criterion cannot really be tested under such experimental conditions, but at least we show that it effectively predicts the instability when it is observed. Furthermore, in agreement with the theoretical prediction for the finger size, a master curve is obtained when plotting the finger number as a function of the yield stress times the sample volume divided by the square initial thickness, in wide ranges of these parameters. This in particular shows that this traction test could be used for the estimation of the material yield stress. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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15 pages, 2490 KiB

Open AccessArticle

Inhomogeneous Flow of Wormlike Micelles: Predictions of the Generalized BMP Model with Normal Stresses

by J. Paulo García-Sandoval, Fernando Bautista, Jorge E. Puig and Octavio Manero

Fluids 2019, 4(1), 45; https://doi.org/10.3390/fluids4010045 - 8 Mar 2019

Cited by 4 | Viewed by 2772

Abstract

In this work, we examine the shear-banding flow in polymer-like micellar solutions with the generalized Bautista-Manero-Puig (BMP) model. The couplings between flow, structural parameters, and diffusion naturally arise in this model, derived from the extended irreversible thermodynamics (EIT) formalism. Full tensorial expressions derived [...] Read more.

In this work, we examine the shear-banding flow in polymer-like micellar solutions with the generalized Bautista-Manero-Puig (BMP) model. The couplings between flow, structural parameters, and diffusion naturally arise in this model, derived from the extended irreversible thermodynamics (EIT) formalism. Full tensorial expressions derived from the constitutive equations of the model, in addition to the conservation equations, apply for the case of simple shear flow, in which gradients of the parameter representing the structure of the system and concentration vary in the velocity gradient direction. The model predicts shear-banding, concentration gradients, and jumps in the normal stresses across the interface in shear-banding flows. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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11 pages, 2176 KiB

Open AccessArticle

Influence of the Homogenization Pressure on the Rheology of Biopolymer-Stabilized Emulsions Formulated with Thyme Oil

by Luis A. Trujillo-Cayado, Jenifer Santos, Nuria Calero, Maria del Carmen Alfaro and José Muñoz

Fluids 2019, 4(1), 29; https://doi.org/10.3390/fluids4010029 - 18 Feb 2019

Cited by 7 | Viewed by 3411

Abstract

Different continuous phases formulated with ecofriendly ingredients such as AMIDET® N, an ecological surfactant, as well as welan and rhamsan gums were developed. An experimental design strategy was been in order to study the influence of the ratio of these two polysaccharides and [...] Read more.

Different continuous phases formulated with ecofriendly ingredients such as AMIDET® N, an ecological surfactant, as well as welan and rhamsan gums were developed. An experimental design strategy was been in order to study the influence of the ratio of these two polysaccharides and the homogenization pressure applied in a microfluidizer on the critical shear stress for the continuous phases developed. A pure rhamsan gum solution was selected as the starting point for further study based on the production of thyme oil-in-water emulsions. The effect of the homogenization pressure on the physical stability, critical shear stress and droplet size distribution was analyzed for emulsions with optimized values of the rhamsan–welan ratio. These bioactive thyme oil-in-water emulgels could be considered as delivery systems with potential applications in the food industry. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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11 pages, 1400 KiB

Open AccessArticle

Milligram Size Rheology of Molten Polymers

by Salvatore Costanzo, Rossana Pasquino, Jörg Läuger and Nino Grizzuti

Fluids 2019, 4(1), 28; https://doi.org/10.3390/fluids4010028 - 18 Feb 2019

Cited by 15 | Viewed by 4220

Abstract

During laboratory practice, it is often necessary to perform rheological measurements with small specimens, mainly due to the limited availability of the investigated systems. Such a restriction occurs, for example, because the laboratory synthesis of new materials is performed on small scales, or [...] Read more.

During laboratory practice, it is often necessary to perform rheological measurements with small specimens, mainly due to the limited availability of the investigated systems. Such a restriction occurs, for example, because the laboratory synthesis of new materials is performed on small scales, or can concern biological samples that are notoriously difficult to be extracted from living organisms. A complete rheological characterization of a viscoelastic material involves both linear and nonlinear measurements. The latter are more challenging and generally require more mass, as flow instabilities often cause material losses during the experiments. In such situations, it is crucial to perform rheological tests carefully in order to avoid experimental artifacts caused by the use of small geometries. In this paper, we indicate the drawbacks of performing linear and nonlinear rheological measurements with very small amounts of samples, and by using a well-characterized linear polystyrene, we attempt to address the challenge of obtaining reliable measurements with sample masses of the order of a milligram, in both linear and nonlinear regimes. We demonstrate that, when suitable protocols and careful running conditions are chosen, linear viscoelastic mastercurves can be obtained with good accuracy and reproducibility, working with plates as small as 3 mm in diameter and sample thickness of less than 0.2 mm. This is equivalent to polymer masses of less than 2 mg. We show also that the nonlinear start-up shear fingerprint of polymer melts can be reliably obtained with samples as small as 10 mg. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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15 pages, 3355 KiB

Open AccessArticle

Piezo-Plunger Jetting Technology: An Experimental Study on Jetting Characteristics of Filled Epoxy Polymers

by Alexander Kurz, Jörg Bauer and Manfred Wagner

Fluids 2019, 4(1), 23; https://doi.org/10.3390/fluids4010023 - 1 Feb 2019

Cited by 4 | Viewed by 3262

Abstract

The droplet formation of Newtonian fluids and suspensions modified by spherical, non-colloidal particles has attracted much interest in practical and theoretical research. For the present study, a jetting technique was used which accelerates a geometrically defined plunger by a piezoelectric actuator. Changing rheological [...] Read more.

The droplet formation of Newtonian fluids and suspensions modified by spherical, non-colloidal particles has attracted much interest in practical and theoretical research. For the present study, a jetting technique was used which accelerates a geometrically defined plunger by a piezoelectric actuator. Changing rheological properties of materials and extending deformation rates towards nonlinear viscoelastic regimes created the requirement to extend dosage impulses towards larger magnitudes. To mimic the rheological characteristics of nonconductive adhesives we modified Newtonian epoxy resins by thixotropic additives and micro-scale glass spheres. Rheological analysis at steady shear and oscillatory shear ensured a differentiation between material and process-related factors. Evaluation of high-speed images allowed the investigation of drop dynamics and highlighted the dispense impulse reduction by material-specific dampening properties. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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8 pages, 2129 KiB

Open AccessArticle

A Comparison of the Effect of Temperature on the Rheological Properties of Diutan and Rhamsan Gum Aqueous Solutions

by Mª Carmen García González, María del Socorro Cely García, José Muñoz García and Maria-Carmen Alfaro-Rodriguez

Fluids 2019, 4(1), 22; https://doi.org/10.3390/fluids4010022 - 1 Feb 2019

Cited by 9 | Viewed by 3080

Abstract

The rheological properties exhibited by gums make its use in applications interesting, such as foods, cosmetics, enhanced oil recovery, or constructions materials. Regardless of application field, the effect of temperature on these properties is of great importance, since these properties can be modified [...] Read more.

The rheological properties exhibited by gums make its use in applications interesting, such as foods, cosmetics, enhanced oil recovery, or constructions materials. Regardless of application field, the effect of temperature on these properties is of great importance, since these properties can be modified and cause the gum not to be useful for those conditions. Diutan and rhamsan gums are biopolymers, belonging to the sphingans, with similar structures which differ in the substituents of their side chains. It is known that both gums exhibit suitable viscoelastic properties and flow behavior when used as a stabilizer, gelling agent, or thickener. Both gums are widely used in food industry, personal care products, construction materials, oil operations, etc. For this reason, to know the effect of the temperature on their rheological properties is very helpful. For this purpose, small amplitude oscillatory shear measurements and flow curves, as a function of the temperature from 10 °C to 60 °C, have been performed, and the results obtained for both gums compared. The obtained results provide interesting information from an industrial point of view, since they reveal that the rheological properties remained almost unaltered in the temperature range assessed with diutan gum aqueous solutions, being slightly more viscous and viscoelastic than rhamsan gum solutions. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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16 pages, 511 KiB

Open AccessArticle

A Continuum Model for Complex Flows of Shear Thickening Colloidal Solutions

by Joseph A. Green, Daniel J. Ryckman and Michael Cromer

Fluids 2019, 4(1), 21; https://doi.org/10.3390/fluids4010021 - 1 Feb 2019

Cited by 1 | Viewed by 2901

Abstract

Colloidal shear thickening fluids (STFs) have applications ranging from commercial use to those of interest to the army and law enforcement, and the oil industry. The theoretical understanding of the flow of these particulate suspensions has predominantly been focused through detailed particle simulations. [...] Read more.

Colloidal shear thickening fluids (STFs) have applications ranging from commercial use to those of interest to the army and law enforcement, and the oil industry. The theoretical understanding of the flow of these particulate suspensions has predominantly been focused through detailed particle simulations. While these simulations are able to accurately capture and predict the behavior of suspensions in simple flows, they are not tractable for more complex flows such as those occurring in applications. The model presented in this work, a modification of an earlier constitutive model by Stickel et al. J. Rheol. 2006, 50, 379–413, describes the evolution of a structure tensor, which is related to the particle mean free-path length. The model contains few adjustable parameters, includes nonlinear terms in the structure, and is able to predict the full range of rheological behavior including shear and extensional thickening (continuous and discontinuous). In order to demonstrate its capability for complex flow simulations, we compare the results of simulations of the model in a simple one-dimensional channel flow versus a full two-dimensional simulation. Ultimately, the model presented is a continuum model shown to predict shear and extensional thickening, as observed in experiment, with a connection to the physical microstructure, and has the capability of helping understand the behavior of STFs in complex flows. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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12 pages, 2606 KiB

Open AccessArticle

Relevance of Rheology on the Properties of PP/MWCNT Nanocomposites Elaborated with Different Irradiation/Mixing Protocols

by Mercedes Fernandez, Arrate Huegun and Antxon Santamaria

Fluids 2019, 4(1), 7; https://doi.org/10.3390/fluids4010007 - 9 Jan 2019

Cited by 6 | Viewed by 3052

Abstract

Linear and nonlinear rheological features and electrical conductivity of two nanocomposite systems based on polypropylene/multiwall carbon nanotubes (PP/MWCNT) are investigated. The nanocomposites were irradiated with an electron beam following two different procedures. Protocol A, where the nanocomposite mixture is irradiated, and Protocol B [...] Read more.

Linear and nonlinear rheological features and electrical conductivity of two nanocomposite systems based on polypropylene/multiwall carbon nanotubes (PP/MWCNT) are investigated. The nanocomposites were irradiated with an electron beam following two different procedures. Protocol A, where the nanocomposite mixture is irradiated, and Protocol B where only the PP matrix is irradiated before mixing with MWCNT. The same irradiation dose adjusted to bring about long chain branching (LCB) but not crosslinking, is used in both types of nanocomposites. The modification of the polymer matrix viscosity caused by irradiation determines the MWCNT dispersion and therefore the rheological and percolation thresholds. Elongational flow results reveal that strain hardening, typical of irradiated PPs, is observed for the nanocomposites irradiated, but not for the nanocomposites prepared with the irradiated PP. The hypothesis of a shear flow modification that aligns the branches into the backbone, eliminating the strain hardening is considered. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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15 pages, 2123 KiB

Open AccessArticle

On the Steady-State Flow and Yielding Behaviour of Lubricating Greases

by Miguel A. Delgado, Sebastien Secouard, Concepción Valencia and José M. Franco

Fluids 2019, 4(1), 6; https://doi.org/10.3390/fluids4010006 - 9 Jan 2019

Cited by 22 | Viewed by 3361

Abstract

Practical steady-state flow curves were obtained from different rheological tests and protocols for five lubricating greases, containing thickeners of a rather different nature, i.e., aluminum complex, lithium, lithium complex, and calcium complex soaps and polyurea. The experimental results demonstrated the difficulty to reach [...] Read more.

Practical steady-state flow curves were obtained from different rheological tests and protocols for five lubricating greases, containing thickeners of a rather different nature, i.e., aluminum complex, lithium, lithium complex, and calcium complex soaps and polyurea. The experimental results demonstrated the difficulty to reach “real” steady-state flow conditions for these colloidal suspensions as a consequence of the strong time dependence and marked yielding behavior in a wide range of shear rates, resulting in flow instabilities such as shear banding and fracture. In order to better understand these phenomena, transient flow experiments, at constant shear rates, and creep tests, at constant shear stresses, were also carried out using controlled-strain and controlled-stress rheometers, respectively. The main objective of this work was to study the steady-state flow behaviour of lubricating greases, analyzing how the microstructural characteristics may affect the yielding flow behaviour. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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20 pages, 874 KiB

Open AccessFeature PaperArticle

Rheological Characterization of Carbopol^® Dispersions in Water and in Water/Glycerol Solutions

by Priscilla R. Varges, Camila M. Costa, Bruno S. Fonseca, Mônica F. Naccache and Paulo R. De Souza Mendes

Fluids 2019, 4(1), 3; https://doi.org/10.3390/fluids4010003 - 4 Jan 2019

Cited by 107 | Viewed by 13373

Abstract

The influence of the solvent type on the rheological properties of Carbopol

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NF 980 dispersions in water and in water/glycerol solutions is investigated. The material formulation, preparation procedure, common experimental challenges and artifact sources are all addressed. Transient and steady-state experiments were [...] Read more.

The influence of the solvent type on the rheological properties of Carbopol

^{®}

NF 980 dispersions in water and in water/glycerol solutions is investigated. The material formulation, preparation procedure, common experimental challenges and artifact sources are all addressed. Transient and steady-state experiments were performed. For both solvent types, a clearly thixotropic behavior occurs slightly above the yield stress, where the avalanche effect is observed. For larger stresses, thixotropy is always negligible. Among other findings, it is observed that, for a given Carbopol concentration, the dispersion in the more viscous solvent possesses a lower yield stress and moduli, a larger power-law index, and a longer time to reach steady state. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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Review

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19 pages, 2126 KiB

Open AccessFeature PaperReview

Rheology of Natural Hydraulic Lime Grouts for Conservation of Stone Masonry—Influence of Compositional and Processing Parameters

by Luis G. Baltazar, Fernando M.A. Henriques and Maria Teresa Cidade

Fluids 2019, 4(1), 13; https://doi.org/10.3390/fluids4010013 - 18 Jan 2019

Cited by 19 | Viewed by 5114

Abstract

This review provides an overview of the recent progress in the field of the rheology of grouts for historic masonry consolidation. During the last two decades, significant research has been devoted on the grouting technique for stone masonry consolidation but most results are [...] Read more.

This review provides an overview of the recent progress in the field of the rheology of grouts for historic masonry consolidation. During the last two decades, significant research has been devoted on the grouting technique for stone masonry consolidation but most results are scattered by scientific papers, congress communications, and thesis. This paper compiles and briefly demonstrates the effect of several intrinsic and extrinsic parameters, such as admixtures, additions, pressure, temperature, and measuring instrumentation, on the rheological performance of natural hydraulic lime-based grouts. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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16 pages, 869 KiB

Open AccessReview

Rheological Behavior of Fresh Cement Pastes

by Francisco-José Rubio-Hernández

Fluids 2018, 3(4), 106; https://doi.org/10.3390/fluids3040106 - 11 Dec 2018

Cited by 35 | Viewed by 7371

Abstract

Rheology of a concrete is mainly controlled by the rheological behavior of its cement paste. This is the main practical reason for the extensive research activity observed during 70 years in this research subfield. In this brief review, some areas of the research [...] Read more.

Rheology of a concrete is mainly controlled by the rheological behavior of its cement paste. This is the main practical reason for the extensive research activity observed during 70 years in this research subfield. In this brief review, some areas of the research on the rheological behavior of fresh cement pastes (mixture method influence, microstructure analysis, mineral additions influence, chemical additives influence, blended cements behavior, viscoelastic behavior, flow models, and flow behavior analysis with alternative methods) are examined. Full article

(This article belongs to the Special Issue Advances in Experimental and Computational Rheology)

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