Measurement of yield stress of cement pastes using the direct shear test

Assaad, Joseph J.; Harb, Jacques; Maalouf, Yara

doi:10.1016/j.jnnfm.2014.10.009

Cited by 61 publications

(21 citation statements)

References 18 publications

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“…Shear viscosity in Newtonian fluids is constant regardless of the shear rate or stress applied, while for non‐Newtonian suspensions there is a change in viscosity with applied stress. Yield stress is another important measurement that is widely used in mineral processing, and it represents the shear stress at which a material starts flowing, or in rheology terminology it can be referred as the transition stress between elastic solid‐like behaviour and viscous liquid‐like behaviour …”

Section: Rheology Measurementsmentioning

confidence: 99%

“…It is also possible to make a direct calculation of yield stress by slowly shearing the material and recording the peak shear stress required to initiate flow . The wall slip effect must be avoided and the vane geometry is probably the most popular one to measure yield stress since slippage is physically impossible and shearing completely occurs with the material . Not all mineral slurries show a yield stress, and it is usually observed at a high solids concentration or in slurries with a high proportion of colloidal particles such as clay minerals .…”

Section: Rheology Measurementsmentioning

confidence: 99%

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Slurry rheology in mineral processing unit operations: A critical review

2019

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Knowledge of slurry rheology in mineral processing is essential for the optimization of wet-grinding, dewatering, transport, and tailings management and it is becoming important in flotation due to the increasing need to process complex ores with a high clay mineral content. Slurries of these ores often display complex rheological behaviour even at low solids concentration, and traditional rheology measurements in mineral processing, such as yield stress and apparent viscosities, may not provide the critical information needed for process optimization. The objective of this paper is to provide a comprehensive review of some of the previous rheology studies performed at the bench, pilot plant, and industrial scale for different unit operations and to discuss the potential for alternative rheology measurements to provide a better insight into colloidal particle interactions in slurries with clay minerals. Firstly, the fundamentals of slurry rheology and the influence of colloidal particles are presented. Secondly, rheology measurements for suspensions are described briefly. Thirdly, a review of rheology studies in grinding, classification, flotation, dewatering, and tailings management is done, outlining possible ways of determining types of particle associations in slurries. Finally, recommendations for future research directions are provided.

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Section: Rheology Measurementsmentioning

confidence: 99%

Section: Rheology Measurementsmentioning

confidence: 99%

Slurry rheology in mineral processing unit operations: A critical review

2019

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“…Obviously, the inclusions (aggregates) and matrix have different mechanical properties evidencing the heterogeneous characteristic of the medium submitted to plane stress states. For the matrix zone, an elastopplastic behavior is assumed following the MohrCoulomb criterion with the parameter values given by, Assad et al [21]: Young´s modulus E is 20 GPa and Poisson ration ν is 0.2, friction angle and dilatation angle are φ = 5º and Ψ = 10%, respectively. The aggregates are considered elastic media with E = 35 GPa and ν = 0.26, Mehta and Monteiro [22].…”

Section: Resultsmentioning

confidence: 99%

Evaluation of a proposed model for concrete at mesoscopic scale

Borges

Quaresma

Fernandes

et al. 2017

Rev. IBRACON Estrut. Mater.

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ResumoThis work deals with numerical modeling of mechanical behavior in quasi-brittle materials, such as concrete. For this propose, a two-dimensional meso-scale model based on RVE existence is presented. The material is considered as a three-phase material consisting of interface zone (ITZ), matrix and inclusions -each constituent modeled by an independent constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes symmetrically and non-symmetrically placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements. The inclusion is modeled as linear elastic and matrix region is considered as elastoplastic material. Our main goal here is to show a computational homogenization-based approach as an alternative to complex macroscopic constitutive models for the mechanical behavior of the brittle materials using a finite element procedure within a purely kinematical multi-scale framework. Besides, the fundamental importance of the representing dissipative phenomena in the interface zone to model the complex microstructural responses of materials like concrete is focused in this work. A set of numerical examples, involving the microcracking processes, is provided in order to illustrate the performance of the proposed modeling.Keywords: homogenization, quasi-brittle materials, cohesive contact finite element, concrete, plasticity.Este trabalho trata da modelagem numérica do comportamento mecânico em materiais quase-frágeis, tal como o concreto. Para este fim, um modelo 2D de escala mesoscópica baseado no conceito de Elemento de Volume Representativo (EVR) é apresentado. O material é considerado como composto por três fases consistindo de zona de interface, matriz e inclusões, onde cada constituinte é modelado independentemente. O EVR consiste de inclusões idealizadas como de forma circular dispostas de maneira simétrica e não simétrica. A zona de interface é modelada por meio de elementos finitos coesivos de contato. A inclusão é modelada como sendo um material elástico linear, já a matriz é considerada como material elastoplástico. Nosso principal objetivo é mostrar que uma formulação baseada na homogeneização computacional é uma alternativa aos modelos constitutivos macroscópicos complexos para o comportamento mecânico de matérias frágeis usando um procedimento baseado no Método dos Elementos Finitos no âmbito de uma teoria multi-escala. Além disso, o trabalho foca na fundamental importância em representar os fenômenos dissipativos na Zona de Transição para obter uma resposta microestrutural de um material complexo como o concreto. Uma série de exemplos envolvendo processos de microfissuração é apresentada de modo a ilustrar o desempenho da modelagem proposta.Palavras-chave: homogeneização, materiais quase-frágeis, elemento finito coesivo, concreto, plasticidade

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“…Furthermore, since hydrodynamic forces at extremely low shear were not strong enough to bring the separated structural elements close together for a reformation of the network bonds, the material would yield in an irreversible manner with "cracks" (visible or invisible) formed in a localized yield area. is explained the existence of a maximum shear stress value followed by a rapid fall off in stress with time on the stresstime response [17][18][19].…”

Section: Mechanical Properties Andmentioning

confidence: 99%

Mechanical Properties of Paste Slurry under Constant Shear Rate in Initial Structure Failure Process

Dai

et al. 2019

Advances in Materials Science and Engineering

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At constant shear rate, the process of deformation of the paste slurry is divided into two stages: one is the initial structural failure process with increasing shear stress; the other is the thixotropic process with decreasing shear stress after yielding. Based on experiments, the mechanical response characteristics of the paste slurry in the initial structural failure process under different shear rate conditions were studied in this paper. At the same time, according to the Maxwell model, the stress-time model equation describing the initial structure failure stage of the paste was deduced and the constant shearing test was carried out on the paste slurry at different mass concentrations; the model equation was used to fit the test data of the initial stress increment stage. The results showed that the model equation had higher prediction accuracy and better popularity. In the initial structural failure stage, the paste had a nonlinear stress-time relationship. At different shear rates (0.05, 0.5, and 1 s−1), the lower the rotation speed, the smoother the curve, and the slurry at various stages in the yielding process could be more clearly reflected; in the range of low constant shear rate (0.03, 0.05, and 0.07 s−1), the initial stress and yield stress of the paste increased with the increase of shear rate at the same mass concentration, and the time to yield was shorter. The yield stress increased exponentially with mass concentration.

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Measurement of yield stress of cement pastes using the direct shear test

Cited by 61 publications

References 18 publications

Slurry rheology in mineral processing unit operations: A critical review

Slurry rheology in mineral processing unit operations: A critical review

Evaluation of a proposed model for concrete at mesoscopic scale

Mechanical Properties of Paste Slurry under Constant Shear Rate in Initial Structure Failure Process

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