Yield Stress Growth Research Articles

Relating early-age hydration and flow loss of mortar prepared with manufactured sand

Cement-based materials prepared with manufactured sand can exhibit quick loss of fluidity. However, the estimation of the flow loss remains difficult given the variable contents and physiochemical properties of the microfines in various sands. This paper studies the fluidity loss of mortar mixtures made with different manufactured sands varying in mineral composition and content of microfines. The effect of microfines on accelerating the early-age hydration of cement before the deceleration period was evaluated by quantifying the generation of early hydration products. Test results show that the growth of yield stress corresponding to the loss of mini-slump flow of mortar mixtures were mainly determined by the formation of early hydration products, in addition to the volume fraction and packing density of aggregate grains and powder particles. An approach was then proposed that can assess the loss of mini-slump flow of mortar mixtures prepared with manufactured sand, regardless of the type and content of the microfine materials in the sand.

Characterization of thixotropic properties of fresh cement‐based materials

AbstractAccurate evaluation of the thixotropy of mixtures is crucial for the design and production of self‐compacting concrete, pumped concrete, and 3D printed concrete. However, there is no uniform standard for the assessment of the thixotropy of fresh cement‐based materials. In this paper, four widely used test procedures (thixotropic index, static yield stress growth curve, thixotropic hysteresis loop area, and three‐stage curve) are compared to determine the relationships between them. The results show that the test procedures based on the break‐down (destruction) process (thixotropic index, thixotropic hysteresis loop area, and degree of breakdown) are difficult to distinguish between reversible and irreversible thixotropic structures and to accurately assess the thixotropy of mixtures. The short‐term structural build‐up rate Rthix is more suitable for characterizing the thixotropic properties. The three‐stage curve can characterize both the degree of structural damage and the reconstruction ability of the paste, nano‐attapulgite clay can significantly improve the structural recovery degree of the mixture at the early hydration stage. This study will provide guidance and a theoretical framework for choosing the thixotropic characterization method of cement‐based materials in practical engineering applications.

Influence of limestone filler on technological parameters of mixtures for 3D concrete printing

This paper focuses on the use of fine-ground limestone filler (LP) from Rakke Limestone production (R0) as SCM in 3D Concrete Printing (3DCP) mixtures to partially replace OPC. Important technical aspects of the mixture, such as flowability, extrudability and buildability, are explored and investigated. To properly deploy 3DCP, two conflicting material qualities must be balanced. On one hand, the mix must be pumpable enough to be delivered by hose from the mixer to the nozzle, and on the other, after extrusion, the mix must retain its shape without any supporting formwork while bearing the load from succeeding filaments. In cooperation with MIRA Ehitusmaterjalid OÜ experimental mixtures with various OPC replacements were produced, which were printed on a gantry printer at Tallinn University of Applied Sciences. A comparison was made using industrial mixtures from Weber Saint-Gobain - Beamix 145-2 and ESL. LP has been found to enhance mix printability despite higher water requirement. This can be attributed to additional finely dispersed flocculation centres provided by LP additive. With the same, LP reduces buildability of the mixtures caused by slower yield stress growth and retarded stiffening.

Synthesis and characterization of Tunisian organoclay: Application as viscosifier in oil drilling fluid

In this study, the viscosifiers for diesel oil drilling fluid were prepared using Tunisian clay modified with cationic surfactant for five concentration levels from 0.5 to 4.0 times the cationic exchange of purified clay (CEC). The organo-modified clay samples were characterized by X-ray diffraction (XRD), Infrared spectroscopy (FTIR), scanning electron micrography (SEM) and specific surface area (BET model). Oil–clays suspensions were investigated using polarized light optical microscopy (PLOM) and double cone rheometer. The influence of surfactant concentration on rheological properties of suspensions is related to the different microstructures development which depend on surfactant arrangement in the interlayer of clay. The results showed the growth of yield stress and consistency coefficient as the surfactant concentration is increased and the best behaviors were observed for the 3.0 CEC concentration. This sample was tested for two weight percents (5 and 10wt%), the higher Herschel Bulkley parameters (τ0=3.6Pa, K=0.397 and n=0.85) were found for the organoclay at 10wt%. The latest sample has the high thixotropy loop area so can be used as viscosity enhancer for the oil drilling fluid.

A rheological approach to study the early-age hydration of oil well cement: Effect of temperature, pressure and nanoclay

Abstract The pumpability of cement slurries during cementing and their ability to resist penetration of formation gas once placed are critical for the success of oil and shale gas well cementing. Pumpability and ability to resist gas migration, which can be quantified through rheological parameters, develop over time due to hydration, which is highly dependent on the well conditions, namely temperature and pressure levels, as well as mix composition, including the use of rheological modifiers. In this study, we utilized a rotational rheometer with a high-pressure cell to investigate the effect of temperature, pressure and nanoclay on the viscosity and static yield stress of oil well cement slurries. The results emphasize the importance of considering shear rate in evaluating viscosity evolution and time to reach the limit of pumpability. The growth of yield stress was described by a non-linear structural build-up model, which connects the static yield stress with hydration, and its ability to predict the effect of temperature, pressure and nanoclay on yield stress evolution was assessed.

Lubrication solution of the flow of a Herschel-Bulkley fluid with pressure-dependent rheological parameters in an asymmetric channel

The lubrication flow of a Herschel-Bulkley fluid in a long asymmetric channel, the walls of which are described by two arbitrary functions h1(x) and h2(x) such that h1(x) < h2(x) and h1(x) + h2(x) are linear, is solved extending a recently proposed method, which avoids the lubrication paradox approximating satisfactorily the correct shape of the yield surface at zero order [P. Panaseti et al., “Pressure-driven flow of a Herschel-Bulkley fluid with pressure-dependent rheological parameters,” Phys. Fluids 30, 030701 (2018)]. Both the consistency index and the yield stress are assumed to be pressure-dependent. Under the lubrication approximation, the pressure at zero order is a function of x only, is decoupled from the velocity components, and obeys a first-order integro-differential equation. An interesting feature of the asymmetric flow is that the unyielded core moves not only in the main flow direction but also in the transverse direction. Explicit expressions for the two yield surfaces defining the asymmetric unyielded core are obtained, and the two velocity components in both the yielded and unyielded regions are calculated by means of closed-form expressions in terms of the calculated pressure and the two yield surfaces. The method is applicable in a range of Bingham numbers where the unyielded core extends from the inlet to the outlet plane of the channel. Semi-analytical solutions are derived in the case of an asymmetric channel with h1 = 0 and linearly varying h2. Representative results demonstrating the effects of the Bingham number and the consistency-index and yield-stress growth numbers are discussed.

Predicting the Formwork Lateral Pressure of Self-consolidating Concrete Based on Experimental Thixotropy Values

Self-consolidating concrete (SCC), despite its many positive advantages, increases the formwork lateral pressure of the mixture due to its high fluidity, leading to the increased cost of formwork construction in the in situ concrete structures. The thixotropy property, as the most significant functional feature including the effect of mixture proportions on lateral pressure, was selected to investigate the behavior of fresh concrete in the mold. In the present study, the thixotropy and formwork pressure characteristics (including maximum lateral pressure and pressure drop rate) of 15 SCC mixtures were investigated by considering a number of mixtures proportions variables including cement content, water-to-cement ratio, and mineral admixtures. In addition to studying the effect of these variables on the thixotropy level and the lateral pressure of the formwork, the relationship between the methods of measuring the thixotropy level (hysteresis methods, the area of structural breakdown, and the yield stress growth rate) was evaluated considering the mechanism of these methods. In this study, formwork pressure simulator device was used to measure maximum lateral pressure and lateral pressure drop rate. In addition, the effects of mixture proportioning variables on thixotropy and its relationship with the formwork pressure were studied. Using these indices, the ability to predict the behavior of concrete in the mold was investigated through modeling. The presented predicting model of the formwork pressure based on thixotropy value showed an acceptable correlation coefficient (R2 > 0.77).

Pressure-driven flow of a Herschel-Bulkley fluid with pressure-dependent rheological parameters

The lubrication flow of a Herschel-Bulkley fluid in a symmetric long channel of varying width, 2h(x), is modeled extending the approach proposed by Fusi et al. [“Pressure-driven lubrication flow of a Bingham fluid in a channel: A novel approach,” J. Non-Newtonian Fluid Mech. 221, 66–75 (2015)] for a Bingham plastic. Moreover, both the consistency index and the yield stress are assumed to be pressure-dependent. Under the lubrication approximation, the pressure at zero order depends only on x and the semi-width of the unyielded core is found to be given by σ(x) = −(1 + 1/n)h(x) + C, where n is the power-law exponent and the constant C depends on the Bingham number and the consistency-index and yield-stress growth numbers. Hence, in a channel of constant width, the width of the unyielded core is also constant, despite the pressure dependence of the yield stress, and the pressure distribution is not affected by the yield-stress function. With the present model, the pressure is calculated numerically solving an integro-differential equation and then the position of the yield surface and the two velocity components are computed using analytical expressions. Some analytical solutions are also derived for channels of constant and linearly varying widths. The lubrication solutions for other geometries are calculated numerically. The implications of the pressure-dependence of the material parameters and the limitations of the method are discussed.

Characterization of yield stress development of cement paste by electrical resistivity

Yield stress development of cement paste is potentially governed by percolation of 3-dimensional links formed by hydration products on the surface of the particles. It rises steadily at a gradual rate before a sudden increase in rate of growth. In this study, a method was proposed to predict the yield stress development based on the diameter of spread (D) of mini slump cone test and gradient from electrical resistivity measurement (Km). To evaluate the significance of (D) and (Km) in terms of yield stress, they were quantitatively compared to the initial yield stress (τ0) and rate of yield stress growth (K) obtained from a rheometer. A mathematical relationship between the yield stress of cement paste, diameter of spread and electrical resistivity characteristic gradient was developed. The equation developed can be used as an alternative method to estimate yield stress of cement paste.

On Poiseuille flows of a Bingham plastic with pressure-dependent rheological parameters

The plane Poiseuille flow of a Bingham plastic with pressure-dependent material parameters is analysed. Both the plastic viscosity and the yield stress are assumed to vary linearly with pressure and analytical solutions are derived for the two-dimensional pressure and the one-dimensional velocity. The effects of the plastic-viscosity and yield-stress growth parameters on the thickness of the unyielded plug and the conditions for the occurrence of flow are discussed.

Numerical models of stiffness and yield stress growth in crystal-melt suspensions

Magmas and other suspensions that develop sample-spanning crystal networks undergo a change in rheology from Newtonian to Bingham flow due to the onset of a finite yield stress in the crystal network. Although percolation theory provides a prediction of the crystal volume fraction at which this transition occurs, the manner in which yield stress grows with increasing crystal number densities is less-well understood. This paper discusses a simple numerical approach that models yield stress in magmatic crystalline assemblies. In this approach, the crystal network is represented by an assembly of soft-core interpenetrating cuboid (rectangular prism) particles, whose mechanical properties are simulated in a network model. The model is used to investigate the influence of particle shape and alignment anisotropy on the yield stress of crystal networks with particle volume fractions above the percolation threshold. In keeping with previous studies, the simulation predicts a local minimum in the onset of yield stress for assemblies of cubic particles, compared to those with more anisotropic shapes. The new model also predicts the growth of yield stress above (and close to) the percolation threshold. The predictions of the model are compared with results obtained from a critical path analysis. Good agreement is found between a characteristic stiffness obtained from critical path analysis, the growth in assembly stiffness predicted by the model (both of which have approximately cubic power-law exponents) and, to a lesser extent, the growth in yield stress (with a power-law exponent of 3.5). The effect of preferred particle alignment on yield stress is also investigated and found to obey similar power-law behavior.