Four-bladed Vane Research Articles

Fresh properties of fly ash-based geopolymer: the role of the testing conditions on the rheological measurements

Rheology is a powerful tool to assess the fresh properties of cementitious systems accurately. However, uncertainties and systematic errors in measurements can impact the obtained values, even though the rheological properties should not depend on the measurement procedure. Contrary to Portland-based systems, few reports systematically assessed the role of the testing conditions on the rheological properties of geopolymers. This study evaluates the effect of testing conditions on the measurement of the rheological properties of fly ash-based geopolymer paste. Different testing geometries, including two sets of parallel plates, two concentric cylinders, and a four-blade vane spindle, were used to obtain flow curves by continuous and stepwise shear rate increments. The results show that reducing the ratio between the spindle and container radii for coaxial geometries can induce wrong shear stress/shear rate calculations and local instability. Additionally, the differences in shear stress measured with ramp and steps protocols increase as the Ri/Ro ratio (i.e., the ratio between the spindle and the container radii) increases. Parallel plates require an extra ring to keep the paste between the plates during shearing. Increasing the maximum shear rate applied reduces yield stress and viscosity values, indicating improved particle dispersion. Comparative tests with a Portland paste demostrated that the mini-slump test was suitable for assessing the yield stress of the geopolymeric system. However, its limitation regarding viscosity assessment was evidenced. Therefore, the measurement setup must be carefully chosen for the geopolymer under evaluation, and preliminary tests are highly recommended to support this selection.

Understanding the effects of processing conditions on the formation of lamellar gel networks using a rheological approach

Lamellar gel networks are multiphase systems which form the basis of many cosmetic and pharmaceutical cream products, thanks to their superior stability compared to typical oil-in-water emulsions, and highly desirable rheological properties inferred by the interconnected structure. There has previously been considerable interest in the formulation of lamellar gel networks, but little interest has been given to the effects of processing conditions on the formation of the desired structure, or the possibility for process optimisation through understanding power consumption. The evolution of the microstructure of an incipient lamellar gel network during processing was investigated by varying the temperature, vane speed and time using a rheometer equipped with a four-bladed vane in cup geometry. Torque and vane speed measurements were recorded at 2 Hz for the duration of the experiment, from which apparent viscosity (taken at a reference shear rate of 200 s−1) and power input were calculated. Samples were then characterised by yield stress and flow curve measurements to determine the impact of processing conditions on the final product microstructure. Increasing vane speed increased the maximum apparent viscosity achieved and yield stress of the sample, and reduced the time taken to reach the peak apparent viscosity. However, the increased power requirements from the higher vane speed were not counteracted by shorter processing times. Increasing the temperature reduced the rate of apparent viscosity increase but did not affect the yield stress of the final lamellar gel network, offering a reduction in power consumption due to a lower apparent viscosity for the majority of the process.

New Insights on the Vane Method to Evaluate Yield Stress of Cementitious Mortars

Abstract The yield stress (τ0) of cementitious materials has a direct influence on concrete casting and postcasting processes, such as stability, formwork pressure, interfacial bond strength between successive lifts, and bond to embedded steel bars. This article provides new insights for reliable τ0 measurements using the four-bladed vane method; it compares the effect of vane configuration (i.e., slotted versus nonslotted) and positioning (i.e., immersed in specimen versus placed flush with upper material surface) on τ0 responses. Test results have shown that the elastic-to-plastic transition region in τ0 profiles occurs progressively with the nonslotted vane, whereas it becomes more abrupt with the slotted vane. The presence of slots is believed to reduce the end effects and strengthen the assumption of shearing that takes place within the suspension along uniform stresses distributed at the cylindrical vane surfaces. For the given configuration, positioning the vane flush with the upper mortar surface minimized the effect of normal stresses on torque measurements, which resulted in decreased τ0 values. Useful equations with good correlation coefficients are established between τ0 measurements with respect to mortar composition, flow, and vane positioning.

Numerical Simulation of Sand Fill to Allow Operation of Pile Driving Rigs on Peaty Soil

Construction sites in undeveloped areas underlain with a thick peat bed require some preparation, usually surcharging with sandy soil. In such conditions, the buildings are erected on pile foundations. To ensure safe operation of pile driving rigs, method statements must specify a minimum sand fill thickness.Numerical simulation of the sand fill was performed in PLAXIS 2D software to establish the required fill thickness over peat. The analysis was performed for sphagnum peat, the samples of which had been taken from undeveloped wetlands. Peat shear strength was determined with a standard vane and was found to be 6 to 10 kPa. Strain and strength properties were calculated on the basis of laboratory tests. To estimate the strength properties, a laboratory unit was built to include a peat sample box measuring 0.5×0.5×0.5 m, a stamp and a linkage system. The pressure applied to the peat was assumed within the range of 12.5 to 35 kPa. Upon load application, a four-bladed vane was submerged into the peat through a hole in the stamp to carry out a torsion shear test. Using the results of sample testing in the laboratory unit, the values of the internal friction angle for sphagnum peat were obtained.A Soft Soil model was used for peat in the numerical simulation. Peat thickness was assumed within the range of 2 to 6 m, and shear resistance - 6 to 10 kPa. The analysis was performed for the most common models of drop hammer and static pressure pile driving units. The design criterion was the minimum sand bed thickness at which peat bearing capacity was ensured. In addition, the maximum soil settlement was estimated that would allow normal operation of pile driving equipment.

From elastic deformation to flow in tempered chocolate

We characterize the yield behavior and flow curve of a commercially available, molten, tempered milk chocolate with a fat content of 30%, from rheological measurements performed with a rotational rheometer fitted with a four-bladed vane spindle in a large-gap setup. We show that the yield behavior can be captured by the viscoelastic White–Metzner model, which indicates that elastic deformation precedes flow as the shear stress is increased. Following an initial fluidization cycle, the shear modulus of the tempered chocolate increases by a factor of 60 to G=4.4×104 Pa. We find that the Bingham model provides the best fit to our extensive flow curve data, where the yield stress is τyield=36.1±0.6 Pa and the Newtonian plateau viscosity is μB=8.7±0.02 Pa s.

Influence of recycled aggregates on dynamic/static stability of self-consolidating concrete

The effect of recycled concrete aggregate (RCA) on rheology and dynamic/static stability of highly flowable self-consolidating concrete (SCC) is not well quantified. Two series of SCC mixtures containing different RCA replacement levels and proportioned using the direct replacement and Equivalent Mortar Volume methods were considered in this study. Test results have shown that the increase in RCA replacement level leads to reduced rate of flow and passing ability, yet resulted in improved static stability given the greater relative water absorption that reduces the detrimental effects of free mixing water in fresh concrete. The use of four-bladed slotted vane rotating in infinite medium was found particularly useful to mitigate aggregate migration and enhance detection of internal friction resulting from RCA skeleton. Four “rheology boxes” enabling easier development and prediction of concrete stability for given application are proposed with respect to the European Guidelines for SCC.

Correlating water extraction to viscosity variations of injection grouts

Cementitious grouts injected by vacuum pressure techniques are expected to loose part of the free mixing water with direct consequences on fluidity and penetrability. A new set-up was developed to enable simultaneous assessment of water extracted due to vacuuming and real-time viscosity changes occurring over several minutes of time. A slotted four-bladed vane was used to prevent migration of cement particles away from the center and enable the vane to remain in contact with new material during motion. Test results have shown that the extraction of water decreases fluidity (i.e., flow time) and increases viscosity, mostly due to increased internal friction within the solid particles. Grouts prepared with low water-to-cement ratio and containing moderate to high concentrations of viscosity-modifying admixtures yielded adequate water retentivity with minor variations in viscosity. “Injectability boxes” are proposed to simplify product development and predict variations in grout viscosity during vacuuming.

Rheology of powders and nanopowders through the use of a Couette four-bladed vane rheometer: flowability, cohesion energy, agglomerates and dustiness

A new four-bladed vane powder rheometer is proposed to study powder and nanopowder rheology at low and high shear rates. As shear rates increase, the powder flow will evolve from a Newtonian regime (low shear rates) to a Coulombic regime (moderate shear rates) and then to a kinetic regime (high shear rates) at which the powder may become self-fluidized because of intense particles collisions. Viscosity measurements of noncohesive glass beads at low shear rates (Newtonian and Coulombic regimes) do not strongly depend upon the particle size and can reach values much larger than commonly used viscosities in some CFDs models. Since, in the kinetic regime, the shear stress is a strong function of the particle size, agglomerate particle size of cohesive powders can be directly inferred from rheograms. Cohesive carbon black and silica nanopowders have been tested and compared to noncohesive glass beads microparticles, chosen as reference. For noncohesive glass bead micropowders, the “agglomerate” diameter average values found from rheological measurements are of the same order of magnitude as the primary diameters of the powder. This indicates that the kinetic theory of granular flows describes well these high shear rate regimes and that such theory can be used to estimate agglomerate diameters. It is also found that estimated agglomerate sizes of nanometric cohesive materials can reach sizes of hundred micrometers depending upon their cohesion strength. Such agglomerate size measurements have been corroborated with those made by microscopy.

Rheological properties of self consolidating concrete with various mineral admixtures

This paper reports an experimental study into the rheological behaviour of self consolidating concrete (SCC). The investigation aimed at quantifying the impact of the varying amounts of mineral admixtures on the rheology of SCC containing natural sand. Apart from the ordinary Portland cement (OPC), the cementitious materials such as fly ash (FA), ground granulated blast furnace slag (GGBS) and micro-silica (MS) in conjunction with the mineral admixtures were used in different percentages keeping the mix paste volume and flow of concrete constant at higher atmospheric tempterature (30ᵒ to 40ᵒC). The rheological properties of SCC were investigated using an ICAR rheometer with a four-blade vane. The rheological properties of self-consolidating concrete (SCC) containing different mineral admixtures (MA) were investigated using an ICAR rheometer. The mineral admixtures were fly ash (FA), ground granulated blast furnace slag (GGBS), and micro silica (MS). The results obtained using traditional workability results are compared with those obtained using ICAR rheometer. The instrument ICAR (International Center for Aggregate Research) rheometer employed in the present study for evaluating the rhelogical behaviour of the SCC is found to detect systematic changes in workability, cementitious materials, successfully. It can be concluded that the rheology and the slump flow tests can be concurrently used for predicting the flow behaviours of SCC made with different cementitious materials.

Small strain deformation measurements of konjac glucomannan solutions and the influence of borate cross-linking

The dynamic rheology of aqueous solutions of konjac glucomannan has been evaluated over a range of concentrations up to 2.35%, and the effect of borate cross-linking of such solutions evaluated in the range 0.02–40mM borate. In preliminary work, conventional parallel plate geometries were employed and in situ cross-linking was investigated. For borate cross-linked samples a superior method, however, was found to be measurement of pre-formed cores of cross-linked polymer into which a four-bladed vane geometry was introduced. In order to compare with other associating polymer systems, rheological data were analysed by defining plateau moduli, corresponding relaxation times and zero shear viscosities and the scaling behaviour of these parameters with polymer and cross-linker concentrations was established. Maxwell fits and time–concentration superposition procedures were investigated. The rheological properties of the cross-linked polymer were shown to be the result of both increased network connectivity and retarded network dynamics.

Nested dipolar Halbach arrays for the determination of magnetorheological properties at variable magnetic field

A new apparatus for the measurement of magnetorheological properties of magnetic fluids in a commercial strain-controlled rheometer is proposed. The new setup makes use of the concept of the Halbach cylinder to generate a homogeneous dipolar magnetic field, using only permanent magnets. Two of these Halbach cylinders are combined, allowing the magnetic field to be varied by simply rotating the cylinders relatively to one another. The magnetic field achieved in the middle of the cylinders varies from nearly zero to about 0.6 T without a significant variation on the high homogeneity (ΔB/B < 2 × 10 − 2) of the resulting field. To perform the rheological experiments inside a strong magnetic field, measurement geometries (concentric cylinders and a four-bladed vane) were constructed from a non-magnetic material (polyoxymethylene). For the first experiments with the new setup, a commercial magnetic suspension of carbonyl iron particles in hydrocarbon oil was investigated. Stress growth experiments at varying shear rates in the steady shear regime, as well as strain sweep experiments at constant frequency in the dynamic oscillatory regime, were performed. The results show a shift of the linear (elastic) regime in oscillatory shear to higher strain values for increasing magnetic field. The steady shear viscosity increases with increasing magnetic field. The behaviour of the magnetic suspension was understood in the context of the ratio from the viscous to the polarisation forces, the so-called Mason number.

Stability of rotation of a vane in a flow

The results of investigation of the stability of permanent rotation of a four-blade vane on a weightless rod in the flow of a homogeneous medium are discussed. The rod rotates about a fixed point where a spherical joint is situated. The vane rotates about the second joint fixed at the other end of the rod. The stability of permanent rotation of the vane is studied when the rod coincides with the dynamic symmetry axis of the vane. The results are compared with the one-joint case. It is shown that increasing the number of degrees of freedom leads to “diminishing” the stability domain projection onto the corresponding subspace of parameters.

Baffled cup and end-effects of a vane-in-a-large cup rheometer for Newtonian fluids

A four-blade vane in a large cup was tested for Newtonian fluids using a controlled stress rheometer. The end-effects of a hypothetical cylinder were evaluated as a function of vane distance from the base of the container. A hypothetical cylinder radius and an effective height of the vane that includes the contribution of the “end-effect” were estimated. Also, the effect of a non-baffled and a baffled cup was investigated. Average values of shear stress and shear rate were calculated assuming that the shear conditions are similar to those existing in an analogous concentric cylinder. Furthermore, experimental angular velocity as a function of torque was correlated when using the power and Reynolds dimensionless numbers. Flow characterization with a vane-in-a-large cup is possible if laminar flow is verified. End-effects are minimized when vane is placed at the surface of fluid and the distance between the bottom of the vane and the base of the container is higher than a half of the vane height (for vane heights equal or higher than the vane diameter). Baffled did not show an effect on the laminar flow contrary to the large effect observed in the turbulent flow. For shear factors calculations of a vane-in-a-large cup, Couette analogy must only be applied using the finite cup radius equations, and corrected for non-Newtonian flow when necessary.

Adaption of a vane tool for the viscosity determination of flavoured yoghurt

In order to determine the viscosity of flavoured yoghurt with incorporated fruit pieces, a four-bladed vane tool fitted to a stress-controlled rheometer was calibrated against a conventional cup-and-bob system in steady shear measurements using several Newtonian and non-Newtonian fluids. The angular velocities obtained with both systems were compared at particular shear stress values, resulting in a conversion factor valid for angular velocities between 10−4 and 100 rad s−1. After checking the validity of the vane tool on carboxymethylcellulose solutions with embedded perspex beads, viscosity measurements were carried out on commercial stirred yoghurt without and with spherical fruit pieces. As flow curves were successfully fitted to the Cross model, the vane tool can be considered to be a suitable method for measuring the flow properties of food systems with large solid particles.

MEASURING AIRFLOW DISTRIBUTION IN PEANUT DRYING TRAILERS

A method to measure airflow distribution exhausted from a filled peanut drying trailer was developed. Six 6.4-m peanut drying wagons were loaded with dry farmer stock peanuts at a local peanut processing facility. Three wagons had floors with 23% O.A. and three had 40% O.A. Peanuts were leveled on each trailer and peanut depth ranged from 114 to 130 cm. A 76-cm diameter, 1750 rpm, four-blade vane axial dryer with a 91-cm long straightening inlet transition was connected to each peanut drying trailer. The rated airflow capacity of the dryer was approximately 510 m3 min-1 at 124 Pa. Total airflow was measured using a pitot tube traverse across the inlet transition. Static pressure was measured in the wagon plenum using a U-tube manometer. The top of the trailer was divided into 40 sections using a 5 8 cell grid. The airflow through each grid cell was measured using a vane anemometer mounted on a conical transition placed in the center of each grid cell. No significant differences in static pressure, total airflow, or airflow distribution due to the percent O.A. of the perforated drying floor were detected. The average static pressure observed for wagons with the 23 and 40% O.A. was identical at 120 Pa. Total airflow measured at the fan inlet averaged 367 m3 min-1 for the 40% O.A. trailers compared to 366 m3 min-1 for trailers with 23% O.A. The total of the air flow measured as it exhausted from the peanuts was 63% of the flow measured using the pitot tube at the fan inlet.

Vane Rheometry for Textural Characterization of Cheddar Cheeses: Correlation with Other Instrumental and Sensory Measurements

The relationship between instrumental (vane method, texture profile analysis (TPA), uniaxial compression) and sensory texture measurements of Cheddar cheeses was investigated. A Haake VT 550 viscotester equipped with a four-bladed vane rotor was used for the vane test. Instrumental TPA was performed with a TA.XT2 Texture Analyser, and compression variables were calculated from TPA data. Vane parameters were significantly correlated with respective variables of compression and TPA ( r=0.56–0.91), and sensory tests ( r=0.54–0.88). Multivariate analysis indicated that seven sensory attributes of ten commercial Cheddar cheeses were satisfactorily predicted (calibration regression coefficient, R cal >0.62) by variables of the vane, uniaxial compression and TPA tests. In particular, cheese firmness and cohesiveness evaluated by sensory panel were well described by vane stress and apparent strain. The results validate the vane method as an alternative to the existing cheese testing methods for rapid evaluation of cheese texture.

Measurement of foam modulus via a vane rheometer

A vane rheometer was used to measure the modulus of foam systems. Modulus development in a reactive polyurethane foam system was captured using a commercial stress-controlled rheometer with a four-blade vane geometry test fixture. The results were compared to those from a temperature programmed flooded parallel plate method. The vane geometry method was shown to be a convenient and accurate way to measure the physical gelation time of the reactive foaming system, without the complexity of the temperature-program method. Shaving cream was used as a calibration material to show the validity of the vane method for foam modulus measurements. For open cell foams, the error in the vane method increases due to the additional compressibility of the foam. The nature and magnitude of this error was analyzed via numerical simulation.

The use of the vane to measure the shear modulus of linear elastic solids

The vane rheometer may be used to obtain an estimate of the shear modulus G of a gelled suspension. Complex variable techniques are used to determine the torque required to turn a two-bladed vane (i.e. a single plate) of diameter 2 a through an angle θ when immersed in a linear elastic material with shear modulus G and Poisson's ratio σ. The torque per unit length is π a 2Gθ(1 + k −1), where k = 3 – 4σ. When σ = 1 2 (a reasonable approximation when studying weak gels) the shear stress τ xy over the surface of the vane is zero, and there is no tendency for slip to occur at the walls of the vane. The more general case of a two-bladed vane in the form of an ellipse is studied, with either a no-slip boundary condition, or a stress-free (slip) boundary condition. This latter case is resolved by representing the complex deformation potentials as infinite series of exponentials. These series are truncated, and the coefficients of each term are determined numerically. Boundary element methods are then used to compute the torque required to turn finite vanes, of length l = l̂a, in a fluid of viscosity μ, at low Reynolds numbers. There is a direct analogy between the governing equations for low Reynolds number flow and the equations governing linear elastic or viscoelastic deformation when σ = 1 2 , with G replaced by μ and θ by the vane's angular velocity Ω. A no-slip boundary condition is assumed over the surface of the vane. The torque is found to be M = 2π a 3μΩ( l̂ + 0.66) for the two-bladed vane, and M = 2π a 3μΩ(1.5 l̂ + 1.20) for a four-bladed vane, when l̂ ⩾ 3. Numerical results on vanes with 3, 6 and 8 blades indicate that the torque per unit length on an n-bladed vane of infinite length is 2π a 2μΩ(2 - 2 n −1). These results were tested experimentally, and good agreement was found between theory and experiment.

Vane rheometry of bentonite gels

We describe the use of a four-bladed vane to measure the yield stress τ 0 of a series of aqueous bentonite clay suspensions. An extension of the vane technique is given, showing how the shear modulus G and the yield strain γ y can also be obtained. These techniques are validated by comparing the results with those obtained from conventional concentric cylinder rheometry at low clay concentrations where wall-slip is absent. A study of the clay concentration dependence is made for volume fractions (φ) up to 0.1. The magnitudes of τ 0, G and γ y are found to scale closely as aφ x over the volume fraction range 0.01–0.1, with x approximating to 3 for τ 0, to 4 for G and to −1 for γ y. Whereas x is largely time-independent, a increases with time for both τ 0 and G as the dispersions spontaneously gel.

On the shearing zone around rotating vanes in plastic liquids: theory and experiment

The fracture zone (or shearing surface) around a four-bladed vane rotating in a Bingham liquid has a diameter D c which is significantly larger than the vane diameter. In typical plastic liquids D c/ D ≈ 1.00–1.05. We have measured D c and the rheology of some automotive greases. We have also photographed the fractural surface in a transparent Bingham liquid and have found it to be approximately cylindrical. Computer simulations of a four-bladed vane rotating in a Bingham liquid have produced a value of D c/ D = 1.025 which agrees well with experimental data on two viscoelastic automotive greases. We have not been able to obtain agreement between experiment and theory on the dependence of D c/ D on τ y/η p. The experimental and theoretical data presented here support the use of the vane for yield stress measurements if the diameter correction is applied. The present experimental data suggests the vane diameter has little or no effect on D c/ D.