Rheological Properties Of Pastes Research Articles

Rheology and printability of alumina-toughened zirconia pastes for high-density strong parts via direct ink writing

Direct ink writing (DIW) is a promising additive manufacturing technique for fabricating structural ceramics, including alumina-toughened zirconia (ATZ), heavily reliant on the rheological properties of the paste. The rheological properties of aqueous ATZ pastes with 25 wt% Pluronic® F127 hydrogel and solid loadings of 28–44 vol% were investigated, complemented by characterization of the parts, including relative density and shrinkage measurements, to assess the printability. The 42 vol% paste was identified as most suitable for producing high-density parts with minimal shrinkage. A controlled drying process gradually decreased humidity from 90% to 30% while raising temperature from 25 to 60°C over 4 days to prevent drying defects. Mechanical testing showed DIW-printed high-density (97.2±2.2%) parts with a mean flexural strength of 670±270 MPa, Vickers hardness of 13.6±2.8 GPa, and fracture resistance of 4.4±0.2 MPa, highlighting the potential for DIW to create high-density ATZ ceramic parts with favorable mechanical properties.

Multidisciplinary approach for the prediction of cement paste rheological properties: physical analysis, experimental rheology and microstructural modelling

AbstractIn this contribution, an interdisciplinary approach was employed to investigate and describe the fresh rheology of cementitious pastes, using analytical techniques, microstructural modelling, and experimental rheometry. The pastes, based on Ordinary Portland Cement and Limestone Calcined Clay Cement at a solid volume fraction of Φ = 0.45, were subjected to various analyses. Physical and chemical analyses were conducted including laser granulometry and isothermal heat flow calorimetry. Dynamic rotational rheometry and static oscillatory rheometry, along with viscoplastic and viscoelastic rheological modelling were used to support the characterization of the pastes. A physics‐based Monte‐Carlo algorithm was developed to numerically describe rheological properties such as structural buildup and yield stress. The results showed that as the physical properties of the pastes became more complex, the correlation of several analysis methods went more challenging. However, the combination of analytical, experimental, and phenomenological rheology allowed for a more distinct characterization of the cement paste. These findings can serve as a basis for further multidisciplinary rheological characterization of cementitious building materials.

Influence of Hazelnut and Walnut Oil Cakes Powder on Thermal and Rheological Properties of Wheat Flour.

The aim of the study was to assess the influence of the addition of powdery hazelnut oil cakes (HOC) or walnut oil cakes (WOC) to wheat flour (WF) on its selected thermal and rheological properties. In the research material, part of the wheat flour (5%, 10%, 15%) was substituted with powdery oil cakes based on hazelnuts and walnuts. The control sample was wheat flour (100% WF). In the tested systems with the addition of hazelnut oil cakes (WFHOC) and walnuts (WFWOC), the characteristics of the gelatinization and retrogradation processes were determined using the DSC method, the gelatinization characteristics of 10% pastes using the RVA method, flow curves and viscosity curves, as well as mechanical spectra. Based on the results obtained, it was found that the type of oil cakes and the level of their addition significantly influenced the thermal and rheological properties of the tested systems. Partial replacement of wheat flour with HOC or WOC significantly influenced most DSC parameters. The highest values of gelatinization enthalpy ∆HG and retrogradation ∆HR were characteristic of the WFWOC5% sample (5.9 J/g) and the control sample (1.3 J/g), respectively. All tested systems showed the properties of shear-thinning non-Newtonian fluids, and the partial replacement of wheat flour with HOC or WOC resulted in a significant reduction in the maximum viscosity of pastes, increasing with the increase in the proportion of oil cakes. WFHOC-based pastes were characterized by higher values of the G' and G″ modulus, while their values and the values of the K' and K″ parameters decreased as the share of oil cakes increased. Gels based on all tested systems showed the nature of weak gels (tan δ = G″/G' > 0.1). Replacing part of the wheat flour with nut oil cakes modified the thermal and rheological properties of pastes and gels, and the observed changes were influenced by both the origin and the level of addition of powdered oil cakes. It was found that WFHOC/WFWOC15% systems had reduced viscosity and weakened viscoelastic properties compared to systems with a lower OC content, which is not a favorable feature from the technological point of view. However, these systems were the most stable, which is an advantageous feature. However, for baking purposes, research should be carried out on the rheological properties of dough made from these mixtures.

Preferential adsorption of superplasticizer on cement/silica fume and its effect on rheological properties of UHPC

The adsorption behavior of two comb-shaped superplasticizers (PCEs) containing only carboxyl groups and both carboxyl and phosphate groups on cement/silica fume, and their influence mechanism on rheological properties of pastes with low w/b of 0.2 were investigated. The preferential adsorption of PCEs on the surface of different powders (e.g. cement and silica fume) was observed. The PCE containing only carboxyl groups adsorbed more on the surface of cement, while phosphate-containing PCE adsorbed more on the surface of silica fume at low dosage and exhibited stronger adsorption capacity both on cement and silica fume at high dosage. For cement paste, PCE containing only carboxyl groups was suggested to improve flow spread. However, as silica fume was introduced, the blends of the two PCEs could achieve higher packing density of particles in paste due to the excellent dispersion of phosphate containing-PCE to silica fume, resulting in higher flow spread (lower yield stress) and lower viscosity.

Effect of anchoring groups of polycarboxylate ether superplasticizer on the adsorption and dispersion of cement paste containing montmorillonite

Four types of polycarboxylate ether (PCE) superplasticizers with -COO- (C-PCE), -NH3+ (D-PCE), –SO3- (S-PCE) and –COOR (H-PCE) were synthesized. Their molecular structures were characterized by Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance spectrum (1H NMR). The adsorption behavior of PCEs was investigated by adsorption amount and layer thickness on cement paste without and with montmorillonite (MMT). Time-dependent flowability and rheological properties of paste were measured and the effects of these PCEs on the hydration of paste were examined. Based on the adsorption behavior of PCEs and fresh properties of pastes without and with MMT, the sensitivity of these PCEs to MMT was also assessed. Results show that D-PCE, S-PCE and H-PCE exhibit lower adsorption amounts, but thicker adsorption layer on cement paste than that of C-PCE. S-PCE shows the best dispersion and retention capability, even in the presence of 3% MMT, and has the smallest sensitivity index. However, H-PCE is the worst one. Paste with D-PCE exhibits comparable initial flowability to that of C-PCE, but higher flowability loss.

Study on the Relationship between the Fluidity of Paste in Stope and the Rheological Properties of Paste

Paste should be kept in homogeneous state without segregation or weak segregation during pipeline transportation, which can reduce the occurrence of pipe blockage accidents in engineering application. Only when the paste is homogeneous can the paste have good stope fluidity, and the stope fluidity is also restricted by the geometric size of the stope and other factors. Therefore, it is very important to study the homogeneity of paste and analyze the influence of paste rheological characteristics on stope fluidity. In this paper, it is pointed out that the vertical settling velocity of solid phase materials in paste in the liquid-phase dense medium is the main factor affecting the homogeneity of paste. Increasing the plastic viscosity and yield stress of the liquid-phase dense medium is beneficial to increase the drag force of aggregate and then reduce the settling speed of aggregate in the liquid-phase dense medium. On this basis, the homogeneity of paste can be judged. In the simplified paste flow field, using Cauchy stress equation and flow boundary conditions, the relationship between paste stope flow performance and paste rheological properties was analyzed, and the relationship model between the slope angle of paste flow formation and paste rheological properties was established. Compared with the experimental results, the error of the model results is small, and the slope angle of paste flow can be well predicted.

Paste Pipeline Transportation of Pumping Backfill Technology with Long Distance and High Stowing Gradient in Cold and High-Altitude Areas

A paste pipeline transportation of pumping backfill technology with long distance and high stowing gradient is proposed to solve the problem of filling slurry transportation with low concentration, the filling body poor quality, and the transportation difficulties with long distance and high stowing gradient in Heiniudong copper mine (HCM). The physical and chemical properties of the backfill material, backfill proportion test, circular pipe experiment, and backfill system analysis evaluation were studied in the laboratory and outdoor, and the application in HCM was carried out to evaluate the technology. The research results show the feasibility of considering classified tailings and binder as backfill aggregates, and the optimum proportion of cement-binder-classified tailings applied in the stope and goaf is 1 : 4 : 8 and 1 : 4 : 15, respectively, with paste rheological properties of mass fractions of both being 74%∼76% and the backfill strength of about 1.5 MPa at 28 d. Furthermore, when backfill proportions and rate of flow are 1 : 4 : 8 and 50 m3/h, the pressure loss of the pipeline is around 0.4 MPa/100 m, and the backfill pump meets the backfill requirements. On this condition, the technology is capable of obvious economic benefits with the backfill cost of only 25.56 yuan/t, remnant ore recovery rate of 80%, and new output value of 1.28 billion. It creates a precedent for the paste pumping backfill technology with long distance and high stowing gradient in cold and high-altitude areas. The technology also provides reference mining experience for similar mines.

Study on the relationship between slurry film thickness and rheology of fillers based on film theory

The key problem of paste filling technology lies in whether paste can meet the requirements of stope structural parameters on cementing strength, pipe transportation and mining methods on filling performance. The separated paste will cause serious wear and even pipe blockage in the pipeline transportation process. If the paste is separated in the stope, the strength of the filling body will be uneven, and accidents such as delamination and stacking will occur. The occurrence of these situations is extremely unfavorable to the filling operation. Just as the material determines the performance, in order to ensure the paste has excellent filling performance, it is necessary to systematically study the internal relationship between paste filling materials and filling performance. Paste is a complex suspension system composed of aggregate, water, cementing materials and additives. Compared with traditional low-concentration classified tailings slurry, it has the characteristics of wide particle size distribution, high solid content, strong chemical action on particle surface, etc. Under the interaction of these factors, paste presents macroscopic characteristics such as plasticity and stability. These macroscopic characteristics are embodied in rheology, that is, rheological characteristics of paste. The research shows that the rheological properties of paste are affected by the gradation, concentration and cementing material of filling material, and the change of gradation of filling material has the most significant effect on the rheological properties of paste. The change of the micro-level composition causes the change of the rheological properties of the paste on the macro level, thus causing the change of the paste filling performance. In the final analysis, the gradation of the traceable filling material is an important factor that determines the paste filling performance.

Assessment of cement characteristics affecting rheological properties of cement pastes

In this study, the cement-based parameters affecting CEMI portland cements-polycarboxylate ether-based high-range water-reducing (HRWR) admixtures compatibility were investigated. For this purpose, eight CEMI cements and three commercial HRWR admixtures were used. The rheological properties of 112 paste mixtures with different admixture dosages and water/cement (W/C) ratios were determined in accordance with Herschel–Bulkley model. Then after, using the experimental data, proper models were established to predict the dynamic yield stress and final viscosity of the pastes. In addition to cement characteristics (such as fineness, compound composition and equivalent alkali content), water-reducing admixture content and its solid material content as well as water/cement ratio of the pastes were considered as input data. Multivariate adaptive regression splines (MARS) and multiple additive regression trees (MART) methods were used in the models. Besides, artificial neural network (ANN) and conventional regression analysis (CRA) including linear, power, and exponential functions were applied to determine the accuracy of the heuristic regression methods. Three statistical indices, root-mean-square error, mean absolute error, and Nash–Sutcliffe, were used to evaluate the performance of the models. Modeling findings indicated that the model with the lowest error for both of the rheological variables in the testing set is the MART, followed by ANN, MARS, and CRA-Exponential methods. The most effective cement characteristics causing incompatibility, hence detraction of paste rheological properties, in decreasing order, were determined as cement fineness, C3S, C3A and equivalent alkali contents. C4AF and C2S contents of the cement were found to have less effect on the cement–admixture incompatibility. It will be possible to determine the rheological properties of mixtures containing different cements without conducting an experimental study by using the model based on MART method.

Effect of polycarboxylate superplasticizer on fluidity and rheology of cement slurry containing silica fume

The effect of polycarboxylate superplasticizer on the fluidity and rheology of cement - silica fume - water paste was investigated. The changes of dispersion degree, yield stress and plastic viscosity of paste with different superplasticizer content were analyzed. The results show that the rheological properties of paste with different superplasticizer content conform to Herschel-Bulkley model. The shear thinning of the slurry is manifested as a typical yielding pseudoplastic fluid characteristic. When the content of superplasticizer is less than 1.0%, the plastic viscosity and yield stress decrease and the fluidity increase with the increase of plasticizer content. When the content of superplasticizer is more than 1.0%, the yield stress decreases slightly and the plastic viscosity increases with the increase of plasticizer content. The fluidity decreases with the increase of yield stress, and there is a good correlation between them.

Modeling and Numerical Study of Ceramic Paste Extrusion

The extrusion processes of ceramic pastes, including 3D printing, are used for the production of high-value products. Ceramic paste extrusion is a complex process which depends on the paste rheological properties, die and extruder geometries, and operational parameters. Modeling and quantitative analysis of paste molding are important to design proper extrusion process for the production of high-value extrudates of desired strength, shape, and morphology. In this paper, the mathematical model of ram extrusion of ceramic materials is established, and the paste continuity and momentum equations for non-Newtonian fluid based on the modified Herschel-Bulkley viscous model were solved numerically. The effects of die geometry and paste feed rate on the distributions of paste velocity and pressure in the extruder and die were investigated numerically. As a result, the steeper radial profile of longitudinal velocity and higher value of longitudinal velocity were obtained in the narrow die. The pressure significantly increases in the die at a high feed rate, and the pressure profile is almost flat in the barrel. The rate of increase of the maximum pressure decreases with an increase of paste feed rate. The pressure steeply increases in the die of small diameter. The maximum pressure linearly increases with the ratio of die length to diameter.

Systemic multi-scale approaches to predict the flowability at various temperature and mechanical properties of cement paste modified with nano-calcium carbonate

In this study, the effect of nano-calcium carbonate (nano-CaCO3) as an additive to the cement paste was evaluated and quantified. Microstructure tests, experimental tests, and modeling were conducted to predict the cement paste's rheological properties namely yield stress (yield point), shear stress limit, viscosity, and stress at the failure of cement at fresh and hardened stages. The cement paste modified with nano-CaCO3 was tested at a water-to-cement ratio of 0.35 with 0.45 and temperatures ranging from 25 to 75 ⁰C. The addition of nano-CaCO3 increased the shear stress limit and the yield stress (τo) by 10.28 to 51.35% and 14.36 to 91.4%, based on the nano-CaCO3 content, w/c, and temperature of the test. TGA tests showed that the 1% nano-CaCO3 additive reduces the weight loss of the cement at 800 ⁰C by 76% due to interacting with the nano-CaCO3 with the cement paste. The nonlinear regressions (NLR) model and Artificial Neural Network (ANN) technical approaches were used for the qualifications of the flow of slurry and stress at the failure of the cement paste modified with nano-CaCO3. Based on the statistical assessments of R and RMSE, the rheological properties such as yield stress, plastic viscosity, shear stress limit and compressive strength of cement paste modified with nano-CaCO3 can be well predicted in terms of w/c, nano-CaCO3 content, temperature, and curing time using two different simulation techniques. Based on the statistical assessments such as coefficient of correlation (R), root mean square error (RMSE), the NLR model is the most effective model to estimate rheological properties and compressive strength of the cement and it is performing better than the ANN model.

Influence of Replacement Part of Starch with Inulin on the Rheological Properties of Pastes and Gels Based on Potato Starch.

The objective of the present study was to determine the influence of replacement part of starch with inulin on the rheological characteristics of pastes and gels obtained on the basis of potato starch. Replacement of the starch by inulin varied from 0 to 40%. Flow curves for pastes and gels were determined, and the viscoelastic properties were characterized using dynamic tests and creep and recovery tests. It was determined that the replacement of part of potato starch with inulin significantly modifies rheological properties of starch pastes and gels, weakening their structure. With the increasing amount of inulin, an increase of viscous properties was becoming more apparent. Moreover, an irregular influence of inulin addition on the parameters of rheological characteristics was determined. Initially, the differences were minor, and the differences at the lowest addition were typically statistically insignificant, followed by strong increase with local restrictions to structural weakening.

Influence of time and temperature on rheology and flow performance of cemented paste backfill

The Cemented Paste Backfill (CPB) technology can provide effective solutions to mining-related environmental and safety problems, and access to achievement of green mining and deep mining. Rheological properties of paste are important factors that affecting the flow characteristics and pipeline resistance calculation. The rheology of fresh cemented paste is influenced by time and temperature typically in pipeline transportation and is in dynamic evolution. By analyzing the effect of time and temperature on paste rheology, a calculation model of the resistance was established, which was implemented with the numerical software, COMSOL Multiphysics, thus the distribution of the flow parameters was obtained. The results show that, with increase in shear time, the yield stress decreases negative exponentially and the plastic viscosity decreases linearly. The rheological parameters gradually become stable after a certain time. The yield stress declines with increase in temperature, and the process could be described with a negative exponential function. Meanwhile, the variation of plastic viscosity is linear and slight. It is concluded that the rheological behavior of paste has time-temperature equivalent effect, and the transformation equation of time-temperature effect was established. Combined with the Buckingham equation, a calculation model of pipeline resistance with time-temperature effect was proposed, implemented in the numerical software, and a new equation of conservation of momentum was established. In this paper, the changes in paste rheological characteristics with shear rate, thixotropic time and temperature are clarified, and a calculation model of paste resistance considering the effects of time and temperature is established. Through three-dimensional simulation, the processes of velocity distribution of paste with time and temperature were displayed vividly. The mathematical model has been verified and is of guiding significance for pipeline transportation in paste backfill engineering.

The impact of vermiculite residual fines in the rheological properties of cement pastes formulated with different waste contents

In the industrial processing of vermiculite, a fine residue is generated for which an application that allows its large-scale use has not been developed yet. The association with Portland cement in mortar and concrete compositions may be an alternative, because of the chemical composition of vermiculite with high amount of aluminum, silicon and magnesium, similar to other additions used in substitution to Portland cement. However, due to high specific surface area of vermiculite compared to cement, its use may affect the rheological properties and the water demand, thus limiting its application. This work was carried out with the objective of evaluating the impact on rheological properties of cement pastes prepared with partial replacement of Portland cement by vermiculite fine residues, both as obtained and calcined. The vermiculite fine residue contents were varied from 5 to 20%, and the compositions were submitted to a stepped flow test, with changes in the shear rate. There were almost no changes in rheological properties in suspensions with 5% of cement substitution by vermiculite fines. However, when >10% of vermiculite was used, considerable changes in flow could be observed as a function of both the residue content and the nature of the vermiculite (as-obtained or calcined). The YODEL and Interference models, based on the physical characteristics of the particles, were applied to estimate the yield stress (YODEL) and viscosity (Interference), and the calculation results indicated that there was a good correlation with the experimental data, indicating than the rheological properties of the pastes were directly related to physical properties of the particles.

Effect of nanosilica particles on the rheological and mechanical properties of cement pastes using polyhydroxyl and polycarboxylate-based superplasticizers

This study assesses the effect of both silica nanoparticles of different sizes and different types of superplasticizers on rheological properties and 28-day compressive strength of Portland cement pastes. The experimental program comprised the utilization of 36 and 264 nm sizes nanoparticles and the superplasticizers used were polyhydroxyl and polycarboxylate-based high-range water reducers. Subsequently, the nanoparticles and superplasticizers were added to cementing pastes on which rheology tests were performed under a controlled rate (CR) mode, in order to quantify the yield stress and the plastic viscosity according to the Binghamian rheological model. As a result, it was found a saturation range between 0.8 wt % and 1.2 wt % of the used polyhydroxyl and polycarboxylate-based superplasticizers, from which the reduction of the rheological properties of the pastes was not further modified. Also, pastes using a simultaneous addition of 0.5 wt % of 36 nm-size nanosilica and 0.6 wt % of polyhydroxyl superplasticizer further optimize both the rheological and mechanical properties of the control mixture, and the compressive strength of the pastes increased up to 9% for using this nanoparticle dosage. It was found that the coarser nanoparticles (264 nm) provide pastes with enhanced mechanical properties and better workability compared to the ones provided by the finer nanoparticles (36 nm). Finally, several practical equations were proposed for the prediction of the rheological properties of yield stress and plastic viscosity of Portland cement pastes based on the nanosilica and superplasticizer additions.

Cow manure ash particle size distribution's effect on concrete paste rheological properties

The influence of cow manure ash (CMA) particle size distribution on some rheological properties of cement paste is the experimental basis for the application of CMA to concrete. Some research studies have been conducted with the purpose of studying this influence. The particle size distribution of CMA particles was measured by laser particle size analyser. The CMA particles in the cement paste samples constituted 5, 10, 15 and 20% of the total cement mass. The apparent viscosity of cement paste was measured with a rotational viscometer; the yield stress and plastic viscosity were calculated by fitting method. Correlations between CMA particle size distribution and some rheological properties (especially steady flow properties) were tested using a grey correlation analysis. The results of the correlation analysis show that: increasing the particle content of 3–32 μm and 32–65 μm size, especially the former, reduces the yield stress value, and increases the plastic viscosity of the slurry viscosity, except for at the level of 15% addition.

Simulation of long-distance pipeline transportation properties of whole-tailings paste with high sliming

Based on Bingham rheological model, a three-dimensional numerical simulation model for long-distance pipeline transportation is established by computational fluid dynamics (CFD) to study the pipeline transportation properties of high sliming paste from a copper mine in China. Based on the rheological properties test, the pressure and velocity of pipeline and elbow are simulated by CFD under different mass concentrations and different stowing capacities. The results show that the pipeline resistance of whole-tailings paste with high sliming while without pumping agent is much higher than that with high sliming and pumping agent at the same mass concentration, and the pipeline resistance of whole-tailings paste with high sliming while without pumping agent is much higher than that with low sliming while without pumping agent. It is very important to add pumping agent to whole-tailings paste with high sliming, and the resistance changes with mass concentration and stowing capacity at the same cement-to-sand ratio of 1:5 and tailings-to-waste ratio of 6:1. However, the change is just limited, that is to say, the paste transportation system is of good stability. Furthermore, at the elbow, the maximum pressure and velocity transfer to the outside of the pipe from the inside. However, lubricating layer is formed at the pipe wall because of high content of fine particles in whole-tailings paste, which will protect the elbow from abrasion. CFD provides an intuitive and accurate basis for pipeline transportation study, and would have a wider application space in the study of paste rheological properties and resistance reduction methods.

Steady and dynamic shear rheology of starches from different oat cultivars in relation to their physicochemical and structural properties

ABSTRACTStarches isolated from eight oat cultivars were tested for their physicochemical, structural, and rheological properties. The isolated starches had low levels of ash and nitrogen contents with amylose ranging from 21.8 to 32.3 g/100 g. The amount of water released from starch gels decreased significantly (p < 0.05) with increase in freeze thaw cycle. The scanning electron micrographs revealed the presence of polygonal to irregularly shaped starch granules. All the starches exhibited A-type X-Ray diffraction pattern typically characteristic of cereal starches. The rheological properties of pastes were well described by the Herschel-Bulkley model at a shear rate of 0–100 s−1 (R2 > 0.99). The starch pastes behaved like a pseudoplastic fluid and exhibited shear thinning fluid characteristics with values of flow behaviour index considerably less than 1. Both the storage and loss moduli of the pastes increased sharply initially and then dropped after reaching the gelatinization peak. The magnitude of the dynamic rheological parameters varied significantly (p < 0.05) between the cultivars. All the starch pastes were highly elastic than viscous as evidenced by the lower tan δ values. Structure property relationships were established between starches using principal component analysis.

Numerical and experimental studies of aggregate blocking in mortar extrusion

Numerical and experimental study of aggregate blocking in extrusion of mortar is presented. The studied system consists of a pipe with a nozzle at the tip. Fresh mortar is modeled by composite particles consisting of hard-core representing a sand particle surrounded by soft-shell layer representing interstitial cement paste. For the experimental study, two kinds of mortars are studied. The first kind is a mortar composed of monosized glass beads. This mortar is used for comparison with numerical results. The second kind of mortar is more realistic, polydispersed particles are used by replacing glass beads by standard sand. The effects of the dimension of the bottom nozzle opening, the rheological properties of the cement paste and the paste volume proportion on the blocking of mortar are studied both experimentally and numerically. For mortars composed of monosized beads, experiments and simulations both show that the main parameter governing aggregate blocking is the ratio ‘a’ between the bottom opening diameter of the nozzle and the beads diameter. Rheological properties of the paste and paste volume proportion are less influential. Experimental results obtained on both kinds of mortar confirm the limit ratio ‘a’ identified numerically in all the cases, except for the lower cement paste volume proportion (0.54 in our study) for which ‘a’ has to be slightly increased to avoid blocking.