Time-dependent Rheological Properties Research Articles

Structuration and yield strength characterization of hybrid alkali-activated cement composites (HACC) for ultra-rapid 3D construction printing

This study investigates the critical time-dependent rheological properties, including structuration rate and yield stress, of hybrid alkali-activated cement composites (HACC). HACC, a blend of geopolymer and cement paste, is examined to evaluate its suitability for ultra-rapid 3D construction printing (3DCP), which refers to a material’s ability to attain rapid structuration and buildability within 5–10 min after mixing, essential for additive manufacturing of 3D structures. The investigation extends to the impact of filler materials like silica sand and PVA fibers on HACC’s rapid structuration. Vicat needle, fast- and slow-penetration resistance measurements indicate that setting time increases with decreasing the Silicon/Aluminum (S/A) molar ratio and the addition of silica sand. Conversely, the addition of fibers reduces setting time while enhancing yield strength. Specifically, HACC mixtures with 0.5% and 1% PVA fiber additions, alongside combined sand (30%, 40%) and fiber (0.5%) mixtures, demonstrate ultra-rapid setting behavior within 3–5 min. Notably, mixtures with 40% silica sand and 0.5% PVA fiber exhibit highest yield strength development, i.e., 14 MPa at 12 min. Remarkably, incorporating 1% fibers into the HACC mixture yields the highest 28-day compressive strength (∼80 MPa) and flexural strength (∼11 MPa). The synergistic interplay between geopolymer and cement facilitates rapid setting time and high early-age strength development in HACC mixtures. The varying effects of silica sand and PVA fiber on setting time and yield strength provide opportunities for designing suitable structuration profiles. These findings underscore the exceptional rapid setting, structuration, and mechanical properties of HACC, positioning it as a promising material for ultra-rapid 3D construction printing.

Effect of temperature on dynamic and steady-state shear rheological properties of Jambolan (Syzygium cumini) pulp

Jambolan is an exotic fruit rich in phenolic compounds with many health benefits. The study of fruit's rheological properties plays key roles in its industrial processing and obtainment of products. The present work evaluated the time-dependent and steady-state shear rheological properties of Jambolan pulp at several temperatures. The Jambolan pulp presented thixotropy as a time-dependent property and also showed shear thinning behaviour with yield stress in the steady shear measurements. The Figoni-Shoemaker and Hershel-Buckley models adequately described both the product rheological phenomena. During the oscillatory analysis, the pulp showed some viscoelastic properties, increasing when the oscillatory frequency (ω) increased. All previous parameters also verified the impact of the temperature. The increment in temperature resulted in a reduction in consistency levels. In the temperature range studied, the viscoelastic solid component presented higher values than the viscous component. The thixotropic phenomenon and the presence of the yield stress can be related to this. Viscoelastic moduli decreased with the increase in temperature. When relevant, the Arrhenius’ Activation Energy of some model parameters were calculated. The data obtained are applicable for future studies, to improve industrial process design, and to evaluate food properties.

Rheology and yield stress evolution of highly flowable cementitious grouting materials: Mechanisms and modeling

To study the rheological properties of grouting materials, the effects of sand-binder ratio, water-binder ratio, and rest time on the rheological model and parameters were studied through rheological tests. Through the cryo-scanning electron microscopy test to observe the structural build-up process of microstructures with rest time, the particle size test to measure the size distribution variation of flocculated structures over rest time, and the low-field nuclear magnetic resonance test to measure the change of water content in the slurry, the evolution mechanism of yield stress was studied. The results showed that the rheological model was consistent with Herschel–Bulkley model (H–B model). The yield stress increased with time. The growth of network flocculated structures and the decrease in the lubrication effect of water caused an increase in the aggregate particles–cement paste interaction stress. Therefore, the yield stress of the grouting materials increased over time. Considering the combined influences of the flocculation effect, hydration reaction, and the aggregate particles–cement paste interaction, a new evolution model was proposed to better describe the evolution law of yield stress with time. The results could provide a basis for the study on flow diffusion of grouting materials and an in-depth understanding of the time-dependent rheological properties of cement-based materials containing aggregate particles.

Calibration of Thixotropic and Viscoelastic Shear-Thinning Fluids Using Pipe Rheometer Measurements

Some non-Newtonian fluids have time-dependent rheological properties like a shear stress that depends on the shear history or a stress overshoot that is a function of the resting time, when fluid movement is started. The rheological properties of such complex fluids may not stay constant while they are used in an industrial process, and it is therefore desirable to measure these properties frequently and with a simple and robust device like a pipe rheometer. This paper investigated how the time-dependent rheological properties of a thixotropic and viscoelastic shear-thinning fluid can be extracted from differential pressure measurements obtained at different flowrates along a circular pipe section. The method consists in modeling the flow of a thixotropic version of a Quemada fluid and solving the inverse problem in order to find the model parameters using the measurements made in steady-state conditions. Also, a Maxwell linear viscoelastic model was used to reproduce the stress overshoot observed when starting circulation after a resting period. The pipe rheometer was designed to have the proper features necessary to exhibit the thixotropic and viscoelastic effects that were needed to calibrate the rheological model parameters. The accuracy of rheological measurements depends on understanding the effects that can influence the observations and on a proper design that takes advantage of these side effects instead of attempting to eliminate them.

Effect of High Pressure on the Time-Dependent Rheological Properties of Cement Paste

Effect of High Pressure on the Time-Dependent Rheological Properties of Cement Paste

Experimental study on time-dependent rheological properties and mechanical performance of cemented fine tailings backfill mixed with polypropylene fiber.

By preparing fine tailings slurry with different mass concentration and fiber content, the rheological parameters of slurry with different fiber content and curing time were tested. In addition, the influence law of fiber content and curing time on compressive strength was analyzed through the prepared fine tailings backfill samples, and the microstructure characteristics of fine tailings backfill were further studied. The results show that when the fiber content is 0.2 ~ 1.2%, the yield stress and plastic viscosity of the slurry increase with the increase of fiber content, and the thixotropy of the slurry also shows the same change characteristics. The bridge effect of fiber makes it easier for forming network structure, which increase the slurry rheology. When the curing time ranges from 0h to 2.5h, the increasing of curing time leads to the increasing trend of rheological parameters, and also increases the thixotropy of slurry. However, the increase of rheological parameters will continuously decrease when the curing time exceeds 1h, indicating that the influence of curing time on yield stress and thixotropy will gradually weaken with the continuous extension of curing time. When the curing age increases from 3 to 56days, the compressive strength of the fine tailings backfill increases with the curing age, but the increasing range of compressive strength decreases gradually. When the fiber content ranges from 0.2 to 1.2%, the compressive strength of backfill increases first and then decreases with the increase of fiber content, and reaches the maximum value when the fiber content is 0.6%. The extension of curing time reduces the generation of large-scale pore structure, which promotes the formation of more compact microstructure of backfill.

Experimental investigation of fresh and time-dependent rheological properties of 3D-printed cementitious material

Unlike traditional construction processes, three-dimensional cementitious material printing requires more accurate control of the pumping flow rate. To this end, the predictability of the rheological properties of fresh cementitious mixtures and the property change over time are critical for the fabrication process. In this paper, the fresh rheological properties of twenty different mixtures were measured in the large gap viscometer, and three non-Newtonian fluid models (Bingham model, modified Bingham model, and Herschel-Bulkley) were applied to predict the dynamic yield stress and plastic viscosity of each material. The applicability of these models was assessed, and their relative deviation was quantified and discussed. Using the well-established Bingham model, the temporal evolution of the dynamic yield stress and plastic viscosity of the material was then characterized. Based on the measured and predicted rheological properties, an open loop control method was then implemented to harmonize the flow volume per unit length during printing processes to improve the printing quality and buildability of the material.

Time-Dependent Rheological Properties of Cemented Aeolian Sand-Fly Ash Backfill Vary with Particles Size and Plasticizer.

The use of cemented Aeolian sand-fly ash backfill (CAFB) material to fill the mining area to improve the surface subsidence damage caused by underground coal mining is in the development stage. Their performance with large overflow water and strength loss is not well understood. Few research has been conducted to understand the effects of aeolian sand and coal gangue on the rheological properties of CAFB with plasticizers. Therefore, this study aims to investigate the effects of a plasticizer on the rheological properties, specifically yield stress and viscosity, of CAFB prepared with aeolian sand and coal gangue. CAFB mixes containing 0%, 0.05%, and 0.1% plasticizers were prepared, and yield stress and viscosity were determined at different intervals. Additional tests, such as thermal analysis and zeta potential analysis, were also conducted. It was found that the rheological properties of CAFB are the comprehensive manifestation of the composite characteristics of various models. Reasonable particle size distribution and less plasticizer can ensure the stability of the slurry structure and reduce the slurry settlement and the risk of pipe blocking. The findings of this study will be beneficial in the design and production of CAFB material.

Effect of molecular structure of polycarboxylate ether superplasticizer on its tolerance to montmorillonite

Two groups of polycarboxylate ether (PCE) superplasticizers with different side chain lengths and densities were synthesized and characterized. Their dispersion capability was evaluated by the time-dependent rheological properties of cement pastes without and with montmorillonite (MMT). The adsorption and intercalation behaviors of these PCEs on MMT were investigated and their interactions with MMT were revealed. Results indicate that PCE with shorter side chains or higher side chain densities exhibits stronger tolerance to MMT than that with longer side chains or lower side chain densities, when they have comparable dispersion capability to cement particles. PCE with shorter side chains has lower adsorption on pure MMT and decreases the proportion of intercalated MMT. The adsorption of PCE on MMT decreases with the increase of side chain density, but the intercalation proportion shows an opposite behavior. The introduction of more side chains increases the intercalation efficiency, and decreases the consumption of MMT to PCE molecules. The adsorption kinetics of PCEs on cement or MMT system are well fitted by the pseudo-second-order adsorption kinetic equation, regardless of PCE type.

Multi-criterion optimization of Low-Cost, Self-compacted and Eco-Friendly Micro-calcium-carbonate- and Waste-glass-flour-based Ultrahigh-Performance concrete

This paper provides a multi-objective optimization approach to designing and manufacturing ultra-high-performance concrete (UHPC) with low cement content. Micro calcium carbonate and ground waste glass were employed as partial substitutes for cement and microsilica (MS) to achieve this goal. A three-factor design of experiments was used to achieve the most desirable rheological and mechanical properties with minimal quantities of cement and MS. In this context, the cement dosage (factor A), water-to-binder ratio (factor B), and superplasticizer dosage (factor C) were taken into account. By utilizing Andreasen & Andersen's (MAA) particle packing theory, dense particle packing was achieved throughout the experimental design. Regression models were developed to simulate the time-dependent rheological and mechanical properties of the UHPC. It was observed that the mathematical optimization was valid experimentally with reduced absolute deviations between 0.22 % and 1.23 % for slump flow and 3.49 % to 4.62 % for compressive strength at 28 days. The study showed that approximately 590 kg/m3 of cement would be most effective for recycled glass UHPC mixes. The proposed design will likely produce a compressive strength exceeding 150 MPa with satisfactory rheological properties at a lower cost.

Printing quality control of cement-based materials under flow and rest conditions

Time-dependent rheological properties of cement-based materials have a significant impact on 3D printing processes, where multiple rheological requirements should be met. A proper high rate of structural build-up is recommended to ensure the buildability and stability of printed elements. However, the loss of workability may occur rapidly, resulting in a significant reduction in print quality. Workability and buildability requirements usually interfere due to the time-dependent rheological behavior of cement-based materials under flow and rest conditions. This research aims to highlight the effects of time-dependent behavior on the printability of cement-based materials. The coupling mechanisms of microstructure development at rest and under shearing conditions are discussed. A new thixotropy index is proposed to quantify the printability window of cement-based materials based on their structuration rates. An experimental study was conducted on printable mortars incorporating a viscosity-modifying agent (VMA) to assess printing quality as a function of the degree of thixotropy. Different types of stability failures were captured and discussed.

Dynamics and rheology of polyampholyte condensates.

Intrinsically disordered proteins (IDPs) are critical for the formation and stability of biomolecular condensates. Yet, their time-dependent dynamical and rheological properties that are central to various biological activities are only beginning to be understood. Given that many IDPs are rich in charged residues, in this work, we delineate how the arrangement of oppositely charged residues influences the equilibrium dynamics and rheology of condensed phases formed by polyampholytic disordered proteins. We show that the dynamics of polyampholytic sequences slow down with increasing charge segregation, and are correlated with the chain-level properties in dilute solutions. Interestingly, the observed trend in dynamics also holds when the protein concentration is fixed, albeit qualitatively, highlighting the effect of charge patterning and dilute phase properties in controlling the condensed phase dynamics. Under steady flow conditions, we show that increasing charge segregation governs the changes in rheological properties due to the changing nature of intermolecular interactions. Finally, guided by the trends in rheological properties, we show that polyampholyte conformations under flow exhibit a scaling behavior with the flow strength, highlighting that their conformational response to flow strength is independent of charge patterning. Our findings reveal the dynamics and rheology of condensates formed by polyampholytic IDPs and their relation to the properties of such IDPs under dilute conditions.

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.

Topological digestion drives time-varying rheology of entangled DNA fluids

Understanding and controlling the rheology of polymeric complex fluids that are pushed out-of-equilibrium is a fundamental problem in both industry and biology. For example, to package, repair, and replicate DNA, cells use enzymes to constantly manipulate DNA topology, length, and structure. Inspired by this feat, here we engineer and study DNA-based complex fluids that undergo enzymatically-driven topological and architectural alterations via restriction endonuclease (RE) reactions. We show that these systems display time-dependent rheological properties that depend on the concentrations and properties of the comprising DNA and REs. Through time-resolved microrheology experiments and Brownian Dynamics simulations, we show that conversion of supercoiled to linear DNA topology leads to a monotonic increase in viscosity. On the other hand, the viscosity of entangled linear DNA undergoing fragmentation displays a universal decrease that we rationalise using living polymer theory. Finally, to showcase the tunability of these behaviours, we design a DNA fluid that exhibits a time-dependent increase, followed by a temporally-gated decrease, of its viscosity. Our results present a class of polymeric fluids that leverage naturally occurring enzymes to drive diverse time-varying rheology by performing architectural alterations to the constituents.

Continuous and adaptable printing path based on transfinite mapping for 3D concrete printing

Three-dimensional (3D) concrete printing is an advanced and promising construction method that shows great development potential in the field of construction engineering owing to its highly flexible and intelligent characteristics. The printing path design that is directly related to the 3D printing process is usually limited by the time-dependent rheological properties of concrete composites and the nozzle opening of the print head. Improper path design is liable to disruption, interfacial defects, self-intersection, and even a certain amount of unfilled areas. This paper proposes a flexible and adaptive transfinite mapping method for the path planning of 3D concrete printing by properly mapping a predetermined continuous-type path to the digital model to be printed. This method combines the morphological features of the digital model and path types to achieve a high-quality and high-continuity adaptive printing path. Meanwhile, the relationship between the extrusion process parameters of cementitious composites is experimentally measured and subsequently incorporated into the path design program to realize zero-gap printing by in-process controlling the extrusion parameters. The advantages of this method in adapting to the diversity of morphological features and path types are verified by a set of free-form structures, and the applicability is experimentally validated.

Characterization of transient rheological behavior of soft materials using ferrofluid droplets

Physical material properties, such as elasticity, viscosity, or viscoelasticity, can be characterized by using rheometers or stick-type solenoid electromagnets. In this work, we developed a magnet measurement setup based on a Helmholtz arrangement of electromagnets. While applying homogeneous magnet fields to ferrofluid droplets inside a soft material of interest, the deformations of the ellipsoidal deformed droplets were measured. Kelvin-Voigt models and corresponding analytical descriptions were used to calculate the values of viscosity and Young’s modulus of materials under test. For calibration purposes of the developed setup, glycerin/water mixtures and methylcellulose/water solutions were characterized as viscous and polyacrylamide gels as elastic materials, respectively. In addition, the interfacial tensions were calculated with respect to the magnetic Bond number from the droplet deformations. For the first time, the transient rheological behavior of viscoelastic material was measured using the method of ferrofluid droplet deformation. When polyacrylamide gel with a shear modulus of 230 Pa was evacuated for less than 40 min during preparation, it showed a strong time-depending viscoelastic behavior several minutes after starting the measurements. Here, Young’s modulus increased up to the value of elastic behavior, whereas the values for viscosity decreased to a baseline. The developed setup can favorably be used in future applications to investigate local and also time-dependent rheological properties of soft materials.

Evaluation of time-dependent rheological properties of cemented paste backfill incorporating superplasticizer with special focus on thixotropy and static yield stress

Evaluation of time-dependent rheological properties of cemented paste backfill incorporating superplasticizer with special focus on thixotropy and static yield stress

Influence of the flocculation effect on the rheological properties of cement slurry

The rheological properties have an important impact on the migration and diffusion of cement slurry in grouting reinforcement applications. The microscopic interaction between particles affects the macroscopic rheological behaviors of cement slurry. However, the detailed influence mechanisms still remain unclear. In this work, five different fineness cements were selected to investigate the rheological properties. The focused beam reflectance measurement (FBRM) system was used to detect the in-situ flocculation characteristics under different water-to-cement ratios, cement fineness, and shear rates. In addition, the initial and time-dependent rheological properties under various conditions were measured by a rotary viscometer. The results reveal that these three factors influence the number and particle size distribution of flocculent particles, and the degree of flocculation increases linearly with time. Cement slurry with a water-to-cement ratio ranging from 0.6:1 to 1.6:1 follows the Bingham model. The yield strength and plastic viscosity decrease with increasing water-to-cement ratio, and increase with increasing cement fineness. The apparent viscosity is reversible with the change of shear rate. The influence of water-to-cement ratio, cement fineness, and shear rate on the flocculation effect is consistent with the influence on rheological parameters. Three factors and time affect the rheological properties by influencing the formation and destruction of the flocculation structure, and then changing the content of free water and intergranular force in cement slurry. Our study has revealed the evolution of rheological properties from a microscopic point of view, which can provide theoretical guidance for the design and application of cement slurry.

Physical aging in aqueous nematic gels of a swelling nanoclay: sol (phase) to gel (state) transition.

Aqueous dispersions of geometrically anisometric, nano-sized sodium-montmorillonite (Na-Mt) display a sol-gel transition at very low solids concentrations. The microstructure of the gel formed at very low ionic strengths is considered electrostatically repulsive with a nematic character, and the gel state at ionic strengths where Debye length is of the order of particle size is conjectured to be free of physical aging. We investigated the nature of osmotically prepared Na-Mt dispersions at low ionic strength (∼10-5 M), below and above the gel point. The sol phase exhibited very low yield stress compared to the gel state, without any sign of physical aging, thus behaving as an equilibrium state. In contrast, the gel exhibited signatures of physical aging, that is, an evolving microstructure that consolidated with time when left undisturbed thus behaving as out of equilibrium state. The physical aging behaviour became more pronounced at Na-Mt concentrations far above the gel point. A critical shear rate existed, below which no stable flows were possible in the gel state representing the microstructural reorganization timescale. Overall, Na-Mt dispersions in the gel state behave like systems that were out of equilibrium with an ever-evolving microstructure, in opposition to the assumption that low ionic strength Na-Mt gels are in an equilibrium phase. The possible origin of physical aging, such as the reversible orientation of Brownian anisotropic particles, stiffening of an existing microstructure, or reorganization of microstructure towards minimal energy configuration is discussed in detail.

Impact of Chemical Admixtures on Time-Dependent Workability and Rheological Properties of Ultra-High- Performance Concrete

Impact of Chemical Admixtures on Time-Dependent Workability and Rheological Properties of Ultra-High- Performance Concrete