Dynamic Yield Stress Research Articles

Correction to: Discrepancies in dynamic yield stress measurements of cement pastes

Correction to: Discrepancies in dynamic yield stress measurements of cement pastes

Machine Learning Driven Fluidity and Rheological Properties Prediction of Fresh Cement-Based Materials

Controlling workability during the design stage of cement-based material mix ratios is a highly time-consuming and labor-intensive task. Applying artificial intelligence (AI) methods to predict and optimize the workability of cement-based materials can significantly enhance the efficiency of mix design. In this study, experimental testing was conducted to create a dataset of 233 samples, including fluidity, dynamic yield stress, and plastic viscosity of cement-based materials. The proportions of cement, fly ash (FA), silica fume (SF), water, superplasticizer (SP), hydroxypropyl methylcellulose (HPMC), and sand were selected as inputs. Machine learning (ML) methods were employed to establish predictive models for these three early workability indicators. To improve prediction capability, optimized hybrid models, such as Particle Swarm Optimization (PSO)-based CatBoost and XGBoost, were adopted. Furthermore, the influence of individual input variables on each workability indicator of the cement-based material was examined using Shapley Additive Explanations (SHAP) and Partial Dependence Plot (PDP) analyses. This study provides a novel reference for achieving rapid and accurate control of cement-based material workability.

Understanding the time-dependent rheological behavior of seawater mixed cement paste with fly ash

Due to the relative scarcity of freshwater resources in coastal regions, the use of seawater in concrete construction has great potential due to its benefits in cost and resource. To further advance the application of seawater concrete, a deeper understanding of its rheological properties is essential. This study investigates the effects of fly ash on the time-dependent rheological behavior of seawater cementitious paste, such as yield stress, plastic viscosity, and structural build-up rate. The underlying mechanisms are analyzed using the theories of water film thickness (WFT), ion concentration, and hydration heat. The research findings confirm that the rheological parameters of seawater paste are generally higher than those of deionized water paste, regardless of the cementitious compositions. As fly ash content increases, the plastic viscosity of seawater paste increase, while the fluidity and dynamic yield stress decreases. Further analysis reveals that the decrease in the yield stress with fly ash content is well related to the increase in the WFT, but it cannot sufficiently explain the change of yield stress over time. Instead, the amount of hydration products in seawater paste shows a linear increasing relationship with the dynamic yield stress at 65 min. By contrast, the plastic viscosity can be related to the ion concentration in the interstitial solution, wherein an increase in the concentration of Ca2+ corresponds to an increase in the plastic viscosity. Moreover, the rheological parameters increase over time, with the growth rates between 5 and 35 minutes being higher than those between 35 and 65 minutes, possibly due to the rapid early hydration of the binder materials. This study offers a fundamental theoretical support for the use of seawater in various concrete applications.

Influence of Grinding Aids on the Grinding Performance and Rheological Properties of Cementitious Systems.

The cement industry is of great importance in terms of raw materials consumed, energy consumed, and greenhouse gases emitted. Grinding aids (GA) are used to reduce energy consumption and costs, as well as to reduce the amount of CO2 released into the environment. In this study, the effect of GA-polycarboxylate ether-based water-reducing admixture (PCE) compatibility on some fresh, rheological and hardened state properties of cementitious systems was investigated. In order to investigate the rheological properties and thixotropic behavior of the mixtures, a total of 51 cement paste mixtures were prepared, containing 4 different types (molasses, MEG, DEA and ethanol) and ratios (0.025, 0.05, 0.75 and 0.1) of GAs and 2 different ratios (0.08% and 0.16%) of PCE in addition to the control mixture. In addition, the effect of the used GAs on the grinding efficiency and compressive strength value was investigated. Additionally, the predictability of the type of GA, dosage and cure time using the Taguchi method was investigated. It was determined that the highest grinding performance was obtained in mixtures containing MEG. It was determined that in cement paste mixtures containing GAs, the dynamic yield stress and viscosity values generally decrease with the increase in PCE usage rate up to a certain value, and these values may increase if the PCE usage increases further. It was determined that such behavior is not present in cement paste mixtures containing GAs and that the structural build-up value of the mixtures generally increases with the increase in the PCE admixture usage rate. It was determined that the use of GAs had a positive effect on 28-day compressive strength.

Interaction between material and process parameters during 3D concrete extrusion process

Extrusion of cement-based materials in additive manufacturing is influenced by a complex interaction of various material and process parameters. This study aims to investigate the impact of rheological properties and printing parameters on the extrudability of cement-based materials as well as the interaction between rheological properties of print materials and extrusion speed, as a key printing process parameter. 20 different print materials with diverse rheological properties were extruded at 10 different extrusion speeds. The effect of material parameters (i.e. rheological properties) and process parameters (i.e., extrusion speed) and their interaction during the extrusion process were evaluated using filament continuity, conformity and consistency. At a constant printing speed, a higher yield stress adversely impacted filament continuity in mixtures with a yield stress of over 260 Pa, whereas viscosity showed minimal influence on filament quality within the tested range of the rheological properties. The results of this study highlighted a significant correlation between material and process parameters and that adapting process parameters to variations in material properties is crucial for meeting printing criteria. The filament consistency of the mixtures with high yield stress was more sensitive to change in the extrusion speed than that of mixtures with low yield stress. An opposite trend, however, was observed for filament conformity where low yield stress mixtures showed a higher sensitivity to the extrusion speed. A procedure was suggested and applied to determine the optimum extrusion speed. Optimal extrusion speeds enabled printing mixtures with a broader spectrum of rheological properties with an acceptable visual quality, filament conformity and consistency requirements. With extrusion speed adjustment, the extrudability window was expanded from dynamic yield stress of 108–126 Pa to 108–263 Pa and plastic viscosity of 8.2–12.3 Pa.s to 5.1–16.4 Pa.s.

3D printable earth-based alkali activated “ink”: Effect of alkali concentration and binder-to-aggregate ratio

This research attempts to investigate the effect of activator concentration (4 mol/L (M) and 8M) and binder-to-aggregate (B:A) ratio (ranging from 1:1 to 1:3 by weight) on extrudability and buildability of 3D printable natural earth-based alkali-activated materials (EAAM). It is found that natural clay in soil, used to replace 25 % of M-sand, imparts higher thixotropy, evident from 90 to 100 % recovery in viscosity compared to 65–80 % for corresponding control (containing only M-sand and no soil). Presence of clay increases the dynamic yield stress than control but reduces the plastic viscosity by 80 – 90 % in EAAM compared to corresponding control where interlocking between sand particles resists smooth extrusion of the material. EAAMs made with 8M NaOH have higher flow retention and maintain 95–100 % recovery in viscosity for longer duration than 4M EAAM. This contributes to superior extrusion quality of 8M EAAM than 4M EAAM. The findings suggest that binder content can be reduced as concentration of NaOH is increased from 4M to 8M. This is evident from lower layer deformation (0.09 % of original height) under self-weight and higher 3D printed buildable height of at least 457 mm in 8M EAAM with B:A of 1:2 compared to a maximum of 375 mm for 4M EAAM at higher B:A of 1:1. Ratios of wet compressive strength to dry compressive strength vary between 0.92 and 1.09 in 8M EAAM compared to 0.79 – 0.85 for 4M EAAM at 28-day age, suggesting lower sensitivity to moisture due to improved clay stabilization. Based on the strength and moisture sensitivity, the developed material can serve as a low-carbon and durable alternative to Portland cement in the construction of masonry elements in buildings, including cavity walls, panels, flooring tiles and façade members.

Rheology of nanocrystalline cellulose (CNC) gels: Thixotropy, yielding, wall slip, and shear banding

This study focuses on the rheological behavior of a cellulose nanocrystal gel. This system [5 wt. % cellulose nanocrystal (CNC) + 20 mM NaCl] is proved to be thixotropic, and the detected shear force tightly depends on the growth and break-up of the aggregates of CNC rods. From strain-controlled experiments, a nonmonotonic steady-state flow curve with a minimum stress value of ≈33 Pa is found, and the negative slope of stress versus shear rate suggests the existence of shear bands. From stress-controlled experiments (creep), the “static yield stress” is determined to be 67.5 ± 2.5 Pa. This difference proves that the local minimum stress of the flow curve does not coincide with the “static yield stress” determined by creep tests. However, this minimum stress can maintain flow provided that the material is already in a yielded state. At nominal shear rates below about 100 s−1, shearing is suggested to be localized in a shear band rather than over the whole material. The “dynamic yield stress” is found as “the minimum stress to maintain flow,” or the onset of shear banding. Moreover, wall slip also occurs at low nominal shear rates which is related to the interaction between the dynamic microstructure of the CNC gel and the wall: it is hypothesized that the low shear rates allow the CNC aggregates to extensively grow and, thus, the oversized CNC aggregates detach from the asperities of the wall. Our finding of the robust connection between yielding, thixotropy, wall slip, and shear banding shall shed new light on the nature of the nonmonotonic flow curves of yield stress and thixotropic materials.

Shear-driven stability of a rigid particle in yield stress fluids

The stability of a rigid particle in yield stress fluids, comprised of soft particle glasses (SPGs), is investigated in shear flow under an applied external force, such as weight, using particle dynamics simulations. Results provide the critical force threshold, in terms of the dynamic yield stress and the flow strength, required to initiate sedimentation of the rigid particle over a wide range of shear rates and volume fractions. The streamlines of the SPGs show local disturbances when the rigid particle settles. The form of these disturbances is consistent with the microdynamics and microstructure response of the neighboring soft particles of the sedimenting rigid particle. Sedimenting particle induces non-affine displacement to the suspensions at low shear rates and high applied forces, while these dynamical events are localized and suppressed at high shear rates. Stability diagrams, which provide the conditions of the sedimentation of the rigid particle, are presented in terms of the applied force and the shear rate. These individual stability diagrams at each volume fraction map onto a universal stability diagram when the external force is scaled by the dynamic yield stress and shear rate with a ratio of the solvent viscosity to the low-frequency modulus of the SPGs.

Direct ink writing 3D printed graphene oxide nanocomposite aerogel for intelligent fire-warning and exceptional fire-shielding

Fabricating intelligent fire-warning sensors with controllable 3D structures and shapes by advanced manufacturing technology is a formidable challenge but remains the critical factor in broadening fire prevention and protection. Herein, the novel fire-warning aerogel with a high-fidelity 3D porous structure and diversiform geometrical features based on graphene oxide (GO), cellulose nanofiber (CNF) and ammonium polyphosphate (APP) was fabricated via direct ink writing (DIW) 3D printing combined with freeze-drying technology. Benefiting from the hydrogen bonding multi-interactions between the molecules as well as the ideal rheological properties, the ink containing 20 wt% of CNF (GA-CNF-20) had a dynamic yield stress of 620 Pa. As a result, the corresponding aerogel had a significantly improved elasticity modulus of 153 kPa and a compressive stress of 400 kPa at a deformation of 39.7 %. Meanwhile, GA-CNF-20 displayed an ultrafast fire-warning trigger time (1.32 s) and a long-term response time (170 s) because of the thermal reduction property of GO together with the in-situ phosphorus doping reaction of APP under fire. Besides, the GA-CNF-20 also exhibited a strong heat-insulating capability, high char-forming property, self-extinguishing performance as well as structure integrity in the burning test. The relevant improvement mechanisms were attributed to the non-flammable gas diluting effect, intumescent char layer barrier effect and fire blowing-out effect in both gas and condensed phases. Such self-supporting printed aerogel can potentially be used as a fire-warning sensor for designated systems with specific precision structure in multi-domains of electrical and traffic engineering.

Evaluation of rheo-viscoelasticity of magnesium-silicate-hydrate mixes incorporating different superplasticizers

This study investigated rheo-viscoelastic behaviors of MgO-SiO2 pastes with three phosphate additives (sodium hexametaphosphate (SHMP), sodium trimetaphosphate (STMP), and sodium orthophosphate (SOP)) as superplasticizers. Static yield stress, dynamic yield stress, median differential viscosity, thixotropic loop area, structural recovery rate, and non-destructive structural build-up were analyzed. Furthermore, assessment of hydration and particle dispersion stability was facilitated by employing isothermal calorimetry, XRD, DTG, and zeta potential techniques. SHMP significantly decreased the static and dynamic rheology, thixotropy, and viscoelastic evolution. Samples incorporating 2 wt% SOP exhibited enhanced rheological parameters, particularly static yield stress, owing to increased brucite formation and a denser microstructure in the fresh paste. Adsorption of phosphate additives on MgO surfaces inhibited formation of brucite and improved interparticle electrostatic repulsion, thereby increasing suspension stability. High-efficiency adsorption of SHMP on MgO surfaces, coupled with the retardation of brucite nucleation-and-growth, and enhancement in suspension stability, greatly restrained the rheo-viscoelastic evolution of MgO-SiO2 system.

Sustainable Support Material for Overhang Printing in 3D Concrete Printing Technology

The advantage of 3DCP technologies is the ability to fabricate free-form structures. However, printing openings in concrete structures are limited by the presence of overhanging sections. While various 3D printing and additive manufacturing technologies have established methods for handling overhangs with temporary supports, many existing techniques for 3D concrete printing still rely on wooden planks and corbelling, which restrict the design flexibility and slope angles. The objective of this study is to develop a removable and sustainable support material with high printability performance. This support material serves as temporary support for overhang sections in 3D-printed structures and can be removed once the primary concrete has hardened sufficiently. This study observed that increasing the recycled glass content in the mixture raises both the dynamic and static yield stresses, with only mixtures containing up to 60% recycled glass remaining pumpable. Optimization of the mixture design aimed to balance high flowability and buildability, and the results indicated that a mixture with 60% recycled glass content is optimal. The effectiveness of the optimized support material was validated through the successful printing of a structure featuring a free-form opening and overhang section.

3D printing hybrid-fiber reinforced engineered cementitious composites (3DP-HECC): Feasibility in long-open-time applications

Hybridization of multi-scale and multi-functional fibers to generate Hybrid-fiber Engineered Cementitious Composites (HECC) offers a promising approach for enhancing ECC in 3D printing (3DP), addressing limitations such as restricted build-up height and operation time. This study strategically combined polyethylene (PE) fiber (1.0 %), steel fiber (0.5 %) and cellulose filaments (CF) at various dosages (0–0.25 %) to investigate the evolution of rheological behavior over different time intervals (0–60 min with 15 min intervals) and optimize the printability of 3DP-HECC with long-open-time. Incorporating of CF or steel fiber enhanced static yield stress, dynamic yield stress and plastic viscosity, particularly benefiting buildability with steel fiber inclusion. Moreover, CF integration effectively moderated the growth rates of static yield stress and dynamic yield stress while maintaining thixotropic index, mitigating extrusion defects and extending operation time to 60 min for structure-level printing. Conversely, steel fiber exhibited contrasting behavior. By integrating the evolution of time-dependent rheological parameters and practical printing observations, an optimum CF dosage of 0.20 % was identified for high-quality 3DP with superior build-up layers. Finally, a fiber hybridization strategy was suggested to optimize the printability of 3DP-HECC, providing theoretical guidance for implementing high-quality applications with extended operation time.

Effects of microstructures on dynamic deformation and spallation damage of high-entropy alloy Al0.3CoCrFeNi under plate impact loading

Plate impact experiments are conducted on high-entropy alloy Al0.3CoCrFeNi with different microstructures to investigate the effects of grain size, precipitates and heterogeneous structure on dynamic response. Free surface velocity histories are obtained. All initial and postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. Nanoscale L12 precipitates result in a considerable increase in dynamic yield stress. Spall strength is higher for the heterogeneous structure, the large grain size (200 μm) and small grain size (63 μm) with L12 precipitates by ∼4%, 19% and 10% than for the small grain size (77 μm) without precipitates. After shock compression, dislocation slip, stacking faults, the Lomer-Cottrell locks and nanotwins are found in the samples without the L12 precipitates. L12 precipitates increase the energy barrier and inhibit deformation twinning. Spall damage is ductile in Al0.3CoCrFeNi. For the homogeneous structures, intragranular voids are predominant. Voids are preferentially distributed in the fine-grain domains or at the fine-grain–coarse-grain domain boundaries of the heterogeneous structure.

Discrepancies in dynamic yield stress measurements of cement pastes

The dynamic yield stress associated with the flow cessation of cement pastes is measured using a rheometer equipped with various shear geometries such as vane, helical, sandblasted co-axial cylinders, and serrated parallel plates, as well as with the mini-cone spread test. Discrepancies in yield stress values are observed for cement pastes at various volume fractions, with one to two orders of magnitude difference between vane, helical and mini-cone spread measurements on the one hand, and co-axial cylinder and parallel plate measurements on the other hand. To understand this discrepancy, the flow profile of a cement paste in the parallel-plate geometry is investigated with a high-speed camera, revealing the rapid formation of an un-sheared band near the static bottom plate. The width of this band depends upon the rotational velocity of the top plate, and upon the shear time. Recalculation of shear stress shows that the reduced sheared gap alone cannot explain the low measured yield stress. Further exploration suggests the formation of zones with lower particle content, possibly linked to cement particle sedimentation. Here, we argue that the complex nature of cement pastes, composed of negatively buoyant non-Brownian particles with attractive interactions due to highly charged nano-size hydration products, accounts for their complex rheological behavior.Graphical abstract

Rheological and Mechanical Properties of Standard Concrete by using locally available Calcareous and Siliceous Material

Abstract: The investigates is basically on the Rheological and Mechanical properties of standard concrete by using Locally available Calcareous and Siliceous material and a comparative study is done for the rheological parameter for mixes with or without using superplasticizer. For rheological parameter, various mixes with water cement ratio of 0.45 and slump value of 120 mm were prepared for the experiment by replacing different percent as (0%,5%,10%,15%) of locally available material such as Metakaolin and tested with German based instrument ICAR Rheometer. Test on Rheometer is done to study flow property of concrete so that concrete mixes can be pumped to high rise building properly. As per the finding, as the metakaolin percentage were increased the static yield and dynamic yield stress decreases this indicate that it is easy to pump at higher blending. For mechanical properties, mixes were prepared and test Performed is compressive strength test. The findings of this experiment have important implication for construction industry basically in the high-rise structure

The Role of Different Clay Types in Achieving Low-Carbon 3D Printed Concretes

Concrete 3D printing, an innovative construction technology, offers reduced material waste, increased construction speed, and the ability to create complex and customized shapes that are challenging to achieve with traditional methods. This study delves into the unique fresh-state performance required for 3D printing concrete, discussing buildability, extrudability, and shape retention in terms of concrete rheology, which can be modified using admixtures. Currently most 3D printing concretes feature high cement contents, with little use of secondary cementitious materials. This leads to high embodied carbon, and addressing this is a fundamental objective of this work. The research identifies attapulgite, bentonite, and sepiolite clay as potential concrete admixtures to tailor concrete rheology. Eight low-carbon concrete mixes are designed to incorporate GGBS at a 50% replacement level and are used to measure the influence of each clay on the concrete rheology at varying dosages. A comprehensive rheological test protocol is designed and carried out on all mixes, together with other tests including slump-flow and compression strength. The objective is to determine the applicability of each clay in improving the printability of low-carbon concrete. The findings reveal that at a dosage of 0.5%, sepiolite was seen to improve static yield stress, dynamic yield stress, and rate of re-flocculation, resulting in improved printability. The addition of attapulgite and sepiolite at a dosage of 0.5% by mass of binder increased compressive strength significantly; bentonite had very little influence. These gains are not repeated at 1% clay content, indicating that there may be an optimum clay content. The results are considered encouraging and show the potential of these clays to enhance the performance of low-carbon concrete in 3D printing applications.

Dynamic response of equiatomic and non-equiatomic CrMnFeCoNi high-entropy alloys under plate impact

A typical Fe-rich non-equiatomic CrMnFeCoNi high-entropy alloy (HEA), Cr10Mn10Fe60Co10Ni10, and the equiatomic Cr20Mn20Fe20Co20Ni20 HEA, are investigated via plate impact experiments along with in situ free surface velocity measurements. Both the initial and postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. These two HEAs contain a single face-centered cubic phase, are texture-free, and have similar grain sizes. Dynamic yield stress and spall strength of the non-equiatomic CrMnFeCoNi are lower by ∼55 % and 15 % than those of its equiatomic counterpart, respectively. After shock compression, dislocation slips, stacking faults, Lomer-Cottrell locks and nanotwins are found in the postmortem samples of both HEAs. Due to the reduced stacking fault energy in the non-equiatomic HEA, more deformation twins and newly formed hexagonal close-packed phases are found. For spallation, intergranular voids are larger in size but smaller in quantity than intragranular voids for both HEAs. Both intragranular or intergranular voids show strong dependence on grain boundary misorientation.

Performance Requirements and Optimum Mix Proportion of High-Volume Fly Ash 3D Printable Concrete

In this study, a procedure for mixture design was proposed with the aim of meeting the requirements of extrudability, buildability, and shape stability in 3D printable concrete. Optimum water/binder ratio, sand/binder ratio, binder type, utilization ratio, aggregate particle distribution and quantity, and type and utilization ratio of chemical admixtures were determined for 3D printable concrete in terms of print quality and shape stability criteria. A total of 32 different mixtures were produced. It was determined that mixtures produced using a binder content with approximately 40% fly ash, a w/b ratio of 0.35, and aggregates with Dmax of 1 mm exhibit acceptable characteristics. Investigations were also conducted into the thixotropic behavior, rheological characteristics, and mechanical properties of the mixes that were deemed acceptable. As a result, it was determined that the increase in the amount of fly ash usage positively affected the buildability of the printed layers. Additionally, the dynamic yield stress ranging from 114 to 204 Pa, viscosity ranging from 22 to 43 Pa.s, and structural build-up value ranges suitable for the production of 3D printable concrete mixtures were determined.

Performance and microstructural development of 3D printable MgO-SiO2 mixes containing magnesium silicate monohydrate

This study investigated the inclusion of magnesium silicate monohydrate (MSMH) crystal in MgO–SiO2 mixes designed for extrusion-based 3D printing. Considering the adjustment and optimization of rheological properties are fundamental for the printability of cement pastes, the dynamic rheology, thixotropy and strength development of the prepared mixes were analyzed to characterize their fresh properties, workability, buildability, and mechanical performance. Furthermore, isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TG/DTG), and scanning electron microscopy (SEM) were employed to investigate the phase composition and microstructural evolution of the pastes, with and without the presence of MSMH. Addition of MSMH at 2 % of the binder component significantly enhanced the plastic viscosity, dynamic yield stress and thixotropy. Pastes incorporating 2 % MSMH exhibited excellent structural build-up without affecting extrudability, with a minimal strain deformation in the printed structure. The compressive strength of all pastes exceeded 20 MPa after 3 days, reaching ∼50 MPa at 28 days with 2 % MSMH inclusion. The introduction of MSMH improved the peak heat flow measured by isothermal calorimetry and enhanced the formation and growth of hydration products after 7 days of curing, resulting in a more compact microstructure.

Influence of Residue Soil on the Properties of Fly Ash-Slag-Based Geopolymer Materials for 3D Printing.

This study investigates the impact of residue soil (RS) powder on the 3D printability of geopolymer composites based on fly ash and ground granulated blast furnace slag. RS is incorporated into the geopolymer mixture, with its inclusion ranging from 0% to 110% of the combined mass of fly ash and finely ground blast furnace slag. Seven groups of geopolymers were designed and tested for their flowability, setting time, rheology, open time, extrudability, shape retention, buildability, and mechanical properties. The results showed that with the increase in RS content, the fluidity of geopolymer mortar decreases, and the setting time increases first and then decreases. The static yield stress, dynamic yield stress, and apparent viscosity of geopolymer mortar increase with the increase in RS content. For an RS content between 10% and 90%, the corresponding fluidity is above 145 mm, and the yield stress is controlled within the range of 2800 Pa, which meets the requirements of extrusion molding. Except for RS-110, geopolymer mortars with other RS contents showed good extrudability and shape retention. The compressive strength of 3D printing samples of geopolymer mortar containing RS has obvious anisotropy.