Higher Yield Stress Values Research Articles

New insight on rheology of self-consolidating earth concrete (SCEC)

Self-consolidating earth concrete (SCEC) is a novel alternative to facilitate the earth-based construction. A new concrete-equivalent mortar (CEM) approach with constant excess-paste (EP) thickness was proposed to evaluate the rheological and thixotropic properties of various SCEC mixtures proportioned with different clay and superplasticizer types. The use of non-esterified polycarboxylate (NE-PC) and sodium polynaphtalene superplasticizer types in combination with a finer clay type led to a thixotropic behavior. Mixtures made with sodium hexametaphosphate resulted in significantly high yield stress and plastic viscosity values. The rheological properties were mainly controlled by the admixture type, followed by the type and content of clay and water-to-powder ratio (W/P). Empirical models were proposed to predict the rheology of earth-based paste, CEM, and SCEC mixtures using the governing key mixture parameters, including the fineness of the powder constituents (i.e., clay, silt, and cement), water content, EP thickness, paste volume, and packing of the granular skeleton.

Mechanical properties, durability performance and interlayer adhesion of 3DPC mixtures: A state‐of‐the‐art review

AbstractIn this study, the strength and durability performance of 3D printing concrete mixtures (3DPC) were examined in terms of the materials used in their production and printing process parameters (interlayer interval time, printing speed, and nozzle shape). Due to the anisotropic nature of 3DPC, it was understood that the compressive strength depends on the loading direction. It was emphasized that it is necessary to control the shrinkage behavior of 3DPC mixtures due to the lack of formwork and the high dosage of binders. It was reported that the interlayer adhesion of 3DPC is highly dependent on the interlayer interval time and printing speed parameters. It was understood that nozzle shape and standoff distance affect the mechanical properties and surface roughness of 3DPC specimens, and this effect is more pronounced in mixtures with high static yield stress values.

Microstructural and Mechanical Characterization of the Aging Response of Wrought 6156 (Al-Mg-Si) Aluminum Alloy

The impact of the artificial aging response on the microstructure and tensile mechanical properties of aluminum alloy 6156 was investigated. Specimens were artificially aged at three different artificial aging temperatures and for various holding times to investigate all possible aging conditions, including the under-aged (UA), peak-aged (PA) and over-aged (OA) tempers. Microstructural investigation as well as tensile tests were performed immediately after the isothermal artificial aging heat treatment. An almost 50% increase in yield stress (around 340 MPa) was noticed in the PA temper and this was attributed to the precipitation of β′ and Q′ phases, consistent with the modelling predictions. This high yield stress value is accompanied by high values of elongation at fracture (>10%) that is essential for damage tolerance applications. The lack of large or interconnected grain boundary precipitates contributes to this high elongation. Slanted fracture was noticed for both UA and PA tempers, exhibiting a typical ductile and shear fracture mechanism. At the OA temper, coarsening of the precipitates along with broadening of the precipitate free zones resulted in a reduction in the strengthening effectiveness of the precipitates, and a small increase in the tensile ductility of approximately 12% was noticed.

Effect of temperature on sedimentation stability and flow characteristics of magnetorheological fluids with damper as the performance analyser

dimentation stability and high yield stress of a magnetorheological fluid (MRFs) are essential parameters for better damping performance for any practical application. Preliminary investigations have been carried out on carbonyl iron particles to determine the morphology, particle size, crystal structure, and saturation magnetization for their feasibility of synthesizing magnetorheological fluids in-house. This study synthesizes various MRFs from various commonly used carrier oils and additives. The MRF samples were prepared for 25% volume fractions of carbonyl iron (CI) powder in either silicone oil (350cSt) or hydraulic oil (50cSt) and by using lithium and calcium-based additives or a combination of both the additives. The sedimentation stability and yield behaviour at different temperatures show a remarkable drop in sedimentation rate and yield stress for all the MR fluid samples. The characterization of the prepared MR fluids reveals that MRF-1, MRF-3, MRF-5 are more stable and have high yield stress values. MRF-1 is selected to further characterize its dynamic performance in magnetorheological damper fabricated based on geometric dimensions obtained from the response surface optimization technique. The results indicate a 164.45% and 135.48% increase in damping force at higher amplitude and higher frequencies at 0A and 1A currents. Further, similar tests have been carried out by synthesizing MRF-7 with silicone oil (50cSt) + lithium base grease as the additive. The sample's stability and yield stress with temperature are carried out, and performance analysis shows a remarkable change in damping force than MRF-1. The dynamic range obtained is practically viable in MRF-7 than MRF-1, with less variability. Finally, temperature characteristics captured from the thermocouple of the MR damper reveal that an average of 43.78% reduction in damping force when the temperature is increased by 19.5 °C with increased dynamic range.

Bioethanol Production and Alkali Pulp Processes as Sources of Anionic Lignin Surfactants.

Lignin is an abundant biopolymer with potential value-added applications that depend on biomass source and fractioning method. This work explores the use as emulsifiers of three native lignin-rich product coming from industrial bioethanol production and alkali or Kraft pulping. In addition to their distinctive characteristics, the different molecular organization induced by emulsification pH is expected to interact in various ways at the water-oil interface of the emulsion droplets. Initially, model oil-in-water (O/W) emulsions of a silicone oil will be studied as a function of lignin source, disperse phase concentration and emulsification pH. Once stablished the effect of such variables, emulsion formulations of three potential bitumen rejuvenators (waste vegetable cooking oil, recycled lubricating oil and a 160/220 penetration range soft bitumen). Droplet size distribution, Z-potential and viscous tests conducted on model emulsions have shown that emulsification pH strongly affects stabilization ability of the lignins tested. Regarding bitumen rejuvenators, lignin emulsification capability will be affected by surfactant source, pH and, additionally, by the dispersed phase characteristics. Lower Z-potential values shown by KL at pH 9 and 11 seem to facilitate emulsification of the less polar disperse phases formed by RLUB and bitumen. In any case, lower particle size and higher yield stress values were found for both bioethanol-derived lignins emulsifying RVO and RLUB at pH 13, which are expected to exhibit a longer stability.

Synergistic Effects of Nonmagnetic Carbon Nanotubes on the Performance and Stability of Magnetorheological Fluids Containing Carbon Nanotube-Co0.4Fe0.4Ni0.2 Nanocomposite Particles.

We investigated the magnetorheological (MR) properties of the carbon nanotube (CNT)-Co0.4Fe0.4Ni0.2 composite suspension to find a high-performance MR fluid with excellent stability. The composites were fabricated by chemical reduction of Co0.4Fe0.4Ni0.2 on the surface of amine-functionalized CNTs. A synergistic effect between the high aspect ratio of the CNTs and the strong magnetic polarization of the Co0.4Fe0.4Ni0.2 led to stronger MR performance of the nanocomposite particle suspension. The MR fluid exhibits an unexpected high yield stress value that is 13 times greater than that of a CNT-Fe3O4 suspension at a magnetic field strength of 343 kA/m. Nonmagnetic CNTs form a three-dimensional networklike structure, imparting surprisingly large additional yield stress to the CNT-Co0.4Fe0.4Ni0.2 nanocomposite MR suspension. The low density of the CNTs resulted in much better long-term stability for the CNT-Co0.4Fe0.4Ni0.2 nanocomposite suspension than the MR fluid containing only Co0.4Fe0.4Ni0.2.

Influence of different fumed silica as thixotropic additive on carbonyl particles magnetorheological fluids for sedimentation effects

The present work reports the influence of different types of surface area, hydrophobic, and hydrophilic fumed silica mixed in silicone oil as a thixotropic additive on carbonyl particles based magnetorheological fluids (MRFs) were prepared. Scanning electron microscopy analysis confirms the fumed silica particles attached to the surfaces of CIPs. The vibrating sample magnetometer result shows the MRF4 and 5 have a better magnetic saturation value of 30.12 emu/gm and 40.12 emu/gm, respectively. The experimental rheological flow curve behaviours are investigated using the magnetorheometer. The Herschel–Bulkley rheological model is found to be in good agreement with the experimental curves and suggested shear thinning property is observed. The results showed that the hydrophilic silica with larger surface area type presented (i.e.MRF 4 and 5) better magnetorheological fluid characteristics in terms of shear stress, with a high value of dynamic yield stress, and have much-improved sedimentation ratio up to seven days.

Flow assessment and development towards sustainable self-consolidating concrete using blended basalt and limestone-cement systems

The development of sustainable high-performance concrete depends on maximizing cement replacement that could govern the required fresh and hardened properties at the same time. Limestone powder (LP) succeeded in evolving the sustainability and practice of high flowable concrete. However, the physical nature of such powders differs from the volcanic type of powders, such as Basalt powder (BP). Therefore, this paper investigates further the flow assessment of partial replacement of cement using BP in comparison to LP (0%–30%) in developing a sustainable Self-Consolidating Concrete (SCC). A total binder content of 400 kg/m3 and water-to-powder ratio (w/p) of 0.48 were adopted. Workability tests showed higher values of yield stress for mixtures with more than 15% BP replacement comparing to LP. Moreover, the values of viscosity were found to be higher in BP mixtures except for those with a 15%–20% replacement where higher values were measured using LP. Significantly, and due to the morphological and chemical nature of the volcanic powder BP, superior and durable performance concerning compressive strength development was observed for mixtures with BP replacement at 56 days.

Addition of Selected Plant-Derived Proteins as Modifiers of Inulin Hydrogels Properties.

The aim of the study was to determine the effects of pea and soy protein addition (1, 3, 6 g/100 g) on inulin hydrogels properties. Inulin hydrogels (20 g/100 g) were obtained by thermal induction. It was stated that tested plant protein might be used as a modifier of inulin hydrogels properties. The addition of pea and soy protein to inulin hydrogels resulted in networks with more a compact and homogeneous structure. The increase of the protein concentration caused the structure of the hydrogels to get smoother, more cohesive, and less granular. Pea and soy protein addition (3–6 g/100 g) to hydrogels allowed to obtain higher values of yield stress, texture (firmness, adhesiveness) and spreadability parameters. At a protein concentration of 6 g/100 g, the firmness of inulin hydrogels was seven times higher for those with pea protein (1.87 N) and ten times higher for those with soy protein (2.60 N) compering to the control hydrogel (0.24 N). The transmission profiles of hydrogels with incorporated 6 g/100 g of soy proteins showed the slowest motion of the particles, which indicates the highest stability of gel. As the concentration of protein addition increased, a reduction in the lightness was observed.

Morphology, rheological, and electrical properties of flexible epoxy/carbon composites cured by UV technique

Abstract

Susceptibility Study to Hydrogen Embrittlement of Welded Joints of API 5L X52 Steel in Sulphide Media

Pipelines for oil and gas, manufactured in high-strength low-alloy steels (HSLA), such API pipes, promote high levels of strength and fracture toughness. Therefore, it is important to ensure this high level of toughness in the welded joint. When the pipelines are exposed for many years to wet H2S environments, they can fail due to hydrogen embrittlement. Thus, it is important to evaluate the influence of different weld specifications in the susceptibility to hydrogen embrittlement. In this case, the aim of this work was to study the susceptibility to hydrogen embrittlement of API 5L X52 steel and in the welded region in wet environments. The welding was performed in the circumferential direction by GMAW process in two different specifications (with lower and higher thermal input). The susceptibility to hydrogen embrittlement was carried out according to NACE TM0177 and SSRT (slow strain rate tensile tests) test, performed according to ASTM G 129 standard. All welded joints and base metal did not show any signal of cracks and susceptibility to hydrogen embrittlement, according to the requirements of the NACE TM0177 test. According to SSRT tensile test, the results showed that the welded joints and base metal are susceptible to hydrogen embrittlement. The tensile tests exhibited a drop in the strain and necking, and higher values of yield stress. The welded joint with the lowest heat inputs employed in the welding process presented the highest susceptibility to hydrogen embrittlement.

Microstructure design of CTAC:FA and BTAC:FA lamellar gels for optimized rheological performance utilizing automated formulation platform.

The main objective of this paper was to optimize hair conditioner performance through variation of composition utilizing automated cosmetic formulation platform and advanced characterization techniques as well as develop understanding of how performance (wet combing and wet lubrication) of hair conditioner is affected by its rheology (i.e. yield stress) and controlled breakdown of the formulations (dilution). The experimental results show that yield stress greatly impacts rheology, stability and performance of the lamellar gels for hair conditioning. All samples were prepared on the Chemspeed Flex Formax. A mechanical rheometer was used to measure bulk viscosity and yield stress in each sample. Dia-stron tensile tester was used to measure the lamellar gels ability to reduce combing force. Potential stronger lamellar gel network formation in the formed lamellar gels potentially leads to higher yield stress exhibited. Viscosity values were also measured after a controlled breakdown (i.e. dilution) of each sample. This was also carried out using a mechanical rheometer. Yield stress of the formulations was engineered through composition variation and was recorded in each system. The highest yield stress value is 251.179Pa at a BTAC/CA ratio of 6:10, and the lowest yield stress is 50.14Pa at a BTAC/CA ratio of 6:5. The highest yield stress value is 50.14Pa at a CTAC/CA ratio of 6:10, and the lowest yield stress is 19.98Pa at a CTAC/CA ratio of 2:10. The highest overall yield stress values can also be observed in the BTAC/CA system, whereas the CTAC/CA system has relatively lower yield stress values. Dilution of each formulation caused a breakdown in viscosity of each formulation with the formulations with highest yield stress maintaining higher viscosity than the other formulations. The formulations with highest yield stress in each system which also maintains the highest dilution viscosity (6% BTAC/10% CA and 6% CTAC/10% CA) have the best effect on reducing overall combing force, that is from dry hair tress to wet hair tress and after product is rinsed off. At a BTAC/CA system of ratio 6:5, there is an 89% reduction in combing force and a 95% reduction in combing force in the BTAC/CA system of ratio 6:10. At a CTAC/CA system of ratio 2:10, there is a 65% reduction in combing force and a 88% reduction in combing force in the CTAC/CA system of ratio 6:10. A 'conditioned' soft feel was observed on each hair tress as the sample was applied and after it was rinsed off. The overall performance of the lamellar gels for hair conditioning can be engineered through optimization of the formulation microstructure and formulation microstructure breakdown on dilution.

Influence of nanoclays on flowability and rheology of SCC pastes

SCC rheology is the key factor of fresh performance and its control is required to overcome cast in place issues regarding pumping and formwork lateral pressure that still limits its widespread use. Nanoclays are good candidates to improve rheological properties of cement pastes as yield stress, viscosity and thixotropy, controlling paste flow behavior. However, some interactions between nanoclays and admixtures can limit their efficiency. In this study, a comparative analysis on rheology and flowability of SCC cement pastes blended with limestone filler and 2% by cement weight of four types of nanoclays, attapulgite, bentonite, and sepiolite in powder form and dispersed in water, is presented. Two water to binder ratios (w/b), 0.35 and 0.45, were considered and a high range water reducing admixture (HRWRA) was used to reach the required flowability. Water adsorption of nanoclays, flowability and rheological properties of SCC cement pastes with nanoclays were evaluated. It was found that HRWRA was less effective on pastes with nanoclays and low w/b, particularly bentonite. Sepiolite showed larger water adsorption and improved rheological properties. It was observed that, the relation of nanoclays and HRWRA was decisive to produce flowability on pastes with low w/b. Besides, flowability was deeply affected by w/b, as water saturation of nanoclays increased HRWRA efficiency. All nanoclays modified rheological properties due to its different particles morphology characteristics. However, sepiolite showed the largest effects and reached the higher values of yield stress, viscosity and thixotropy ratios used.

Assessing Mechanical and Rheological Properties of Potato Puree: Effect of Different Ingredient Combinations and Cooking Methods on the Feasibility of 3D Printing.

The effects of agar, alginate, butter, olive oil, and carrots on the mechanical and rheological properties of potato puree prepared by two different cooking methods (microwave heating (MP) and boiling (BP)) were investigated and interpreted in terms of starch microstructural changes. Microscopic observations revealed more aggregated and densely concentrated starch granules in MP samples. This consequently led to a significant increase (p < 0.05) in mechanical and rheological properties up to five times more than BP samples. All samples exhibited shear thinning non-Newtonian behavior. Butter proved its ability to maintain stiff network formation with starch molecules forming lipid-starch complexes characterized by high retention properties and increased stability due to high thixotropic and yield stress values. The pseudo-plasticity combined with high self-supporting ability (high yield stress and mechanical values) comprised by MP samples allows them to better behave during advanced technological processes such as extrusion 3D food printing.

Purified salep glucomannan synergistically interacted with xanthan gum: Rheological and textural studies on a novel pH-/thermo-sensitive hydrogel

The gelation properties and gel structure of purified salep glucomannan (S) blended with xanthan (X) in different ratios (3:1, 1:1, and 1:3) and at various pH values (water, pH 5.5 and pH 4.0) were investigated. The results indicated that the gelation temperature was rate-independent in varied environments, but the sol-gel transition temperature determined in water and at a pH of 5.5 decreased from 58 to 53 °C when the pH was 4.0. The early structural development of highly concentrated xanthan solutions was observed during the cooling process. In the gelled samples, 3XS and XS had more linear viscoelastic regions and higher yield stress values than 3SX when more stress was applied and the pH decreased. The gel was strong at a low frequency but weak at a high frequency. The early transition frequency of these gel types was observed for 3SX at low pH values, indicating that it had fewer junction points, and the average size of the junction points in the gel network were lower. The melting temperatures of the gels showed the thermo-sensitive behavior of the gels, which was determined to be higher for 3XS due to the stronger and more abundant junction zones. Thus, 3XS had a higher thermal stability than XS and 3SX. Other data supporting this result were observed by determining the creep-recovery parameters, color and gel strength values. The synergistically interacting salep-xanthan gels were shown by FTIR and these gels exhibited high water holding capacities. The usage of the same proportion of polymers and high salep ratios seems more preferable in the water system, while higher xanthan ratios were needed at low pH values if better a gel behavior was desired, such as for the potential use of these materials in food and biomedical applications.

Effects of Metakaolin and Nano clay on the Rheological and Flow Characteristics of Oil-Well Class G Cement Slurry

The rheology of Oil-Well Cements (OWCs) [is generally more complicated than that of the conventional cement pastes. To contend with a wide range of pressure and temperature, several additives are used. The slurries, however, exhibit different rheological characteristics depending on the combination of admixture used. This research investigated the rheological properties of class G cement partially substituted with Metakaolin (MK) in the presence of Nano clay (NC) additives. The variables were randomized using 5 – 15% MK by weight of cement and 5 – 15% NC by weight of MK. The blends obtained were tested for rheology at the bottom hole circulating temperature (BHCT) of 70 oC. The result showed a high dependency of MK and NC admixture on the rheological properties of OWC slurries. The viscosity decreased significantly at high MK irrespective of the NC dosage. The MK in the range of 10 – 15% improved fluidity and required less energy to flow. On the contrary, the slurry with 100% Class G cement has higher values of yield stress and Gels at 10- seconds and 10-minutes, hence require more energy. The analysis showed the Herschel-Bulkley Model with Sum of Square Error (SSE) of 0.001329 and the coefficient of correlation (R2) of 0.9982 adequately fitted the rheological behavior. The partial substitution using the MK and NC improved the pumpability and other rheological properties of the Class G cement.

Analysis of Silica Pulp Viscoelasticity in Saline Media: The Effect of Cation Size

The effect of alkali metal chlorides on the viscoelastic behavior and yielding properties of silica suspensions was studied through creep-recovery and dynamic oscillatory tests with stress control. Then, the viscoelasticity of the pulps was correlated with the silica zeta potential, aggregate size, and the percentage of cations adsorbed on the surface of the ore. The results indicate that larger cations are more prone to adhere to the silica surface, which increases the number of ionic bonds that bind the particles. This generates stronger particle networks and a greater agglomeration of particles, especially those smaller than 10 µm. As the size of the bare cations increases, the rheological response provides higher values of yield stress, complex viscosity, and viscoelastic moduli, but in turn, pulps undergo minor deformations under the application of stress. Dynamic oscillatory tests suggest structural changes, with the phase angle following the inverse relationship with the bare cation size, indicating that the liquid-like character of the pulps increases as the size of the cations increases.

Environmental effect on mechanical properties of a gamma-prime strengthened nickel-based alloy: Effect of the surface oxidation and formation of gamma-prime free zones

The mechanical behavior of X-750 in rough vacuum environment was explored and compared with the mechanical behavior in air at a large range of temperatures (from room temperature to 900°C) for both Heat-Treated and Non-Heat-Treated X750 alloy. In the intermediate range of temperatures where the Portevin Le Chatelier (PLC) effect is observed, the effect of testing in air versus rough vacuum did not yield statistically significant different PLC characteristics. At temperatures above 650°C for Heat Treated and 750°C for Non-Heat-Treated X-750, the samples tested under rough vacuum had higher yield stress values than the respective samples tested under air. The decrease in yield stress under air was attributed to an oxide scale induced surface softening effect and the loss of strengthening efficiency for the gamma prime precipitates. At higher temperatures in air, around 800°-900°C, sinusoidal stress serrations in the stress strain curves indicated the occurrence of dynamic recrystallization (DRX). The vacuum environment however removed all stress serrations attributed to DRX, indicating that the surface oxidation with the concomitant formation of a γ’ free zone underneath the oxide layer plays a role in the DRX presence.

Cereal type significantly affects the composition and reconstitution characteristics of dried fermented milk-cereal composites.

Dairy and cereal products are frequently combined to create composites with enhanced nutritional benefits. Commercially available dried dairy-cereal composites are typically reconstituted and cooked to produce porridge or soup. Dried fermented milk-cereal composites (FMCC) with ∼193 g kg-1 protein were prepared by blending fermented milk with parboiled oats (FMCCo), wheat (FMCCw), or barley (FMCCb), incubating the blend, drying, and milling. Cereal type significantly affected the composition of the FMCC and the properties of the reconstituted, cooked FMCC (R-FMCC). The FMCCo had a higher starch and fat content and lower levels of lactose, lactic acid, and amylose than FMCCb. The R-FMCCo had higher viscosity during cooking at 95 °C and cooling to 35 °C, and higher values of yield stress (σ0 ), consistency index (K) and viscosity on shearing from 20 to 120 s-1 at 60 °C than R-FMCCb. The FMCCw had lower levels of fat and β-glucan than FMCCo or FMCCb, but was otherwise closer to FMMCb with respect to composition, cooking properties and flow behavior. Differences in composition and consistency associated with cereal type are likely to affect the nutritional value of the FMCC. © 2018 Society of Chemical Industry.

Application of Pickering Emulsion with Cyclodextrin as an Emulsifier to a Transdermal Drug Delivery Vehicle.

The emulsion prepared with β-cyclodextrin as an emulsifier (βCDE) is considered to be a Pickering emulsion. We examined the characteristics of βCDEs using captopril (CP) as a model drug, and studied the in vitro skin permeation of CP from βCDEs through hairless mouse skin. The stability of βCDE was increased with increasing βCD concentration and conversely decreased with increasing CP concentration. The yield stress value from the rheological measurement results was suggested to be one of the factors determining the stability of the βCDE, and βCDEs with higher yield stress values were more stable. We found that the skin permeability of CP could be improved by using βCDE with isopropyl myristate as the oil phase and that the flux of CP depended on the free CP concentration in the water phase of βCDE.