Rheological Properties Of Matrix Research Articles

An Overview on the Dispersion of Steel Fiber in Ultra-High-Performance Concrete

Abstract Ultra-high-performance concrete (UHPC) is widely recognized for its high toughness, which is directly affected by the dispersion of steel fiber and its loading mode. To investigate the reinforcement effect of steel fiber, this paper summarizes the influencing factors, evaluation methods, and theoretical models of steel fiber dispersion in UHPC. First, the results reveal that a scientifically designed mixture can reduce the cost of steel fiber dosage in UHPC and improve fiber dispersion by adjusting matrix rheological properties. The optimum plastic viscosity of the slurry should range from 30 to 80 Pa·s for achieving the best fiber dispersion effect. Second, during slurry placement, the orientation of fibers in UHPC can be improved by up to 80 % through flow induction and the wall effect, which increases the bending strength, tensile strength, and toughness of UHPC matrix by 5–67 %, 30–90 %, and 13–200 %, respectively. Moreover, although the dispersion of fiber in two-dimensional space has been extensively studied, further characterization in three-dimensional space is required. Lastly, some theoretical simulation results have been achieved on fiber orientation, but factors such as aggregate or reinforcement must be considered.

Critical assessment of the formation of hydrogen peroxide in dough by fermenting yeast cells

Fermentation of bread dough leads to strengthening of the dough matrix. This effect has previously been ascribed to the action of hydrogen peroxide (H2O2) produced by yeast in dough. In this study, we re-evaluate the production of H2O2 by yeast in dough and aqueous fermentation broth. Results show that the previously reported high levels of H2O2 in fermenting dough were most probably due to the lack of specificity of the potassium dichromate/acetic acid-based method used. Using the chemiluminescent HyPerBlu assay, no yeast H2O2 production could be detected in fermented dough or broth. Even though the formation of low levels of H2O2 cannot be ruled out due to the presence of catalase in flour and the fast reaction of H2O2 with gluten proteins, our results suggest that the changes in dough matrix rheological properties upon fermentation are not due to production of H2O2 by yeast.

Improving the workability and rheological properties of Engineered Cementitious Composites using factorial experimental design

In the development of Engineered Cementitious Composites (ECC), micromechanics-based design theory is adopted to properly select the matrix constituents, fiber, and fiber–matrix interface properties to exhibit strain hardening and multiple cracking behaviors. Despite the micromechanics design constraints, practical applications show that the workability and rheological properties of matrix can affect the fiber dispersion uniformity, which have also direct concerns on composite mechanical properties. For this reason, in this research, parameters of micromechanics-based optimized ECC mixture design, which most possibly affecting the workability and rheological properties, are investigated. An experimental program that contains 36 different ECC mixtures was undertaken to quantitatively evaluate the combined effects of the following factors on workability and rheological properties: water-binder (w/b), sand-binder (s/b), superplasticizer-binder (SP/b) ratios and maximum aggregate size (Dmax). A mini-slump cone, a Marsh cone and a rotational viscometer were used to evaluate the workability and rheological properties of ECC mixtures. Compressive strength and four point bending tests were used for mechanical characteristics of ECC mixtures at 28days. The effects of studied parameters (w/b, s/b, SP/b and Dmax) were characterized and analyzed using regression models, which can identify the primary factors and their interactions on the measured properties. Statistically significant regression models were developed for all tested parameters as function of w/b, s/b, SP/b and Dmax. To find out the best possible ECC mixture under the range of parameters investigated for the desired workability and mechanical characteristics, a multi-objective optimization problem was defined and solved based on the developed regression models. Test results indicate that w/b, s/b and SP/b parameters affect the rheological and workability properties. On the other hand, for the range of studied aggregate sizes, Dmax is found to be statistically insignificant on the rheological and workability properties of ECC.

Migration of a sphere in a viscoelastic fluid under planar shear flow: Experiments and numerical predictions

Solid–liquid disperse systems are complex fluids, extensively used for a variety of applications. The flow behavior of such materials is strongly dependent on the matrix rheological properties: when the suspending fluid shows viscoelastic behavior, isolated suspended particles in confined flow fields tend to migrate across the streamlines. In this work, we carry out a detailed experimental investigation of such migration phenomenon for a rigid, spherical particle in planar shear flow, and compare the experimental findings with 3D numerical simulations based on finite elements. A highly elastic non-Newtonian fluid is chosen as the suspending medium. The migration is studied by varying the confinement, the external shear rate and the fluid normal stresses. The particle is always found to move towards the closest wall, regardless of its initial position. For a fixed set of geometrical and flow parameters, the trajectories from different initial positions can be shifted in time to overlap on a single curve. Migration dynamics is governed by an exponential law as the particle is in the region around the midgap. Stronger confinements, higher shear rates and higher levels of normal stresses all enhance the migration speed. We found qualitative agreement between predictions from numerical simulations and experimental results.

Influence of protein content on the physicochemistry of poly(ϵ‐caprolactone) microparticles

AbstractThe aim of this work was to determine the influence of protein content on the physicochemical properties of protein‐loaded poly(ε‐caprolactone) (PCL). To achieve this goal, bovine serum albumin (BSA), an example of protein was encapsulated within PCL matrix by emulsion solvent evaporation method. The polymer matrix's rheological properties, hydrophobicity, molecular weight (MW), and thermal behavior were determined. Particle characteristics such as BSA loading, surface area, mean size, morphology, and in vitro release profile were also assessed. After encapsulation process, the polymer crystallinity and crystallization point were markedly increased suggesting that a nucleation phenomenon occurred. The increase in PCL MW (from 46. 7 to 179.4 kDa) led to an increase of both particle size and encapsulation efficiency that was consistent with rheological data. The increase of protein content from 1.6 to 11.5% (w/w) influenced considerably particle's specific surface area and decreased the rate of protein release. Together, these results suggest that beside the nature of the carrier polymer, protein content may have implication on their controlled release, the coating of particle by protein, and on the carrier polymer chemistry and degradation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1042–1050, 2006

Cast-in-Place Cellulose Fiber-Reinforced Cement Paste, Mortar, and Concrete

Fiber-reinforced concrete is a fast-growing technology. This research considers the use of cellulose fibers as an inexpensive alternative to synthetic fibers. This study characterizes the behavior of cellulose fiber-reinforced paste, mortar, and concrete and investigates rheological, dispersion, and mechanical properties of the materials. The addition of cellulose fibers to a cementitious material stiffens the matrix. This stiffening limits the maximum usable fiber volume. At fiber volumes used, fibers offer little improvement in flexural properties. Optical and scanning electron microscopy are used to inspect fiber dispersion. A technique is developed to locate fibers in hardened specimens. Correlations among fiber dispersion, mechanical performance, and rheology are investigated. Restrained ring shrinkage tests are performed on paste and mortar. Fibers are found to reduce the width of shrinkage cracks in both materials. Fiber dispersion, matrix rheology, and mechanical performance cannot be correlated. Fibers disperse well under normal mixing conditions, regardless of matrix rheological properties.

Studies of the effect of fiber surface and matrix rheological properties on nonwoven reinforced elastomer composites

AbstractThe influence of fiber type and fiber‐surface properties on matrix flow behavior was investigated using structural reaction injection‐molding (SRIM). The influence of fiber type, fiber‐surface properties, and matrix type on strength properties in elastomeric composites reinforced with nonwoven fibrous structures was investigated using tensile tests on elastomer composite samples from SRIM and latex coagulation (LC) fabrication methods and the microbond strength method on individual fibers. The fibers used were PET, LLDPE, and p‐aramid. Fibers were treated with epoxy, styrene, and isocyanate derivatives, which make the surface chemically reactive. Treatments were also made with NaOH and a copolymer of polyester and polyol ether, causing a change in the fiber surface energy. The matrix types were polyurethane elastomer and natural rubber. The results show that the surface treatments which produced a change in the surface energy influenced the flow rate of the matrix polymer during the composite fabrication process. The treatments resulted in chemically reactive fiber surfaces which improved the fiber‐matrix bond strength without affecting the Young's modulus of the composite material. Good correlation was found between bond strength and surface energy including the dispersive component of surface energy in the case of polyurethane elastomer and surface‐modified PET fibers. The age of the polyurethane matrix has a marked influence on the bond strength. The fiber volume fraction in composites has a strong influence on the Young's modulus of the elastomer composite. © 1995 John Wiley & Sons, Inc.

The influence of matrix rheological properties on acoustic emission and damage accumulation in GRP tubes

In this study, the effect of matrix properties on the acoustic emission response of glass fibre reinforced plastic tubes has been investigated. Two kinds of composite materials have been considered, differing essentially in the matrix: one is polyester-based composite and the other a vinylester-based composite. It is shown that the viscoelastic behaviour of the matrix can affect the acoustic emission response (i.e. the damage accumulation rate of the composites). This is observed throughout different experimental methods, essentially by checking the effect of the influence of hygrothermal ageing, which influences the rheological properties of the pure matrix on the Felicity ratio measurement, and also by measuring the influence of strain rate on the mechanical response of the tested composite.