The origins of thixotropy of fresh cement pastes

A thixotropy model for fresh fluid concretes: Theory, validation and applications

Steady state flow of cement suspensions: A micromechanical state of the art

Properties of fresh and hardened concrete

A new criterion is introduced for the onset of shear thickening in a concentrated dispersion. The criterion follows from the assumption that shear thickening occurs when the shear forces overrule the interparticle forces. A force balance at small interparticle distances is used to predict the dependence of this critical shear rate on the volume fraction. It is deduced that the critical shear rate is proportional to the interparticle distance, has a linear dependence on the magnitude of the stabilizing force, an inverse linear dependence on the dispersion medium viscosity, and an inverse linear dependence on the particle radius. The model is confirmed experimentally with viscosity measurements on various electrostatically stabilized dispersions. The validity of the model is also checked with data obtained from the literature. Experiments indicate that polydisperse dispersions exhibit pronounced shear thickening but with a less dramatic increase in viscosity than monodisperse dispersions.

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Shear thickening (dilatancy) in concentrated dispersions

The adsorption of polyacrylamide (PAAm) on silica particles and its effect on the rheological properties of the suspensions were studied with a coaxial cylinder type rheometer. The following two unique observations are reported: (1) For suspensions prepared with PAAm solution in glycerin, the apparent viscosity of suspensions is lower than that of the medium. From the adsorption experiments, it is concluded that the decrease in polymer concentration in the liquid phase by adsorption is primarily responsible for the decrease in the apparent viscosity of the suspensions. (2) For suspensions prepared with PAAm solutions in glycerin/water mixtures, the apparent viscosity of suspensions irreversibly increases when the critical shear rate is exceeded. Considering that the polymer adsorption is irreversible, this behavior may originate from flocculation by shear‐induced irreversible bridging.

Rheological Properties of Silica Suspensions in Polyacrylamide Solutions

Time-dependent flow of cement pastes

The rheological properties were studied for suspensions of two titanium dioxide (Anatase) powders with different particle sizes dispersed in water by adding sodium pyrophosphate as the dispersing agent. Using a capillary viscometer, flow measurements were made under conditions of varying amounts of dispersing agent as well as shear histories of suspensions. The sedimentation behavior and zeta‐potential were also measured as a means of studying the stability of the suspensions against flocculation. The onset of dilatancy was observed at higher shear rates and the extent of dilatancy decreased with an increase in a dispersion stability varied by the amount of dispersing agent as well as in a degree of dispersion varied by the shear history. The suspension with large particles showed dilatant behavior similar to that of the stable suspensions. Relationships between the rheological properties and the stability of suspensions against flocculation were discussed on the basis of the theory of the stability of lyophobic colloids.

Effect of Flocculation on the Dilatant Flow for Aqueous Suspensions of Titanium Dioxides

The adsorption of polyacrylamide (PAAm) on silica particles and its effect on the rheological properties of the suspensions were studied with a coaxial cylinder rheometer. The two unusual observations are reported. First, for suspensions prepared with PAAm solution in glycerin, the apparent viscosity of suspensions is lower than that of the medium. Adsorption experiments showed that a large amount of polymer was adsorsed on the particles. It is concluded that the decrease in polymer concentration in the liquid phase by adsorption is primarily responsible for the decrease in the apparent viscosity of the suspensions. Second, for suspensions prepared with PAAm solution in a glycerine/water mixture, the apparent viscosity irreversibly increases above the critical shear rate. This behavior may be originated from flocculation by shear-induced irreversible bridging.

Kaoru Umeya

Papers

Rheological Properties of Silica Suspensions in Polyacrylamide Solutions

Time-dependent flow of cement pastes

Effect of Flocculation on the Dilatant Flow for Aqueous Suspensions of Titanium Dioxides

Adsorption of polyacrylamide on silica particles and its effect on the rheological properties of suspensions

Viscoelastic properties of bronchorrhoea sputum in bronchial asthmatics.