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Author index ►Irina Masalova, Willy Mbasha, Rainer Haldenwang, Alexander Ya. Malkin

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Rheokinetics of cement paste hydration during the dormant phase

Appl. Rheol.28:1 (2018) 15452 (9 pages) ►

The hydration kinetics of four CEM I 52.5 N cements in the presence of two different superplasticizers was studied. The kinetics was characterized by monitoring the evolution of the dynamic modulus at constant frequency on a rotational rheometer. The method consists of predicting the time dependence of the elastic modulus by a kinetic equation of the self-acceleration type and fitting the equation to the experimental data. The model defines two main characteristic constants i.e. the characteristic time which defines the initial rate of hydration and the self-acceleration coefficient. It is shown that the model can accurately predict the initial hydration of cement paste with and without superplasticizer. The effect of the different cement properties and their interaction with superplasticizers can be observed in the kinetics of hydration.► Cite this publication as follows:

Masalova I, Mbasha W, Haldenwang R, Malkin AY: Rheokinetics of cement paste hydration during the dormant phase, Appl. Rheol. 28 (2018) 15452.

Measuring the rheological properties of multi-component (and multi-phase) systems meets with many special problems which are absent in flows of homogeneous materials. Such complex fluids have inherent structure and all the peculiarities of their behavior are determined by stress-induced temporal-spatial structure rearrangements. This paper is a review devoted to the physical origin and classification of problems encountered in the flow of multi-component materials. Stress-driven phenomena can be related to phase transformations (the formation of a new phase in polymerization, crystallization, amorphous phase separation), molecular and structure orientation, and various forms of self-organization. Some of these time effects are considered to be thixotropic phenomena. Thixotropy of multi-component matters leads to absence of an upper Newtonian plateau, time (rate)-dependence of yield stress and the layered flow in the range of high shear rates. The flow of such matters can lead to the formation of spatially divided structures with different properties and displacement of structures at the macroscopic level that excludes traditional measures of their rheological properties. In addition, the flow of multi-component systems is accompanied by the appearance of anisotropy of their properties. It is emphasized that the stressdriven evolution of rheological properties are not taken into account in the existing widely used constitutive equations.► Cite this publication as follows:

Malkin AY, Kulichikhin V: Spatial-temporal phenomena in the flows of multi-component materials, Appl. Rheol. 25 (2015) 35358.

► Cite this publication as follows:

Malkin AY, Kulikov-Kostyushko F: IV International Conference on Colloid Chemistry and Physicochemical Mechanics, Appl. Rheol. 23 (2013) 240.

The yield stresses of five samples (two highly concentrated emulsions, two Kaolin dispersions and mayonnaise) were determined in two ways. In one case, steady shear experiments were performed over a range of incrementally decreasing shear rates. The resulting flow curves, plotted as shear stress against shear rate, clearly showed the existence of a yield stress for each sample, the Herschel-Bulkley model being fitted to obtain values. In the second case, oscillatory amplitude sweeps were performed at three frequencies, and the .dynamic yield stress. was defined as the stress at which deviation from linearity occurred; this procedure has often been used to determine the yield stress of emulsions. It was found that the dynamic yield stress is frequency dependent, and cannot therefore be thought of as physically meaningful material property. At no frequency did the dynamic yield stress correlate with the yield stress obtained from the flow curves.► Cite this publication as follows:

Masalova I, Malkin AY, Foudazi R: Yield stress as measured in steady shearing and in oscillations, Appl. Rheol. 18 (2008) 44790.

The concentration and size dependencies of elastic properties of highly concentrated w/o emulsions were studied. The range of weight concentration of the disperse phase was 90 - 96%, the range of the average droplet size was 16 - 20 μm, and the droplet size distribution remained unchanged. The disperse phase consists of droplets of over-cooled concentrated aqueous solutions of inorganic salts. The concentration range being studied lies above the limit of maximal close packing, φ > φ_{m}. The droplet size distribution is fairly wide and the shape of droplets is polygonal.These factors alone determine possible new rheological effects, such as the elasticity and visco-plastic behaviour of emulsions, as well as the observed form of concentration and size dependencies of rheological properties of emulsions. The complete flow curves were measured for these fairly new emulsion systems. It emerged that they were similar to the entire concentration and droplet size ranges being studied. The concentration dependencies of the yield stress and storage modules corresponded to the Princen-Kiss theory with critical volume concentration approximately 0.71 - 0.74. However, this theory describes the size dependence of elastic modules incorrectly. A new model is proposed, which correctly describes the dependencies of elastic modules on both determining parameters - those of concentration and droplet size.► Cite this publication as follows:

Masalova I, Malkin AY: Rheology of highly concentrated emulsions - concentration and droplet size dependencies, Appl. Rheol. 17 (2007) 42250.

The answer to this provocative question is .no.! This is demonstrated by experiment and analysis for two very different materials . a highly concentrated emulsion and an 8%v/v Kaolin clay suspension. The flow curves of both materials clearly showed a low shear Newtonian asymptote and a pseudoplastic domain. The difference in the accuracy of the fitting equations relates mainly to the low shear rate domain. While the Cross equation is adequate over the full flow curve, the power law and the Herschel-Bulkley equations are clearly inadequate for the low shear rate range. These equations as well as the direct numerical method (using the Rabinowitsch- Weissenberg integral) were used for the calculation of the laminar pipe flow transport characteristics and the results were compared with experimental pipe flow data. It was shown that in all cases the maximum error did not exceed 5%, which is quite acceptable for engineering design, indicating that the choice of the flow curve fitting equation was unimportant.► Cite this publication as follows:

Malkin AY, Masalova I, Pavlovski D, Slatter P: Is the Choice of Flow Curve Fitting Equation Crucial for the Estimation of Pumping Characteristics?, Appl. Rheol. 14 (2004) 89.

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