The mixing of powders and liquids is a process ubiquitous to many industrial, research and household applications, from the production of foodstuffs, pharmaceutical and cosmetic products to the preparation of hot drinks or cement. The final mixed state of powders and liquids can be broadly split into two distinct regimes identified respectively as having low- and high volume fraction, ∅. Low-∅ systems are typified by flowing suspensions whereas samples prepared with high-∅, beyond some threshold value, produce solid agglomerates which are unable to flow. These two regimes are the focus of two separate scientific disciplines; suspension rheology and granulation. Within the field of suspension rheology there has been recent advances in the understanding of a phenomena known as shear thickening, which describes the increase in a suspension's viscosity with increasing applied stress. In this thesis we aim to unify the phenomena of shear thickening and granulation within this new theoretical framework. We study shear thickening and granulation using a well characterised model system developed for this purpose, comprising polydisperse glass particles with a mean diameter of ≃ 7 μm and a glycerol-water mixture (90:10 %vol). We measured the rheological behaviour as a function of applied stress, σ, of suspensions at various volume fractions. We observed shear thickening behaviour, with divergences in the low-stress viscosity, η1(∅), and the high-stress viscosity, η2(∅), at ∅RCP = 0:662 and ∅m = 0:572 respectively. These divergences mark the transition between continuous shear thickening, discontinuous shear thickening and a state in which flow is not possible, with increasing volume fraction. Using a recently developed theory of shear thickening (Wyart and Cates, 2014), we were able to fit our rheological data quantitatively. The WC theory predicts a stress-dependent crossover in the fraction of contacts which are frictional in nature, following a stretched exponential function. In order to improve numerical agreement between our data and the model, we developed a method taking into account the volume-weighted contribution of particle sizes in our polydisperse system. Bulk mixing of the same model system in a custom-built high-shear mixer also exhibited three different mixing regimes with the change in behaviour coinciding with the location of the viscosity divergences, ∅m and ∅RCP, measured in the rheology experiments. For ∅ < ∅m suspensions are formed at both high and low stress; for ∅ ≥ ∅RCP granules are formed at all stresses; for ∅m ≤ ∅ < ∅RCP transient granules are formed, which are solid at high stresses, but can relax to a flowing suspension state at low stress. This transient behaviour is reversible with the application of high stress. This coincidence of viscosity divergence in the rheology measurements and mixing behaviour change in the high-shear mixing strongly suggests that the two phenomena are related. Thus we used the stress-dependent jamming volume fraction, ∅J(σ), predicted by the WC theory, to define the transition between the formation of suspensions and granules. We were able to calculate a quantitative phase diagram, with which the regions of the ∅-σ phase space in which granules or suspensions are formed can be easily identified, in agreement with our high-shear mixer data. Thus, using small-scale rheological measurements, requiring relatively small volumes of sample, we are able to define the parameter space in which granules can be prepared, thus eliminating the need for trial and error granulation experiments in order to define this space. We measured the volume-weighted mean granule size as a function of ∅ in the range ∅m → ∅ ≃ 0:85. Based on our observations of granule structure and measurements of granule size distributions, we modelled the granules as an ensemble of core-shell agglomerates with a log-normal size distribution. The packing in the granule cores was assumed to be ∅J(σ ), i.e. ∅m at high stress and ∅RCP at low stress. Appealing to conservation of mass arguments, our model predicts that the mean granule size decreases with increasing volume fraction and stress, in quantitative agreement with experimental data.

Thesis (Doctor of Engineering in Civil Engineering)--Cape Peninsula University of Technology, 2018. / Rheological properties of most ordinary Portland cements are dictated by the hydration reactions that their different phases experience. Cement clinker has four main phases with aluminate being the most reactive. Once in contact with water, the aluminate phase reacts rapidly and generally impedes the early hydration of other cement compounds such as calcium silicates that are responsible for the strength of cement systems. Consequently, the obtained matrix is stiff without much strength. Alternatively, calcium sulphate bearing materials are added within the clinker as set regulators of the aluminate phase hydration. For this purpose, natural gypsum is moslty gound with cement clinker as a source of sufficient sulphate, thereby keeping the cement paste plastic for a certain amount of time, allowing the hydration of silicate phases that are responsible for the early and later strength. However, the heat generated within the mill during the grinding process of clinker and gypsum causes a partial dehydration of natural gypsum into hemihydrate. The final ground cement product is thus comprised of two unexpected types of calcium sulphate bearing materials in an unpredictable proportion. Due to the difference in their solubility, the hydration of the aluminate phase can variably be altered which consequently affects the rheokinetics of the cement paste. Currently, the effect of the available amount of hemihydrate and natural gypsum in the cement sulphate phase, on both the hydration and rheology of ordinary Portland cements (OPC), are not well-understood. An ordinary Portland cement clinker was sampled during the production process of CEM I under stable kiln operations at a local cement plant. This was ground without any form of calcium sulphate bearing material and the final product was considered as relatively pure cement clinker. The degree of natural gypsum degeneration was achieved by partially replacing fractions of hemihydrate with those of natural gypsum. Firstly, the individual effect of these calcium sulphate bearing materials on the hydration kinetics was studied by varying their concentrations from 2-7% within the cement system. Secondly, the effect of their mix proportions at an optimum calcium sulphate concentration on cement paste rheokinetics was investigated. This research confirmed the findings of previous investigations relative to the effect of calcium sulphate on the hydration kinetic , giving new insight on the rheokinetics of cement paste with mix proportions of various calcium bearing materials. Results showed that the reaction rates of cement systems with hemihydrate were faster than those with natural gypsum and generally tended to decrease with the increase in their concentrations. Cements with hemihydrate experiencing shorter dormant durations than those with natural gypsum, likely due to the fact that the consumption rate of calcium sulphate was higher in cement systems with hemihydrate than those with natural gypsum. Consequently, before the exhaustion of sulphate ions, cement systems with hemihydrate had higher degrees of hydration and became almost similar thereafter. More ettringite and portlandite were formed in cement systems with hemihydrate as compared to those with natural gypsum. The amount of ettringite increased with the increase in calcium sulphate concentration up to 4% and thereafter remained constant. Conversely, the amount of portlandite decreased with the increase in calcium sulphate and also remained unchanged after 4%. The strength development of the cement microstructure depended on the concentration of hemihydrate within the suspension. The rigidification of the newly formed network was affected at higher hemihydrate fractions. Rheological parameters were more pronounced when the concentration of hemihydrate exceeded 50%. Below this hemihydrate concentration, cements had almost similar flow properties as those with only natural gypsum. Large changes in yield stress values and variation in plastic viscosity values of approximately 50% were observed. The trend of mixes dynamic yield stress were similar to their corresponding strength rate developments. This rheological behaviour was primarily attributed to the morphology change of ettringite that was triggered by the presence of a higher hemihydrate concentration. It was also noticed that physical performances of cement systems depended on their respective microstructure developments.

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In this thesis, we propose a new microstructural model to describe the rheology of entangled linear polymers. In order to reduce the number of non-linear adjustable parameters, we develop a model capable of predicting both the linear and the non-linear response, using a single set of material parameters. In a first step, a linear differential formulation of the thermal constraint release mechanism is introduced and validated against experimental results for linear polystyrene melts. In a second step, we extend the linear model to the non-linear regime by generalizing the state variables to conformation tensors and accounting for the relevant non-linear relaxation phenomena. The numerical predictions of the resulting model are then compared to experimental data for entangled polymer melts and solutions in different flow regimes. Finally, we show, on a simple reptation model, how the single generator bracket formalism of non-equilibrium thermodynamics can be used for the phenomenological improvement of microstructural constitutive models.

The Upper Devonian Grosmont reservoir in Alberta, Canada, is the single largest carbonate bitumen reservoir in the world, with an estimated 400 billion barrels of bitumen in place. The Grosmont bitumen formed from light crude oil via extensive biodegradation, which produced extremely high in-situ viscosities of >1 million cP. Forty nine samples from fifteen wells were selected for rheological behavior, viscosity, and biodegradation pattern analysis. In addition, various methods of viscosity determination were compared. Results indicate that the Grosmont bitumen is essentially a non-Newtonian fluid at in-situ conditions, exhibiting a distinctive shear-thinning behavior at T < 40C. Neglecting this character will cause inaccurate viscosity measurements. The viscosity variations in the Grosmont reservoir are cyclic with depth and are stratigraphically controlled. The bitumen exhibits 3 levels of biodegradation. Biodegradation parameters from hopanes and tricyclic terpanes may potentially be used for bitumen quality prediction.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2009. / Includes bibliographical references (leaves 179-194). Also available online.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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