Band 26, Heft 2

Particle motion in fluid is discussed for one-particle systems as well as for dense suspensions, such as cementitious materials. The difference in large particle motion between larger particles and behaviour of fines (< 125 μm) is explained, motion of one particle is shown by numerical simulation. It is concluded and highlighted that it is the particular motion of the fines that to a large extent contribute to the rheological properties of a suspension. It is also shown why larger ellipsoidal particles do not necessarily contribute to the increase of viscosity.

Resonance phenomena are discussed in detail. The influence of significant parameters as the moment of inertia and the measuring constants are enlightened and verified with measurements. It is shown that resonance frequencies weekly depend upon the moment of inertia and strongly on the geometrical coefficient of the measuring system. Both parameters form the configuration constant. If a measuring system is replaced, the moment of inertia changes little but the configuration constant changes more. Thus resonance frequencies can be shifted some decades. The comparison between the developed formalism and measurements gives good results for different rheological measuring modes. Even at pronounced resonances measurements provide proper results. The formalism can be used for the simulation of measuring values. However, deformation oscillations along the rotating axis generate resonances of higher order at higher frequencies. These phenomena contribute systematically errors and should be avoided.

The addition of certain ingredients in conventional concrete is essential for improving rheological properties of this construction material. The effect of limestone and superplasticisers on the hydration kinetics of self-compacting concrete (SCC) was investigated on cement paste scale. These additives interact mostly with cement paste, since aggregates are considered to be inert materials. The understanding of the effect of these mineral and chemical additives on the hydration kinetics of cement paste is the key to design a self-compacting concrete with great properties. Four CEM I 52.5 N Portland Cements, limestone (LS) and one type of superplasticiser (SP) were used in this research. The hydration kinetics were evaluated by monitoring the storage modulus growth and different coefficients of a self-acceleration kinetics equation were used to depict the effect of different concentrations of SP with and without the optimum concentration of limestone (30%) on the hydration kinetics of cement pastes. It was observed that the rate of hydration increased with the increase in SP concentration depending on the cement used. The addition of limestone in the superplasticised cement paste significantly retarded the hydration kinetics for all four cements. The rheological behaviour of self-compacting cement paste was found to be very sensitive to the chemical and physical properties of the cements used.

Removing drilled cuttings from the drilling fluid flowing out of an oilwell is essential for obtaining good drilling conditions. Currently this solids control process is performed by use of shale shakers and vacuum devices. Throughout the last decades, the design and performance of the primary solid control devices have changed significantly. Flow through screens is strongly dependent on the rheological properties of the drilling fluid. Drilling fluids with high extensional viscosity seldom have a very strong gel structure, and are generally not affected equally much by vibrations. This explains why solids control is more difficult using a KCl/polymer water based drilling fluid than using an oil based drilling fluid. This article focuses on describing how the drilling fluid viscous properties alter when being exposed to vibrations like those on primary solids control devices. It is based on theoretical analysis, and rheological studies in the laboratory. The solids control efficiency resulting from using different screen configurations is outside the scope of this article, as this topic requires a higher focus on separation technology.