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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.
Southern African Society of Rheology Meeting (SASOR 2015)
Appl. Rheol. 26:4 (2016) 62-62 ►
► Cite this publication as follows:
Haldenwang R: Southern African Society of Rheology Meeting (SASOR 2015), Appl. Rheol. 26 (2016) 62.
R. Elmakki, I. Masalova, R. Haldenwang, A. Malkin, W. Mbasha
Effect of limestone on the cement paste hydration in the presence of polycarboxylate superplasticiser
Appl. Rheol. 26:2 (2016) 25122 (8 pages) ►
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 behavior of self-compacting cement paste was found to be very sensitive to the chemical and physical properties of the cements used.► Cite this publication as follows:
Elmakki R, Masalova I, Haldenwang R, Malkin A, Mbasha W: Effect of limestone on the cement paste hydration in the presence of polycarboxylate superplasticiser, Appl. Rheol. 26 (2016) 25122.
Willy Mbasha, Irina Masalova, Rainer Haldenwang, Alexander Malkin
The yield stress of cement pastes as obtained by different rheological approaches
Appl. Rheol. 25:5 (2015) 53517 (11 pages) ►
Different rheological methods for yield stress estimation of cement pastes during initial hydration were used and results were compared. These methods include measuring of the hysteresis loop, flow curves (recalculated to the same time of hydration) and large amplitude oscillating strain (LAOS). Experiments were performed with four Ordinary Portland Cements from one manufacturer, produced at different factories and one polycarboxylate acid based superplasticiser (SP). The yield stress values obtained by constructing flow curves is the only method which gives information about the evolution of the rheological properties, reflecting structure evolution of cements pastes. It was shown that the yield stress values established by the LAOS method and that calculated from the flow curves are similar while the values found from the downward part of the hysteresis loops are much lower. Differences in the yield stress values obtained by various methods are related to the different states of the material corresponding to the kinetics of hydration. The hysteresis loops provide information about thixotropic characteristics of the material including characteristic times of rebuilding and the rate of yield stress evolution of cements. The rheological properties are very sensitive to the chemical and physical differences of the cements and could be used for their characterization.► Cite this publication as follows:
Mbasha W, Masalova I, Haldenwang R, Malkin A: The yield stress of cement pastes as obtained by different rheological approaches, Appl. Rheol. 25 (2015) 53517.
5th Southern African Society of Rheology Conference (SASOR 2014)
Appl. Rheol. 25:1 (2015) 53-53 ►
► Cite this publication as follows:
Haldenwang R: 5th Southern African Society of Rheology Conference (SASOR 2014), Appl. Rheol. 25 (2015) 53.
Reinhardt Kotze, Johan Wiklund, Rainer Haldenwang
Optimization of the UVP+PD rheometric method for flow behavior monitoring of industrial fluid suspensions
Appl. Rheol. 22:4 (2012) 42760 (11 pages) ►
Ultrasonic Velocity Profiling (UVP) is a powerful technique for velocity profile measurements in research and engineering applications as it is the only available method that is cost-effective, relatively easy to implement and applicable to opaque fluid suspensions, which are frequently found in industry. UVP can also be combined with Pressure Drop (PD) measurements in order to obtain rheological parameters of non-Newtonian fluids by fitting theoretical rheological models to a single velocity profile measurement. The flow properties of complex fluids are almost exclusively obtained today using commercially available instruments, such as conventional rotational rheometers or tube (capillary) viscometers. Since these methods are time-consuming and unsuitable for real-time process monitoring, the UVP+PD methodology becomes a very attractive alternative for in-line flow behavior monitoring as well as quality control in industrial applications. However, the accuracy of the UVP+PD methodology is highly dependent on the shape and magnitude of the measured velocity profiles and there are still a few problems remaining with current instrumentation and methods in order to achieve the robustness and accuracy required in industrial applications. The main objective of this research work was to optimize an UVP+PD system by implementing new transducer technology and signal processing techniques for more accurate velocity profile measurements as well as rheological characterization of complex fluids under industrial/realistic conditions. The new methodology was evaluated in two different pipe diameters (22.5 and 52.8 mm) and tested with three different non-Newtonian fluids in order to obtain a wide range of rheological parameters. Results were also compared to conventional rotational rheometry and tube viscometry. It was found that rheological parameters obtained from accurate velocity data across the pipe radius, especially close to pipe walls where the velocity gradient is high, showed better agreement to conventional rheometry than when compared to results obtained using profiles measured with conventional UVP instrumentation and commercial software (Met- Flow SA Version 3.0). The UVP+PD method is now more robust and accurate. The main challenge remaining is to successfully implement a complete non-invasive system in industrial processes that is able to achieve real-time and accurate complex flow monitoring of non-Newtonian fluid suspensions.► Cite this publication as follows:
Kotze R, Wiklund J, Haldenwang R: Optimization of the UVP+PD rheometric method for flow behavior monitoring of industrial fluid suspensions, Appl. Rheol. 22 (2012) 42760.
Reinhardt Kotze, Rainer Haldenwang, Paul Slatter
Rheological characterisation of highly concentrated mineral suspensions using an Ultrasonic Velocity Profiling with combined Pressure Difference method
Appl. Rheol. 18:6 (2008) 62114 (10 pages) ►
The rheological behaviour of non-Newtonian, highly concentrated and non-transparent fluids used in industry have so far been analysed using commercially available instruments, such as conventional rotational rheometers and tube viscometers. When dealing with the prediction of non-Newtonian flows in pipes, pipe fittings and open channels, most of the models used are empirical in nature. The fact that the fluids or slurries that are used normally are opaque, effectively narrows down the variety of applicable in-line rheometers even further, as these instruments are normally based on laser or visible light techniques, such as Laser Doppler Anemometry. In this research, an Ultrasonic Velocity Profiling technique (UVP), in combination with a pressure difference (PD) measurement, was tested to provide in-line measurement of rheological parameters. The main objective of this research was to evaluate the capabilities of the UVP-PD technique for rheological characterisation of different concentrations of non-transparent non-Newtonian slurries. Kaolin, bentonite, Carboxymethyl Cellulose (CMC) and water solutions were used as model non-Newtonian mining slurries. Results determined by the UVP-PD method were compared with results obtained by off-line rheometry and in-line tube viscometry. The agreement between the UVP-PD method, tube viscometry and conventional rheometry was found to be within 15 % for all of the highly concentrated mineral suspensions investigated over a given range of shear rates.This method, if used in combination with a pressure difference technique (PD), has been found to have a significant potential in the development process of new in-line rheometers for process control within the mining industry.► Cite this publication as follows:
Kotze R, Haldenwang R, Slatter P: Rheological characterisation of highly concentrated mineral suspensions using an Ultrasonic Velocity Profiling with combined Pressure Difference method, Appl. Rheol. 18 (2008) 62114.
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