Today's concrete is no longer a simple combination of cement, aggregates and water. With increased use of various types of waste materials as supplementary cementitious materials and chemical admixtures, material incompatibility problems have been observed in concrete construction. As a result, some of the greatest problems in concrete manufacturing occur when concrete does not stiffen or harden on time. To this end, a new innovative type of cementing technique (based on the principles of magnetorheology) is presented that allows for the real-time control over the stiffening or setting behavior of concrete. In traditional magnetorheological (MR) fluids, magnetic particles are mostly submerged in Newtonian carrier fluids using high volumetric contents (40-50%) of magnetic particles. A key interest in this work was to investigate if using a non-Newtonian carrier fluid like cement paste with low dosages of magnetic particles would yield an MR effect. Rheological tests were conducted on paste mixtures containing small dosages of magnetic particles (less than 2% volume fraction) and when a magnetic field was applied, it was determined that the shear resistance of the paste could be altered significantly. The response of the paste was found to be dependent on the magnitude of the applied field, concentration of the magnetic particles and surface chemistry of magnetic particles. Furthermore the magnetic particles used in this research to create the MR cement paste did not have any effect on cement hydration products or on compressive strength results. It was shown that the rheological behavior of cement paste could even be adapted to simulate "setting" behavior when an MR-based approach is used. Thus, the potential to create a cement-based material whose fresh state behavior can be adapted on-demand by the user to achieve a desired behavior may soon be a reality. Such a material can be useful in applications in which controlling the fresh-state behavior is critical, and could transform the way cement-based materials are cast. In addition, possibilities to create a smart cement-based composite from the fresh to the hardened state may be possible if the magnetic particles could later be used for structural health monitoring. / text

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Mycronic is a company that manufactures a solder paste printer used to manufacturecircuit boards. Inside the printer solder paste is fed with the help of a screw pump.The solder paste, consisting of relatively soft metals has a tendency to stick to thescrew surface and form particles. These are then detached and passed on in thesystem and can clog the nozzle of the printer. This project investigated the possibilityof creating a model test where different parameters can be varied to evaluate itsinfluence on the amount of solder paste sticking to the surface of the screw. Testingthese parameters directly in the solder paste printer would be time consuming andexpensive.A pin-on-disk set up with some modified parts was used to emulate the solder pastemotion in the screw pump. The results were then analyzed in light optical microscope(LOM) and scanning electron microscope (SEM) equipped with energy dispersivex-ray spectroscopy (EDS).The parameters that were varied were pressure, temperature, rotation speed,substrate, content of the paste and the shape of the profile, which is supposed toemulate the ridge of the screw. It was shown that the profile shape, the substrate andthe pressure was of great importance in the deformation of the solder balls while therotation speed and the paste content had a small or no effect.The goal of the project is to recreate the agglomerates that have led to malfunctionsin the printing and evaluate which parameters that have the greatest significance.

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ABSTRACT There is currently a ubiquitous drive for South African industries to improve on water usage as large volumes of raw water are consumed and saline effluents (brines) are produced during their operations. This dissertation addresses the use of paste technology to co-dispose brines as well as solid wastes, from the SASOL Secunda complex in a sustainable manner. The findings from this study indicated that the properties of pastes with relatively high solids concentrations (e.g. 70%) are dependent on the physical properties of fly ash, such as carbon content and fineness thus impacting on the transportability of the paste. In order to overcome this effect, the paste with a 65% solids concentration will be less sensitive to the physical properties of the fly ash. Furthermore the chemical composition and salt load of brines affect the transportability and salt retention of paste. It was also observed that salinity of the brine affects the settling rate of the paste. The availability of various brines at SASOL provides an opportunity to investigate the blends of brines that will provide suitable settling and salt retention of paste. The other opportunity identified was the use of SASOL solid wastes such as incineration ash (IA) and gasification ash as additives to improve paste properties. It was also discovered that the mode of salt retention is predominantly chemical rather than physical, which increases the credibility of this technology. The overall conclusion is that paste technology is a potential solution for sustainable co-disposal of ash and brines. Further research areas are proposed to improve the understanding of paste technology and its implementation.

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Thesis (doctoral)--Rostock, 1934.

Thesis (doctoral)--Rostock, 1934.

This dissertation covers concrete and cement paste (CP) containing portland-limetsone cement (PLC) for the purpose of understanding mainly mechanical property behaviors. PLC has been consistently investigated by researchers over the past decade who have found equal and often superior performance with PLC, but few researchers have found reasons why. Throughout this dissertation CP cylinders are used to help understand concrete. By understanding the CP (cementitious materials, water, admix, and no fine or coarse aggregates) portion of concrete, it is believed further understanding can be achieved. The interaction of CP and aggregates, or paste aggregate bond (PAB), is exceptionally important. Literature review suggests PAB can be affected by chemical and physical properties of aggregates as well as cement which dictates the mechanical property performance of concrete. CP measurements used herein are mainly compressive strength, however there were other measurements, such as thermal setting, collected as well. CP properties whether thermal or mechanical, generally agreed with concrete results. Additionally, CP compressive strengths were found to have value beyond what was previously known. Mainly that CP compressive strengths can help diagnose concrete behavior. CP used with concrete measurements can give some indication, not previously available, concerning PAB and bonding efficiency. However, the CP measurements had high variability. As such, a new CP production method was developed alongside different analysis techniques to reduce the variability. CP was further used with concrete to recommend a factor for balancing fineness and limestone percentage in PLC. Next, CP measurements were used with 74 concrete mixtures for investigating the Mississippi Department of Transportation fly ash replacement level limits for ordinary portland cement (OPC) and PLC for implementation into the Mississippi market. Lastly, this dissertation delved into non-production concrete mixtures with few ingredients (washed aggregates, cementitious materials, and water) to discover mechanisms behind PLC and OPC behaviors. From CP and concrete measurement perspectives, it is recommended that PLC in the MS marketplace be implemented without hesitation. From the conclusions herein, there does not appear to be many cases where OPC considerably outperforms PLC. In almost every case, PLC performs equivalent or better than OPC when numerous properties are considered.