Sedef Dikmen

Effect of mixing water types on the time-dependent zeta potential of Portland cement paste

Abstract The measurement of zeta potential (ZP) has important applications in a wide range of industries including ceramics, pharmaceuticals, medicine, mineral processing, electronics, cement industry and water treatment. It provides new information on cement hydration, gel structure formation and the effects of chemical and mineral admixtures. In this study, ZP and pH measurements of Portland cement suspension prepared at wt% 1 cement/water ratio in the presence of four different types of waters, i.e., pure water, tap water, and salted (NaCl and CaCl2) water, were carried out depending on the time. Also, vicat tests of Portland cement pastes prepared at a water-to-cement ratio of 0.34 were performed. After the vicat tests, X-ray diffraction analysis and scanning electron microscopy investigations were performed on the samples. The most important result obtained from this study is that setting time and time-dependent ZP values of Portland cement paste have different values depending on the used mixing water type. Among the water types, water with CaCl2 gives the lowest ZP as absolute value, so this leads to minimum initial and final setting times for the cement paste prepared with this type of water.

Effect of Particle Size Distribution on the Sintering Behaviour of Fly Ash, Red Mud and Fly Ash-Red Mud Mixture

In this study, the characterization and microstructure observation of the sintering behaviour of F (from Seyitomer Thermal Power Plant) and C (from Soma Thermal Power Plant) types fly ashes, red mud and red mud–fly ash mixtures at 4 and 8 h milling times with a mortar type ball are investigated. The particle size distribution (PSD) was carried out by laser technique. The PSD analysis revealed that the particle size decreased with increasing milling time. After milling, the samples were pressed into a cylindrical form without using any additive or binder. The formed samples were sintered at 1050 °C. Phase evolutions and microstructures of the formed samples were carried out by using X-ray diffraction method (XRD) and scanning electron microscope (SEM) method, respectively. The water absorption and compressive strength were tested to determine some physico-mechanical properties. The results of mineralogical analysis as well as the microstructural observations reveal that phase transformations occurred during the sintering treatments. The results showed that at the chosen optimum conditions (F type fly ash-red mud mixture with 1:1 ratio, sintering temperature of 1050 °C and milling time of 4 h), the best characteristics of sintered glass ceramic could be obtained. Values obtained from mechanical testing showed that the fly ash–red mud sintered ceramic materials had increased strength compared to other sintered ceramic materials. The sintered materials from red mud have the highest water absorption value.