Kinetics and mechanism of hydration of blended cement pastes containing silica fume at different porosities

The industrial wastes such as silica fume and blast-furnace slag or by- product as cement kiln dust cause many environmental and health hazards and represent a burden for all factories, nowadays. In the present work, granulated slag and raw [or washed] cement kiln dust were used to make blended cement. Silica fume was utilized as a partial substitute for slag. Past-hydration of the various slag- cement dust-silica fume mixtures was carried out at room temperature for different curing periods. The initial water/solid ratios used were 0.30, 0.40 and 0.50. From the results of combined water and free lime contents of the hardened pastes at various hydration ages, the mechanism of the hydration process could be specified. The beginning and duration of each hydration period depended primarily on the amount of silica and the porosity of the paste

Effect of limestone as a substituent on the physicochemical characteristics of Portland cement and mortars

Hardened cement pastes were made with and without limestone as a partial substituent of ordinary Portland cement and using the standard water of consistency suitable for each blend. The effect of the limestone as a partial substituent of Portland cement on the physicochemical and mechanical properties of the various blended cement pastes was reported. The results obtained were discussed on the basis of the chemical composition and physical state of the hydration products of the various pastes investigated as well as their initial porosities as controlled by the initial water/cement ratios

Electrochemical studies on corrosion of stainless steel electrodes II Chronopotentiometri studies of the stainless steel electrodes

Chronopotentiometric studies have been carried out in potassium chloride solutions of different concentrations and pH at various scan rates. From these measurements calculations of the thickness of the formed film and specific charge transfer are obtained. By the help of the scanning electron microscope and the X-ray probe, elemental analysis of selected areas of the electrodes in chloride had been followed. At pH 2 and 8 neither chloride nor potassium are detected, whereas at pH 4 only the chloride peak is observed

Electrochemical studies on corrosion of stainless steel electrode: III Inhibition of pitting corrosion

The inhibition of corrosion of 18-8 Cr-Ni stainless steel by quaternary ammonium salts been investigated in de-erated 0.1N-KGl solution at different pH values. The electrochemical studies employed is the cyclic polarization measurements at a scan rate of 0.025 V/min. over the potential range -1.5 V to +1.5 V. The percentage inhibition efficiency is found to decrease according to the type of quaternary ammonium compounds, tetramethyl > tetraethyl > tetrabutyl ammonium chlorides