Metakaolin Mixtures Research Articles

Heat evolution in alkali activated synthetic slag–metakaolin mixtures

In this study the calorimeter was applied to follow the early hydration of mixtures produced using three different synthetic slag vitreous materials, differing with alumina to silica ratio and mixed or not with synthetic two different metakaolin additions (kaolin heated with sodium containing admixture or without admixture). These mixtures were processed with sodium/potassium hydroxide solutions and placed inside the chamber of calorimeter. The kinetics of hydration process was thus characterized and the hydraulic properties of slag–metakaolin mixtures were very well assessed. Substantial heat evolution was found in the presence of activators, in many cases exceeding 100 J g–1 for 24 h process; heat evolved on hydration with water only was very poor, below 20 J g–1 after 24 h. The rate of heat evolution vs. time plots showed specific shape, more or less similar to the typical heat evolution curves reported for cements. Finally, some conclusions were drawn and the amount/concentration of activators was selected for further studies.

Hydration behaviour of lime–co-calcined kaolin–petroleum effluent treatment plant sludge

Petroleum effluent treatment plant (ETP) sludge contains hydrocarbons and its ash is pozzolanic in character. The hydrocarbon may be utilized in the calcination of clay. The present communication reports on the hydration behaviour of lime–metakaolin mixtures produced in the presence of the sludge. The hydration products were characterized by using FTIR, TG, DTA and XRD methods. Use of sludge in metakaolin preparation increases the initial hydration rate and enhances the production of C–S–H or C–A–S–H gel.

Mechanism of hydration of the metakaolin–lime–water system

The reaction kinetics of a mixture of metakaolin and lime (calcium hydroxide) in water at 60°C has been investigated using thermal analysis. The numerical results have been used to determine the nature of the reaction. It is shown that, on the whole, this pozzolanic reaction is diffusion controlled and can be represented by the Jander diffusion equation. The paper discusses a new rapid method for monitoring the reaction, utilizing a microwave oven to stop it at any desired reaction time. The nature and quantity of the reaction products were determined by differential thermal analysis (DTA), thermogravimetry (TG) and X-ray diffraction (XRD).

SYNTHESIS OF GRANULAR LOW-MODULUS ZEOLITES FROM METAKAOLIN USING MECHANOCHEMICAL ACTIVATION AND ULTRASONIC TREATMENT

The process of synthesis of granular low-modulus zeolites from a mixture of metakaolin and solid sodium hydroxide depending on the method of pre-treatment (mechanochemical activation or ultrasonic treatment) has been investigated. The vibration roller-ring mill VM-4 (vibration frequency 930 min–1) was used for mechanochemical activation (MCA) of the powder mixtures. Ultrasonic treatment of the aqueous suspensions was carried out in the ultrasonic disperser UD-20 (oscillation frequency 22 kHz). X-ray diffraction analysis, IR spectroscopy and scanning electron microscopy have been used for the study. It was established that Na2Al2O4 and SiO2 are formed in the system after MCA as a result of leaching, and after UST, Na2Al2O4 is formed only. It was shown that thermal treatment at 650 °C of the mixture after mechanochemical activation and ultrasonic treatment leads to the synthesis of sodium aluminosilicates of cubic syngony, but with different parameters of the crystal lattice. Thermal treatment of the mixture without treatment gives the formation of sodium aluminosilicates and silicon oxide. It was found that after hydrothermal crystallization in NaOH solution with a concentration of 2 mol l–1, the LTA zeolite is synthesized. Crystallization in an alkali solution with a concentration of 6 mol l–1 gives the formation of SOD. It was ascertained that the use of ultrasonic treatment of the initial mixture results in the synthesis of a maximum amount of LTA zeolite (80 %) and SOD (98 %).