Effect of Molarity and Temperature of Alkaline Activator Solution on the Rheological Properties and Structure Formation
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EFFECT OF MOLARITY AND TEMPERATURE OF ALKALINE ACTIVATOR SOLUTION ON THE RHEOLOGICAL PROPERTIES AND STRUCTURE FORMATION OF ALKALI-ACTIVATED REFRACTORY MATERIALS I. Pundiene,1, 2 I. Pranckeviciene,1, 3 and Ch. Zhu1, 4 Translated from Steklo i Keramika, No. 2, pp. 18 – 23, February, 2020.
The effect of the molarity (from 3.64 to 1.74 M) of an alkaline activator solution (AAS) and temperature (from 10 to 20°C) of a mixture of alkali-activated materials (AAM) based on chamotte and metakaolin on the rheological properties, structure development on solidification, and strength of samples after firing at temperatures 800 and 1000°C was studied. It was determined that reducing the molarity of AAS and raising the temperature reduces the viscosity of the AAM mixture. Increasing the molarity of AAS and the temperature of the mixture accelerates structure formation and increases the strength of samples from 8.8 to 22 MPa on solidification and from 6.8 to 20 MPa after firing at temperature 1000°C. The density of the samples after firing increases from 1270 to 1510 kg/m3, and water absorption decreases from 15.4 to 13.4%. Key words: alkali-activated materials, viscosity, structure development, strength in compression.
Research performed in the last 25 years has shown that alkali-activated binders can replace conventional cements in building materials [1, 2]. In the process of obtaining alkaliactivated materials (AAM) amorphous or crystalline aluminosilicates are activated by solutions of sodium and potassium hydroxides, silicates, or aluminates [3, 4], which results in destruction of their structure and formation of a three-dimensional polymer framework of the AAM [5 – 7]. This reaction requires significantly less energy than cement production [8 – 11]. The kinetics of the reaction and structure of AAM are primarily affected by the chemical composition of the initial materials as well as the properties and concentration of the alkaline activator solution (AAS) [12]. AAS gives a high pH of the medium in which the reaction occurs and improves the rheology and versatility of the binder [13, 14]. If the concentration of the AAS is too low (for example, NaOH concentration < 1 M), the dissociation of ions will be incomplete, and if the concentration of the AAS is too high (> 15 M), a layer of dissolved products can form around the unreacted particles, which stops or significantly inhibits the 1
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dissociation of the ions. Even if such an undesirable layer is not formed around the particles, polymerization will be incomplete, which will result in a material with lower mechanical strength [15, 16]. The rheological behavior of a freshlyprepared mixture of the AAM plays the key role in its practical application [17]. In most cases the water/AA ratio is increased in order to improve the rheological properties of the AAM [18]. The rheological properties of freshly prepared mixture of the AAM depends on the amount, shape, and geometric properties of the particles in the mixture [19] as well as on the temperature of the AAM [2
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