The influence of thermodynamic parameters of the alkaline activator on the mechanical properties of geopolymers

Abstract

In order to optimize process of geopolymerization, the investigation of thermodynamic parameters of alkali activators are important. The aim of this research was to investigate the influence of thermodynamic parameters (density, viscosity, refractive index and sound velocity) of alkaline activators on mechanical properties (compressive strength and hardness) of synthesized geopolymer samples. Geopolymers were synthetized by alkaline activation of metakaolin, having the density 2.524 g/cm3, using the activators at elevated temperature of 60 oC for two days. Based on the obtained results thermodynamic properties has been selected to predict the properties of materials. Four series of alkaline activators have been used. Activators remarked as AA1, AA2, AA3 and AA4 present the mixtures of Na2SiO3 and solutions of NaOH, of different molarities 2M, 4M, 6M and 8M respectively. The volume ratio of Na2SiO3 and aqueous solution of NaOH was the same for all samples. Densities, viscosities and refractive indices of alkaline activators were determined over the temperature range 15-60 oC of process of geopolymerizations. The values of density, viscosity and refractive index decrease with temperature increase over the investigated temperature range. Increasing molarity of alkali activator solutions, the sound velocity of activators is changed. For sample AA2 the values of sound velocity rises from room temperature to 45 °C and then begins to decrease while for the sample AA3 sound velocity grows until 30 °C and then starts to decrease with further increasing of temperature. Four series of geopolymer samples GP1 to GP4 were synthesiyed using the constant ratio of solid and liquid phase. FTIR, XRD, SEM-EDS methods were used for physicochemical further characterization of geopolymer samples.