Influence of Mix Proportions on Physical and Dielectric Properties of Fly Ash-based Geopolymer Mortar

Abstract

In this paper, physical and dielectric properties of mixture materials and various mixes of fly ash-based geopolymer mortars were investigated to determine the feasibility of application microwave energy in curing geopolymer. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were used as an activator. The mass ratios of Na2SiO3-to-NaOH (NS/NH) of 0.5 to 2.0 and the fly ash-to-activator (FA/AS) of 2.0 to 3.0 were used. The test results revealed that fly ash could be used as aluminosilicate material for production of geopolymer mortars. The flow values of the samples without an additional amount of water were not in accordance with the ASTM C 109 standard, therefore water was added to the geopolymer mortar. For setting time of geopolymer paste, it was found that the initial and final setting time was lower than that of cement paste, and these values decreased when the ratios of FA/AS and NS/NH increased. In the case of dielectric properties, the relative dielectric constant (εr′), relative dielectric loss factor (εr″) and loss tangent coefficient (tan δ) were studied, and it was found that the dielectric properties of liquid portions (water, Na2SiO3 and NaOH) eg. εr′, εr″ and tan δ  were higher than that of the solid portions (fly ash and sand). For geopolymer mortars, it was found that the dielectric properties decreased with increasing the time after mixing, and had the highest value at the end of mixing. In addition, the geopolymer mortars with more liquid (additional water, NaOH and Na2SiO3) contents had high dielectric properties values as well. The dielectric properties results indicated that geopolymer could be cured with microwave energy.

Keywords : Dielectric Properties / Geopolymer / Microwave Energy