Synthesis of dry-mix of fly ash based geopolymer

Abstract

Due to its superior properties against conventional Portland concrete, geopolymer currently becomes more attractive as an alternative for environmentally friendly building materials. However, at the moment the preparation process is still challenging since it requires high concentration of liquid alkali as an activator causing complications in the application. Therefore, formulation of a dry process in the preparation of geopolymer is necessary. In the present study, geopolymer was prepared from type C fly ash through a dry process which consisted of three main steps i.e. activator forming, synthesis of geopolymer powder and synthesis of geopolymer paste. The activator was synthesized through calcination of a mixture of 44 wt% solid sodium hydroxide in fly ash powder at 750°C. The activator was then pulverized and mixed with fine fly ash (53 micron). The amount of activator was varied at 10%, 15% and 20% of the total weight. Water was added to the mixed-powders to form a paste of geopolymer which was molded in 7cm x 4cm x 1cm shape for flexural strength test samples. Flexural strength of the samples was measured after 1, 3, 5, 7, 14, 21, 28, 56 days of aging. After 56 days, it was found that maximum flexural strength of 207.13 N/cm 2 was achieved from samples with 20% activator addition. The strength of the samples tends to increase beyond 56 days of aging. Fourier transformed infrared measurement indicated formation of geopolymer bonds in the samples during the aging. Results from this work provides important indication that geopolymer can be prepared through a dry-process which eases the applications of the materials.