The effects of fineness level of fly ash and accelerator on the setting time and the compressive strength of geopolymer mortar

Abstract This experimental study is part of fly ash based geopolymer research development. The type F fly ash which is the quite abundant by-product materials from power plant burning coal in Tanjung Enim, South Sumatera was the background of this research. However, this kind of fly ash was being treated before it would be used. As known that the mechanical properties of the harden of cementitious material is affected by its fineness of the binder material. The beginning researches about this fly ash based geopolymer concluded that early harden process was being difficult. By this problem, in this research some of accelerator/fly ash ratios are used as the one of the variables. This study aimed to determine the contribution of the fineness level of the fly ash as well as the accelerator/flyash ratio to the setting time and its compressive strength of the geopolymer mortar. The sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as the activator and the accelerator with the 0%, 0.5%, 1%, 1.5% and 2% as the accelerator/fly ash ratios are used in this study. The 3 zones of the fineness level of flyash are being the other variable of the research. The results showed that the fineness level based on fall zone and the accelerator/flyash ratio affect the setting time and compressive strength significantly. The fineness level based on the fall zone increased the compressive strength and tended to produce the shorter setting time. While the higher accelerator/flyash ratio gives the higher compressive strength of geopolymer mortar. The initial setting time and final setting time ranged from 90 minutes to 225 minutes.