A STUDY ON FACTORS AFFECTING GEOPOLYMERIZATION OF LOW CALCIUM FLY ASH

Abstract

This paper presents some factors affecting geopolymerization of low calcium fly ash for
geopolymeric matrices. Low calcium fly ash samples were collected from two different coal-powered
facilities: an Indonesian fertilizer plant and a Japanese power plant. Several series of tests were conducted
using various ratios of fly ash to activator as well as ratios of activators to sodium hydroxide molarity. Each
matrix consisted of a set molar ratio of three variations of Si/Al (1.5, 2, 2.5), Na2O/SiO2 (0.3-0.38), H2O/SiO2
(2.8 to 3.5), H2O/Na2O (9 to 10.6), and mass ratio of water/solid (0.31 to 0.45). The setting time of Japanese
ash-matrices were longer than Indonesian ash. The compressive strength revealed that the Japanese and
Indonesian matrices with activator ratios of 1.5 achieved 47.7 and 57.5 MPa respectively, while activator
ratios of 2.5 reached 50.9 and 50.5 MPa. In addition, microstructural characterizations–XRF, XRD, SEM,
EPMA-were performed. This study concludes that even ashes categorized as the same class, their mineral
composition is different. Furthermore, coal combustion techniques modify ash particles, which in turn causes
differences in setting time, while strength is not significantly affected.