The influence of fly ash properties on strength and stucture of geopolymer paste

This study explores the correlation between fly ash properties and compressive strength of geopolymer paste produced. Fly ash (FA) was obtained from 3 (three) power plants in Indonesia. This current work was applied X-ray fluorescence (XRF), X-ray diffraction (XRD), particles size distribution, scanning electron microscopy (SEM) and dissolution behaviour to characterize the fly ash. The activator was composed of 17%wt of Na2O and molar modulus (Ms = molar SiO2/Na2O ratio) of 1.1. Paste were made by mixing fly ash and the alkali-activator in constant liquid to solid ratio of 0.54. The compressive strength test samples were acquired by casting the pastes in an acrylic cylinder moulding having 20 mm in diameter and 40 mm in height. After 24 hours, specimens were demoulded and kept wet in the plastic container. The test was conducted after 3, 7 and 28 days of casting. The fractured surface morphology was observed by SEM technique. It is concluded that soluble Si/Al ratio of fly ash in corresponding alkali solution plays as a key parameter affecting the strength of geopolymer.