EARLY MICROSTRUCTURE DEVELOPMENT OF FLY-ASH BASED GEOPOLYMER

The alkali activation of waste materials has become an important area:of research due to its potential to synthesize, at ambient or low temperature conditions, a binder with similar properties as Portland cement but without the drawback linked to greenhouse gas emissions. Coal fly ash has been used for the synthesis of geopolymers using sodium silicate and a mixture of sodium silicate and sodium hydroxide as alkaline activators. One sample was activated only with sodium silicate while the second sample used a mixture 50:50 of sodium silicate and 8 m NaOH solution. Fresh geopolymer paste was immediately placed in the FEI Quanta 200 Environmental SEM chamber for observation using the ESEM mode. The sodium silicate activator dissolves rapidly and begins to bond fly ash particles. Open porosity can be observed and is rapidly filled with gel as soon as the liquid phase is able to reach the ash particle. The liquid phase is important as a fluid transport medium. During this ESEM experiment, the reaction was limited to the surface of the fly ash particles. The reaction products examined had a gel like morphology and no crystallized phase was observed.