Effect of Slag Addition on Mechanical Properties of Fly ash Based Geopolymers

This work describes improvement of mechanical properties of alkali activated binders – geopolymers made of fly ash from coal combustion in fusion boiler. The effect of addition of amorphous phase on physico-mechanical properties of geopolymers was examined. The studied properties were: flexural strength, compressive strength and water absorption. Effect of preparation process on the final properties of samples was also discussed. Amorphous phase was added in form of slag from the same coal combustion boiler. Samples were tested after 7, 28 and 90 days. With increasing amount of slag, the ascending trend of compressive strength was observed at the early stages of maturing. Compressive strength values measured after 90 days of maturing were found almost the same for all slag concentrations, and outperformed the compressive strength value of reference sample. On the contrary, the flexural strength was not positively affected by addition of the slag. Regarding the water absorption, the higher the slag addition, the lower water absorption was measured.