Improving reactivity of fly ash and properties of ensuing geopolymers through mechanical activation

• Effects of mechanical activation of fly ash on properties of fly ash and geopolymers were studied.
• Mechanical activation was conducted in ball mill.
• Mechanical activation resulted in exceptional increase of compressive strength.
• Strength increase was related to the physical and structural changes of fly ash.

This paper investigated the effects of mechanical activation of fly ash (FA) from thermal power plants on physical–mechanical properties and structure of geopolymers. FA from different power plants in Serbia was mechanically activated in planetary ball mill. Geopolymerization was conducted by use of sodium silicate (water glass) at elevated temperature (95 °C) for 4 h. It was observed that mechanical activation of FA for 15 min resulted in drastic increase of geopolymer compressive strength (in all cases >1000%). High strength values were associated with improved FA reactivity obtained mainly by the reduction in particle size and reduced water/binder ratio.