Effects of Ultrafine Fly Ash on Setting, Strength, and Porosity of Geopolymers Cured at Room Temperature

This paper presents the effects of ultrafine fly ash on setting, strength and porosity of geopolymer paste specimens cured at 20 degrees C. Addition of ultrafine fly ash reduced setting time and improved compressive strength of geopolymers based on fly ash only or fly ash blended with 15% ground granulated blast-furnace slag (GGBFS) or 10% ordinary portland cement (OPC). With the addition of ultrafine fly ash, a reduction in porosity was observed by the mercury intrusion porosimetry (MIP) and a denser microstructure was observed by the scanning electron microscope (SEM) photographs. Thus, for room temperature curing conditions, a control on the setting time and improvements of strength and porosity of geopolymers could be achieved by varying the percentage of ultrafine fly ash.