Development of a high strength fly ash-based geopolymer in short time by using microwave curing

In this study, an experimental program was conducted to investigate the effect of microwave curing on the strength of geopolymer. Volumetric heating provided by microwave curing results in faster strength development as compared to conventional heat curing that depends on heat transmission from the outside to the core of a specimen. Initially, the effect of different traditional curing methods (ambient air, water, and oven) on the strength development of Class F fly ash activated by sodium silicate and sodium hydroxide was investigated. Later, microwave curing and oven curing were introduced at higher temperatures in short periods of time (<= 60 min) as alternative curing methods. Results showed that the compressive strength of geopolymer pastes cured in a microwave oven was superior to those of the control cured in a conventional oven at 90 and 120 degrees C for the same period. When the size of specimen size reduced from 50 mm to 25 mm, the strength development rate of the geopolymer decreased as the microwave curing time increased. A 56 MPa compressive strength was obtained for 25 mm size geopolymer paste cured in a microwave oven for five minutes.