In this study, Na2CO3 was used as an activator to roast and activate high aluminium fly ash (HAFA) via conventional heating. Microwave roasting technology was then used to strengthen the activation process and the reaction mechanism was discussed and compared with that of conventional heating. Microwave heating had an obvious effect on the HAFA activation process: with an aluminium leaching rate of approximately 93.00%, both the roasting time (30 min) and temperature (700 degrees C) were comparatively reduced, and the mass ratio of HAFA to Na2CO3 employed was 1:0.8. XRD analysis showed that the phase evolution of HAFA was not changed during microwave heating, but the Na2CO3-HAFA activation reaction was promoted. And SEM analysis showed that the micro-structure of roasted materials varied greatly with respect to the different heating methods. With microwave heating, overall breakage of mullite particles occurs and there is higher degree of breakage than conventional heating. (C) 2020 Elsevier B.V. All rights reserved.