Self-cementitious properties of fly ash from circulating fluidized bed combustion boiler (CFBC) with limestone addition were investigated, especially the effect of lime on self-cementing process. The CFBC fly ash is self-cementitious and its main hydration products are ettringite (AFt), hydrated calcium silicate (CSH), portlandite, and gypsum. Slaking of free lime has a great effect on the self-cementing process of CFBC fly ash, accelerating the setting process. The self-cementing process of CFBC fly ash paste is based on three main reactions: (1) generation of Ca(OH)(2) micelles by quick slaking of lime, (2) generation of AFt by active alumina reacting with CaSO4 and Ca(OH)(2), and (3) generation of CSH by active silica reacting with Ca(OH)(2). (C) 2012 Elsevier Ltd. All rights reserved.