| Due to lack of effective ways to utilize the bottom ashes of circulating fluidized bed combustion (CFB ashes), it is difficult to use widely the advanced technology of circulating fluidized bed combustion and defulfurization. In this paper, the properties of the CFB ashes are systematically analyzed and then a series of methods are proposed to evaluate the reactivity of CFB ashes. Meanwhile, the factors influencing and the method activating the reactivity of CFB ashes, and the expansion properties are investigated experimentally. The spontaneous setting, and the mechanism of activation of reactivity of CFB ashes and its expansion are investigated by XRD and SEM. Finally, the utilization in building materials of CFB ashes is studied.The results show that: (1) The CFB ashes is different from the ashes of common coal boiler for there are great difference in forming condictions such as the combustion temperature, combustion environment, the degree of combustion, desulfurizer and the efficiency of desulfurization. While CFB ashes have the properties of cement and expansion for its containing SO3 and f-CaO, so it is a special pozzolanic material. (2) The SO3 and f-CaO have their properties for their typical forming condition. SO3 is fixed in ashes at 850~900℃, and it exists in Ⅱ-CaSO4 and has different solubility with the natural anhydrite and the plaster calcined at 400℃. It is the first time to prove that the particles of f-CaO is coated withⅡ-CaSO4 by investigating the process of forming f-CaO, the microstructure, spathic type and optic parameter and the hydrating process. Results also show that the microstructure can slow down the hydrating and deteriorate the reactivity of CFB ashes. (3) The current method evaluating reactivity of pozzolanic materials has great limits to evaluate the CFB ashes. A series of new methods are developed which can evaluate the reactivity and its devotion to strength really and directly. (4) The reactivity of CFB ashes is attributed to the amorphous SiO2 and Al2O3, but the SO3 and f-CaO of CFB ashes can influence its reactivity and expansion, and there is an optimum content. The higher reactivity can be achieved if the fineness is bigger. (5) The common method can activate its reactivity, but the result of activation is not ideal in the point of strength. It shows that steam curing and high-pressure steam curing is best to activate CFB ashes, especially for high-pressure steam curing. (6) The expansion mechanism of CFB ashes is the expansion of the forming of ettringite and the solution and crystallization of Ⅱ-CaSO4. (7) Fineness is beneficial to stabilize the expansion ofCFB ash. FA and clinker are advantageous to reduce the expansion and stabilize expansion. The higher alkalinity in liquid phase is, the more expansion.The properties of CFB ashes show it is difficult to utilize CFB ashes in building materials, however reasonable using its properties is possible in building materials. As concrete fine aggregate, it can improve structure of interface between aggregates and cement paste for its reactivity, then can increase the concrete flexural strength. As concrete additive can fully activate the reactivity, and can partly compensate the concrete shrinkage. Because of performance of the fresh concrete and durability, it is better to use it with FA. They both influence performance of the fresh concrete. It can produce CFB ashes-fly ash mortar used indoors and CFB ashes-fly ash-clinker mortar used outdoors with low shrinkage by using the cement and expansion of CFB ashes. CFB ashes mixed with lime, FA or cement, can be used for roadbed mixture in road engineering...
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