Research on the Ettringite Formation in Cementitious Material of Spontaneous Combustion Coal Gangue

The ettringite formation of active Al_2O_3 in the spontaneous combustion coal gangue cementitious material is analyzed by XRD.The results show that active Al_2O_3 hydrates with sodium sulfate to form ettringite.How- ever,in the same condition when the same content sulfate comes from gypsum there is ettringite and unhydrated gyp- sum in the hydration pastes.When it hydrates with sodium sulfate and no white lime,at first the gypsum is formed and with the process of hydration the gypsum transfers into ettringite.At the same time,when the hydration goes with white lime,the ettringite is formed directly.The slag promotes the hydration of active Al_2O_3 in spontaneous combus- tion coal gangue to form ettringite.