Improving strength of calcinated coal gangue geopolymer mortars via increasing calcium content

In this study, the calcinated coal gangue was mixed with granulated blast furnace slag (GBFS) and slaked lime in making geopolymer based on increasing calcium content to improve the strength. Besides, the coal gangue geopolymer were characterized for performance, phase transformation, molecular structure and microstructure by means of Thermogravimetric Analysis (TGA), X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), and Scanning Electron Microscope (SEM) analysis. Results showed that low content of active calcium in coal gangue was the main reason for low strength of geopolymer. The strength of geopolymer improved gradually with the increase of GBFS and slaked lime due to the addition of activated calcium content. However, the increase of the compressive strength of geopolymer was not obvious when the content of GBFS was more than 40%, and the compressive strength of geopolymer dropped sharply when the slaked lime content exceed over 5%.