Preparation and microstructure of coal gangue-based geopolymer

The orthogonal experimental was used to study the influence of milling time, modulus of alkali solution, solid content and liquid-solid ratio on uniaxial compressive strength and elastic modulus of coal gangue-based geopolymer (CGGP). The microstructure difference of CGGP with different mechanical properties were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The results show that the uniaxial compressive strength and elastic modulus decrease with the increase of alkali solution modulus and liquid-solid ratio, but firstly increase and then decrease with the increase of solid content. The effect of solid content is the most significant, liquid-solid ratio and modulus are more significant, and ball milling time is the least. The SEM results show that the CGGP with higher uniaxial compressive strength have denser and smoother micro-physical surface without obvious coal gangue particle outline, indicating that the geopolymerization reaction is sufficient. The XRD spectra results show that the crystalline phase structure of CGGP is single, mainly quartz. The higher uniaxial compressive strength of CGGP have more Si(Al)-O structural types in wavenumber 1 200-950 cm-1 of FTIR spectra. The formation of CGGP can be characterized by the appearance of 27Al NMR narrow peak between chemical shift of 56.36×10-6-57.51×10-6 (AlQ4(4Si)) and 29Si NMR wide peak at between -93.18×10-6-88.66×10-6 (Q4(3Al)). © 2021, Editorial Board of Journal of CUMT. All right reserved.