On the incorporation of class F fly-ash to enhance the geopolymerization effects and splitting tensile strength of the gold mine tailings-based geopolymer

Mine tailings (MTs) are ore residuals after valuable metals were extracted during mineral processing, which can be reused to produce the geopolymer concrete for construction and building applications, to mitigate the storage, economic, and environmental pressures. However, the pure MTs did not have enough reactive aluminum or amorphous aluminosilicates for better geopolymerization effects. It is necessary to add other materials as the additional aluminum source and amorphous additives to change the Si: Al ratio for better geopolymerization. In this study, class F fly ash (FA) was utilized as the additional aluminum source to adjust the Si: Al ratio for better geopolymerization effects. Raw materials (MTs and FA) were first characterized by performing a series of laboratory tests, such as X-ray diffraction (XRD), scanning electron microscopy with Energy dispersive X-ray analysis (SEM-EDS) and Fourier-transform infrared spectroscopy (FTIR). The Brazilian indirect tensile tests (BT) were conducted to evaluate the influence of different FA additions, 5%, 10%, 15%, and 20%, on the tensile strength of the geopolymer. Moreover, the microscopic morphological, chemical, and mineralogy properties of the geopolymer with different FA additions were evaluated by using SEM/EDS and FTIR respectively. Finally, digital image correlation (DIC) was used to track the strain behavior of the specimen surface during BT loading. Results show that at currently moisture content, the adding of FA can increase the mechanical behavior. However, due to the lacking of water for addition geopolymerization, the tensile strength of the geopolymer when adding 20% FA decreased comparing to 15% FA addition. The splitting tensile strengths experience a first increase followed by a decrease with the FA addition at current water to MTs ratio. SEM micrographs show that the geopolymer gel was getting more homogeneous when adding FA. FTIR spectrums show that the absorption band shift at 1000 cm-1 indicates the formation of new produced amorphous geopolymer phase.