The impact of slag on the process of geopolymerization and the mechanical performance of mine-tailings-based alkali-activated lightweight aggregates

Abstract

Alkali-activated lightweight aggregates (LWAs) made of alkali-activated aluminosilicate-rich mine tailings (MTs) offer a promising alternative to natural lightweight aggregates. The comprehensive investigation of lightweight aggregate production using aluminosilicate-rich MTs in combination with commercial slag as a reactive aluminosilicate remains largely unexplored. In this study, mixtures of MTs and slag were pelletized through the application of a pan pelletizer machine. The study focused on examining the impact of different slag concentrations on the chemical, physical, mechanical, mineralogical, and morphological properties of the produced LWAs. Furthermore, a comparison was made between the physical and mechanical characteristics of the resulting LWAs and those of flay-ash (FA)-based LWAs. The results revealed that the inclusion of slag in LWAs, as compared to FA, led to the production of LWAs with superior physical and mechanical properties. Specifically, as the slag content increases, the water absorption, dissolution, and porosity of LWAs significantly decreased, while the bulk density and compressive strength increased. It is important to note that these changes occur without affecting the specific gravity of the LWAs. The scanning electron microscope (SEM) images clearly showed that the addition of slag, similar to FA, especially at concentrations of more than 20% and higher, promoted uniform geopolymerization within the specimens. Furthermore, the energy-dispersive X-ray spectroscopy (EDS) analysis revealed that all LWAs with concentrations of 20% slag and higher exhibited a Si:Al ratio exceeding three, indicating a higher likelihood of geopolymer backbone formation. The X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) analyses revealed that the alkali activation process led to the depletion of gypsum, originally present in the MTs, and the emergence of sodalite and zeolite in the LWAs. Thermogravimetric analysis (TGA) tests provided additional confirmation of the ongoing geopolymerization process in slag-based LWAs, particularly those containing 20% slag or higher.