Reactivity of Raw Mine Tailings with Supplementary Cementitious Materials

This study further investigates the microstructural and chemical evolution of cementitious pastes incorporating raw milled mine tailings (MT) in combination with metakaolin (MK), silica fume (SF), and slag (SG) as supplementary cementitious materials (SCMs) for sustainable binder development. Five binder systems were prepared at a constant water-to-binder ratio of 0.50. Microstructural and elemental analyses were performed using SEM and EDS to examine the morphology, elemental distribution, and compositional ratios (Ca/Si, Ca/Al, and (Ca + Al)/Si) associated with hydration and pozzolanic activity. The results showed that replacing cement with raw mine tailings alone produced a porous and weakly bonded matrix dominated by unreacted silicate and ferric phases due to the tailings’ low reactivity. However, combining mine tailings with reactive SCMs substantially enhanced the hydration products and matrix densification. The incorporation of metakaolin promoted alumina substitution within the C–S–H structure, while silica fume generated the most refined and homogeneous microstructure through rapid secondary C–S–H formation. The silica fume blend exhibited the lowest Ca/Si (3.97) and (Ca + Al)/Si (4.38) ratios, indicating advanced silica polymerization and efficient calcium hydroxide consumption.