Effect of age, cement/tailings rate, and MK-GP dosage on mechanical features and evolution mechanism of cementitious paste fill

As the cost of cemented paste fill (CPF) is a major factor limiting its further dissemination since cement-related costs are high (∼70 % of total fill costs). In contrast, metakaolin-based geopolymer (MK-GP) can partly switch cement and states superior stability/strength. This paper takes full iron mine tailings as the research object, incorporating MK-GP to substitute for part of cement and preparing a new fill type. It mostly focuses on features like age, cement/tailings (c/t) rate, and MK-GP dosage. Using uniaxial compressive strength (UCS), thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) tests, this research aims at exploring the strength evolution pattern of CPF, clarify its microscopic features, and interpret its strength response mechanism. Results specify that the strength of CPF firstly rises and later falls by growing MK-GP dosage. When MK-GP content reaches 12 %, fill's strength reaches its peak. Besides, X-ray diffraction (XRD) and thermo-gravimetric-differential thermal analysis (TG-DTA) results show that calcium hydroxide (CH) initially increases and then decreases with adding MK-GP. Backfill strength exhibits a quadratic function link with the CH content. For a MK-GP content of 12 %, the amount of CH reaches its maximum. However, when the addition number of MK-GP increases to 16 %, the trend reverses, possibly due to an excessive amount of MK-GP increasing inter-particle connections, hindering further hydration, leading to a fall in hydration products and finally causing a drop in fill strength. Lastly, this study offers new visions intended for manufacturing new fill products and afford confident references for the engineering intention of fill mix ratios at other similar mining operations.