Effects of nano-Al2O3 dosage on pyrolysis kinetics and formation of hydration products in tailings wet shotcrete

The use of tailings as aggregate for the preparation of wet shotcrete is one of the most important technical approaches to the sustainable development of mines. In this study, the pyrolysis kinetics of tailings wet shotcrete with different Nano-Al2O3(NA) dosage and the formation mechanism of hydration products are carried out based on the theory of pyrolysis kinetics and various micro characterization methods. The findings show that 1% NA dosage(NA1) specimen significantly improves uniaxial compressive strength by 48.72% and 34.69% compared to NA0 and NA2, respectively. Pyrolysis of concrete has 3 stages: dehydration of ettringite(AFt) and calcium silicate hydrate(C-S-H), dehydroxylation of calcium hydroxide(CH), and CO2 release from calcium carbonate decomposition. These stages conform to the S-B model. The average apparent activation energy for NA1 specimen during the first pyrolysis stage is 114.01 kJ/mol, indicating an increased energy barrier for the pyrolysis of hydration product, which diminishes when NA dosage exceeds 1%. Furthermore, NA1 specimen exhibits enhanced kinetic parameters, including a notable increase in the preexponential factor during the first pyrolysis stage. This suggests higher activation and effective collision of molecules, leading to optimal AFt and C-S-H formation at 1% NA dosage. Microscopic and thermal analyses reveal that NA aids TWSC hydration through gap filling, nucleation, bond-breaking recombination on tailings surfaces, and calcium (alumino) silicate hydrate(C(A)-S-H) formation. This process augments hydration product generation, decreases microstructural porosity, and enhances macroscopic strength. However, exceeding 1% NA dosage inversely affects these properties, highlighting an optimal NA concentration for maximizing TWSC performance.