Effects of curing age and magnesium slag grinding time on mechanical properties and hydration characteristics of magnesium slag-based backfill materials

Through comprehensive analysis methods, including uniaxial compression tests, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, the macroscopic mechanical properties and microscopic hydration mechanisms of magnesium slag-based (MS-based) backfill under different curing ages (3, 7, and 28 d) and different MS grinding time (0, 40, 60, and 80 min) were systematically investigated. The effects of these two variables on the deformation characteristics and compressive strength of MS-based backfill were examined. Additionally, the influence mechanism of MS grinding time on the micro-morphology and hydration products of MS-based backfill was elucidated. The results suggest that the stress-strain responses of MS-based backfill under different conditions exhibits typical four-stage evolution characteristics. Grinding time has a promoting effect on the strength development of MS-based backfill. When the grinding time is 80 min, the strengths of the backfill at 3, 7, and 28 d reaches 1.558, 3.110, and 10.975 MPa, respectively, meeting the strength requirements of typical mine backfill. Linear and quadratic polynomial functions effectively illustrate the relationship between both curing age as well as grinding time with respect to compressive strength in MS-based backfill. The application of grinding activation treatment proves beneficial in enhancing hydration among MS particles while significantly increasing hydration products within the MS-based backfill. The diffraction peak intensity of the Ca(OH) 2 decreases with increasing curing age, while the diffraction peak intensity of the C-S-H increases. The grinding activation treatment of MS improves the microstructure characteristics of MS-based backfill and enhances the micro-densification degree of the backfill. The content of C-S-H gels in the ground MS-based backfill has increased, leading to the intertwinement of agglomerates and filamentous gels, which together form a denser network structure. The research results can be used as a theoretical foundation to encourage the utilization of MS in mine filling.