Microscopic pore structure characteristics of magnesium slag-based backfill based on mercury intrusion porosimetry and scanning electron microscopy

The microscopic pore structure characteristics are of significant importance to the strength properties and engineering applications of magnesium slag-based backfill (MSB). The pore size distribution, porosity, specific surface area, and pore fractal characteristics of MSB were investigated using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Concurrently, SEM images were quantitatively processed to analyse various pore parameters within specific regions of the MSB. The results indicate that the cumulative mercury intrusion curve of MSB exhibits three stages: slow growth, rapid growth, and high-pressure rapid growth. With increasing curing age, the pore size distribution of MSB gradually concentrates around the dominant pore diameter range (10–100 nm), and the overall pore diameter decreases. As curing age increases, the MIP-derived porosity and specific surface area of MSB initially decrease and subsequently increase. Quantitative SEM analysis reveals that the pore probability entropy exceeds 0.95, the pore fractal dimension ranges from 1.17 to 1.25, and the average form factor ranges from 0.31 to 0.37. At the micropore scale (<10 nm) and minipore scale (10–100 nm), the backfill strength exhibits a significant positive correlation with the pore volume percentage. The SEM-derived porosity of MSB exhibits a significant negative linear correlation with compressive strength.