Pore Structure Evolution of Cemented Paste Backfill Observed with Two-Dimensional NMR Relaxation Correlation Measurements

Cemented paste backfill (CPB) technology is a favored approach with which to dispose of solid mining waste in underground voids. Knowledge of the evolving material properties of CPB under the conditions of hypersaline water-initiated hydration is crucial for its enhanced utilization as passive support material in mining operations. Here, we investigate the hydration behavior of CPB samples using1H NMRT1-T2correlation measurements at a low magnetic field (2 MHz), contrasting hypersaline and tap-water-hydrated CPB comprising 5 wt % cement binder for up to 28 days. Our results reveal a complex and rapidly evolving hierarchical pore network within the CPB structures. Relaxation peaks are assigned to a combination of pore water populations and pore-to-pore exchange dynamics with the aid of additional relaxation-exchange correlation measurements. Differences in the hydration behavior of hypersaline and tap-water-hydrated materials are further discussed in terms of observed exchange processes and evolving pore surface chemistry.