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 using 1H NMR T1–T2 correlation 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.