Cemented paste backfill (CPB) comprising mineral tailings, binders and mixing waters is an important potential support material in the mining industry. As the mechanical properties of CPB are significantly influenced by its microstructural characteristics the development of measurement tools to better understand its pore structure evolution is important for its increased utilisation. This study reports the application of low-field nuclear magnetic resonance (NMR) relaxation time measurements to characterise the microstructural evolution of CPB materials over 56 days of hydration, contrasting common tap water and hypersaline water (~22 wt% salt) as mixing waters. Distinct NMR relaxation time populations were evidenced within each CPB sample, revealing the presence of both capillary (T1,2 ≈ 10 ms) and gel pore water (T1,2 ≈ 300 -500 µs), with time-dependent relaxation measurements facilitating characterisation of capillary pore structure evolution over the hydration period assessed. Hypersaline samples demonstrated a time-lag in this measured capillary pore evolution, relative to those hydrated with tap water, while pore structure evolution rates were observed to increase with increased CPB binder content. Further, both T1 and T2 NMR relaxation times were found to correlate with the uniaxial compressive strength of the CPB materials investigated, facilitating the formulation of a predictive correlation function between NMR relaxation characteristics and mechanical properties.

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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 1 H NMR T 1 −T 2 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.

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