## 3 Results and Discussion
### LF-NMR Analysis  
Water, as the main dispersion medium of backfill slurry, provides an efficient medium for particle-to-particle contact through changes in its existence. LF-NMR was utilized to determine the transverse relaxation time T\({}_{2}\) of \({}^{1}\)H protons of water molecules in different DSPB at 15, 30, 45, and 60 min. The higher the T\({}_{2}\) peak, the more free water molecules in the slurry. Because the water in the slurry is related to the agglomeration structure of the solid particles and the hydration reaction products, understanding the rate of diffusion and exchange of water molecules between the free and bound water can help to study the rheological properties and the solidification process. The T\({}_{2}\) profile can be categorized into four peaks, with T\({}_{24}\) usually appearing after 15 min of reaction, of which T\({}_{21}\) (0.1-0.5 ms), centered at 0.2 ms, and T\({}_{22}\) (1-2 ms), centered at 1.5 ms, represent the water in slurry capillaries (bound water); T\({}_{23}\) (10-60 ms) represents a large amount of free water in the inter-particles; and T\({}_{24}\) (100-700 ms) represents a small amount of free water within large pores in the slurry [77]. Figure 11 shows that the T\({}_{21}\) and T\({}_{22}\) peaks of HCDA80 were the highest, and the peaks decreased with the increase in HCDA amount, reaching the lowest value at HCDA95 and remaining consistent throughout the 60 min reaction process, which indicates that the proportion of capillary water was higher when the HCDA doping amount was 80%. The two peaks of T\({}_{23}\) and T\({}_{24}\) can be defined as the oozing water and unreacted water in the slurries [78]. T\({}_{23}\)Control \(>\) T\({}_{23}\)HCDA85 \(>\) T\({}_{23}\)HCDA80 \(>\) T\({}_{23}\)HCDA95 throughout the 60 min, and its peak area decreased with reaction time, with the greatest reduction at 15-30 min. This indicates that when the HCDA doping was 90%, the more unexplored pores there were in the system, the higher the free water content was, and the more and larger the generated drain channels were, the larger the particle spacing was. With the increase in reaction time, the free water content decreased more at 30 min, when the fluidity became worse, which is also consistent with the mini-slump value decreasing more obviously at 30 min. Therefore, high free water content in slurries is a key element in improving and preserving the rheological properties. At the same time, the peak of T\({}_{24}\) began to appear. This is because the hydration products C-S-H gel and ettrinigite began to be generated, the hydration products were agglomerated and adsorbed to each other, and the early microstructure of the slurry began to be generated, with the appearance of a small amount of free water that existed in the large pores [43]. Figure 12 shows that T\({}_{21}\), T\({}_{22}\), and T\({}_{23}\) of PCE0.3 were the highest in all the samples, and the peak of T\({}_{23}\) of PCE1.2 was the maximum at 30 min. As the reaction time continued to be extended, the highest value was still PCE0.3. Throughout the reaction process of 60 min, the peak area of T\({}_{23}\) did not change much with time, which indicates that the addition of PCE had a significant effect on the retention of free water content in the system, which was conducive to maintaining the good fluidity of the slurry. As shown in Figure 13, when no activator SS was added, the T\({}_{23}\) peak was the highest and significantly higher than that of the other samples with added activators, while the T\({}_{21}\) and T\({}_{22}\) peaks were smaller than those of the other groups and the peaks were left-shifted. This indicates that the hydration degree of the sample without activator was much smaller than that with the addition, at which time there was less generation of small void structures in the slurry, a lower proportion of capillary water, a slower rate of hydration reaction, and less free water consumed.