Evolution of water migration in fresh ultrafine tailings cemented paste backfill containing anionic polyacrylamide

• Identify three water states (adsorbed, floc, free water) in fresh UTCPB and their residual APAM-regulated migration via NMR. • 20 g/t is determined as optimal APAM dosage, balancing flowability (free water) and stability (floc network) to reduce pipeline blockages. • Propose "quasi-active water" (floc water + free water) as the key factor governing UTCPB pipeline transport performance. Anionic polyacrylamide (APAM) flocculants used for efficient thickening of ultrafine tailings exert a profound influence on the moisture distribution within fresh ultrafine tailings cemented paste backfill (UTCPB) during pipeline transportation. This study systematically investigated the influence of residual APAM on water migration and flow characteristics in fresh UTCPB by employing nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and fractal dimension analysis for quantitative characterization of water states and microstructural evolution. Key findings indicate the presence of three distinct water states in fresh UTCPB: adsorbed water, floc water, and free water. The highest free water content in fresh UTCPB containing residual APAM was observed at 20 g/t APAM. Microstructural analysis revealed enhanced particle aggregation and reduced internal pore space in fresh UTCPB with increasing residual APAM dosage. Quasi-active water (defined as the sum of floc water and free water) was identified as the primary factor regulating pipeline transport performance. The primary conclusion is that an optimal residual APAM dosage of 20 g/t balances free water retention for flowability and structural stability, thereby minimizing the risk of pipeline blockage. This study provides critical theoretical and parametric support for the safe pipeline transportation of flocculant-containing fresh UTCPB.