Multi-scale valorization of high-volume fly ash backfill: Synergistic regulation of hydration kinetics and energy evolution by sodium lignosulfonate

The valorization of high-volume fly ash (HVFA) in cemented backfill is a critical strategy for sustainable mining but is often hindered by the technical trade-off between slurry fluidity and mechanical strength development. This study investigates the synergistic regulation of sodium lignosulfonate (SL) on HVFA backfill, employing a multi-scale approach that integrates rheological tests, mechanical testing with Digital Image Correlation (DIC), energy evolution analysis, and quantitative microstructural characterization via Thermogravimetric Analysis (TGA) and X-ray Diffraction (XRD). Results indicate that an optimal SL dosage of 0.3 % effectively balances workability and setting properties, increasing slump by 9.6 % while maintaining a controllable setting delay. Crucially, quantitative hydration kinetics analysis reveals a distinct reversal in performance over time: while SL retards early-age hydration, the 0.3 % dosage significantly enhances long-term reaction efficiency. At 28 days, this optimal dosage achieved the highest chemically bound water content of 16.17 % (surpassing the 15.83 % of the control group) and a ∼22 % reduction in residual C 3 S peak intensity, providing robust evidence for enhanced cement hydration and pozzolanic activity. This microstructural densification directly dictates the macroscopic failure mechanism: DIC and energy analysis demonstrate a transition from ductile, energy-dissipating damage to a stable, energy-storage-dominant mode with localized fracture. We establish a clear process-structure-property relationship in SL-modified HVFA systems, providing a scientific basis for engineering high-performance, low-carbon mining backfill. • 0.3 % sodium lignosulfonate increased slump by 9.6 % and 28-day UCS by 2.7 %. • TGA confirms 0.3 % SL yields the highest bound water (16.17 %) for densification. • XRD shows a ∼22 % reduction in residual C 3 S intensity at the optimal dosage. • DIC reveals a transition to stable, energy-storage-dominant localized fracture. • SL regulates hydration kinetics to overcome the rheology-strength trade-off.