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A High-Phosphogypsum Multi-Solid-Waste Cementitious Binder for Backfill: Cross-Scale Insight into Pore Structure and
Jianhua Hu1, Xingjian Jiang1, Fengwen Zhao2
1Zijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, China.
Materials (Basel, Switzerland)
|May 27, 2026
Summary
This study demonstrates that clinker-free binders with 40% phosphogypsum (PG) can achieve sufficient strength for phosphate mine backfill. The binder
Area of Science:
- Materials Science
- Geotechnical Engineering
- Waste Valorization
Background:
- Phosphogypsum (PG) is a major industrial waste with limited application in cementitious materials due to strength reduction at high dosages.
- Developing sustainable binders using industrial waste is crucial for reducing environmental impact and resource consumption.
- Phosphate mine backfill requires cost-effective and environmentally sound materials to ensure stability and safety.
Purpose of the Study:
- To evaluate a novel clinker-free multi-solid-waste binder incorporating 40 wt.% phosphogypsum (PG) for cemented paste backfill applications.
- To investigate the relationships between hydration products, pore structure evolution, and strength development in PG-based binders.
- To assess the feasibility of using steel slag powder (SSP) and granulated blast-furnace slag (GBFS) as co-binders with PG.
Main Methods:
- Preparation of clinker-free binders with PG, SSP, and GBFS, using phosphate mine tailings and slime as aggregates.
- Assessment of uniaxial compressive strength (UCS) at 7 and 28 days.
- Characterization using X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR), coupled with image-based pore-structure analysis.
Main Results:
- AFt and C-S-H-like gels were identified as key hydration products contributing to pore refinement and strength gain.
- All tested mixtures met the minimum UCS requirements for backfill (0.5 MPa at 7 days, 1.0 MPa at 28 days).
- Porosity, pore probability entropy, and fractal dimension were negatively correlated with UCS, indicating their detrimental effect on strength.
Conclusions:
- The developed clinker-free binder containing 40 wt.% PG shows promising potential for sustainable cemented paste backfill in phosphate mines.
- The binder's performance is linked to the formation of specific hydration products and controlled pore structure development.
- Further research can optimize the binder composition for enhanced mechanical properties and long-term durability.
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