Rheological behavior, mechanical strength, and hydration of hemihydrate phosphogypsum backfill material: Effect of...

Utilizing the cementitious characteristics of hemihydrate phosphogypsum (HPG) to dispose of dihydrate phosphogypsum (DPG) for mine filling, which contributes a new perspective for its resource application. Nevertheless, the poor workability of high-concentration slurry and the unclear compatibility between different superplasticizers and gypsum-based hydration systems remain key barriers. Moreover, the comparative mechanisms linking superplasticizer type with adsorption behavior, rheological evolution, hydration regulation, and microstructural development in hemihydrate phosphogypsum backfill material (HPBM) have not been elucidated. Herein, the compatibility of polycarboxylate superplasticizers (PS), melamine superplasticizers (MS), naphthalene superplasticizers (NS), and aliphatic superplasticizers (AS) with HPBM was evaluated, and the performance evolution was investigated. Results revealed that the fluidity and rheological properties of the paste were noticeably improved, attributed to the dispersing function of superplasticizers in disrupting the flocculation structure of the hydration system. Particularly, PS, MS, NS, and AS increased the paste fluidity by 65.44%, 56.62%, 47.79%, and 44.85%, respectively. Nonetheless, excessive superplasticizer dominated poor fluidity, potentially related to the paste separation phenomenon. The rheological behavior of fresh HPBM paste conformed to the Herschel-Bulkley model, where adding 0.9% PS reduced the yield stress by 103.777 Pa. It is worth noting that PS played a remarkable role in delaying setting time and maintaining paste flow capacity. Additionally, MS contributed to superior mechanical strength due to the promotion of the hydration process. Simultaneously, this was also reflected in the improvement of microstructure and optimization of pore characteristics. The research findings can provide guidance for optimizing the pipeline transportation performance of HPBM paste, facilitating the efficient and large-scale application of phosphogypsum in mine filling engineering.