Investigation on the hydration mechanism and water resistance of anhydrous-hemihydrate phosphogypsum-slag compound material
Year: 2025
Type: article
Abstract: To achieve precise regulation of the setting time in the anhydrite-GGBS system and meet diverse engineering demands for controlled hardening. In this study, anhydrous-hemihydrate phosphogypsum-slag compound material (PGSCM) was synthesized through the blending of HPG (Hemihydrate phosphogypsum) with APG (Anhydrous phosphogypsum) and GGBS, followed by activation using Ca(OH)2 solution. The setting time, compressive strength, and water resistance of PGSCM were tested by experiments. The hydration mechanism of the PGSCM was investigated through X-ray diffraction (XRD) and thermogravimetric analysis (TG-DTG). The hydration mechanisms of APG in water and Ca(OH)2 solution at the nanoscale had been clarified through molecular dynamics simulation. The results demonstrated that incorporating HPG enables precise regulation of the setting time in anhydrite-GGBS systems. The HPG0 (without HPG) exhibited an extended initial setting time of 136 minutes, whereas the addition of 10-20% HPG achieved significantly reduced setting times of 14-19 minutes. Notably, the addition of HPG retained its properties, maintaining a stable compressive strength of 45 MPa, controlling water absorption below 5%, and achieving a softening coefficient of approximately 0.85 at 28 days. The XRD and TG indicated that the addition of HPG can promote hydration and generate a large amount of CaSO4·2H2O to provide compressive strength at an early age. At 28 days, the sustained hydration of GGBS in Ca(OH)2 solution generated a substantial number of C-(A)-S-H, which enveloped both APG and CaSO4·2H2O. This physical encapsulation hindered their contact with water and OH⁻ ions, thereby resulting in only a small fraction of APG being hydrated. Molecular dynamics simulations revealed that the interaction energy of APG with Ca(OH)2 solution was significantly higher than that with water, while Ca2+ ions underwent rapid and substantial surface accumulation. Driven by the common ion effect, this synergistic mechanism markedly accelerated both the dissolution and crystallization processes of APG.
Source: Minerals Engineering
Authors: Junlin An, Guangcheng Long, Yutong Zhang, Ning Li
Institutions: Central South University, Qingdao University of Technology
Language: English
Subfield: Civil and Structural Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,220
OpenAlex ID: W7083306637