Research on the application of phosphogypsum in magnesium oxysulfate cement: A comparison with sand

Phosphogypsum (PG), as an industrial by-product, has historically suffered from challenges in achieving efficient utilization, resulting in enormous accumulation and environmental contamination. In this study, a certain proportion of PG was employed as a substitute for sand in magnesium oxysulfate cement (MOSC). The effects of PG on the properties, pores distribution, phase composition and microstructure of MOSC were investigated. The results showed that the introduction of PG yielded several beneficial effects, including enhanced volume stability and water resistance, alongside reduced apparent density. However, it also entailed several drawbacks, such as decreased paste flowability, prolonged setting time and increased water absorption rate of the specimens. PG incorporation induced no new crystalline phase, but moderate PG could promote nucleation and development of 5Mg(OH)2 center dot MgSO4 center dot 7H2O (5 center dot 1 center dot 7 phase) and the group at 10% PG substitution has the highest compressive strength of 68.2 MPa. PG demonstrated the capability to hinder precipitation of Mg(OH)2, thereby enhancing the mechanical properties of MOSC. Due to the affordability and favorable environmental sustainability, PG-MOSC displayed considerable potential for various applications. This study elucidates the mechanism by which PG influences MOSC, providing reference and approach for the recycling of PG.