Research on the Effect of Sodium Aluminate on the Early Performance Enhancement and Mechanism of Phosphogypsum-Based Cementitious Materials

Phosphogypsum (PG) is used to prepare eco-friendly cementitious materials, representing a high-value resource utilization approach. However, there are some shortcomings, such as a long setting time and low early strength in phosphogypsum-based cementitious materials (PBCMs), which limit their engineering applications. This work aimed to improve their early performance by adding sodium aluminate. In particular, the effects on the compressive strength, setting time, and fluidity of PBCMs were investigated. Additionally, the effect of sodium aluminate on hydration was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the addition of sodium aluminate results in a significant enhancement in 3 d compressive strength and an obvious procoagulant effect on setting time in PBCMs. When the content of sodium aluminate reaches 1 wt.%, the 3 d compressive strength of PBCMs can reach 10.72 MPa. Compared with the control group (A0, without sodium aluminate), the 3 d compressive strength is improved by 587.39%, and the final setting time is shortened by 4 h 4 min. The microscopic test results show that sodium aluminate can provide sufficient aluminum components at the early stage of hydration, which could effectively enable more phosphogypsum to participate in hydration and accelerate the early part of the process of the hydration reaction. This is conducive to increasing the number of early hydration products of ettringite (AFt) and C-A-S-H gel to improve the early compressive strength and shorten the setting time.