Setting Time Optimization of Excessive-Sulfate Phosphogypsum Slag Cement for Self-Compacting Concrete Based on a Paste Rheological Threshold Theory

Abstract

The accumulation of phosphogypsum (PG) has become a significant environmental and economic challenge, making PG reuse an urgent concern. This study aims to explore the potential of combining PG with steel slag (SS), ground granulated blast-furnace slag (GGBS), and cement clinker (CC) to create excessive-sulfate phosphogypsum slag cement (EPSC) for use in self-compacting concrete (SCC). However, residual acid and other impurities in PG can significantly slow down the setting time of EPSC. To optimize the setting time, different methods including wet grinding, washing, and the addition of pure gypsum, limestone powder (LP), and aluminum cement (AC) are used. Results show that the wet grinding method and washing method remove soluble phosphorus impurities and reduce fluorine ion levels by 64%. However, nonsoluble impurities that cannot be removed by wet grinding and washing continue to affect EPSC’s setting time. Furthermore, the addition of LP shortens the setting time, but not enough. Using a 3% dosage of AC successfully reduces the setting time to a satisfactory level and EPSC SCC with a 28-day strength greater than 40 MPa is produced using the paste rheological threshold method.