The effects of admixtures on the durability properties of phosphogypsum-based cementitious materials

This study involved proportionally blending beta-hemihydrate phosphogypsum (beta-HPG) with raw phosphogypsum to prepare a phosphogypsum-based composite cementitious material (PGCM). The admixtures of quicklime (1-3%), cement (12-18%), and silica fume (5-9%) were selected to fabricate the PGCM mixture. The effect of each admixture on the durability performance of PGCM was evaluated using a single-factor experimental approach. The results showed that cement reduced significantly the dissolution rate and increased the strength coefficient, exhibiting the best effect on the antifreeze performance of PGCM. Quicklime and silica fume had no significant effect on the early antifreeze performance of PGCM but improved the later antifreeze performance. Moreover, the quicklime improved the weathering resistance of PGCM, whereas a high content of quicklime reduced the PGCM's strength coefficient. Silica fume improved the weathering resistance of PGCM in later phases, and cement had little effect on the weathering resistance of PGCM. Additionally, an increasing amount of cement significantly improved the water resistance of PGCM, and quicklime and cement significantly increased the length of PGCM specimens. Microscopic analysis showed that the generation hydration products mainly filled aggregate pores of raw phosphogypsum and enhanced raw phosphogypsum aggregates' interfacial adhesion, thereby improving the macroscopic mechanical and water resistance properties of PGCM. The findings on PGCM's durability properties can provide more theoretical foundations and technical supports for advancing phosphogypsum recycling.