Effect of the phosphogypsum calcination time on the compressive mechanical properties of phosphogypsum-based composite cementitious materials

In this study, phosphogypsum-based composite cementitious materials (PGCMs) were prepared by adding fixed proportions of additives to calcined phosphogypsum (PG). Samples with dimensions of 40 × 40 × 80 mm and 150 × 150 × 300 mm were used to study the effect of the PG calcination time on the PGCM compressive strength, stress–strain relationship, and failure mode and its mechanism. The test results indicated that the PGCM compressive strength gradually increased as the calcination time increased. When the PG calcination time was 180 min, the compressive strengths of the smaller and larger samples increased by 3 and 3.6 times, respectively, compared with the strengths at a calcination time of 20 min. The main reason for the strength increase was the formation of ettringite and hydrated calcium sulfate dihydrate in the PGCM gel system. Additionally, the PGCM compressive strength was significantly related to the sample size, and its reduction coefficient was between 0.60 and 0.69 at different PG calcination times. As the PG calcination time increased, the peak stress of the PGCM stress–strain curve and the corresponding axial strain increased gradually; moreover, brittle failure became more evident.