Recycling waste gypsum and calcium carbide slag for the production of all-solid-waste supersulfated cement

The appropriate use of industrial solid waste is an effective method for alleviating environmental pollution. In this study, the potential of using desulfurized gypsum (DG), phosphogypsum (PG), gypsum dihydrate (G), and calcium carbide slag (CS) in the production of supersulfated cement (SSC) was investigated. The effects of various types of gypsum and their dosages on the performance and hydration process of SSC were thoroughly examined. The results indicate that as the ratio of CS to gypsum (CS/G) increased, the pH of SSC increased, whereas fluidity and setting time decreased. For the same CS/G ratio, SSCs activated by DG and CS (D-CSSC) and by PG and CS (P-CSSC) exhibited longer setting times and lower pH values than those activated by G and CS (G-CSSC). Mineralogical analysis and microstructural characterization revealed that the type of gypsum influenced the hydration rate, microstructure, and hydration products (type and quantity) of the SSC, thereby affecting its compressive strength. The loose pore structure of G-CSSC significantly reduced its compressive strength. Owing to the formation of a significant amount of Calcium aluminum hydrate (C-A-H) gel, D-CSSC demonstrated greater early strength; however, hannebachite hindered its late strength development. PG continuously participated in hydration, leading to more hydration products and a denser microstructure in P-CSSC, which significantly increased its late strength. This study elucidates the effect of gypsum type on SSC performance and offers valuable insights for enhancing it.