Performance and microstructural analysis of modified magnesium oxysulfate cement with additions: Roles of FA and GGBS

Magnesium oxysulfate (MOS) cement, with its low carbon footprint, faces challenges in water resistance and volume stability. This study examines how fly ash (FA) and ground granulated blast-furnace slag (GGBS) improve MOS cement properties. Findings show that adding FA and GGBS significantly enhances the mechanical properties, water resistance, and volume stability of MOS cement. An optimal admixture content of 45 % and an FA to GGBS ratio of 2:1 increase compressive and flexural strengths to 71.8 MPa and 16.5 MPa. The study also reveals that FA and GGBS do not introduce new hydration crystalline phases and limited secondary reactions occur due to the low alkalinity of MOS cement. The improvement of MOS cement is primarily attributed to the micro-aggregate effect, which optimizes the pore structure by reducing harmful pores and total porosity. The findings suggest that FA and GGBS are effective in enhancing the performance of MOS cement.