Effect of Fly Ash on Rheological Properties of Magnesium Oxychloride Cement

This paper studies the effect of fly ash on rheological properties of magnesium oxychloride cement (MOC) paste. Six different dosages of fly ash (0%, 15%, 20%, 25%, 30%, and 35% by weight of MgO) samples are prepared to investigate the rheological properties of fly ash–magnesium oxychloride cement (FA-MOC) paste. The effects of fly ash on fluidity, setting times and mechanical properties of MOC paste are measured. Phases and microstructures of FA-MOC paste are analyzed by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). An optical microscope is used to evaluate the flocculation of fresh FA-MOC paste. The results reveal that fly ash can improve fluidity and retard the setting time of MOC paste. The water-absorbing ability and the morphology effect of fly ash have combined effects on the rheological properties of FA-MOC paste. At the same time, the results show that fly ash used in MOC paste does not change the phases composition of hardened paste, but increases the amount of 5Mg(OH)2·MgCl2·8H2O (Phase 5). However, fly ash weakens the structure of hydration products and results in poor mechanical properties of MOC paste.