Swelling and behavioral transformation of magnesia-sand mixtures: experimental characterization of physical properties and undrained shear strength

Magnesia-based refractories (magnesia) are the second most used refractories worldwide and are generally discarded in landfills after their service life even though they are highly expansive when in contact with water. Thus, to ensure the safe disposal of magnesia and to enable the use of landfill areas as future construction sites, it is important to investigate the physical and mechanical behavior of magnesia-containing soil. In this study, the physical properties, swelling characteristics, and undrained shear response of magnesia–sand mixtures at various magnesia contents were measured and compared before and after hydration. After hydration, the behavior of the magnesia changed from a sand-like behavior to a clay-like behavior, where the change in behavior was accompanied with a reduction in the particle size and an increase plasticity. In addition, the swelling strain (SS) and swelling pressure of the magnesia-sand mixtures increased with an increase in the magnesia content in the mixture, showing high expansivity (SS > 25%) compared to that of natural expansive soil. Before hydration, the magnesia content had no significant effect on the average normalized peak shear strength (S_u/σ′_c = peak shear strength/confining pressure) of the magnesia–sand mixture. However, after hydration, the average S_u/σ′_c of magnesia–sand mixture decreased with an increase in the magnesia content. Particularly, the average S_u/σ′_c of pure hydrated magnesia was comparable to that of normally consolidated clay.