Effect of partial MgO replacement on the properties of magnesium oxychloride cement

Magnesium oxychloride (MOC) cement is a promising binder for various niche applications. It has many advantageous properties over Portland cement-based binders and could be used for a broader range of applications if its water resistance is improved. This paper assesses the potential of four supplementary cementitious materials (SCMs) to enhance its performance. Fly ash, slag, metakaolin and calcined iron-rich kaolinitic clay were added to magnesium oxychloride cement by replacing up to 30% of MgO. The effect on the fresh properties, compressive strength and water resistance of MOC cement was investigated. Analytical techniques such as XRD, TGA, NMR and SEM were used to assess mineralogy and microstructure. Unlike some previous studies, no significant additional reactions products were observed, regardless of the SCM employed. Findings also indicated that the water resistance of magnesium oxychloride cement paste increased with replacement of MgO by SCMs, particularly when metakaolin was used. The particle size distribution was one of the main differences between the different SCMs used suggesting the need for a detailed study focused on the effect of particle size on the performance of additives within MOC cement.