Abstract
MgO based cement for the low-temperature calcination of magnesite required less energy and emitted less $CO_2$ than the manufacturing of Portland cements. Furthermore, adding reactive MgO to Portland-pozzolan cement can improve their performance and also increase their capacity to absorb atmospheric $CO_2$. In this study, the basic research for magnesia cement using $MgCO_3$ and magnesium silicate ore (serpentine) as starting materials was carried out. In order to increase the hydration activity, $MgCO_3$ and serpentinite were fired at a temperature higher than $600^{\circ}C$. In the case of $MgCO_3$ as starting material, hydration activity was highest at $700^{\circ}C$ firing temperature; this $MgCO_3$ was completely transformed to MgO after firing. After the hydration reaction with water, MgO was totally transformed to $Mg(OH)_2$ as hydration product. In the case of using only $MgCO_3$, compressive strength was 35 $kgf/cm^2$ after 28 days. The addition of silica fume and $Mg(OH)_2$ led to an enhancements of the compressive strength to 55 $kgf/cm^2$ and 50 $kgf/cm^2$, respectively. Serpentine led to an up to 20% increase in the compressive strength; however, addition of this material beyond 20% led to a decrease of the compressive strength. When we added $MgCl_2$, the compressive strength tends to increase.
