Effects of Different Reactive MgOs on the Hydration of MgO-Activated GGBS Paste

Abstract

Reactive MgO has recently emerged as a potential activator for ground-granulated blast-furnace slag (GGBS), which is one of the most widely used by-products in the cement industry. However, it is known that the characteristics of reactive MgO vary significantly, which may affect the activation process and hence the performance of MgO-GGBS blends. In this study, seven commercially available reactive MgOs, whose characteristics vary widely, were chosen to activate GGBS. The unconfined compressive strength (UCS) of MgO-GGBS pastes up to 90 days was measured, and the hydration products were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The primary hydration products were identified as calcium silicate hydrate (C-S-H) and hydrotalcitelike phases (Ht). Minor hydration products included magnesium silicate hydrate (M-S-H) and ettringite. The reactivity and calcium oxide content of the MgO samples were found to be the two major factors affecting the hydration process of the MgO-GGBS blend. Higher reactivity did not change the hydration products, but resulted in more hydration products in the same time. Sufficient CaO content increased the pH of the system, which enhanced the slag dissolution degree and was beneficial to the strength development.