Mechanism of reactive magnesia - ground granulated blastfurnace slag (GGBS) soil stabilization

Reactive magnesia (MgO)-activated ground granulated blastfurnace slag (GGBS), with fixed GGBS dosages but varying MgO/GGBS ratios, was used for stabilization of two soils and compared with brucite (Mg(OH)(2))-activated GGBS and hydrated lime (Ca(OH)(2))-activated GGBS. A range of tests, including unconfined compressive strength testing, X-ray diffraction, and scanning electron microscopy, was conducted to study the mechanical, chemical, and microstructural properties of the stabilized soils, and then to investigate the mechanism of MgO-GGBS soil stabilization. Results indicate that the Mg(OH)(2) had a minimal activating efficacy for GGBS-stabilized soil, while the reactive MgO yielded a higher activating efficacy than the Ca(OH)(2). The activator-soil reactions in the stabilized soil slowed down the activating reaction rate for GGBS; this effect was less significant in MgO-GGBS-stabilized soil than in Ca(OH)(2)-GGBS-stabilized soil, and hence the GGBS hydration rate in the former was less reduced by the soil than the latter. The Mg2+ and OH-ions produced from MgO dissolution participated in the GGBS hydration reactions without precipitating Mg(OH)(2). The common hydration products in all GGBS-stabilized soils were calcium silicate hydrate-like compounds. Additionally, hydrotalcite and calcite could be produced in MgO-GGBS- and Ca(OH)(2)-GGBS-stabilized soils, respectively, especially with a high activator/GGBS ratio.