Influences of Activity Index on Mechanical and Microstructural Characteristics of Carbonated Reactive Magnesia-Admixed Silty Soil

Carbonated reactive magnesia (MgO)-admixed soil is employed for stabilizing soft soil through absorbing gaseous CO2, which is an innovative and sustainable technique recently developed in the realm of ground improvement. With this in view, a systematic study that targets the influence of the MgO activity index (c(A)) on mechanical and microstructural characteristics of carbonated silty soil with different ratios of initial water content to MgO content (represented as w(0)/c) is initiated in this paper. In this context, the mechanical properties are investigated through unconfined compression tests, and the microstructural properties are obtained from X-ray diffraction, scanning electron microscopy, thermogravimetry, and mercury intrusion porosimetry analyses. The results demonstrate that cA and w(0)/c are the two crucial factors controlling the mechanical and microstructural characteristics of carbonated MgO-admixed soils. A simplified equation with combination of cA and w(0)/c is proposed for accurately predicting the unconfined compressive strength of carbonated MgO-admixed soils. The analyses of microstructural characteristics indicate that dypingite or hydromagnesite and plentiful crystalline nesquehonite play an important role in reducing the pore volume, and the latter is the primary micromechanistic reason for the strength gain of the carbonated MgO-admixed soils. (C) 2016 American Society of Civil Engineers.