Influence of Initial Moisture and Reactive MgO Content on Mechanical and Microstructural Characteristics of Carbonated Reactive Magnesia Treated Soft Clay

Abstract

Soft clay presents many problems in the construction of infrastructures, which can be well solved by using effective solidification materials and technologies. The carbonated reactive magnesia (CRM) comes to the fore for its superiority in energy-saving and high solidification efficiency. Nevertheless, research on the applicability of CRM in soft clay solidifying is limited. In the current study, two major factors, including initial moisture content (w0) and reactive MgO content (Cm), were examined by measuring the unconfined compressive strength (UCS), mass and volume variations, and moisture content variation of CRM-treated soft clay. The intrinsic mechanisms were discussed based on the mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The findings reveal that carbonated specimens with low Cm (≤ 25%) or w0 (≤ 25%) suffer from severe volumetric expansion and cracks, which cause serious reductions in UCS, and the strength of these specimens can be even much lower than that of the uncarbonated ones. Specimens with high Cm and w0 acquire satisfactory strength by carbonation, and the highest UCS can exceed 4 MPa, indicating that the CRM is capable of solidifying soft clay. Water and MgO are both vital for the crystallization of hydrated magnesium carbonates (HMCs), and Cm is also beneficial for restricting volumetric expansion and reducing macropores; while proper w0 is required for the formation and evolution of HMCs, especially the nesquehonite.