Experimental investigation on expansion characteristics and strength of carbonating reactive magnesia solidified clay

Abstract

The carbonated reactive magnesia (CRM) method is superior in energy conservation, carbon capture, and rapid solidification in soil improvement. It has been revealed that CRM method could cause apparent volumetric expansion during carbonation, which may cause apparent compaction impact on the surrounding soils when used for soft foundation improvement. However, this expansion hasn’t been discussed systematically. In this study, the evolutions of expansion stress (σEx) and volumetric expansion (ΔV) during carbonation process were successfully monitored. Two factors, including reactive MgO content (Cm) and net confining pressure (Pnc), were investigated. The internal relations between σEx, ΔV, and unconfined compressive strength (UCS) together with the influences of Cm and Pnc on them were discussed. Besides, the intrinsic mechanisms were discussed based on density variations, pore structures, and microstructures. According to the findings, σEx and ΔV invariably exhibited a three-stage behavior consisting of stability-rapid increase-stability. By increasing Cm or Pnc, the σEx, UCS, and density were all significantly increased, while the volume increment was obviously reduced. For the completely confined specimen, the σEx and UCS were found to approach 3 MPa and 9 MPa, respectively. The increase in Cm promoted the crystallization of hydrated magnesium carbonates (HMCs), leading to lower porosity in solidified soils. Increasing Pnc also improved the crystallization of HMCs and modified pore structures, causing further increases in σEx and UCS.

Keywords

• Carbonated reactive magnesia
• Expansion stress
• Volumetric expansion
• Confining pressure
• Clay