Experimental study on mechanisms and applications of MgO-carbonated composite pile

A kind of MgO-carbonated composite pile (MCP) is proposed based on the MgO-carbonation solidification technology for soft soil improvement. The MCP is formed by injecting CO₂ gas into the MgO-mixing column through a gas-permeable concrete pile (inner core) to achieve carbonation. The laboratory model tests are conducted to analyze and demonstrate the application effectiveness of this technology in silt and silty soils, including the temperature, physical and mechanical characteristics during and after carbonation. The model test results indicate that under the full hydration of MgO in the mixing column, the carbonation reaction is relatively uniform at different depths. There are effective and maximum carbonation distances around the gas-permeable concrete pile, and satisfactory carbonation effects can be achieved within the effective carbonation distance. Then the formation mechanisms and influencing factors of the MCP are summarized. Field trials are carried out to confirm the engineering applicability of the MCP. The results demonstrate that the MCP exhibits good pile formation performance with high pile strength, with an average N-value of 39 for standard penetration tests. The ultimate vertical bearing capacity of the MCP is 1920 kN, which is 37.1% higher than that of the PHC (prestressed high-strength concrete) piles. The laboratory model tests and field trials have demonstrated that the MCP possesses both carbon fixation and reinforcement effects, which are of great significance for the low-carbon development of geotechnical engineering.