Field Testing and Validation of CFG Piles Made with Basic Magnesium Sulfate Cement Concrete

Cement-fly ash gravel (CFG) piles are widely used for soft soil ground improvement. However, their conventional binder, ordinary Portland cement, is a high-carbon material and thus does not align with the current emphasis on low-carbon development. Based on the current research situation, this study proposes to replace traditional Portland cement concrete with low-carbon modified basic magnesium sulfate cement concrete (BMSCC) and apply it to the engineering of soft foundation CFG piles for feasibility analysis and preliminary verification. Through laboratory mix proportion tests, a BMSCC mix with 20% BMSC content was determined, achieving a 28-day standard-cured compressive strength of 24.7 MPa. Field validation was then performed on the soft soil subgrade of the Tiantian Expressway (Tongling Section), where test sections using BMSCC and control sections following the original design were established. Single-pile composite foundation static load tests and core drilling strength tests were conducted. The test sections exhibited a characteristic bearing capacity of 180 kPa for the single-pile composite foundation. The representative strengths of the core samples were 22.6 MPa and 25.8 MPa, showing close agreement with the standard-cured strength of 24.7 MPa. All results met the original design requirements. The test results demonstrate that the static load p-s curves of the BMSCC piles exhibit a gradual transition, indicating effective pile-soil interaction. This confirms that the construction process offers good strength stability and site adaptability. Although the mix with 20% BMSC content adopted in this application is higher than the 7.64% cement content in conventional mixes, the study successfully verifies the reliability of BMSCC for soft-ground CFG pile engineering. Furthermore, it reveals significant potential for further optimization of the mix proportion and cost reduction by referencing existing research, thereby presenting a new technical approach for low-carbon ground treatment.