Long-Term Performance Evolution and Micromechanism Analysis of SRPC and OPC Concrete Test Piles Fully Embedded in Saline Soil

Abstract Concrete structures buried in saline soil environments are concealed and difficult to monitor. Sulfate-resistant cement has been widely used in early sulfate corrosion environments, yet an objective evaluation of its performance under real-world conditions remains urgently needed. In this study, test piles of ordinary portland cement concrete (OPCC) and sulfate-resistant portland cement concrete (SRPCC) were embedded in the field in 2005 and retrieved after 15 years for laboratory analysis. Strength, scanning electron microscope, X-ray diffraction, nuclear magnetic resonance, and sulfate ion ( SO 4 2 − ) concentration were measured at 56 days and 15 years to assess concrete performance evolution and underlying micromechanisms in actual service conditions. The results indicate that after 15 years, the strength of fully buried OPCC and SRPCC increased compared to 56 day values. The densification effect from ettringite and calcium carbonate formation primarily contributed to the strength gain, while a small amount of thaumasite was observed, and gypsum did not form in the corrosive environment. Pore structure analysis revealed that at 56 days, OPCC test piles exhibited slightly higher pore signal intensity than SRPCC, with a lower proportion of gel pores and a higher proportion of large and transitional pores. After 15 years, pore signal intensity in OPCC was significantly lower than in SRPCC. Although SRPCC contained a higher proportion of capillary and large pores than OPCC, these pores represented a smaller fraction of the total pore volume in SRPCC. Except in the surface layer, sulfate ion ( SO 4 2− ) concentration at equivalent depths was lower in SRPCC than in OPCC. The reduced C 3 A content in SRPCC limited the formation of deleterious products such as ettringite and delayed sulfate attack progression. These findings provide valuable insights into the macro- and microscale evolution of underground concrete structures exposed to long-term corrosion and serve as a reference for durability assessment.