Mechanism analysis of strength evolution of concrete structure in saline soil area based on 15-year service

Abstract

This paper investigates the strength evolution of pile foundation concrete structures in saline soil areas of inland China after 15 years of service using field exposure field tests. NMR, XRD, SEM, and other test methods investigate the mechanism. According to research findings, the strength of concrete with different mix ratios has increased after 15 years compared to the strength of the pouring period (56 days). The continuous hydration of cementitious materials can continuously refine the pore structure of concrete and reduce the porosity of concrete, which is the main reason for the improvement of concrete strength. In saline soil, pile foundation concrete is susceptible to erosion by SO42– and CO32–. With sufficient space, a large amount of C-(A)-S-H gel generated during concrete hydration, calcite and other products produced during carbonization, and secondary ettringite generated during sulfate attack on concrete can effectively fill the pores in the concrete. These properties confer improved strength to concrete. The reinforcement corrosion tests reveal that most steel bars have not corroded. Only a small portion of the steel bars near the bottom of the pile foundation has eroded due to the thin reinforcement protection layer. After fifteen years, the concrete with a high water-binder ratio (0.59) mixed with corrosion inhibitors deteriorated in pore structure and suffered mild thaumasite sulfate attack. The concrete has low porosity and a high proportion of tiny pores due to its low water-to-binder ratio (0.35) and corrosive inhibitor. These characteristics effectively prevent external corrosive ions from corroding the concrete while protecting the internal steel bars, making them suitable for long-term use in inland saline soil areas of China.