This paper addresses the issue of reduced lifespan of coastal concrete piles due to chloride ion corrosion. A combination of concrete mix optimization and pile geometry improvement measures is proposed. Based on the diffusion coefficient optimization of Fick’s second law, the service life prediction of concrete piles in corrosive environments is completed. The results show that, compared to single slag incorporation and the “slag-fly ash” dual-component mix, the “slag-fly ash-corrosion inhibitor” triple-component concrete achieves a 28-day compressive strength of 67.4 MPa, and the chloride ion diffusion coefficient is reduced to 1.14 × 10⁻¹² m²/s, significantly improving overall performance. Finite element simulations reveal that, compared to ordinary square piles, cut-corner square piles can effectively alleviate stress concentration at the pile tip and reduce settlement. The maximum stress is 3.94 MPa, and the settlement is 22.64 mm, representing reductions of about 16.3% and 15.5%, respectively, compared to ordinary square piles. Concrete service life prediction confirms that the concrete with corrosion inhibitors has a predicted service life of 31.5 years, extending 7.4 years and 13.3 years longer than the single slag and the “slag-fly ash” dual-component groups, respectively. The “material-structure” optimization theory proposed in this study provides a theoretical basis and technical path for the long-life design of coastal engineering pile foundations.

To elucidate the corrosion behavior of cracked reinforced concrete under pressurized permeation at 0.3 MPa, three exposure conditions were established, namely a low-concentration chloride-sulfate solution, a high-concentration chloride-magnesium sulfate solution, and a high-concentration chloride-magnesium sulfate-carbonate composite solution, and cyclic permeation tests were conducted. Based on the chloride ion (Cl⁻) content distribution, permeation behavior, and steel half-cell potential measurements, together with XRD and SEM microstructural analyses, the results showed that Cl⁻ transport was significantly enhanced. At a depth of 15 mm, the Cl⁻ content increased from 0.011% under unpressurized conditions to 0.211% at 90 d and further to 0.322% at 365 d, while it remained close to zero at depths of 35 mm and below. Under the low-concentration condition, permeation ceased after about 3 months, and the half-cell potential recovered from −550 to −580 at 46 d and stabilized at −250 to −340 in the later stage, indicating a certain self-healing capacity of the cracks. Under the high-concentration and composite conditions, permeation persisted throughout the 12-month period, and the half-cell potential dropped to −800 to −900 at 34–40 d and remained at −580 to −840 in the later stage, indicating that the steel remained in an active corrosion state for a long time. XRD and SEM results further showed that corrosion products such as AFt increased, and the internal concrete structure gradually deteriorated.