## 5 Conclusions  
The durability of concrete structures exposed to aggressive environments is significantly affected by the ingress of deleterious ions, particularly chloride ions, which are a primary cause of reinforcement corrosion. In partially saturated concrete, the transport mechanisms of chloride (CI\({}^{-}\)) and other ions (Na\({}^{+}\), Ca\({}^{2+}\), K\({}^{+}\), OH\({}^{-}\)) become complex, due to the coexistence of liquid and gas phases within the pore structure. Accurate and reliable prediction of ion transport under these multiphase conditions is essential for evaluating the service life and long-term performance of reinforced concrete structures. This study aimed to clarify the mechanisms of ion diffusion in partially saturated concrete and to propose predictive methods based on mathematical modeling and numerical simulation. The key findings are as follows:  
A multi-species transport model was developed based on the Nernst-Planck equation and implemented using a parallel finite element method. The model was formulated under the assumptions of electroneutrality and zero current, and it incorporated the coupled effects of moisture and temperature gradients in concrete. Material properties such as moisture and heat capacities were obtained from the literature, while coupling parameters for ion diffusivity were calibrated using experimental data. A hygro-chemo-thermo transport model was numerically implemented within a parallel finite element framework. A large linear system of equations was derived and discretized using the Crank-Nicolson semi-implicit method. A computational framework was developed in C++ and integrated numerical algorithms from libraries including Triangle, ParMETIS, PETSc, and MIP. The code was parallelized using the Single Program Multiple Data (SPMD) model and overlapping domain decomposition techniques. Experimental validation was conducted to ensure model reliability. Chloride ponding tests were performed under varying initial temperature conditions (20 \({}^{\circ}\)C, 35 \({}^{\circ}\)C, and 50 \({}^{\circ}\)C), water-to-cement ratios (0.55 and 0.65), and relative humidity differences (100% and 60%) between the concrete surface and interior. The results confirmed that the proposed transport model, accounting for diffusion mechanisms, ion interactions, and temperature effects, accurately predicted chloride ingress under both isothermal and non-isothermal conditions. Additionally, numerical simulations revealed the inward migration of the moisture front, which eventually stabilized at 100% relative humidity, indicating a steady-state condition. This moisture gradient was found to significantly enhance the transport of chloride, sodium, and calcium ions, thereby accelerating their penetration rates. The model proposed in this study was developed to account for the effects of relative humidity and temperature on ion penetration in concrete. Its significance lies in the implementation of a parallel algorithm combined with the finite element method. Moreover, the model is advantageous in that it can be applied for the simulation and analysis of entire large-scale structures. However, additional experimental validation of the coupling parameter is necessary to enhance the reliability of prediction results. Conceptualization, G.L. and O.N. ; data curation, O.N. ; formal analysis, O.N. ; funding acquisition, G.L. ; investigation, G.L. and O.N. ; methodology, G.L. and O.N. ; supervision, G.L. ; validation, O.N. ; visualization, O.N. ; writing--original draft, O.N. ; writing--review and editing, G.L. and O.N. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The data presented in this study are available in the article.