Enhancing the Durability of Reinforced Concrete Structures Using Carbonation-Inhibiting and CO2-Absorbing Microcapsules

This study aimed to establish fabrication methods for two types of functional microcapsules (MCs) and to verify their fundamental performance in cementitious materials. The alkaline-supplying and CO2-absorbing MCs were evaluated independently. It was hypothesized that alkaline-supplying MCs could suppress carbonation while limiting strength loss to ≤20%, whereas CO2-absorbing MCs could increase long-term CO2 uptake by ≥30% relative to plain mortar. The alkaline-supplying MCs reduced the 24-week carbonation depth by approximately 35%, with a ~20% reduction in compressive strength at a 5% addition level. In contrast, CO2-absorbing MCs resulted in a ~30% strength reduction at 5% addition but increased CO2 uptake by 1.4 times that of plain mortar over 140 d. In conclusion, the results demonstrate that MCs can effectively impart carbonation-resistance or CO2-absorption functionality; however, a clear trade-off exists between functional enhancement and mechanical degradation due to capsule stiffness and density limitations. Because the two types of MCs rely on different mechanisms, they were tested in separate mortar systems. As this study focused on MC fabrication and fundamental functional verification, future work should optimize shell design, density control, and amine selection to balance structural performance with durability enhancement and CO2-sequestration capability.