Ho-Jin Kim

An integrated rainwater management system is necessary due to the frequent occurrence of localized torrential rainfall and heat waves caused by an abnormal climate. It is necessary to develop a rainwater detention system that can implement rainwater infiltration and detention simultaneously. In this study, the safety, durability, and eco-friendliness of an eco-friendly rainwater detention system developed using an eco-friendly inorganic binder, which involves red clay, were evaluated and its economic feasibility was compared with that of the existing detention system. After 14 days, analysis of the maximum compression load and computational finite element analysis confirmed that the strength standard was satisfied and the structure was safe. No heavy metals or organic compounds were detected in the leaching test. Thus, the eco-friendly rainwater detention system is structurally safe and eco-friendly with no impact on the soil and groundwater environment, and is economically feasible because the construction cost and life cycle cost are approximately 30% and 58% lower, respectively, than those of the existing polyethylene infiltration detention tank system. These results indicate that improved safety, eco-friendliness, and economic feasibility can be achieved, compared to those of the existing system, if the eco-friendly rainwater detention system is applied in the field.

This study investigated the physical properties of section-restoration mortar with calcium nitrite (Ca(NO₂)₂) and carbon dioxide (CO₂) nanobubble mixing water to develop materials and methods for the repair and reinforcement of cracks in reinforced concrete (RC) structures. As the calcium nitrite content increased, the generation rate and generated amount of nitrite-based hydration products also increased, owing to the rapid reaction between NO₂⁻ ions in calcium nitrite and C₃A(Al₂O₃). Further, the reaction with C₃S and C₂S was accelerated, thereby increasing the generation rates of Ca(OH)₂ and C-S-H. The large amount of Ca²⁺ ions in these hydration products reacted with CO₃²⁻ ions in CO₂ nanobubble water, thereby increasing the generation of calcite-based CaCO₃ in the cement matrix. This appears to have affected strength development and durability improvement via the densification of the structure. These results suggest that the performance of polymer cement mortar for repairing concrete structures can be improved if calcium nitrite and CO₂ nanobubble water are properly combined and applied.