Concrete structures deteriorate over time due to cracks induced by various physical, chemical, and environmental factors. This performance degradation not only reduces their service life but may lead to human casualties and other property damage as well. While concrete crack repair can help address this problem, the implementation of the optimal repair method is important according to the environmental conditions. In this study, epoxy, impregnating, and epoxy/impregnating methods were used to repair concrete cracks. Epoxy was used for crack injection, and a supernatant was used for surface protection. The epoxy/impregnating method was used to protect both cracked areas and surfaces. Activated cracks were induced using flexural strength tests, and the stiffness of the specimens according to the repair method was compared to examine the structural performance. In addition, after the flexural strength tests, the strength, carbonation, chloride, and freeze–thaw durability were evaluated for the concrete core specimens. The impregnating method yielded the best repair performance for strength, epoxy/impregnating method for carbonation, epoxy and epoxy/impregnating methods for chloride, and epoxy/impregnating method for freezing and thawing. The results of our study enable selection of the optimal repair method to be used in practical applications based on physical, chemical, and environmental factors.

Recently, extreme climate change has been occurring globally not only in the simple form of temperature increases but also in a wide range of extreme climatic events, such as abnormal drought conditions and frequent typhoons. Among these various events, the greatest problem is found in global warming. The earth`s temperature has risen since the period of rapid industrial growth in the 1970s, and global warming occurs at the local level of regions and cities as well as the national level. The greenhouse gases that influence global warming include various types of chemical components, such as carbon dioxide (CO₂), perfluorocarbons (PFCs), nitrous oxide (N₂O), and methane (CH₄). In addition, climate change is extending the construction period of concrete structures. Whereby increasing related economic losses. Pushing through construction projects without considering climate change is leading to concrete quality deterioration, causing poor constructions and consequently resulting in humans casualties and property damage. In particular, atmospheric CO₂ generates calcium carbonate by reacting with concrete hydration products. This result is reinforcing bar corrosion and concrete durability reduction due to lowered alkalinity. Therefore, in this study, concrete durability performance with respect to carbonation resistance from curing conditions change due to wind speed and sunlight exposure time is evaluated. Based on concrete carbonation resistance data obtained using curing conditions of various wind speed and sunlight exposure time, performance based evaluation (PBE) is performed using the satisfaction curve (SC) developed from the carbonation resistance test results. Using the developed PBE of concrete performance, future concrete performance is predicted based on future climate scenario. Also, the concrete mix design solutions to the concrete performance degradation due to climate change effect is proposed.

Reinforced concrete (RC) structures age with time, which results in performance degradation and cracks. These performance degradations do not recover easily, but a performance higher than the existing structures can be expected through reinforcement. There are various reinforcement methods for RC structures. This study selected four reinforcement methods: near-surface mounting (NSM), external prestressing (EP), external bonding (EB), and section enlargement (SE). In the past, steel bars were often used as reinforcements. However, this study uses fiber-reinforced polymer (FRP), which is an alternative to steel bars owing to its high tensile strength, and its non-corrosive and lightweight properties. It is a basic strengthening material, along with a carbon-fiber-reinforced polymer (CFRP) and glass-fiber-reinforced polymer (GFRP) in bar and sheet forms. Various strengthening materials such as a CFRP, GFRP, and prestressing (PS) strand are applied to the NSM, EP, EB, and SE methods, followed by flexural experiments. In addition, changes in the ductility of the RC structures were examined. The concrete EP and near-surface mounting prestressing (NSM(P)) methods have a stiffness that is almost double the non-strengthened specimen. However, because the EP and EB methods are brittle, the NSM(P) method with ductile behavior is considered the most effective.

The external prestressing method was developed to improve the load carrying capacity of concrete bridges damaged by ageing or other external environmental factors. Therefore, it is necessary to examine the performance of the structure before and after strengthening, and verification and confirmation of the actual strengthening effect should be preceded. However, for reasons such as securing deteriorated bridges and the absence of design data, the strengthening effect of an actual bridge is rarely analyzed. Hence, in this study, the strengthening effect was verified by conducting a set of material property tests and four-point loading tests before and after strengthening of an actual bridge, which had been utilized for over 45 years. As a result, it was determined that confirming the strengthening effect before cracking is challenging due to the nature of the external prestressing method, which has an insignificant effect on the stiffness; however, the effect of increasing the crack load of the external prestressing method was experimentally verified. The result of the study is expected to contribute to the determination of the load carrying capacity and required strengthening amount when strengthening existing prestressed concrete girder bridges.

Concrete structures crack as they age due to deterioration phenomena such as carbonation, chloride attack, and freeze–thaw. Cracks may also occur due to corrosion of steel reinforcements, which can rapidly degrade the structural integrity. Therefore, this study uses strength and durability tests to examine the materials used to repair cracks in concrete; namely, epoxy, impregnant, and epoxy/impregnant. The results show that epoxy has the greatest strength; epoxy/impregnant is most effective for repairing carbonation damage; impregnant is most effective for repairing chloride damage; epoxy and epoxy/impregnant are most effective for repairing freeze–thaw damage, depending on environmental and physical factors, as well as the crack width. These results can be used to improve the quality of repairs and increase the safe operating life of structures.

Prestressed concrete composed of steel materials is increasingly used in various social infrastructures, such as bridges (cables), nuclear containment structures, liquefied natural gas (LNG) tanks, and structural reinforcements. This study aimed to substitute the steel in bridge cables with fiber-reinforced polymers (FRPs) to prevent the damage caused by the performance degradation of corroded prestressed steel. An optimized single-anchorage system was derived by applying multiple variables, such as the surface treatment, number of insert layers, and sleeve processing companies, to improve the maximum load and bonding with the anchorage system sleeve using the carbon FRP (CFRP) cable. The B-L-4 specimen (sleeve specifications of company B, longitudinal surface treatment, and four insert layers) was determined to be the optimized single-anchorage system. When the tensile test was conducted after applying the optimized single-anchorage system to the three- and seven-multi-anchorage systems, the tensile performances of B-L-4 were 100 and 95% of the one-multi-anchorage system, respectively. Considering that the problems associated with the construction of three- and seven-multi-anchorage systems have been addressed, these systems can be applied to actual bridges in the future, and can significantly benefit their maintenance.