# Experimental Evaluation of the Durability of Concrete Repair Materials
## 1 Introduction  
Concrete structures deteriorate over time due to physical and chemical processes such as carbonation, chloride attack, and freeze-thaw. Such processes cause cracking, a serious problem that accelerates structural deterioration [1, 2]. Concrete carbonation is the reaction between atmospheric CO\({}_{2}\) and concrete. Immediately after construction, concrete is highly alkaline due to its Ca(OH)\({}_{2}\) content, which protects steel reinforcements from corrosion [3, 4]. However, atmospheric CO\({}_{2}\) reacts with the outside of the concrete to produce CaCO\({}_{3}\), which reduces the alkalinity over time [5, 6, 7]. As the CO\({}_{2}\) penetration depth increases, it is more likely to reach the steel reinforcements and cause corrosion. Chloride attack destroys the passive film on steel reinforcements, and causes corrosion when chloride ions penetrate the concrete and reach the steel reinforcements [8, 9, 10, 11]. Carbonation and chloride attacks penetrate faster when there are existing cracks; carbonation is also accelerated by the increase in atmospheric CO\({}_{2}\) caused by global warming. These processes cause corrosion, which increases the volume of steel reinforcement and leads to concrete spalling, additional cracking, and a sharp reduction in concrete durability [12]. In contrast, freeze-thaw is a physical process where water penetrates the concrete and freezes. In general, when water freezes, it expands by approximately 9%. This causes deterioration in the form of scaling, microcracks, and pop-outs on the surface [13, 14]. Deterioration phenomena caused by carbonation, chloride attack, and freeze-thaw shorten the service life of structures and, as mentioned earlier, they are all closely related to cracks. Therefore, damage to concrete structures may be prevented by repairing cracks to prevent physicochemical phenomena and aging; this may extend the service life of the structures. In South Korea, the Korea Authority of Land and Infrastructure Safety provide detailed guidelines for safety inspection and diagnosis; however, there is only a brief discussion on crack repair. Crack repairs can be divided into injection, filling, and surface treatment methods, and they are applied based on the crack width [15]. In practice, repairs performed in the field often depend on subjective decisions made by the person in charge. Furthermore, there is little or no consideration of local environmental or chemical factors. Therefore,it is necessary to provide guidelines for the selection of suitable repair materials and methods for specific situations. There have been some studies related to crack repairs in South Korea and overseas. For example, [PERSON] et al. evaluated the long-term performance of reinforced concrete structures using a surface impregnant silane external coating [16]. [PERSON] et al. repaired notched concrete with epoxy and evaluated its performance in a marine environment [17]. [PERSON] et al. used a water-repellent surface impregnant and evaluated the chloride resistance of reinforced concrete structures and the role of cracks [18]. [PERSON] et al. conducted a durability test for the immobilization of a photocatalyst using impregnant [19]. [PERSON] et al. changed the material properties of surface pollutants, such as their concentration and viscosity, to evaluate and enhance the performance of concrete [20]. [PERSON] et al. evaluated concrete durability using a surface impregnant [21]. Most of these studies considered single variables, such as the crack width, material properties, and chemical response. Therefore, this study will consider composite methods using epoxy injection and impregnant surface treatment. These treatments can protect cracks and surfaces according to the width of inactive cracks. In addition, compressive and flexural strength tests will be conducted to assess the performance of different crack repair methods. Environmental and chemical features will be used to evaluate the durability performance with respect to carbonation, chloride attack, and freeze-thaw.