## 1 Introduction  
Concrete structures have the advantages of cost effectiveness and durability; however, calcium hydroxide inside cement may form ettrinigite or calcium carbonate, or may even be dissolved in the outer surface, as in the case of leaching, depending on the external environment [1, 2]. Deterioration factors such as chloride attack and carbonation do not have a significant effect on hardened concrete, but bring forward the corrosion initiation time of the internal reinforcement and accelerate corrosion, which may lead to critical problems in terms of structural safety. Active studies have been underway on the ion transport and reaction of deterioration factors, and in all countries, a durability design is performed before the construction of concrete structures--referred to as specifications or structural codes [3, 4, 5]. In the case of chloride attack, a number of studies have been performed considering the dissociation of chloride ions and phase equilibrium, as well as the penetration and diffusion mechanism of chloride ions [6, 7, 8]. These studies have been further extended to corrosion modeling with the consideration of the hydration degree and oxygen penetration. Some studies have developed coupled analysis modeling, which also considers the reduction in the structural load-carrying capacity under continuous deterioration actions [8; 9; 10]. In the case of carbonation, thermodynamic coupled analysis models have been developed, taking into account the diffusion of carbon dioxide and reactions with the hydration products inside and carbon dioxide [8; 11; 12]. The progress of the service life modeling of the sulfate attack was relatively slow because the formation of ettringite from the reaction between calcium hydroxide and sulfate ions expands the concrete volume, making quantitative modeling with a simple diffusion analysis difficult. In addition, another reason for the difficulty of a performing quantitative analysis in this context is that concrete is always exposed to the ground, and other types of deterioration factors--such as freezing and thawing--also occur in addition to sulfate attack [13; 14]. In recent years, with the increase in the construction of sewer pipes and underground structures, durability design against sulfate attack has emerged as an important issue [15; 16]. For the analysis of sulfate ingress, previous studies have mainly employed methods such as the evaluation of the deterioration depth, considering the sulfate ion diffusion coefficient and the cement components [14; 17], evaluation of the rate of strength reduction through an accelerated sulfate ion resistance test [13; 18], or diffusion analysis considering the multiple deteriorated layers [19; 20]. Furthermore, underground structures are always exposed to ground water and are difficult to maintain, so repair techniques that are resistant to bio-chemical deterioration are required. For a long time, organic material-epoxy and inorganic material-cement mortar have conventionally been used for repairing materials, and recently, polymer-cement materials have been widely adopted for enhancing adhesion and decreasing the curing period [21; 22]. Using inorganic coating is currently very effective and has a good cost-benefit ratio in the short term, however, many problems have been reported due to the peeling-off and delamination of the coating layer due to its different dimensional integrity, which cannot guarantee a long service life after repair. Polymer-cement-based material has engineering advantages such as high resistance to chloride ingress and adhesive strength; however, it has a relatively high repair price and several defects have been reported in instances of low-quality material and construction skills [23]. The previously mentioned techniques are usually utilized for resisting chloride ingress and carbonation progress since the main deterioration mechanism is not bio-chemical penetration but diffusion and permeation.