Corrosion of the tendons is a common issue in post-tensioned prestressed concrete (PC) beams and this paper describes the flexural behavior of PC beams having damaged tendons. The tendons of the PC beams were intentionally damaged by core drilling from the side of the PC beam or accelerated corrosion process. Beam flexural tests were carried out to confirm the influence of damage location and degree of damage of the tendons on the load carrying capacity of the PC beams. A nonlinear pushover analysis was performed using fiber model and the analysis results were verified by the experiment results. From the analysis it was found that the load carrying capacity of the PC beams having damaged tendons can be estimated with a relatively high accuracy by using the proposed fiber model, obtained by converting the mass reduction rate of the PC tendon and the influence length of rupture to the sectional area of the PC tendon. Furthermore, the fiber model was applied for a PC box girder, assuming the location of the corrosion and the grout filling condition of PC tendon. The analysis results were used to estimate the safety of the PC box girder for different failure criteria such as tendon fracture and bending fracture.

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 Evaluation of filling ability and drying shrinkage properties of concrete, mixing with ferronickel slag fine aggregate or copper slag fine aggregate with two types concrete ingredients consists of crushed stone and crushed sand and crushed stone and pit sand was studied. The first one was for low quality concrete with aggregate consisted of crushed stone and crushed sand made from sand stone. And the second one was for high quality concrete with aggregate consisted of crushed stone and pit sand.
 The box-shaped filling ability test and L-type flow test with internal vibrator was performed. Two tests had the R2 type of the obstacle with steel bars in the middle of flow direction. It was found that the filling ability to the vertical direction of ferronickel slag fine aggregate concrete was higher than the normal concrete. On the other hand, the filling ability of copper slag fine aggregate concrete was decreased. By the result of L-type flow test, it was observed that the passing ability through obstacle to the horizontal direction had been improved due to the mixing of ferronickel slag fine aggregate or copper slag fine aggregate. The bleeding capacities of concrete were larger with the mixing of these slag fine aggregates than that of the normal concrete mix without slag fine aggregates. However, the bleeding capacities of the concrete mixed with these slag fine aggregates and low quality normal aggregate were smaller than that of these slag fine aggregates with high quality normal aggregate. The final strain generated by drying shrinkage of concrete mix with these slag fine aggregates was smaller than the normal concrete. In particular, the reductive effect of the concrete mix with these slag fine aggregates with low quality normal aggregate was larger than the concrete with high quality normal aggregate.

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 Long term curing using Water-Repellent Sheets was applied to seven actual structures and it was confirmed that the substance permeability was improved by a nondestructive test. In addition, the effect of quality improvement was analyzed under blending conditions of concrete such as cement type, unit water volume and water cement ratio. As a result, we confirmed the proportional relationship between water cement ratio of concrete and surface water absorption rate by long term curing and when its water cement ratio is large, its suppressing effect is high. This indicates that the hydration reaction is continued by suppressing dissipation of free water by sheet curing, the concrete surface becomes dense, and the increase in surface water absorption rate can be suppressed.

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 In recent decades, a number of studies have been reported that exposure of concrete structures to the high concentration of chloride ions near marine causes the chloride attack, leading concrete to deteriorate. However, current studies on this issue have insufficient information to assess the mechanisms of deterioration and countermeasures. In order to understand the details of chloride attack phenomena and select an appropriate countermeasure systematically. In this study, follows were investigated; the various factors affecting concrete deterioration, including the variation of chloride ions levels in tidal zones and tunnels with leakage, and the penetrating routes of chloride ions into tunnel structures, as well as influence range of chloride ions on concrete structures induced by leakages. Consequently, we clarified the mechanisms of chloride attack occurred at box type tunnels in subway lines. In addition, an appropriate and simple method of investigation was conducted to estimate the influence range of chloride attack for subway tunnels under short hours and tight spaces for work. Furthermore, the most suitable repaired material and method were selected for repair works. Based on this research and study, the countermeasure system for preventing the chloride attack which is able to identify locations need repair work and countermeasure under various environmental conditions was developed.

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 In maintaining and managing social infrastructure, saving labor and improving efficiency in visual inspections is one of the urgent issues in the recent years. In this research, in order to solve this problem, we apply image recognition using deep learning to images acquired by digital cameras and conducted evaluations on a method that automatically assesses classifications related to ranking by detecting deformations. Additionally, through verification using images from actual structures, it was verified that image recognition using deep learning is an effective method of saving labor and improving efficiency in visual inspections.

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