The accident in the Sasago Tunnel in 2012 was a tragic event in which the tunnel ceiling panels collapsed, victimizing nine people. It provided us a very important opportunity to face the problem of aging civil infrastructures, bringing the issue to light and calling for the attention of the public. Under the lead of the government, a variety of measures have been implemented since then, ranging from promotion of technical development to review on the related laws and regulations. This report outlines the problem of aging civil infrastructures and its social circumstances, and introduces useful technologies own by Taiheiyo Cement Group.

View full abstract

 Reinforced concrete structures in a high chloride environment are subject to the risks of corrosion. Although it is important to inspect chloride penetration depth in them, the inspection process usually causes irreversible damage to them during the corrective maintenance. Maintenance can be reasonably planned by using a non-destructive method to predict when corrosion will occur. Radio frequency identification (RFID) is a method of uniquely identifying an object by means of wireless radio transmission. Concrete structures will be more efficiently maintained if RFID with sensory functions can be used as a non-destructive inspection method to monitor the condition of structures. We have developed a wireless monitoring system for concrete structures, named WIMO^Ⓡ, using the RFID technology. Wireless corrosion sensors in the system are embedded in reinforced concrete to predict the time when corrosion of the steel bars occurs. Verification experiment was carried out with multiple sensor specimens tagged to individual steel specimens and embedded in concrete which was exposed to an environment with excessive chlorides. Inspection was performed, and the results verified that the corrosion sensors worked properly as expected. This system is already in practical application in both newly constructed and renovated structures.

View full abstract

 This study is an experimental investigation performed by optical fiber sensing on corrosion expansion behavior of rebars which has influence on corrosion cracking of reinforced concrete structures.
　Corrosion reaction increases the volume of rebars as iron is transformed into various types of corrosion products. In order to clarify the volumetric expansion behavior due to corrosion, an electrolytic corrosion test was conducted by using embedded-type optical fiber sensors attached to the rebars in concrete. It was found that progress of rebar corrosion could be successfully monitored by using the optical fiber sensors, and that corrosion cracking could be clearly detected from the expansion strain induced by the rebar corrosion. The volumetric expansion ratio of corrosion products in concrete was in the range of 1.2-2.0, being smaller than the theoretical one estimated from the density and the atomic weight of corrosion products due to the presence of restraint. Analysis of the corroded surfaces by EPMA after the corrosion test showed that corrosion products mostly remained in the interface between the rebar and the concrete and did not diffuse into the inside of concrete through micro-pores in the paste.

View full abstract

 In this study strain distribution calculated by digital image correlation method (DICM) was used to evaluate the efficacy of alkali-resistant glass (ARG) fiber mesh in controlling distribution of strain due to drying shrinkage. Digital images of mortars with ARG fiber mesh in a dry environment (30℃, 40%RH) were obtained by using a full-field strain measuring device with a line scanner, and surface strain distribution in them was calculated by the DICM. The results showed that local strain in the mortar reinforced with ARG fiber mesh was effectively distributed, and that the effect was dependent on the orientation of ARG fiber mesh embedded in the mortar. It was also found that the DICM could be applied to detection of strain concentration and development of micro cracks as well as to prediction of the development of visible cracks in concrete.

View full abstract

 Recently, various strengthening methods have been utilized to enhance the structural performance and extend the life cycle of reinforced concrete (RC) structures. However, the existing strengthening methods still have some drawbacks especially in the durability aspect. In this study, focus was placed on the features of ultra high strength fiber reinforced concrete (UFC) which was excellent in strength, ductility and durability, and a new flexural strengthening method was developed for RC beams using precast UFC panels. In order to obtain greater strengthening effect and durability, prestressing strands were used to pretension the panels. The panels were subjected to a heat curing procedure to compensate for the loss during hydration process and eliminate the effect of shrinkage. Using this novel technology, this research was conducted to investigate the flexural strengthening effect and the corresponding behavior of the RC beams strengthened with pretensioned UFC panels. Bending test was carried out using five pretensioned UFC panels and eight strengthened RC beams. Two different experimental parameters, i.e., prestress level and amount of prestressing strands, were used. The undercut anchor bolts were used for sufficient bonding between the panels and beams. Exact prestress levels were computed from the bending test results of the panels in order to obtain the calculation of the loss in the prestressing force. The results with the strengthened beams revealed that the pretensioned UFC panels greatly enhanced the loading capacity of the RC beams, and that each variable parameter had influence on different structural characteristics. To ensure compatibility along the cross-section of the strengthening system, the compatibility along the panel specimens and the strengthened RC beams was investigated. The results showed that strain compatibility was satisfied at the mid-span of the beam where the calculation of loading capacity of the strengthened beams could be carried out by using the conventional flexural section analysis.

View full abstract

 Refrete system is a repair and rehabilitation technique developed for concrete structures which can be applied to carbonated or frost-damaged concrete. This system already has a long history of successful applications to many structures. One of the advantages of this system is that the most appropriate method can be selected for each specific case according to the damage and condition of the structure based on the experiences and expertise. The system also has a wide range of applications ranging from building structures to civil engineering structures. However, only a few reports have been published that introduce actual cases of application or follow-up verifications on them or provide a technical overview of the system. The purpose of this report is to present actual examples of application of Refrete system to deteriorated concrete and verification of the repair effect by follow-up inspection. The study results showed the improved durability of the repaired structures and the concrete properties after long-term exposure. These technical data will be useful for further development of the system.

View full abstract

 The Internet of things (IoT) has been a topic in the IT industry. It has found a lot of applications especially in automated control of manufacturing processes and health care. Studies have been started also in the construction industry, including the i-Construction project by the Ministry of Land, Infrastructure, Transport and Tourism. However, it is difficult to apply this technology in practice to civil engineering structures which have no devices connected to the network. We have been developing some IoT-based solutions for civil engineering structures based our studies using IC tags. The purpose of this report is to introduce a part of such research.

View full abstract

 Ductal Form^Ⓡ is a construction technology certified by the Public Works Research Center of Japan in 2002 which has been increasingly adopted mainly to prevent wearing of agricultural or power-plant water facilities or to protect bridge piers from salt damage. This article reports Ductal Form^Ⓡ and its application to special levees of the Abashiri River in Hokkaido. The concrete sheet piles used for the levees have shown some damage or exposed reinforcement since 2001. It has been found by surveys that the major causes of these problems include the followings: floating ice blocks of frozen river water which wear the surface of sheet piles and cause micro-cracks in them; and corrosion of internal reinforcement and spalling of concrete which are caused by frost or salt damage. Protective repair has been made to the levees using Ductal Form^Ⓡ since 2013.

View full abstract

 Many test methods have been proposed and employed to evaluation of alkali-silica reaction (ASR). These tests are usually conducted in a laboratory using aggregates or concrete cores. The purpose of this article is to present petrographic characteristics of aggregates produced in Japan and introduce various ASR test methods, including the background of their establishment, an overview of the test methods, determination criteria and issues to be solved in the future.

View full abstract