Go Igarashi

Evaluation of Irradiation Effects on Concrete Structure: Background and Preparation of Neutron Irradiation Test

Methods for assessing the soundness of concrete exposed to irradiation are being developed within the framework of a project of the Nuclear Regulation Authority (NRA) “Japan Ageing Management Program for System Safety”. This paper presents the background of this project and recent research works. The major reason for deterioration of concrete under irradiation conditions is expansion of aggregate due to neutron and gamma-ray irradiation. Dislocation of atoms in covalent structures of aggregate minerals, and resultant lattice constant change and alteration to amorphous phase are produced by fast neutrons. In addition, through electronic exertion, some energy deposition is accumulated as permanent distortion/strain in atomic structures. Other effects are also summarized. We plan to conduct a neutron irradiation test from May 2013. In selecting mix proportions and concrete components for the irradiation test program, sample size as a function of capsule size and gamma-heating, cement type, and aggregate size and type are determined based on preliminary experiments.Copyright

Effect of Cognitive Load on Seating Posture in Children

Although children are frequently required to sit upright, it is often difficult to maintain this posture when performing cognitive tasks. Information about the relationship between a cognitive tasks and postural seating control is important for children to complete tasks more effectively. To determine the muscle activity and body sway of children in a seated posture while performing a cognitive task, changes in muscle activity and center of pressure (COP) were recorded while 4(th) grade children performed arithmetic tasks. Electromyography was recorded from the internal oblique and lumbar multifidus muscles, and the COP was recorded using a baropodometer placed on the stool. These variables were measured during easy (EA) and difficult (DA) arithmetic tasks. EMG activity decreased during the EA and DA tasks, while the COP was displaced in the DA task. The results of the arithmetic tasks were not related to the EMG or COP changes. Attention to maintain a seated posture may be reduced when children perform cognitive tasks. Therefore, it may be better to allow children to alter their posture especially when they are performing difficult tasks. In this research, we only used arithmetic tasks as the cognitive exercise, and therefore, other types of tasks should be examined.

Selection of Activity Items for Development of the Activity Card Sort–Japan Version

The Activity Card Sort (ACS) can both record the clients’ participation and any changes, which is a useful tool for practitioners to establish tailored occupation-focused goals. However, there is a limitation to apply the ACS to Japanese older adults as it consists of culturally relevant activities in the United States. The aim of this study was to select activity items reflecting Japanese older adults’ lifestyles and opinions to develop the Activity Card Sort–Japan Version (ACS-JPN). In the item selection process, a two-round questionnaire survey was conducted for community-dwelling Japanese older adults (Round 1: n = 177, M age = 69.9 years; Round 2: n = 178, M age = 74.9 years). Seventy-two activity items were finally included in the ACS-JPN and were classified into four domains. The ACS-JPN has some unique features compared with other ACS versions. This study only selected activity items. Further work on psychometric properties is needed.

Experimental Study on Time-Dependent Behavior of Cracked UHP-FRCC Under Sustained Loads

Ultra-high-performance fiber-reinforced cementitious composite (UHP-FRCC) has been successfully developed over the last decade. UHP-FRCC shows very high strength and high durability because of its very low water binder ratio and dense microstructures. Moreover, by incorporating a combination of steel and mineral fibers with different sizes in the mixture design, UHP-FRCC also exhibits high ductility and high energy absorption capacity, even under uniaxial tensile stress. The high ductility of UHP-FRCC materials shows strain hardening behavior with multiple cracking after the occurrence of the first crack. While extensive research on the tensile and bending behavior of this composite under short-term loading is reported, only limited results can be found on time-dependent behavior of UHP-FRCC under sustained long-term loading, which is strongly related to the situation of real structures. This paper presents experimental results concerning the time-dependent behavior of cracked UHP-FRCC specimens under sustained bending load. In bending creep test, sustained load with 50 % of the pre-cracking load was applied to a pair of prismatic specimens of 50 × 100 × 400 mm under a 4-point bending setup. The performance of UHP-FRCC is compared with those of conventional fiber reinforced cementitious composites (FRCC) using steel and synthetic fibers, which are investigated within the Round Robin Test (RRT) organized by RILEM TC 261-CCF. The results showed that UHP-FRCC exhibited smaller creep deformation at the sustained loading condition than the conventional FRCC, even when the initial deformation of the UHP-FRCC is much larger than the conventional FRCC. Cracking pattern, in terms of crack width and number of cracks, was also studied in both composites under sustained loads. As a result, the superior resistance of UHP-FRCC was obtained with respect to conventional FRCC.

Ecological and Mechanical Properties of Ultra High Performance – Fiber Reinforced Cementitious Composites Containing High Volume Fly Ash

Ultra High Performance – Fiber Reinforced Cementitious Composites (UHP-FRCC) has successfully developed in the last decades. They show excellent mechanical properties and durability, due to the highly dense microstructure produced by extremely low water/binder ratio and large amounts of cement. Thus, replacing part of the cement content with High Volume Fly Ash (HVFA) could be an effective way to improve also the ecological properties of UHP-FRCC. Indeed, most of the carbon footprint of cement-based composites is caused by the CO2 production of cement manufacturing. On the other hand, HVFA tends to reduce the mechanical properties of UHP-FRCC, especially at the early age. To evaluate the effect of some cement replacement (20, 50 and 70% by weight), a series of uniaxial compression and tensile tests have been performed and described in this paper. At the same time, through the Eco-Mechanical Index (EMI), ecological performances are evaluated on the basis of the measured mechanical properties. As a result, the application of UHP-FRCC in full-scale structures (e.g., composite concrete columns) is really convenient in the presence of HVFA, although the material properties (the compressive strength, in particular) show an opposite trend.