In February 2017, the Architectural Institute of Japan published the “Recommendations for Mix Design, Production and Construction Practice of Concrete with Expansive Additive and/or Shrinkage Reducing Admixture”. These Recommendations, which are the culmination of work carried out since 2017 to update the previous recommendations, constitute a technical standard for rationally determining methods such as mix design, production and transport, construction and quality control of concrete using expansive additive and/or shrinkage reducing admixture for the purpose of reducing shrinkage of concrete and suppressing cracks caused by such shrinkage, with the aim to contribute to improvement of the quality of concrete structures. This paper outlines the content and background of the establishment of these Recommendations.

In order to build a sustainable recycling system, it is necessary to achieve the following three objectives from the viewpoint of the life cycle assessment (LCA) of structures: (1) securing of safety and quality, (2) reduction of environmental load, and (3) cost reduction. This report presents the results of building a recycling system designed for the use of low-quality recycled aggregate made from concrete waste for structural concrete. The proposed system aims for the use of low-quality recycled aggregate for structural concrete through the aggregate replacement method, besides the use for recycled crushed stone as conventional roadbed material. Through actual large-scale use, we were able to achieve the three above-mentioned objectives, which are traditionally held to be difficult to achieve with resource recycling technology.

The authors have developed a half-precast structure for application to the sidewalls of tunnel boxes in order to improve productivity at large-section box culverts (structure rationalization and construction labor saving). To determine which shear reinforcing method to use for this half-precast structure, the authors conducted shear tests using the shear reinforcing method as a parameter, using downsized quarter scale sidewall members of the proposed design as specimens. Then, in order to verify whether the half-precast structure has flexural capacity equivalent to or better than that of an RC structure, a bending test was carried out along with a bending test introducing axial force, using quarter scale specimens as in the shear experiment.

The stay-cables of cable-stayed bridges and extradosed bridges being located at relatively large heights, there are many places where visual inspection is difficult because it requires aerial work vehicle for close visual inspection or rope access technology. Further, the high-strength steel wire used for stay-cables is at risk of corrosion due to penetration of degrading agents or the like, as well as fatigue rupture caused by stress fluctuation, but inspection for damage of such steel in protective pipes requires effective non-destructive inspection equipment. This paper describes a self-propelled diagonal member inspection device developed to allow the visual inspection of diagonal members in high locations and the detection of damage in high-strength steel members.