In steel-concrete composite structures, the connectors that join dissimilar materials, dissimilar structural members and systems are important structural elements. Fundamental force transfer mechanism and resistance mechanisms in connectors include bonding, friction, and mechanical shear connections. Whereas heretofore mechanical shear connectors, consisting mainly of headed studs, have been commonly employed in the building structures, in view of the trend toward the diversification of composite structures, it will be necessary to introduce also high-strength and high-rigidity mechanical shear connectors such as perfobond strips, which are used in the civil engineering structures, into the construction field going forward. The “Recommendations for Structural Design of Steel-Concrete Shear Connections” published this time lay forth a structural performance evaluation method for headed studs and perfobond strips in line with joint details in the building structures.

Toward the goal of achieving carbon neutrality by 2050, technology development for the reduction of CO₂ emissions is progressing in various fields. In the field of concrete, the development of technology to reduce CO₂ emissions at each of the material stage, manufacturing stage, curing stage, and service stage is required. The authors conducted an experimental study to develop a technology to fix CO₂ during concrete manufacturing. The newly developed technology was found to be able to fix about 10 kg of CO₂ per 1 m³ of concrete. Further, the combined use of a two-stage mixing method, which divides the concrete mixing process into two separate steps, was found to produce concrete that, notwithstanding CO₂ fixing by the above-mentioned method, exhibits no reduction in compressive strength nor loss of strong alkalinity, and thus is suitable for application to reinforced concrete structures.

The air permeability of cover concrete is considered to be important from the standpoint of the durability of concrete, and various studies have been conducted and domestic standards have been established in this regard. The authors have developed a simple air permeability test (cylinder method) that uses a cylinder, which is a highly portable measuring device that does not require a power supply, and are currently conducting investigations on this measurement method and its evaluation. This paper is a summary of the main findings regarding the usefulness of the cylinder method from studies done to date.

This paper describes a proposed method for the assessment of the durability of RC structures, which are required to have long-term durability, by considering not only oxidative corrosion, which is generally applied to the corrosion of rebar in concrete structures, but also the transition to a reducing atmosphere, where the oxygen concentration becomes very low owing to the consumption of oxygen during oxidative corrosion. It is suggested that a lower corrosion rate may be expected in a low oxygen corrosion environment through the high densification of concrete combined with the use of prestressed concrete that can reduce the assumed in-service crack width and possibly achieve zero crack width, or chemical prestressed concrete with a higher level of crack control.