Japan Concrete Institute published the “Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures 2022” as a revised edition of the 2009. This guideline designed for everyone interested in concrete cracking codifies the entire process from crack discovery to investigation, cause estimation, evaluation, judgement, and repair and reinforcement.

Precast concrete is manufactured using steam curing to accelerate strength development and allow early demolding. However, deterioration caused by delayed ettringite formation (DEF) in the case of excessively high concrete temperatures is a concern. In this study, we investigated the actual conditions of steam curing facilities and conducted experiments under conditions reproducing actual production, and we investigated temperature control methods for the suppression of DEF. Based on the results of the experiment, points to be kept in mind regarding the measurement position of the ambient temperature and the specification and position of the steam outlets for controlling steam were determined. Further, it was determined that when a member is thick and thus ought to be considered as mass concrete, the concrete temperature may exceed 70℃, which is the concrete temperature level at which DEF may occur, depending on the production conditions.

Repair materials that consist of an inorganic material such as cement mixed with rebar corrosion inhibiting material are widely used for the repair of salt-damaged RC structures. However, there are few examples of the use of organic materials such as epoxy resins, which are widely used as repair materials, as a countermeasure against salt damage. Making possible the use of epoxy resin as a repair material for salt damage would allow the implementation of salt damage countermeasures across a wide range of applications. This paper reports on the properties of salt adsorption type epoxy resin made by adding a salt-adsorbing agent to organic epoxy resin as a repair material, and examples of its application to reinforced concrete structures that have suffered salt damage.

In recent years, PCa construction has been attracting attention as a means of improving productivity in pier construction. Usually, PCa construction involves the fabrication of PCa members for the pier superstructure in a land yard near the site, their erection by floating crane after the driving of steel pipe piles, and placing of cast-in-place concrete at the joints (hereafter, “site PCa”). In this context, the authors propose a unit-type precast pier construction method in which all PCa members are manufactured at a factory, transported to the site by land transportation, and then PC-bonded together with prestressing (hereafter, “the proposed construction method”). This paper presents an overview of the construction method and experiments on the load capacity of PC press joints. This is followed by a comparison of the productivity and CO₂ emissions of conventional cast-in-place, site PCa, and the proposed construction method.