Precast composite concrete combines half-precast members manufactured in a factory with concrete placed at the construction site. The method of construction using precast composite concrete is characterized by stable quality ensured by the use of half precast members, continuity provided by the cast-in-place concrete, reduction of the environmental burden through decreased use of sheathing, rationalization of construction, and labor saving. On the other hand, points to keep in mind regarding the introduction of this construction method is that it requires a detailed construction plan, appropriate work procedures and methods, and careful quality control. All the above is covered in Recommendations for Construction Practice of Reinforced Concrete with Half Precast Concrete Members of the Architectural Institute of Japan. The Recommendations were revised in October 2019, and this paper presents an outline of the revised edition.

As the number of port facilities turning 50 years old is increasing rapidly, reducing the life cycle cost required for the construction and maintenance of facilities is urgently needed. Among harbor structures, the superstructure of wharves is most susceptible to deterioration due to chloride attack, and as inspections cannot be carried out easily as part of periodic inspection and diagnosis, improving the ease of inspection has long been sought. A possible solution is wharves that allow easy removal of their superstructure through the use of replaceable slabs. This paper presents the results of a fi eld demonstration test using replaceable slabs and their technical evaluation.

Prior research by the authors established the fact that steam-cured concrete undergoes drying during steam curing, especially during the cooling stage, and that this drying causes the pore structure of the concrete surface layer to become coarse. Further, the prior research suggests that water sprinkling during steam curing suppresses the drying of concrete during steam curing and allows the concrete surface layer to develop a dense pore structure. In the present study, we reexamined this in light of new findings. As a result, we found that the use of water sprinkling during steam curing does affect the pore structure of the concrete surface layer, and that this effect actually extends to the pore structure inside the concrete.

Using four types of water-cement ratio of 40%, 50%, 60%, and 60% with viscosity agent added, we examined the effect of different viscosity and compaction conditions on the filling ability and quality of the cover while focusing on the plastic viscosity of the mortar phase of concrete. A comprehensive evaluation was carried out from mix proportions to the construction results, based on the evaluation of the filling ability of concretes with the same slump, the ultrasonic wave propagation velocity inside and outside the rebar after hardening, and the compressive strength of the sampled cores. For the water-cement ratio of 60%, the addition of viscosity agent was found to improve segregation resistance and compaction ability. On the other hand, the water-cement ratio of 40%, which had the highest viscosity, yielded excellent segregation resistance but reduced compaction ability, indicating the importance of selecting appropriate mix proportions in consideration of the construction conditions.