The Japan Society of Civil Engineers established a subcommittee on construction technology for the renovation of reinforced concrete slabs over steel girder road bridges (hereinafter, the Subcommittee) in 2016. The Subcommittee collected information on the current status of maintenance and repair of RC slabs and the latest construction projects and construction technology with a focus on RC slab renovation technology, whose use it expected to spread in the future. Further, the Subcommittee held information exchange sessions to ascertain that the renovation of RC slabs can be carried out safely and effectively according to the given construction conditions, and proceeded with the compilation of a report. This paper presents an overview of that report, entitled “Design and Construction Technology for Renovation of Reinforced Concrete Slab over Steel Girder Road Bridges”, which was published in April 2020 as a result of the Subcommittee's three years of activities.
An automatic rebar arrangement inspection system using a stereo camera was developed as a solution for maintaining the accuracy of reinforcement inspections while saving manpower and labor. Over 30 trials were conducted at 15 sites with different solar radiation and weather conditions and rebar arrangement specifications. And a trial of the proposed inspection system in combination with telepresence technology was conducted at the Nishiki Tunnel. Further, the inspection system was applied for the first time to construction phase confirmation at the Higashinegawa Bridge superstructure construction work site, which is a trial site of the “Project for Introducing and Utilizing Innovative Technology to Dramatically Improve the Productivity of Construction Sites” of the Ministry of Land, Infrastructure, Transport and Tourism. As a result, the inspection system was found to yield measurement accuracy sufficient to judge compliance with specified rebar spacing, reduce inspection time to about one third, and the time required for working at high places can be reduced, and contribute to improved safety by reducing time spent working at high elevations and preventing the spread of Novel coronavirus infections through its labor-saving effect.
Knowing the pumpability of concrete is extremely important for concrete work, yet there is no established laboratory test method to quantitatively evaluate the pumpability of concrete. As a result, concrete pumping tests at actual construction scale, which require considerable expenditure of money and effort, are depended on. Therefore, in this study, for the purpose of evaluating the pumpability of concrete with slump of 8 cm to 21 cm by an indoor test, a testing apparatus for simulating accumulated pressure, which is one of the characteristics of concrete, was built, verification of the validity of said apparatus and the proposed test method using said apparatus was conducted, and the possibility of field application was examined.
As a tsunami countermeasure for the megafloat anchored in the harbor of the Fukushima Daiichi Nuclear Power Plant, work is being carried out to stabilize the megafloat by relocating it, grounding it, filling the inside with mortar, and preparing the upper part of the megafloat for effective use as a harbor yard. As this work is carried out in a radiation controlled area, many procurement-related restrictions and issues apply regarding the materials to be used. Therefore, a plant was established on the site to manufacture the artificial ground material to be used for the megafloat grounding mound, the internal filler of the megafloat, and the revetment blocks for the construction of the gravity wharf. This paper presents an outline of the construction, the specifications of the construction materials, and the application results.
In construction projects where the time between concrete placing and formwork removal is relatively short, such as lining concrete in mountain tunnels and secondary lining concrete in shield tunnels, development of the required strength for formwork removal often has a significant impact on the construction cycle of the project. However, depending on the environmental and proportioning conditions, it may be difficult to rapidly the required strength sufficiently rapidly. Currently, this is dealt with by promoting strength development by means such as adjusting the proportioning conditions and the curing practice. Against this background, construction was carried out using various formulations of concrete combined with curing accelerator and high-early-strength type expansive admixture in order to improve the initial strength of concrete. This paper reports the results of laboratory tests conducted during the development process of this method and examples of on-site application.