The precast concrete is one of the technologies that can greatly contribute to productivity improvement through on-site labor saving, manpower saving, and shortening of the construction period, and expansion of its use is desirable. The Concrete Committee of the Japan Society of Civil Engineers (JSCE) published Concrete Library 158, “Guidelines on Plan, Design, Manufacture, Construction and Maintenance for Structures using Precast Concrete”, which presents technical points on structural planning, design, manufacture, construction, and maintenance of structures using precast concrete based on the concepts of JSCE's Standard Specifications for Concrete Structures. This paper presents an overview of these Guidelines.
It is well known that quality of concrete cover plays important role for durability of concrete structure. In Japan, NDIS 3436 has been established as standards for non-destructive air permeability test of concrete cover. This report deals with a outline of the standards including round-robin test and so on. Furthermore, trend of foreign countries on standardization of non-destructive air permeability of concrete cover, mainly on Torrent sir permeability tester, is introduced. In near future, relevant usage of standardized test methods to evaluate and control the quality of concrete structure on site would be expected.
In carrying out floor slab replacement work, it is important to keep the traffic regulation period as short as possible and to complete the work within the scheduled period. For this reason, precast concrete is used as one means to shorten the renewal process. However, the timing of the lifting of traffic regulation may be affected by the waterproofing of slabs in the final stage of construction, as this process is easily affected by weather conditions. In this study, focusing on the excellent water-blocking performance of UFC, we aimed to develop floor slabs that are not affected by the weather by applying UFC as a waterproofing layer on precast PC slabs in advance. This paper reports on the findings of this study, namely that the water-blocking performance of UFC as a waterproofing layer is satisfactory, that the integrity of the slab as a composite of UFC and concrete is durably maintained, and that the occurrence of microcracks can be suppressed by water curing.
The inspection of floor slabs is mainly carried out by visual inspection from the underside and visual check of the paved surface. However, the correlation of sedimentation on the top surface of RC floor slabs and their external appearance is not clear, and the current inspection methods carry the risk of overlooking the occurrence and progress of sedimentation. This paper focuses on water retention on the upper surface of floor slabs, which is considered to be the cause of sedimentation, and summarizes the findings of an examination of a water retention detection method for the upper surface of floor slabs using electromagnetic wave radar, which is a non-destructive inspection method. It was confirmed that it is possible to visually determine the areas affected by water and the penetration route of water based on differences in the reflection intensity of electromagnetic waves, and to detect water retention on the upper surface of slabs based on differences in the maximum amplitude of the reflected waves.
The authors are developing an AI-based total measurement method to determine the slump value of concrete by analyzing images of the concrete flowing down the chute of a truck agitator as an alternative to the slump test that has been in use for many years as an acceptance test for ready-mixed concrete. In FY2020, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) implemented the Project on Introduction and Utilization of Innovative Technologies for Drastic Improvement of Productivity at Construction Sites using the Public/Private R&D Investment Strategic Expansion PrograM, and the accuracy of AI-based estimation was confirmed through total measurement at actual construction sites. We also introduce findings that improve the accuracy of AI-based estimation by applying the principle of in-pipe flow with slip of Bingham fluid to concrete in the slump flow area.