Steel bars mechanically anchored with plate heads are being applied in place of 180-deg hooks. The method uses the bearing plates attached to the ends of the reinforcement to secure anchorages, and it is hoped that it will provide a solution to the problem of greater difficulty of execution and associated increased costs due to the requirement for higher-density reinforcement to improve seismic design, in recent years. Therefore I developed a plate nut fixed in the reinforcing steel bar. About the plate nut which we developed, we made the performance examination of each case. As a result of examination, the nuts with plate confirmed a thing having performance at the same level as conventional 180-deg hooks.
This study aimed at developing a new crack inducing contraction joint system, which enables us to decrease additional thickness of section width. This system adopts bumped steel plates embedded in the member section as well as notch shape section defect on wall surface. To verify the system's crack concentration ability, direct tensile loading test for beam specimens with the joins was implemented. As a result, the proposed joints successfully demonstrated superior crack inducing performance to the existing ones. Next, wall specimens with the contraction joints were subjected to shear loading to demonstrate shear structural performance, which showed those joints did not deteriorate structural performance. Finally crack inducing performance was confirmed in an actual structure. In the application, cracks were effectively induced in the joints, and the practicality of the joint system was successfully demonstrated.
This study aims at investigating the scaling resistance of steam-cured concrete using blast-furnace slag cement exposed to chloride, focusing on widespread application of precast concrete products. First, varying types of cement and curing methods, test of scaling based on RILEM-CDF is performed. Since the results reveal that the scaling of steam-cured concrete using blast-furnace slag cement exposed to chloride is remarkably accelerated, the effect due to decreasing water-cementitious ratio on scaling resistance is researched. Further, the durability evaluation of concrete considering both scaring and chloride permeability associated with respective condition is performed.
The residual life of a concrete structure can be estimated if crack appearance is accurately predicted. In that case, maintenance and life cycle cost can be reduced. However, it is very difficult to predict the residual life before crack appearance because the design sheets, especially for old structures, do not exist. Moreover, it is difficult to get data from the concrete structures by sampling tests on actual structures. In this study, the amount of corrosion when the crack appeared was predicted using electrical accelerated test and FEM analysis. The accuracy of the prediction by both methods was evaluated by comparing it with the actual amount of corrosion. The amount of corrosion measured in the electrical accelerated test was between 26 and 30 mg/cm2 when the area of corrosion on the reinforcing bar was 50%. For the verification of re-deterioration of repaired concrete, also the electrical accelerated test and FEM analysis methods were used. The corrosion mechanisms of repaired concrete were cleared by both the electrical accelerated test and the FEM analysis. In the FEM analysis, the condition, such as cover thickness and tensile strength were input and the residual life was accurately predicted. This prediction method is very useful in the case that the residual life of a reinforced concrete structures is cleared, and data from the FEM simulation can be directly used. With the FEM analysis performed in this paper, the amount of corrosion when the crack appeared and the re-deterioration between the concrete and the repair mortal were predicted.
This paper describes the design procedure for the material selection and mix proportion of the self-compacting mortar used for low diffusion layer cementitious material in the sub-surface radioactive waste disposal facility in Japan. The low diffusion layer is required for reducing transportation by controlling diffusion of a radionuclide. Therefore the low diffusion, cracks control, and low leaching are the important matters in the mix design. The process to select mortar mix design of the low diffusion layer is explained in detail. Of 33 kinds mix proportions used in laboratory comparative testing, the combinations of low heat portland cement, fly ash, lime powder and expansive addition was provisionally set to the mix proportion of the self-compacting mortar used for low diffusion layer.
This paper describes a required initial performance of the low diffusion layer in sub-surface radioactive waste disposal facility which will be constructed firstly in Japan after carry in out a full-size model test by a general method of construction with selected materials and mix proportion. Field demonstration tests conducted by using full-size models are described in order to confirm the actual constructoin peformance on site under 100m deep land level and the crack control effect of the low diffusion layer with the mix proportion selected from the laboratory tests. It was demonstrated that the design procedure for the materials and mix proportion was evaluated as being appropriate and the low diffusion layer could exhibit the required initial performance such as compressive strength, Young modulus of elasticity, void content, effective diffusion coefficient of tritium and the crack generating situation. A calculating method is also proposed for the effective diffusion coefficient of tritium.
In this paper, three kinds of ferronickel slag coarse aggregates made by the different manufacturing process, was examined to confirm the physical and chemical characteristics. The fundamental properties of fresh concrete, the mechanical properties and the durability of hardened concrete incorporating slag as coarse aggregates were investigated. The combinational use of ferronickel slag fine aggregates and coarse aggregates was also studied. As the results, it was confirmed that the mixture proportion, the bleeding of concrete and the mechanical properties of hardened concrete were greatly affected by the characteristics of these slag aggregates. Frost susceptibility of concrete with ferronickel slag aggregate was improved by forming the adequate air void system, due to reducing the excessive bleeding of fresh concrete. From these result, it was judged that ferronickel slag coarse aggregates examined in the study were promising as high quality aggregates for production of concrete.
In this study, cement paste and mortar specimens were immersed in NaCl solution for 2 months. After that three points bending test of the specimens and chemical analyses were conducted so as to determine tension softening curves, which can be applicable to meso-scale analysis, from load-displacement curves using a back analysis and to clarify how amount of cement hydrates affects the tension softening behavior. It was found, as a result, that tensile strength, Young's modulus and fracture energy of mortar specimens become smaller as the amount of cement hydrate CH decreases. Furthermore tension softening model which can consider the change in amount of cement hydrates was proposed.