Shinichi Miyazato

Influences of Bending Crack and Water-Cement Ratio on Chloride-Induced Corrosion of Main Reinforcing Bars and Stirrups

This study experimentally investigated the influences of bending crack and water-cement ratio (w/c) on the chloride-induced corrosion on main reinforcing bars and stirrups. Special features of this study included crack formation through application of bending load, consideration of main reinforcing bars and stirrups together, and measurements of both macrocell and microcell currents. An indoor examination investigated the corrosion of main reinforcing bars and stirrups on model beams. To clarify the indoor examination results, larger-scale beams exposed to an outdoor environment were investigated. Results showing the influences of bending cracks and w/c on the corrosion rate were reported.

Proposal of Corrosion Rate Analytical Model of Reinforced Concrete with Crack

The initiation stage can be estimated by analyzing the penetration of chloride ions in concrete. In addition, it is necessary to predict the corrosion rate after the propagation stage. On the basis of this background, in this paper, a basic model that estimates a steel corrosion rate in reinforced concrete with a crack is proposed. Therefore, first, a model that can calculate the microcell and macrocell corrosion rates is constructed. The input data of this model are the anodic polarization curve, cathodic polarization curve, polarization resistance, and electrical resistivity of concrete. This model is further verified using a mortar specimen and a concrete specimen. The experimental parameters are the watercement ratio, crack width, and humidity. Consequently, it can be confirmed that the analyzed and measured values are equal. Moreover, the engineering value of this model is confirmed. Based on the above results, the following conclusions can be drawn: 1) a model that can be used for analyzing the steel corrosion rate of the reinforced concrete with the crack is proposed. 2) By carrying out the experiment using the mortar specimen and the concrete specimen with a crack, we can confirm the validity of the model. 3) The influences of the water-cement ratio, crack, and humidity on the steel corrosion rate can be confirmed by using this model.

Study on Triage for Deteriorated Concrete Structures by JSCE-342

In Japan, with the ageing of both structures and society, a social system should be constructed that reasonably maintains and manages safe concrete structures. Therefore, a Subcommittee on Priority in Maintenance and Management of Deteriorated Concrete Structures (JSCE-342) was organized to study schemes for determining the priorities during inspections and repairs. Four working groups investigated environmental action, performance evaluation and inspection to develop a priority-determination system. This paper outlines a midterm report; a maintenance procedure for structures based on priority determination is presented, and problems for the transition period from preemptive maintenance to preventive maintenance are identifies.

Application of Electrodeposition Method for Repair of Mortar Damaged by Drying Shrinkage Cracks.

In this study, the application of electrodeposition method to repair reinforced concrete damaged by drying shrinkage cracks was investigated experimentally. Especially, it was clarified that electrodeposition had an effect on the reduction of water permeability and carbonation. The contents of this study were as follows; (1) the selection of external solution, (2) the influence of electrodeposition on the crack closure, and the effect of electrodeposition on the water permeability and carbonation restraints, (3) the influence of electrodeposition on the surface coating and minuteness on the non-cracked mortar, and the effect of electrodeposition on carbonation restraint, (4) the water permeability and adhesive strength after the electrodeposition. As a result, it was clarified that the electrodeposition led to improvement of mortar watertightness and carbonation restraints.