In this paper, the experimental investigation for visualization of the area of internal crack and rebar corrosion in concrete structure by using electromagnetic wave radar was carried out. Firstly, the specimens with the rebar cover thickness (30, 60 mm) were made in which local corrosion area with different corrosion rate were introduced by electrolytic corrosion experiment, and the crack width and distribution characteristics and the corrosion distribution of the rebar were evaluated. Then, the visualization of internal cracks and corrosion areas by applying Self-Organizing Map (SOM) is tried by using indexes that the difference of electromagnetic wave reflection waveform data between damaged and sound parts are considered. As a result, by applying one-step SOM to corrosion specimens, it was confirmed that corrosion areas of rebar can be detected. Moreover, we propose a method to evaluate internal cracks and corrosion amount by two-step SOM and verified the applicable range. It was confirmed that the presence of internal cracks can be quantitatively and clearly evaluated, and it was confirmed that internal cracks of 0.1 to 0.4 mm and corrosion rates of about 4% can be detected.
The purpose of this paper is to verify the applicability of a simple water supply method using water supply curing system as an external solution supply method in electrochemical corrosion control method. The study was conducted focusing on (a) the design method, (b) the repair effect of the amount of solution, the distance between the concrete surface and the anode, and the type of anode material, and (c) the applicability to the actual structure.
As a result, a design method for selecting the suction port position and suction machine based on computation fluid dynamics was established. In addition, there was no effect of the amount of solution on the realkalization and desalination effects. On the other hand, the electrodeposition effect was found to differ depending on the type of anode material. It was also found that the greater the distance between the concrete surface and the anode, the greater the effect. Furthermore, as a result of application to actual structures, it was confirmed that the simple water supply method was easy to construct and could be applied to complex surface shapes, and also contributed to the suppression of external solution disappearance.
Airborne chlorides from sea surface consists of small particle of seawater, generated by interaction of wave, wind and coastal structures. Airborne chlorides, which is transported by wind sticks to the surface of structures, harms long-term durability of the structures. In this study, field observation of surface chloride concentration from sea surface were carried out in the coast where the wave-dissipating concrete blocks were installed. Prediction model for surface chloride concentration, based on geographical condition in the coast, is also developed. From the results, it was shown that the amount of the surface chloride is related to the geographical condition that wave-dissipating concrete blocks installed in the coast. The increased amount of surface chloride is estimated by classifying and quantifying a locations of the wave-dissipating concrete blocks. It was confirmed that calculation results of surface chloride concentration of concrete agree with the field measurements data.
This paper deal with the strength and hysteretic behavior during an earthquakes associated with the anchorages considering the effects of flexural cracks developed in reinforced concrete. In the experiments, eight reinforced concrete specimens with four headed anchor bolts are used. These specimens include two types of anchorages depending on the failure modes: the bolt yield type and the concrete failure type. The Results of cyclic loading tests (static tests) show that the effects of the flexural cracks in the anchorage strength appears more obviously in the concrete failure type than the bolt yield type. However, the strength can be recovered by applying crack repair with the epoxy injection. In addition, a series of the shake table tests (dynamic tests) present that the nonlinear hysteretic behavior of the anchorages under the dynamic loads demonstrates well those under the static loads.
The authors developed a new retrofitting method aimed at improving the productivity of seismic retrofitting works. The developed method is seismic retrofitting method using divided precast panel, high strength fiber reinforced mortar and steel plate. The mortar is poured into the gap between the objective column and precast panels around it assembled with steel plate and bolt. There are few cases using high strength fiber reinforced mortar for seismic retrofitting, and its ductility is not clear. Therefore, in this paper, in order to clarify the ductility of the RC members retrofitting by this method, amount of steel plate, the high strength fiber reinforced mortar and the sectional dimensions were set as variables, and cyclic loading tests was conducted. As a result, the influence of high strength fiber reinforced mortar on ductility was clarified and an calculation formula was reconstructed.
The purpose of this research is to realize lightweight and high strength prestressed concrete slab by using lightweight concrete mixed with short fibers.
In this paper, it was confirmed that the PVA short fiber mixing ratio should be 0.5vol.% or less in order to obtain mechanical performance equivalent to those of lightweight aggregate concrete with a compressive strength of 50 MPa. In addition, it was confirmed that the lightweight PC slab mixed with 0.5vol.% PVA short fibers had the same punching shear capacity as the normal PC slab. Furthermore, the increase in shear capacity of lightweight PC slab mixed with short fibers was considered to be due to suppression of crack extension in the RC section and the accompanying tide arch formation in the PC section.