Nobuaki Otsuki

Evaluation of AgNO 3 Solution Spray Method for Measurement of Chloride Penetration into Hardened Cementitious Matrix Materials

Recently the number of reinforced concrete structures damaged by chloride attack has increased. It is important to establish a simple method for measuring chloride content in concrete. Observation of discolored area after spraying certain indicator solutions on a fractured surface of the specimen has been considerd as one of these methods. For example UNI (Italian Standard) has recommended such a method for chloride contents using AgNO3 solution. The authors have examined the chloride content at the color change boundary and measured the electrochemical properties of steel bars in the discolored area to clarify the engineering significance of this method.

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.

Evaluation of the AgNO3 solution spray method for measurement of chloride penetration into hardened cementitious matrix materials

Recently, the number of reinforced concrete structures damaged by chloride attack has been increasing. Therefore, it is important to establish a simple method for measuring chloride content in concrete. Observation of the discoloured area after spraying certain indicator solutions on a fractured surface of the specimen has been considered as one of these methods. For example, UNI (Italian Standard) has recommended such a method for chloride contents using AgNO3 solution. The authors have examined the chloride content at colour change boundary and measured the electrochemical properties of steel bars in the discoloured area to clarify the engineering significance of this method.

Crack closure of reinforced concrete by electrodeposition technique

Abstract The electrodeposition method for rehabilitation of cracked reinforced concrete, based on the electrochemical technique, is presented here. Investigations on reinforced concrete beams of size 15×15×125 cm were conducted in this study. Specimens cracked by chloride attack for 18 months were immersed in a ZnSO 4 solution, and were applied with a constant current for 8 weeks. The development of crack closure due to the precipitation of electrodeposits (ZnO) was evaluated. Water permeability, chloride ion concentration, polarization curve and half-cell potential were measured in order to assess the effectiveness of this method in the improvement of concrete properties. The results indicate that electrodeposits formed on the concrete surface were able to close the concrete cracks and to decrease the concrete permeability. In addition, the investigation shows that the application of electrodeposition have effects on the desalination of concrete and re-passivity of the reinforcing steel in concrete.

Condensation of Chloride Ion in Hardened Cement Matrix Materials and on Embedded Steel Bars

It is shown that condensation of the water-soluble chloride ion in concrete and on embedded steel bars is surprisingly significant in concrete structures submerged in seawater. That is, the chloride ion concentration of the pore solution in these concrete structures can be a great deal higher than the surrounding seawater. Also, the chloride ion concentrations of the solution on steel bars can exhibit much higher, and these concentrations are closely related to the electrochemical property of steel bars. Also, the formation of Friedels salt is confirmed to be closely related to the binding of intruded chloride ion in materials with cement matrix.

Long-term forecast of Ca leaching from mortar and associated degeneration

The purpose of this study is the long-term forecast of Ca leaching from mortar and degeneration with Ca leaching. First, a technique for long-term forecasting of Ca leaching from mortar was constructed. Here, Ca is made to dissolve out by combining the electrochemical acceleration test with the diffusion test; it was converted on the basis of Ca leaching rate in real time and was carried out to a long-term forecast of Ca leaching. Next, the long-term forecast technique of mortar degeneration with Ca leaching was constructed. Here, Ca is made to dissolve out by the electrochemical acceleration test, and the mortar was evaluated experimentally. The result of the accelerated degeneration test was checked with the real time conversion result obtained by the long-term forecast of Ca leaching. Finally, predicted results of the degradation with Ca leaching were compared with the survey result of existing structures used for 30 years.

CORROSION OF STEEL BARS WITH RESPECT TO ORIENTATION IN CONCRETE

Corrosion of steel bars (main steel and stirrup) with respect to the orientation in concrete is presented. A detailed study on macrocell and microcell corrosion of steel bars in concrete was conducted on horizontal and vertical steels, depending on the casting direction. The horizontal steel was divided into top and bottom halves. The study was conducted with chloride ions in concrete. Water-cement ratios were 0.5 and 0.7. The electrochemical investigations, microscopic, and physical observations of steel bars were performed. The laboratory investigations were verified with the long-term (23 year) exposure investigations on reinforced concrete beams. The study also focused on the influence of stirrup on macrocell formation of main steel, and corrosion of plain and deformed steel bars. It was concluded that orientation of steel bars has a significant influence on macrocell and microcell corrosion of steel bars in concrete. Formation of gaps under the horizontal steels cause significant corrosion. Stirrups play an important role in increasing macrocell corrosion of main steel. The deformed bar corroded more than the plain bar.

Evaluation of mineral admixtures on the viewpoint of chloride ion migration through mortar

Abstract Recently, it has been said that deterioration of concrete structures occurs due to migration of ions, such as Cl− or Na+, through concrete. In addition, some electrochemical methods which control migration properties through concrete, like desalination or re-alkalization, are becoming more important. However, the mechanisms of ion migration, in electric fields, through concrete are not well understood. Moreover, the effects of mineral admixtures, such as fly ash, silica fume and ground-granulated blast furnace slag on ion migration through concrete have not been closely investigated. From this viewpoint, for the evaluation of mineral admixtures, the properties of chloride ion migration through mortar containing fly ash, silica fume and ground-granulated blast furnace slag have been investigated.

Influence of Cement Type and Temperature on the Rate of Corrosion of Steel in Concrete Exposed to Carbonation

Abstract This paper presents the results of a laboratory investigation on the influence of cement type and temperature on the rate of corrosion of steel in concrete exposed to accelerated carbonation (15% carbon dioxide [CO2] concentration). In this study, reinforced concrete specimens (10 cm by 10 cm by 40 cm) having a water/cement ratio of 0.55, exposed to different temperature conditions (20°C, 30°C, and 40°C) were investigated. Measurement of carbonation depth, void ratio, oxygen permeability, and corrosion rate were performed in the laboratory to assess the influence of cement type and temperature on steel corrosion in concrete. The test results show that concrete containing ordinary Portland cement (OPC) has better corrosion resistance at lower temperatures than blastfurnace slag cement (BFSC). On the other hand, BFSC concrete performs better at higher temperatures (30°C and 40°C), especially when exposed over a longer period of time. In general, corrosion rate in the specimens increased with temper...

Application of electrochemical techniques for the control of cracks and steel corrosion in concrete

Electrochemical techniques are becoming increasingly popular as a means of rehabilitating deteriorated reinforced concrete. In this paper we explore the possibility of using an electrodeposition technique for repairs of land-based cracked concrete structures and investigate the effect of this technique on various concrete properties. Concrete specimens reinforced with steel rebars were used as test specimens in this study. The specimens were first precracked by exposing rebars to chloride-induced corrosion, and then immersed in a solution of zinc sulfate and subjected to a constant d.c. current. The current was applied between the reinforcing steel in the concrete and an external electrode immersed in the solution for eight weeks. The degree of crack closure, water permeability, condition of reinforcing steel, and chloride concentration were investigated in order to assess the effectiveness of this method as a potential rehabilitation technique. The results indicate that the formation of electrodeposits caused the closure of cracks and led to improvement of the concrete watertightness. In addition, the investigation shows that the application of the electrical current increases the passivity of steel in concrete.