Makoto Hisada

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.

Marine Durability of 23-Year-Old Reinforced Concrete Beams

This paper gives findings of marine durability tests of 23-yr-old reinforced concrete beams exposed to marine tidal and atmospheric environments. The study mainly focused on corrosion of steel bars with respect to orientation in concrete, carbonation and chloride-ion induced corrosion of steel bars, quantitative evaluation of corrosion based on the electrochemical data, and the influence of stirrups on macrocell formation. Experimental work covered electrochemical investigations, chloride ion profile and carbonation depth measurements, microscopic steel concrete interfaces, and visual observation of steel bar corrosion. The study found that chloride-ion induced corrosion is significantly influenced by the orientation of steel bars in concrete. Cracks and interfacial gaps between steel and concrete must be accounted for in order to predict corrosion of steel bars in concrete.

THEORETICAL EVALUATION OF DIFFUSION COEFFICIENT OF CHLORIDE ION IN MORTAR FROM MOBILITY

Many researchers have been trying to evaluate the diffusion coefficient of chloride ion in concrete by using qualitative and quantitative electromigration tests. Up to now, however, there has been no sufficient method to closely determine the diffusion coefficient of chloride ion through electromigration tests. This paper investigates the diffusion coefficient of chloride ion in mortar by mobility through an electromigration test. The concept of Einsteins equation, which can relate the diffusion coefficient of the chloride ion and the mobility in an ideal solution with very low concentration, is adapted. Then, for compensating the influence of the concentrations, the Debye-Huckel theory is used. For considering the effect of other existing ions, namely, OH-, Na+, and K+, the electrical neutrality is taken into account. Therefore, using Einsteins equation, the Debye-Huckel theory, and electrical neutrality, the diffusion coefficient of chloride ion can be calculated theoretically from the mobility. The correctness of the calculation is checked by a series of tests.

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.