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Niigata-shi, Japan

Saito T.,Tokyo Institute of Technology | Sakai E.,Tokyo Institute of Technology | Morioka M.,Denki Kagaku Kogyo Co. | Otsuki N.,Tokyo Institute of Technology
Journal of Advanced Concrete Technology | Year: 2010

The carbonation of γ-Ca2SiO4 (γ-C 2S) and mechanism of vaterite formation have been investigated by evaluating the crystal structures of both γ-C2S and vaterite. The samples used were autoclaved calcium silicate hydrate hardening bodies prepared from Ordinary Portland Cement (OPC), γ-C2S and a-quartz and then subjected to accelerated carbonation. The ratio of OPC to γ-C2S was varied. Ca2+ in both γ-C2S and vaterite was found to be coordinated to six O2-. In addition, both γ-C2S and vaterite have similar atomic arrangements of O2- and Ca2+ and Ca-O bond distances. Therefore, it is proposed that vaterite mainly forms from γ-C2S via a topotactic reaction during accelerated carbonation. Copyright © 2010 Japan Concrete Institute.

Ueda T.,Tokushima University | Kameda T.,Tokushima University | Nanasawa A.,Denki Kagaku Kogyo Co.
Separation and Purification Technology | Year: 2011

In this study, a new electrochemical rehabilitation method is proposed and experimental investigation on the viability of this method is carried out. This rehabilitation method employs an anode system that bonds to concrete surface with the aid of ductile fiber reinforced cementitious composites which works to improve both durability and mechanical performance. From results of chemical analysis of concrete and half-cell potentials of steel bars, protective and repair effects against steel corrosion were achieved by the proposed method. In addition, results of flexural bending test of treated specimens showed that bending strength and flexural ductility of the specimens was improved by bonding of the anode system and strengthening effect was not reduced by the electrochemical treatment. © 2011 Elsevier B.V.

Ueda T.,Tokushima University | Kushida J.,Tokushima University | Tsukagoshi M.,Tokushima University | Nanasawa A.,Denki Kagaku Kogyo Co.
Construction and Building Materials | Year: 2014

Complex deterioration mechanism due to both chloride attack and ASR are greatly affected by environmental temperature. In this study, the influence of environmental temperature on concrete expansion and steel corrosion was experimentally investigated. As a result, some protection effect against steel corrosion was found in the cases of storage at 30 °C or 40 °C, although ASR expansion was promoted. This would be caused by the formation of alkali silica gel around the steel. As a remedial measure against such a complex deterioration, electrochemical penetration of lithium from the electrolyte solution was also investigated. It was clarified that electrolyte temperature greatly affected the extent of lithium penetration and the treatment at 40 °C remarkably accelerated lithium penetration into concrete compared with the case of 30 °C. Regarding the kind of lithium salt, LiNO3 solution was most effective among a number of different kinds of lithium salt. © 2013 Elsevier Ltd. All rights reserved.

Ueda T.,Tokushima University | Wakitani K.,Tokushima University | Nanasawa A.,Denki Kagaku Kogyo Co.
Electrochimica Acta | Year: 2012

Chloride attack is a serious deterioration mechanism of reinforced concrete structures, causing steel corrosion in concrete. As a repair method, the electrochemical chloride removal technique named desalination was developed and has been applied to many concrete structures. Desalination can extract chloride ions (Cl-) from hardened concrete but it is impossible to remove all Cl- contained in concrete. Therefore, it is important to improve chloride removal efficiency in order to help prevent early deterioration of concrete after desalination. In this study, the influence of the temperature of the electrolyte solution on electrochemical chloride removal efficiency is investigated by chemical analysis to evaluate electrochemical migration of several kinds of ions. As a result, it was found that chloride removal percentage and transference number of Cl- increased by about 10% with a rise of temperature ranging from 20 °C to 40 °C. © 2012 Elsevier Ltd. All rights reserved.

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