The deterioration of reinforced concrete structure due to the corrosion of steel bar is caused by the penetration of chloride ion into concrete, particularly in marine environment. In order to estimate the lifetime of concrete structure located close to such as marine environment, it is very important to predict the penetration behavior of chloride ion, and Fick’s law theory with diffusion coefficient of chloride ion is generally used. So the diffusion coefficient has to be calculated theoretically and exactly.
　In this paper, calculating apparent diffusion coefficient (Da) of concrete under a non-steady state has been considered theoretically and as a consequence, it was cleared that the solution formula of Fick’s second low can be used calculate Da only if the chloride biding isotherm is linear. In addition, the accuracy of Da obtained by calculation has been studied. The measurement of chloride ion concentration profile, which causes the error of Da, is influenced by the thickness of sampled layers. Electron probe microscopy analysis (EPMA), can measure a large number of chloride concentrations with thin layer thickness, resulting in an accurate profile, and consequently and accurate calculation of diffusion coefficient. The measurement method using EPMA is excellent especially in the cases of high resistance concrete to chloride penetration containing mineral admixtures. The resistance properties of blast furnace slag and meta-kaolin were evaluated quantitatively using Da determined by EPMA. Consequently, it became clear that the chloride penetration resistance of meta-kaolin is about three times higher compared to that of blast furnace slag, and the type of cement does not have any influence on the resistance properties.

View full abstract

 Chloride ion is an important deteriorating factor which governs the durability of the reinforced-concrete structures under marine environments. The main penetration mechanism of chloride ion into concrete is diffusion phenomenon and numerous methods have been proposed to determine the diffusion coefficient of chloride ion quickly. In this paper, two methods of electrically accelerated experiments were carried out in order to evaluate the chloride diffusivity into concrete at different curing ages. And the effective diffusion coefficient in steady state was calculated by measuring the amount of chloride ions migrated across the diffusion cells by applying electrical potential.
　In this study, the test results showed that effective diffusion coefficient and chloride binding ability are dependent on the type of cementitious materials used and curing age. OPC-based concrete specimens showed lower effective diffusion coefficient than LHC-based. The effective diffusion coefficients with slag substitution showed lower values than no substitution and fly-ash substitution from the early curing age of 28 days. So, it can be said that slag substituted concrete structures can be exposed to marine environments much earlier than the other with less chloride induced deterioration.

View full abstract

 Ecocement was a new type of cement which was developed to use municipal waste incineration ash as its principal raw material. It was broadly categorized into two types: Normal type and Rapid-hardening type. The Normal-Ecocement could be used in reinforced concrete because of its low content of chloride ion (0.1% or less). This paper examines the applicability of concrete with Normal-Ecocement to offshore structures. The study was evaluated by comparing the compressive strength and chloride ion penetration of Normal-Ecocement concrete and Ordinary Portland Cement concrete, after exposure of both types to a marine environment for three years.
　These results showed that after exposure for three years, the compressive strength of Normal-Ecocement concrete slightly increased and chloride ion penetration was faster than Ordinary Portland Cement concrete of the same water-cement ratio. Therefore, to delay this chloride ion penetration, it is necessary to reduce the water-cement ratio of Normal-Ecocement concrete while maintaining its compressive strength the same as that of Ordinary Portland Cement concrete.

View full abstract

 This paper discussed the changes of the flesh and strength properties by the various ambient temperatures about high-flexural strength polymer-modified mortar, and the expression of the strength as well as the difference of the dynamic property and the durability between this mortar and the ordinary concrete. These results showed that the flow value of the high-flexural strength polymer-modified mortar was as big as 280mm and this value was self-compactability property. When cured with steam, the flexural, compressive and tensile strengths were respectively 15.3N/mm², 78.0N/mm² and 6.7N/mm² at 14days, the flexural and tensile strengths were respectively 2.1times and 3.1times compared with the ordinary concrete with the similar steam curing. Furthermore, the mortar also had excellent resistance to freeze-thaw, carbonation and chloride penetration, and improved the resistance to hydrochloric acid and sulfuric acid.

View full abstract

 The Codex Committee is currently formulating and international reference value of cadmium (Cd) content in food, such as brown rice and soybean grains. Reduction of Cd content in staple crops is of a matter of urgent. A project of restoration for Cd-contaminated paddy soil was started in April 2003, under the three research teams’cooperation, i.e., NIAES soil chemistry unit, Taiheiyo Cement Corp., and Nagano Agricultural Research Center. The joint research team adopted a chemical remediation method by washing contaminated paddy soils with chemicals. Appropriate chemicals are added to the Cd-contaminated soils and mixed thoroughly with water to extract soil-absorbed Cd to the water layer, which is, in turn, treated by a wastewater purification system.
　Calcium chloride was selected as a washing chemical and the best condition of the soil-washing was established in the laboratory test. The on-site test of the soil-washing was conducted in a farmer’s paddy field. In the washed plot the soil-Cd extracted with 0.1M-HCL decreased from 0.714mg/kg to 0.592mg/kg corresponding to 17.1% of the removal efficiency. And the extractable Cd by ammonium nitrate solution in the washed plot decreased to 30% of that in the unwashed plot. The Cd and other metal cations contained in the wastewater of the soil-washing were removed by using the chelating-resin based purification apparatus. Rice growth was not significant different between the washed plot and the unwashed plot. The Cd content of the brown rice decreased below 0.2mg/kg which has been proposed a new reference value of Cd content in brown rice.

View full abstract

 In this report, several kinds of cementing materials and other agents are used to investigate the effect of immobilizing the soil contaminated by the heavy metal.
　On lead and arsenic, it was confirmed that we could predict the immobilization effect acco9rding to each content in the contaminated soil.
　Especially in case of the soil contaminated by trivalent arsenite, it was found that the application of oxidizer was effective before immobilizing by cementing materials.
　As some examples of the case studies, the effect of immobilizing the soil contaminated by the heavy metal was investigated by means of the convection dispersion analysis taking account of the permeability of stabilized soil mass and the average precipitation in Japan.

View full abstract

 Hydrogen Energy is paid attention to as clean energy in the future. Hydrogen storage material is one of key technology in its system. Taiheiyo Cement Corporation introduced techniques of Hydrogen storage materials from Hiroshima University and has collaborated on Graphite and Lithium based hydrogen storage materials with it.
　Nano-structural Graphite, which is produced by mechanochemical method by using ball milling, adsorb a large amount of hydrogen (～6mass%). However we found that its property strongly depended on iron component contaminated during milling and that the graphite did not absorb more than 1mass% after it desorbed hydrogen by heating over 300℃.
　Other hand, new Lithium based hydrogen storage material, which is nano-composite of LiNH₂ and LiH by ball milling, desorbs a large amount of hydrogen(～6mass%) in the temperature from 150℃ to 250℃ and reversibly absorbs hydrogen by doping a small amount of proper catalyst such as TiCl₃. Its chemical reaction is as follows: LiNH₂ + LiH ⇔ Li₂NH + H₂. It is one of the promising candidates for hydrogen storage.

View full abstract