Steel, used in from familiar products such as automobiles and electrical appliances to large structures such as buildings and ships, is inextricable and basic materials of our lives. Steel has made significant progress in both quantity and quality with the development of society. Galvanized steel has evolved most significantly in these 20 or 30 years, being recognized that the steel is the most suitable material for automobiles, with rapid increase in automotive production and emerging demand of anti-corrosion bodies for a background. In this paper, the author firstly would like to describe the development details of galvanized steel, particularly GA (Galvannealed Steel: Hot-dip Zn-Fe alloy steel) achieved through cooperative work among automotive companies, steel companies and paint companies in Japan. At present, galvanized steel became one of the biggest shipping steel products in Japan and in the world as well. If the strong demand for galvanized steel continues in the future like today, it is said that the zinc source will be depleted in 20 years. Aluminum is thought to be the most probable alternative element for zinc, but there are still several problems in its substitution. Eventually, as a tentative measure, only remedy for this matter is to save zinc resources and therefore the development of both hot-dip and electro galvanizing process which makes possible to reduce the zinc usage is required.
Recently, old narrow tunnels are reused by widening their sections for economic efficiency. New design concept will be required in their construction because excavation damaged zone (EDZ) might be already formed around old tunnels. Especially, estimation of EDZ extent is necessary for safe construction and stability assessment of a widening tunnel. In this study, EDZ around an old tunnel constructed in the Neogene soft rock seventy years ago was estimated based on P-wave velocity and observation of the face during widening. Deformation caused by widening the old tunnel was also measured. It was found that EDZ estimated by reduction in P-wave velocity was in good agreement with that estimated by observation of the face. It was also found that deformation of the widening tunnel was much less than that of either the old tunnel or a new tunnel constructed near the widening tunnel. In the widening tunnel, most of EDZ had been excavated and non-damaged zone outer side of the EDZ had been little excavated. It can be expected that deformation of a widening tunnel is little when the section size of that is almost equal to extent of EDZ.
From the viewpoints of multiple-utilization of land, environmental safeguards, energy conservation, etc, a temporary storage of hot water in openings excavated in rock may be worthwhile. In this case, the rock mass around the openings will respond by coupled thermo-mechanical effects induced by the hot water. In this study, flow-through experiments on a single fracture in granite has been carried out under confining pressures of 5-10 MPa, and at temperatures of 20-90°C. The fracture aperture and the permeability monotonically decreased with time at room temperature, and reached a quasi-steady state. Then, after the temperature was raised to 90°C, the aperture decreased again throughout the rest of the experiments. Fluid samples were taken from the outlet to examine the elemental concentrations that were evaluated by inductively-coupled plasma atomic emission spectrometry (ICP-AES) . The elemental concentrations increased with increase of temperature. After the flow-through experiments, the fracture surface was observed by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) . The formation of a few kinds of precipitated minerals such as silica and calcite was revealed. The precipitation was limited to quite local and small areas. However, the precipitated minerals seemed to have had some influences on the permeability.
When considering a geological isolation of high level radioactive wastes, the evolutions of the mechanical, hydraulic, and transport properties of the targeted rocks should be evaluated in advance because those may be degraded by the coupled thermal, hydraulic, mechanical, and chemical effects induced by the emplacement of the wastes. Chemical reactions such as mineral dissolution and precipitation that is dependent on temperature and pH conditions, may be one of the key issues that may trigger off the degradation. Therefore, the dissolution mechanism of the targeted rocks should be thoroughly examined under various temperature and pH conditions. In this work, a suit of flow-through experiments in granite has been conducted at temperatures of 30, 50, and 70°C, and at pHs of 6, 9, and13, to examine the granite dissolution behavior. An apparent dissolution rate equation of the granite is defined under arbitrary temperature and pH conditions. The acquired dissolution rates are compatible to those evaluated in the literature. Utilizing the dissolution rates, the evolution of the element concentrations measured in the permeability experiments on the granite fracture is replicated. The predicted concentrations follow the experimental measurements both qualitatively and quantitatively. Although showing in a good agreement with the experimental measurements, the predictions slightly underestimate the actual. This is attributed likely to the unaccounted effects of mineral dissolution at the contacting asperities, indicating that a more sophisticated dissolution equation should be achieved by considering such a dissolution mechanism.
Bentonite has been studied as the buffering materials in the project of the low-level radioactive waste disposal and high-level radioactive waste disposal, since bentonite has high abilities of water interception, self-sealing, absorption, chemical buffring and material migration retardation. In order to realize those abilities, it is prefer to install bentonite under the high density condition. The granular bentonite was developed which utilize the different size of bentonite particles, it make it possible to realize the easy installation under the high density condition. In this study, swelling process of the bentonite is visualized and analyzed by X-ray CT method. The soaking tests of bentonite under the displacement constraint using acrylic molds were conducted during over 200 days. The swelling and homogenization process during soaking tests were visualized, and the soaking and swelling process were analyzed from X-ray CT image data. The parameters, such as water content ratio, wet density and dry density were also measured and the fundamental properties of the bentonite were verified. It was also found that those parameters can be accurately evaluated from X-ray CT image data. The water permeation tests under the displacement constraint and displacement free conditions were also conducted. The evaluated intrinsic permeability were low enough in both conditions, and it was confirmed that the displacement constraint does not gives crucial effects to the permeability of bentonite.
We conduct CO2-water-rock interaction experiments at a temperature of 25 °C and pressure of 1 MPa to investigate rock dissolution phenomena and to predict long-term CO2 fixation efficiency. The rock samples selected for our experiments are basalt, granodiorite and tuffaceous sandstone. Our experiments show that tuffaceous sandstone provides the fastest acid-neutralizing reaction (the fluid reacting with tuffaceous sandstone shows the highest pH) . However, most cations eluted from tuffaceous sandstone and granodiorite may be caused by dissolution of constituent carbonate minerals, which will not contribute to the long-term CO2 mineral fixation. On the other hand, basalt shows the fastest Si release rate corresponding to silicate mineral dissolution. We conduct a long-term CO2 fixation efficiency simulation using Ca, Mg and Fe release rates. On the assumption that (1) CO2 injection rate to be 1,000 ton/day (2) injection time period to be 50 years (total amount of injected CO2 is 18,250,000 t) (3) target aquifer porosity 20% (4) CO2 density 500 kg/m3 (5) injected CO2 to groundwater volume ratio 1:1, the time required for mineral fixation of 18,250,000 tons of CO2 is simulated to be about 180 years for granodiorite, about 15,000,000 tons of CO2 fixed as a carbonate mineral in 200 years for basalt and 4,000,000 tons of CO2 fixed in 200 years for tuffaceous sandstone. This simulation data strongly suggests that the geochemical trapping of CO2 will proceed much faster than the results of previous studies and is an important mechanism not only for long-term but for shorter-term security of CO2 storage.