Acoustic emission monitoring could be a powerful technique for various forthcoming rock engineering projects, because it provides information on failure mechanism and possibly on fracture prediction of rock structures. The author has been engaged in researches and developments on the monitoring technique for more than ten years. In this paper, acoustic emission monitoring during hydraulic fracturing, heating fracturing and excavation of an underground powerhouse is reviewed, mainly based on works of the author. Through the reviewing, the applicability of the monitoring to rock engineering projects is also discussed.

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In order to prospect current recycling status in Korea, wastes generation and recycling rate were reviewed. Approximately 180,753 ton/day of wastes was generated in 1996 ; 49,925 ton/day of domestic waste and 130,648 ton/day of industrial waste. During the last five years, waste management laws such as waste disposal law, recycling law and environment friendly industry law were prepared. In this article, concerning over waste generation and recycling, recycling law, Korean Resources Recovery & Reutilization Corporation and the problems and technological developments associated with recycling were summarized.

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In order to realize the automation of breaking task of huge rocks, it is necessary to detect the huge rocks and to make the breaker tip move to the surface of the huge rock automatically. In the previous study, the image processing procedure to detect the huge rocks was proposed. In this study, a method to obtain the three dimensional information of huge rock was investigated by using the laser spot light. A simple shape object was used instead of huge rocks to examine the accuracy of this measuring system. From the comparison between the estimated object position and actual position, it was found that this measuring system works well.

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Tricalcium aluminum hydrate (3CaO·Al2O3·6H2O：C3AH6) is synthesized mechanochemically from mixtures composed of calcium hydroxide (Ca(OH)2) and pseudo-boehmite (γ-AlO(OH)) powders by room temperature grinding using a planetary ball mill. Use of the boehmite sample with inferior crystallinity is more favorable for the mechanochemical synthesis rather than that with well crystalline one. The time required to form C3AH6 from the Ca(OH)2-γ-AlO(OH) mixture is much longer than that from the Ca(OH)2-gibbsite (Al(OH)3) one. Adsorbed water from air during grinding plays a significant role in the formation of C3AH6 from the former mixture. After water addition to Ca(OH)2-γ-AlO(OH) mixtures ground for various times, excess hydrated calcium aluminates such as C2AH8, C3AH8-12 and C2A0.5H6.5 are formed in the starting and the short time ground mixtures, while a few amount of these compounds is formed in these hydrated mixtures after prolonged grinding. Formation of these excess hydrated compounds, which belong to layered structural materials, is enhanced in the presence of free Ca, Al compounds and water.

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Applicability of magnesium oxide as a neutralizing agent in mine water disposal has been investigated using an artificial mine water containing ferrous iron of 1,000 mg dm-3 in terms of the reagent dosage and the reaction time. Ferrous ions were more effectively oxidized to ferric ions by aeration of the solution in the presence of magnesium oxide than by that in the presence of limestone. Aeration of the solution decreased the magnesium oxide dosage and the reaction time required for lowering the iron concentration to the acceptable value. Furthermore, recycling of the sludge showed the effects of reduction of the reagent dosage, shortening of the reaction time and densification of the sludge. Sludge recycle processes without and with aeration formed a sludge with the solid concentration of 0.155 and 0.373 g cm-3 by the addition of magnesium oxide of 1.25 and 1.5 equivalents for ferrous iron and sulfuric acid in the solution, respectively. In both processes, the reaction times were 30 minutes.

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Cation-exchange treatments of a Na-A zeolite under various conditions have carried out to clarify exchange characteristics. Repeated cation exchange treatments using the diluted 0.1M cation solution gave more exchange amount than that by one-time treatment using the concentrated 2M-solution prepared with various cations such as Mg2+, Ca2+, Co2+ or Ni2+. As illegal charge balances were often obtained from analyses of zeolites by the atomic absorption spectrophotometry and the flame photometry, possible chemical interferences were examined for all of related substances. Althongh the concentration of HF was found to give negative interference to the absorbances of both Al and Si, the influence is rather serious in determination of Al content. Matching of HF concentrations between sample and standard solutions is thus very important to obtain regular values of the charge balances. Another interference to be reminded is the enhancement of emission for K by the existence of Si as well as of Na. Considering above mentioned interferences, the deviations of charge balances in zeolite analyses were depressed below 2 % or less by using the atomic absorption and flame photometoric methods.

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An experimental study was carried out to determine the standard Gibbs energy of formation of zinc orthosilicate, Δ (Zn2SiO4), for the purpose of controlling zinc vapor pressure by utilizing the equilibrium reaction between Zn2SiO4 and a CO-CO2 gas mixture. A CO-CO2 gas mixture of fixed composition was passed through a column of synthesized granular Zn2SiO4 placed in a uniform temperature zone of a furnace, and the equilibrium CO-CO2-Zn(g) gas mixture from the following reaction Zn2SiO4(s) + 2CO(g) = 2Zn(g) + 2CO2(g) + SiO2(s) was contacted with a molten Cu-Zn alloy placed in the same uniform temperature zone, where another equilibrium was made attain between the gas phase and the molten alloy. From the zinc content and the known thermodynamic data of the alloy, pZn in the gas phase was obtained and from which, being combined with the composition of the CO-CO2 gas mixture, pCO and pCO2 were calculated. Those partial pressures were then used to calculate the standard Gibbs energy change of the above reaction, which was combined with the available standard Gibbs energies of formation of CO, CO2, and SiO2 to determine Δ (Zn2SiO4). The result is as follows : Δ (Zn2SiO4) = 0.613T-1,951(±7) (kJ/mol) [1,423-1,573 K]

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In order to facilitate better understanding of the mechanism of reduction of TiCl4 by Mg in a reaction mediator salt, TiCl4 was injected in to a molten salt mixture containing Dy2+ ions. The salt mixture was equilibrated with a Mg-Ag-Ni alloy kept in a tube and isolated from TiCl4. Fine titanium powder was produced in the molten salt without any physical contact between Mg reductant and TiCl4. During the reduction experiment, the oxidation-reduction potential(ORP) of the molten salt mediator, and the electrochemical potential of the injection tube relative to Mg/Mg2+ reference electrode were continuously monitored. Based on the result obtained, reaction pathways for titanium chloride in the salt mediator are discussed. The new concept of an electronically mediated reaction(EMR) is outlined with the aid of isothermal chemical potential diagrams. Although the overall reduction reaction can be represented in terms of neutral species, as in the conventional treatment of the Kroll process, the electrochemical analysis using the i-E diagram gives a better insight into the mechanistic aspects of the reduction involving the movement of ions and electrons.

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The preparation process of Ge-Ga-S glasses is studied and its glass-forming region is presented. The effects of Ga and S contents on properties：glass transition temperature, density, and refractive index are investigated. The S content dependence of glass transition temperature and refractive index are divided into three regions relating to three bond types：1)the cation excess region with the contribution of Ge-Ge bonds, 2)an anion excess region with the dominant contributions of GeS2 tetrahedra connected by the S-S bonds, and 3)the other anion excess region with the contributions of S-S bonds and S8 rings. The solubilities of rare earth ion, Nd3+ in Ge-Ga-S, Ge-In-S and Ge-Sb-S glass systems are discussed using ionicity parameter, which based on the electronegativity between cation and sulfide anion.

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