• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.206-211
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• 2015

Recently, for UHPC (Ulta High Performance Concrete) which is researched actively, as the tensile strength is absolutely influenced on the content of steel fiber, in this paper, experiments of compressive strength, elasticity modulus and tensile strength were performed according to compressive strength and content of steel fiber as variables. By the test results, compressive strength, elasticity modulus and tensile strength are proportioned and have a good correlation and according to content of steel fiber, compressive and tensile strength are also proportioned and have a good correlation. In case of elasticity modulus, the difference between test and present design code is not large, so it is possible to adapt to present design code. On the other hand, in case of tensile strength, as there is no specification of present design code, new prediction equation is proposed by using nonlinear regression analysis and the proposed equation have a good correlation to test results.

• Resources Recycling
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• v.26 no.3
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• pp.39-46
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• 2017

AlN powder was prepared by carbon reduction and subsequent nitridation method through lab- scale experiments. AlN powder was synthesized using the mixture of high purity $Al_2O_3$ powder and carbon black at $1,600{\sim}1,700^{\circ}C$ for 0.5~6 hours under nitrogen atmosphere (flow rate of nitrogen gas: $4.7{\times}10^{-6}{\sim}20{\times}10^{-6}m^3/sec$) with variation of charged height of the mixture powder. Experimental results showed that size of the synthesized particles grows with increasing of temperature. The reaction activation energy was calculated as 382 kJ/mol at the temperature range, and it was considered that chemical reaction is the rate determining step. Content of oxygen and nitrogen of the prpared samples were 0.71~0.96 wt% and 30.7~35.1 wt%. The results was similar with those of the commercial AlN product.

• Resources Recycling
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• v.25 no.3
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• pp.3-10
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• 2016

The passive treatment was required a large area for the treatment of acid mine drainage (AMD), and pollutants were discharged with mine drainage by the increased flow rate in summer. This study was performed to improve the turbidity and to precipitate the pollutants quickly using coagulants and flocculants in AMD of abandoned mine sites that were difficult to build the passive treatment system. The coagulant PAC (Poly aluminium chloride) and flocculant PAM (Polyacrylamide) were selected to improve turbidity in W mine waters. We also tested the particle size analysis, ICP-OES and/or SEM-EDS for water and sludge samples.

• Resources Recycling
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• v.18 no.6
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• pp.46-53
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• 2009

The stone dusts produced during the manufacturing process of stone blocks are considered as one of industrial waste materials. This stone dusts are managed to either burying under the ground or stacking in the yard, but this disposal process is required an extra costs. The stone dust disposal like burying or stacking also cause environmental pollution such as ground pollution and subterranean water pollution. Thus, this study was conducted to explore the possibility of recycling stone dusts as a concrete mixing material in order to extend recycling methods. Based on the experiment results on various ratios of cement to stone dust content, the compressive strengths of concrete were recorded in the range of $20{\sim}30\;N/mm^2$. The results did not show any decrease in compressive strength due to the stone dust content. It can be concluded that the stone dusts produced by stone block manufacturing can be sufficiently recycled as one of concrete mixing materials in the aspect of compressive strength.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2006.05a
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• pp.47-55
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• 2006

Recovery of acids from the waste etching solution of containing nitric, hydrofluoric and acetic acid discharged from silicon wafer manufacturing process has been attempted by using solvent extraction method. With EHA (2-Ethylhexlalcohol) for acetic acid and TBP(Tri-butly Phosphate) for nitic and hydrofluoric acid as extraction agent was carried on experiment to obtain the process design data in separation procedure. From the McCabe-Thiele diagram analysis, we obtained the optimum conditions of phase ratio(O/A) and stages to separate the each acid sequently from the mixture acids. The recovery yield was obtained 90% above for acetic acid from the acid mixtures, 90% above for nitric acid from acetic acid extraction raffinate and then 67% above for hydrofluoric acid from final extraction raffinate.

• Tunnel and Underground Space
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• v.29 no.5
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• pp.318-331
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• 2019

A three-dimensional(3D) equivalent continuum modeling was performed to analyze hydraulic behavior of rock mass considering discontinuities by using DFN model and smeared fracture model. DFN model was generated by FLAC3D and smeared fracture model was applied by using FISH functions, which is built-in functions in FLAC3D, for equivalent continuum model of fractured rock mass. Comparative analysis with 3DEC, which is for discontinuum analysis, was conducted to verify reliability of equivalent continuum analysis by using FLAC3D. Similar results of hydraulic analysis under the same conditions could be achieved. Equivalent continuum analysis of fractured rock mass by using DFN model was implemented to compare with existing analytical methods for inflow into the tunnel.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.71-78
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• 2012

Recycled aggregates are made from construction wastes, and they have many national and social benefits by saving energy, developing substitute resources, and protecting environment. However, low-quality recycled aggregate with low density and high absorption rate cannot be used for structural concrete aggregate but is used mainly for low added value. Therefore, this study aims to identify the characteristics of the materials of recycled aggregates made after crashing and pulverizing waste concrete. For this, their major physical characteristics of cement content, absolute dry density, absorption rate, etc. were reviewed to make a mix design (draft) for the production of the secondary product and performance evaluation was done on the bending strength, absorption rate, bending strength after freezing and thawing, compressive strength, air-dried gravity, etc. of the test products produced by applying the mix design to compare the results with the quality standards of GR mark. The results of the tests showed that the substitution rate of recycled aggregate increased to 50~90 %, which is of superior quality than the performance standards of GR F 4007. Therefore, it is thought that they can be used for various construction works with certain physical characteristics applicable to the production of secondary concrete products using recycled aggregates.

• Journal of the Korean Society of Mineral and Energy Resources Engineers
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• v.55 no.6
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• pp.576-587
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• 2018

This study has focused on analysis factors affecting safety monitoring system at tailings sites, and the evaluation equipment to monitor the factors. Twenty sites at eighteen mines with unsafe conditions were selected to examine the equipment. There were three main factors influenced safety in the sites including surface erosion, piping, and slope instability. In detail, the surface erosion was divided into three sub-factors (planting, soil-topping layer, and tailings), piping into three sub-factors (liner, rain protection facility and leachate), and slop instability was also divided into three sub-factors (slop, concrete wall, and reinforcing wall). As results of in-field measurement, a CCTV was the most effective facility, and electrical resistivity survey, acoustic sensing, thermal liner sensor, structure inclinometer, rainfall meter, and flowmeter were also highly effective. According to applications of the facilities in the unstable tailings, structural defects were mainly found in the piping, which was the most important monitoring factor for safety management of tailings sites.

• Journal of Korean Society of Forest Science
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• v.112 no.3
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• pp.374-381
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• 2023

The travel time of flash floods along mountain streams is mainly governed by reach-average velocity, rather than by the point velocity of the locations of interest. Reach-average velocity is influenced by various factors such as stream geometry, streambed materials, and the hydraulic roughness of streams. In this study, the reach-average velocity in mountain streams was measured for storm periods using rhodamine dye tracing. The point cloud data obtained from a LiDAR survey was used to extract the average hydraulic roughness height, such as R_a, R_max, and R_z. The size distribution of the streambed materials (D₅₀, D₈₄) was also considered in the estimation of the roughness height. The field experiments revealed that the reach-average velocities had a significant relationship with flow discharges (v = 0.5499Q^0.6165 ), with an R² value of 0.77. The root mean square error in the roughness height of the R_a-based estimation (0.45) was lower than those of the other estimations (0.47-1.04). Among the parameters for roughness height estimation, the R_a -based roughness height was the most reliable and suitable for developing the reach-average velocity equation for estimating the travel time of flood waves in mountain streams.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.764-769
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• 2009

하천과 바다가 만나는 하구는 자연적인 기능 뿐만 아니라 공학적인 측면에서도 매우 중요한 자원이다. 우리나라는 국토의 개발에 따른 용수 사용의 증가, 홍수재해대책 등으로 인해 한강을 제외한 4대강에 하구둑을 건설하였으며 강물과 바닷물을 인위적으로 차단하는 구조물이므로 하천의 생태적인 기능을 손상시키는 것은 불가피 하다. 하지만 이러한 단점에도 불구하고 하구둑이 건설되는 가장 큰 목적 중의 하나는 주변지역의 안정된 용수공급이다. 1987년에 완공된 낙동강 하구둑은 건설 이 후 약 20년 동안 안정된 용수공급과 효율적 운영으로 관리되어 왔지만 그동안 기상 및 수리 수문뿐만 아니라 환경적으로 크고 작은 변화가 있었다. 하천의 기수역인 하구에서 유체는 하구둑이라는 구조물이 존재하지 않을 때도 매우 복잡하게 거동한다. 하천의 유량, 지형학적 요소 그리고 조위의 상태 등 여러 가지 요인으로 인하여 비정상적으로 변화하며 이러한 하구에서 유체의 거동을 보다 더 정확하게 묘사하려면 흐름방향, 수심방향, 하폭방향의 3차원적인 해석이 필요하다. 하지만 하천과 바다를 밀도가 같은 하나의 상으로 가정하고 수행한 수문학적인 분석이나 1 2차원 수치모형을 활용한 수리 분석 결과는 시간적 공간적으로 경제적이고 양호한 결과를 산출해낼 수 있다. 본 연구에서는 낙동강 하구둑의 수리특성을 분석하기 위하여 미국 기상청의 홍수추적모형인 FLDWAV 모형과 미수로국(WES)의 2차원 유한요소 모형인 RMA-2 모형을 활용하였으며 낙동강유역 주요 수위관측소의 실측자료를 토대로 매개변수 검정을 실시하였다. 분석결과 조위가 고려된 2차원 유속장을 구현하였으며 하구둑 유지 관리 개선에 기여코자 하였다.