• Korean Journal of Metals and Materials
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• v.50 no.8
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• pp.599-603
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• 2012

The microstructure of a hammer scale excavated from the Bogam-ri was examined in an effort to understand the iron technologies applied in the manufacturing of an iron forging process technology. The microstructures of oxide layer in the hammer scale were found to have crucial information about the ancient iron forging process treatment. The microstructure observed in the hammer scale can be distinguished by the forging process. First, the microstructure of the oxide layer in the hammer scale created by the forging process is Wstite (FeO) in the form of leaves. Latterly, the microstructure of the $W{\ddot{u}}stite$(FeO) in the hammer scale is observed to be in the form of a flat shape formed by a repeating forging process.

• Advances in concrete construction
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• v.11 no.3
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• pp.231-238
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• 2021

The present work aims at investigating the effects of using various fine mineral additions as partial replacement to Portland cement on the tribological properties of concrete. To achieve this goal, concrete mixtures were prepared with different percentages (10, 20 and 30%) of limestone fillers (LF) and natural pozzolana (NP), and (20, 40 and 60%) of blast furnace slag (BFS). The interface yield stress (τ0) and viscous constants (η) that allow characterizing friction at the concrete-pipe wall interface were determined using a rotational tribometer. In addition, the compositions of the boundary layers that formed in the pumping pipes of the different concretes under study were also identified and analyzed. The experimental results obtained showed that the concretes studied have a linear tribological behavior that can be described by the Bingham model. Furthermore, the use of different mineral additions, especially limestone fillers and blast furnace slags, even at high rates, had a beneficial effect on the optimization of the volume of paste present in the boundary layer, which made it possible to significantly reduce the viscous constant of concrete. However, a maximum rate of 10% of natural pozzolana was recommended to achieve tribological properties that are favorable to the pumpability of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.325-328
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• 2006

Recently, repair mortars have been mainly used for repairing old concrete structures. In this study, a new repair mortar including shotcrete admixture, slag, silica fume, sulphate and calcium carbonate, was developed for repairing shotcrete layer and the fresh properties and mechanical characteristics of the repair mortar was measured, Test results showed that the shortcrete admixture and other additives reduce the final setting time from about 7 hours to within 20 minutes and increase very early strength and stiffness (within 5 hours after cast).

• Steel and Composite Structures
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• v.45 no.6
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• pp.877-894
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• 2022

Geopolymer concrete (GPC) has emerged as a feasible choice for construction materials as a result of the environmental issues associated with the production of cement. The findings of this study contribute to the development of machine learning methods for estimating the properties of eco-friendly concrete to help reduce CO₂ emissions in the construction industry. The compressive strength (f_c) of GPC is predicted using artificial intelligence approaches in the present study when ground granulated blast-furnace slag (GGBS) is substituted with natural zeolite (NZ), silica fume (SF), and varying NaOH concentrations. For this purpose, two machine learning methods multi-layer perceptron (MLP) and radial basis function (RBF) were considered and hybridized with arithmetic optimization algorithm (AOA), and grey wolf optimization algorithm (GWO). According to the results, all methods performed very well in predicting the f_c of GPC. The proposed AOA - MLP might be identified as the outperformed framework, although other methodologies (AOA - RBF, GWO - RBF, and GWO - MLP) were also reliable in the fc of GPC forecasting process.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.33-43
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• 2002

Recently, as large constructions on the coast increase, an application of a surface layer stabilization method which is one of the improvement methods for dredged soft clay has increased. However, there are few studies about this. The purpose of this study is clarifying characteristics of ultra-soft marine clay and hardening agent. Also, it is verifying an optimal mixture ratio of hardening agent through the laboratory tests according to designed experiments and proving by statistical analysis and pilot tests. Laboratory tests were performed with proper hardening agent and test soil in accordance with the design of experiments. Regression equations between hardening agents materials and unconfined compressive strength were derived from the tests. The applicability of regression equations were also verified by pilot tests. From the test results, it was found that hardening agent materials(cement, slag, fly-ash, inorganic salts, arwin, gypsum etc.) have some effect upon compressive strength. The optimal mixture ratio which satisfies the required compressive strength was derived from the statistical analysis. The effect of ground improvement by cements and hardening agents was confirmed through the pilot tests. This study will suggest data for design or construction criteria of stabilization of surface layer on ultra-soft marine clay.

• Journal of The Korean Society of Agricultural Engineers
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• v.64 no.2
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• pp.37-45
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• 2022

In-situ pilot experiment was carried out to establish a countermeasure on the soil loss from the hill side uplands that was rehabilitated by soil remediation method nearby abandoned mine sites for 2 years. It was considered that the affect of an inclination of cover surface, a stabilization treatment of cover layer by lime and steel refining slag (SRS) and a vegetation of soil surface as an effect factors in the experiment. It was constructed 4 lysimeters (plots, 22 m long, 4 m width) on the hilly side (37% inclination). One plot was control and two plots was treated by 1% lime and SRS. A remind one plot was modified a inclination to 27% to compare the affect of inclination on the amount of cover soil loss. It was attached a reservior tank and water level gauge in the end of lysimeters to measure the amount of the surface water flow and soil loss. It was also installed the automated sensors that could be collect the precipitation, soil moisture content, tension of cover layer in each plots. It was observed that the event of precipitation were caused the soil loss and it were related the physical and chemical properties of cover soil and inclination of surface layer of plots. During the experiment, it was exceeded the national regulation (50 t/ha/yr) in 37% inclination plots even though it was vegetated on the cover soil surface. However, in 27% inclination plot, it was shown that the amount of soil loss was maintained below the national regulation and, more ever, vegetation could reduce the the amount of soil loss. Therefore it was expected that such results could be applied to the future design of rehabilitation projects on the polluted farmland nearby abandoned mine sites.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.6
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• pp.1367-1375
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• 2015

The purpose of this paper is to suggest 10 mm aggregate specification for thin layer asphalt pavement using steel slag. Aggregate gradations of conventional dense-graded asphalt mixtures were made by fuller's model, whereas 10 mm dense-graded asphalt mixture was obtained tender mix due to close to the maximum density line. The proposed aggregate gradation specification was made to have enough VMA and well-interlocking refer to foreign standards. The correlation between the proposed aggregate gradation and the properties of mixtures were analyzed using Gradation Ratio (GR) and Compacted Aggregate Density (CAD). The CAD index has a high $R^2$ of 0.86-0.99 because the CAD index is able to reflect various aggregate properties. As the results of evaluation by CAD index the proposed aggregate gradation provides more reliable stability and VMA. The percent passing (%) of aggregate size smaller than 0.3 mm was limited 10% or more for improving crack resistance. This limitation increased for 15% of the asphalt mixture's toughness.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.51-51
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• 2010

Recently just as in the automobile industry, shipbuilders also try to reduce material consumption and weight in order to keep operating costs as low as possible and improve the speed of production. Naturally industry is ever searching for welding techniques offering higher power, higher productivity and a better quality. Therefore it is important to have a details research based on the various welding process applied to steel and other materials, and to have the ability both to counsel interested companies and to evaluate the feasibility of implementation of this process. Submerged-arc welding (SAW) process is usually used about 20% of shipbuilding. Similar to gas metal arc welding(GMAW), SAW involves formation of an arc between a continuously-fed bare wire electrode and the work-piece. The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool and a shielding gas is not required. Prior to welding, a thin layer of flux powder is placed on the work-piece surface. The arc moves along the joint line and as it does so, excess flux is recycled via a hopper. Remaining fused slag layers can be easily removed after welding. As the arc is completely covered by the flux layer, heat loss is extremely low. This produces a thermal efficiency as high as 60% (compared with 25% for manual metal arc). SAW process offers many advantages compared to conventional CO2 welding process. The main advantages of SAW are higher welding speed, facility of workers, less deformation and better than bead shape & strength of welded joint because there is no visible arc light, welding is spatter-free, fully-mechanized or automatic process, high travel speed, and depth of penetration and chemical composition of the deposited weld metal. However it is difficult to application of thin plate according to high heat input. So this paper has been focused on application of the field according to SAW process for thin plate in ship-structures. For this purpose, It has been decided to optimized welding condition by experiments, relationship between welding parameters and bead shapes, mechanical test such as tensile and bending. Also finite element(FE) based numerical comparison of thermal history and welding residual stress in A-grade 3.2 thickness steel of SAW been made in this study. From the result of this study, It makes substantial saving of time and manufacturing cost and raises the quality of product.

• Journal of the Korean Geosynthetics Society
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• v.20 no.3
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• pp.1-10
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• 2021

The purpose of this study is to present the possibility a utilization of the tertiary mudstone in Pohang as road subsoil material through pilot experiments on the road embankment structure. This mudstone is an unconsolidated rock that is distributed in the soft rock sedimentary layer, the tertiary layer of the Cenozoic, and causes physical problems such as slaking, swelling, and reduced shear strength and chemical problem like acid drainage. In order to solve various complex problems, an laboratory mixing test was conducted, and the optimal mixing conditions of the tertiary mudstone (90%), composite slag (steel making 70%, blast furnace 30%), and neutralization and coating agent treatment were derived. In order to prove its utilization, a real-scale road embankment structure was constructed and tests were conducted for each section. The pre-processing section is stable due to the design of optimal mixing conditions, while in post-processing section, natural weathering proceeded rapidly, and structural problems were concerned. Since the effect of neutralizing and coating agents was confirmed in temporary-staking section, the neutralizing and coating agents can be applied during the temporary storage period.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.320-323
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• 2002

This paper presents a new generation of system for pressure vessel and shipbuilding. Typical pressure vessel and ship building weld joint preparations are either traditional V, butt, fillet grooves or have narrow or semi narrow gap profiles. The fillet and U groove are prevalently used in heavy industries and shipbuilding to melt and join the parts. Since the wall thickness can be up to 6" or greater, welds must be made in many layers, each layer containing several passes. However, the welding time for the conventional processes such as SAW(Submerged Arc Welding) and FCAW(Flux Cored Arc Welding) can be many hours. Although SAW and FCAW are normally a mechanized process, pressure vessel and ship structures welding up to now have usually been controlled by a full time operator. The operator has typically been responsible for positioning each individual weld run, for setting weld process parameters, for maintaining flux and wire levels, for removing slag and so on. The aim of the system is to develop a high speed welding system with multitorch for increasing the production speed on the line and to remove the need for the operator so that the system can run automatically for the complete multi-torch multi-layer weld. To achieve this, a laser vision sensor, a rotating torch and an image processing algorithm have been made. Also, the multitorch welding system can be applicable for the fine grained steel because of the high welding speed and lower heat input compare to a conventional welding process.