• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.5
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• pp.19-27
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• 2008

This study was performed to evaluate the compressive strength and acid-resistant of polymer concrete using redispersible polymer powder(RPP) and blast furnace slag powder(BSP). Material used were ordinary portlant cement, recycled coarse aggregate, natural fine aggregate, redispersible polymer powder and blast furnace slag powder. The main experimental variables were the substitution ratio of redispersible polymer powder and blast furnace slag powder, when the substitution ratios of RPP were 0, 1, 2, 3, 4, 5 and 6%, and those of BSP were 10%. The compressive strength and acid-resistant of polymer concrete using RPP and BSP were compared with those of ordinary concrete(Basis). When the substitution ratio of RPP was 1%, at age of 28 days, the compressive strength were more higher than those of Basis by 24%, and it was decreased with increasing the RPP content, respectively. Also, the water absorption ratio was decreased with increasing the RPP content. But, the acid-resistant was improved with increasing the RPP content.

• Computers and Concrete
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• v.5 no.6
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• pp.559-572
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• 2008

The effects of fly ash and superplasticizer (SP) on workability of concrete are quite difficult to predict because they are dependent on other concrete ingredients. Because of high complexity of the relations between workability and concrete compositions, conventional regression analysis could be not sufficient to build an accurate model. In this study, a workability model has been built using artificial neural networks (ANN). In this model, the workability is a function of the content of all concrete ingredients, including cement, fly ash, blast furnace slag, water, superplasticizer, coarse aggregate, and fine aggregate. The effects of water/binder ratio (w/b), fly ash-binder ratio (fa/b), superplasticizer-binder ratio (SP/b), and water content on slump were explored by the trained ANN. This study led to the following conclusions: (1) ANN can build a more accurate workability model than polynomial regression. (2) Although the water content and SP/b were kept constant, a change in w/b and fa/b had a distinct effect on the workability properties. (3) An increasing content of fly ash decreased the workability, while raised the slump upper limit that can be obtained.

• Journal of Welding and Joining
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• v.8 no.2
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• pp.27-39
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• 1990

The effect of silicon and manganese, in the ranges of 0.3% to 1.0wt% Si and 0.7 to 2.6wt%Mn, on the microstructure and mechanical properties of flux cored arc welded deposits have been investigated for the purpose of improving mechanical properties. Microstructure of weld metals was mainly influenced by manganese content, and manganese increased the volum fraction of acicular ferrite and refined the microstructure. Also, tensile properties were governed by manganese content, ultimate tensile strength and yield strength were increased by approximately 82MPa and 58MPa per 1% Mn addition to the deposit. Toughness was improved by increasing Mn content and lowering Si content. Optimal impact properties were obtained at above 1.8wt% Mn and below 0.5wt% Si. Acicular ferrite was predominant factor in improving mechanical properties. Formation of acicular ferrite was promoted by manganese and no direct relationship between AF(acicular ferrite) proportion and oxygen in weld metal was found.

• Journal of Welding and Joining
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• v.22 no.5
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• pp.53-57
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• 2004

Friction stir weldability of AZ31B-H24, AZ61A-F and AZ91C-F Mg alloys were studied using microstructural observation and mechanical tests. The microstructure of stir zone(SZ) was coarse in AZ31B-H24 alloy whereas it was very fine both in AZ61A-F and AZ91C-F alloys. The hardness of SZ was remarkably increased by very fine recrystallized grains both in AZ61A-F and AZ91C-F alloys. On the other hand, the hardness of SZ was decreased in AZ31B-H24 due to the coarse microstructure. In SZ, AZ91C-F alloy showed very high hardness values because of dispersion hardening of $Mg_{17}$Al$_{12}$($\beta$ phase) and Al solid solution hardening. Because of more $Mg_{ 17}Al_{12}($\beta$ phase)$ intermetallic compounds, Mg alloy with high Al content showed poor mechanical properties.s.

• Geomechanics and Engineering
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• v.31 no.2
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• pp.167-181
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• 2022

Soil liquefaction has been one of the most important concerns in geotechnical earthquake engineering in recent years, due to its damages to structures and its destructive effects. The cyclic liquefaction of silty sands, in particular, remains of great interest for both research and application. Although many factors are known that affect the liquefaction resistance of sands, the effect of fine grain content is perhaps one of the most studied and still controversial. In this study, 48 deformation-controlled cyclic simple shear tests were performed on BS and CS silt samples mixed with 5%, 15% and 30% by weight of Krk085, Krk042 and Krk025 sands in constant-volume conditions to determine the liquefaction potential of silty sands. The tests were carried out at 30% and 50% relative density and under 100 kPa effective stress. The results revealed that the liquefaction potential of silty sand increases with increasing average particle size ratio (D_50sand / d_50silt) of the mixture for a fixed silt content. Furthermore, for identical base sand, the liquefaction potentials of coarse grained sands increase with increasing silt content, while the respective potentials of fine grained sands generally decrease. However, this situation may vary depending on the silt grain structure and is affected by the nature of the fine grains. In addition, the variation of the void ratio interval was shown to provide a good intuition in determining the liquefaction potentials of silty sands, while the intergranular void ratio alone does not constitute a criterion for determining the liquefaction potentials of silty sands.

• KCI Concrete Journal
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• v.11 no.3
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• pp.19-28
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• 1999

This study treated self-compacting high Performance concrete as two Phase materials of Paste and aggregates and examined the effect of powder and aggregates on self-compacting high performance, since fluidity and segregation resistance of fresh concrete are changed mainly by paste. To improve the fluidity and self-compactibility of concrete, optimum powder ratio of self-compacting high performance concrete using fly ash and blast-furnace slag as powders were calculated. This study was also designed to provide basic materials for suitable design of mix proportion by evaluating fluidity and compactibility by various volume ratios of fine aggregates, paste, and aggregates. As a result, the more fly ash was replaced, the more confined water ratio was reduced because of higher fluidity. The smallest confined water ratio was determined when 15% blast-furnace slag was replaced. The lowest confined water ratio was acquired when 20% fly ash and 15% blast-furnace slag were replaced together. The optimum fine aggregates ratio with the best compactibility was the fine aggregate ratio with the lowest percentage of void in mixing coarse aggregate and fine aggregate In mixing the high performance concrete. Self-compacting high performance concrete with desirable compactibility required more than minimum of unit volume weight. If the unit volume weight used was less than the minimum, concrete had seriously reduced compactibility.

• Journal of the Korea Furniture Society
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• v.17 no.2
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• pp.9-23
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• 2006

Control particleboards were significantly higher in thickness swelling than wood particle-polypropylene fiber composites and their thickness swelling increased with the increase of target density. In the composites, thickness swelling did not vary significantly with the increase of target density but increased with the increase of wood particle content. And the composites with fine wood particles were significantly lower in thickness swelling than those with coarse wood particles irrespective of target density and formulation. In the scanning electron microscopy, significantly higher thickness swelling in the composites with coarse wood particles was thought to be the result of more interfacial separations by higher swelling stresses.

• Geomechanics and Engineering
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• v.14 no.3
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• pp.211-224
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• 2018

In this paper, a predictive method accounting for the scaling effects of rockfill materials in the numerical deformation analysis of rockfill dams is developed. It aims to take into consideration the differences of engineering properties of rockfill materials between in situ and laboratory conditions in the deformation analysis. The developed method is based on the modification of model parameters used in the chosen material model, which is, in this study, an elasto-plastic model with double yield surfaces, i.e., the modified Hardening Soil model. Datasets of experimental tests are collected from previous studies, and a new dataset of the Nam Ngum 2 dam project for investigating the scaling effects of rockfill materials, including particle size, particle gradation and density, is obtained. To quantitatively consider the influence of particle gradation, the coarse-to-fine content (C/F) concept is proposed in this study. The simple relations between the model parameters and particle size, C/F and density are formulated, which enable us to predict the mechanical properties of prototype materials from laboratory tests. Subsequently, a 3D finite element analysis of the Nam Ngum 2 concrete face slab rockfill dam at the end of the construction stage is carried out using two sets of model parameters (1) based on the laboratory tests and (2) in accordance with the proposed method. Comparisons of the computed results with dam monitoring data indicate that the proposed method can provide a simple but effective framework to take account of the scaling effect in dam deformation analysis.

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.7
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• pp.11-19
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• 2003

In this study, unsaturated polyester resin, artificial lightweight coarse aggregate, artificial lightweight fine aggregate, heavy calcium carbonate and steel fiber were used to produce a steel fiber-reinforced lightweight polymer concrete with which mechanical properties were examined. Results of this experimental study showed that the flexural strength of unnotched steel fiber-reinforced lightweight polymer concrete increased from 8.61 to 13.96 MPa when mixing ratio of fiber content increased from 0 to 1.5%. Stress intensity factors($K_{IC}$) increased with increasing fiber content ratio while it did not increase with increasing notch ratio. Energy release rate ($G_{IC}$) turned out to depend upon the notch size, and it increased with increasing steel fiber content.

• Journal of Powder Materials
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• v.1 no.1
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• pp.27-34
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• 1994

Commercial pure iron powder and iron powder of coated 0.45% phosphorus were mixed with graphite powder in dry mixer to control carbon content from 0 wt% to 0.8 wt%. Mixed powder was pressed in the mould under the pressure of 510 MPa. Compacts were sintered at 118$0^{\circ}C$ for 40 min. in cracked ammonia gaseous atmosphere. Some of these sintered specimens were quenched in oil, and tempered in Ar gas. All of these specimens were investigated for microstructure, density and hardness in relation to coated phosphorus and carbon content. The results obtained were as follows: (1) The microstructure of the sintered speciments revealed that the amount of pearlite was increased with increasing C content but decreased by P-addition. (2) The P-addition affected the microstructure of pores in which the pore shape became round and its mean size was decreased by P-addition. (3) After tempering of sintered specimens the structure of pearlite was changed from fine structure to coarse one in P added specimen. (4) Hardness was higher in P added specimens.