• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.4
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• pp.270-278
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• 2005

Recycled aggregate concrete has lower strength and durability compared to concrete with natural aggregate. Therefore, metakaolin is used to improve the properties of recycled aggregate concrete. Main components of metakaolin are $SiO_2$ and $Al_2O_3$. and specific surface area is 9 times larger than that of ordinary portland cement. Quality of demolished-recycled aggregate(DRA) satisfies the type 1 of KS F 2573, but quality of source-recycled aggregate(SRA) does not satisfy with the type 2 of KS F 2573. When metakaolin was replaced with 20% of cement, compressive strength of concrete with SRA and DRA develops about 40~64% of control concrete. Water absorption ratio was reduced about 2% by replacing 20% metakaolin and it represents low compared to the natural aggregate concrete without metakaolin. In addition, the resistance to freezing and thawing, of concrete with DRA is indicated to remarkably enhanced due to the contribution of metakaolin. However, when metakaolin is replaced with 20% of cement, relative dynamic modulus of elasticity of concrete with SRA was below 60% at 210 freezing and thawing cycles.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.597-607
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• 2002

Electric arc furnace and converter slag are produced by about 6 millions tons in Korea at 2000 year. But compared with blast furnace slag, those are utilized only in unvalued material like landfill and road construction. There are unstable materials, like free CaO, in electric arc furnace and converter slag at steel-manufacturing process. This might cause volume expansion in concrete, if electric arc furnace and converter slag aggregates were used in concrete. This expansion may reach to crack or collapse of concrete. It is therefore settled by standard specification for concrete that electric arc furnace and converter slag aggregates have not to use in concrete. First of all, volume stability and stabilized process should be solved in electric arc furnace and converter slag aggregate to use in concrete. In this study, 6 types of aging are evaluated for effects of stabilization to reduce the expansion of electric arc furnace and converter slag. h converter slag aggregate, these types of aging are not good for volume stability for concrete aggregate, and even if converter slag aggregate is treated with aging, concrete with it has some problems that strength is reduced with curing days. But in electric arc furnace slag aggregate treated with hotwater and steam aging, the expansion of electric arc furnace slag aggregate is reduced about two times than that of converter slag aggregate, and electric arc furnace slag aggregate concrete has good results in strength compared with control concrete using crushed stone.

• International Journal of Control, Automation, and Systems
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• v.1 no.3
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• pp.289-300
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• 2003

In this paper, we introduce an identification method in Fuzzy Relation-based Fuzzy Neural Networks (FRFNN) through a hybrid identification algorithm. The proposed FRFNN modeling implement system structure and parameter identification in the efficient form of "If...., then... " statements, and exploit the theory of system optimization and fuzzy rules. The FRFNN modeling and identification environment realizes parameter identification through a synergistic usage of genetic optimization and complex search method. The hybrid identification algorithm is carried out by combining both genetic optimization and the improved complex method in order to guarantee both global optimization and local convergence. An aggregate objective function with a weighting factor is introduced to achieve a sound balance between approximation and generalization of the model. The proposed model is experimented with using two nonlinear data. The obtained experimental results reveal that the proposed networks exhibit high accuracy and generalization capabilities in comparison to other models.er models.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.705-710
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• 2002

Recently, there has been for a number of reasons growing interest in the use of porous concrete, and it is used as an ecological material. But, because the valuation methods of the quality on the fresh porous concrete aren't established up till now, it is difficult that the harden porous concrete is made sure of its required quality. This study is to present the measurement method of the void ratio on the fresh porous concrete and to analyze the influence of water-cement ratio and vibrating time on the binder content covered a coarse aggregate. Results of this study were shown as follows; The measurement methods of the void ratio and aggregate-binder weight ratio on the fresh porous concrete can be useful as data for the quality control of fresh porous concrete.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2000.10a
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• pp.284-289
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• 2000

This study is performed to evaluate an the crack properties and repair-reinforcement of concrete introduced crack. Materials used are portland cement, coarse aggregate, fine aggregate, unsaturated polyester resin and fly ash. Specimen is used beam of 76${\times}$76${\times}$412mm for measurement of pulse velocity, dynamic modulus of elasticity and bending strength and is introduced crack artificially. The following conclusions are drawn; Pulse velocity, dynamic modulus of elasticity and bending strength of concrete introduced crack is shown the lower 1.24∼11.91%, 3.42∼17.21% and 38.17∼61.0% than that of the control concrete, respectively. Pulse velocity, dynamic modulus of elasticity and bending strength of concrete repaired and reinforced crack is shown the higher 0.5∼2.60%, 1.57∼3.07% and 28.17∼47.25% than that of the concrete introduced crack and the lower than that of the control concrete, respectively.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.195-199
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• 2003

BEE 802.11 Wireless LAN protocol uses fixed transmission power. It does not consider a power control mechanism based on the distance between the transmitter and the receiver in order to improve overall channel utilization. In home environment, where stations generally lie around an AP, the AP is subject to use transmission power more than it needs. And wireless LAN stations may require different minimal desired received power. If there are many adjacent BSSs in densely populated WLAN area, they might cause RF interference to one another. In this paper we focus on the improvement of aggregate utilization by mitigating RF interference among BSSs. We show that RF interference by APs can be reduced by controlling transmission power using Link Margin information. The reduced interference will then lead to the increased aggregate throughput which is efficient resource utilization.

• Journal of the Korea Institute of Building Construction
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• v.9 no.3
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• pp.73-78
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• 2009

Coal ash is a by-product of the combustion of pulverized coal, and much of this is dumped in landfills. The disposal of coal ash is one of the major issues for environmental problems. In this paper, the effects of the kinds and replacement ratio of coal ash on the durabilities of concrete mixtures are investigated. Fine aggregate was replaced with coal ash(fly ash and bottom ash) in five different ratios, of 0%, 10%, 20%, 35%, and 50% by volume. Test results indicated that the compressive strength increased with the increase in fly ash percentage. The loss of compressive strength of bottom ash concrete mixes after immersion in sulphuric acid solution was less than in the control mix(BA0). In addition, the carbonation depth of fly ash concrete mixes was lower than the control mix(FA0).

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.327-328
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• 2021

In the manufacturing process of ready-mixed concrete, quantity management directly affects the workability and strength of concrete. Therefore, water quantity is the most important management factor for water quality control of ready-mixed concrete. It can be said that the number of unit water in the mix design, the water quantity due to the surface water contained in the aggregate used, and the water quantity taking into account the concentration of sludge contained in the recycling water when using the recycling water are factors that affect the quantity management of ready-mixed concrete. In this study, as a stable quality control method of ready-mixed concrete, a quantity management method by aggregate surface water and a sludge concentration management method according to the use of recycling water were proposed. Thus, we tried to suggest an efficient quantity management method for stabilizing the quality of ready-mixed concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.76-77
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• 2021

compared and reviewed the water repellency and strength characteristics by controlling the surface stamping size and fine aggregate ratio of cement mortar mixed with water repellent as a method to control the ecological imitation surface structure. As a result of measuring the contact angle, the higher the ratio of fine aggregate, the larger the contact angle. The contact angle increased when the surface structure was changed by stamping, and increased as the stamping size became smaller. In the surface stamping of mesh#150, the contact angle was particularly increased.

• Journal of Korean Society of Forest Science
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• v.102 no.2
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• pp.239-246
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• 2013

This study observed changes of understory vegetation to evaluate the role of forest aggregate after 15% aggregated retention harvest in mature oak forest (> 100 years) in Gyungsangbukdo Bonghwagun in 2010 and 2011. Spontaneous responses of understory vegetation cover (%), species richness, abundance of plant growth forms (herbaceous and woody plants), and overall attributes (by Ordination analysis) were estimated in aggregate area (0.15 and n=36) and clear cut area (0.85 and n=192) in experimental site and control site (1 and n=300). Based on ordination analysis, overall change of species composition in aggregated sites were relatively lower than in harvest area. Right after treatment, total cover of cutted area slightly decreased from 15.6% to 14.7%, and species richness increased from 14 species to 22 species. Cover and richness in the both of aggregate and control sites increased. In plant growth forms, 15% aggregate harvest revealed positive effects on the abundance (cover and richness) of herbaceous plants than woody group. After retention treatment, overall, edge effect likely played major component of vegetation changes in aggregate forest and in harvested area, mechanical damage from harvest operation and change of forest structure by clear cutting were critical. As pre-treatment data, which are rare in ecological studies in Korea, were critical for interpretation between patterns that may have arisen from spatial distributions in the original forest, our experimental design have higher opportunity for long term monitoring on the effect of forest aggregate and vegetation regeneration in clear cutted area.