• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.108-112
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• 2005

In this research, the physical properties of fresh concrete using lime stone powder as a part of cement were investigated. Fresh concrete using lime stone powder was prepared with various lime stone powder replacement($5{\sim}12$ volume %) for cement and the quantities of sand aggregate ratio in concrete were 47.3%, 48.5% and 49.4% of ratio of sand aggregate. The workability, flowing characteristics, air content and bleeding of concrete using lime stone powder were tested and the results were compared with those of ordinary portland cement concrete. In the experiment, we acquired satisfactory results at the point of fresh concrete characteristics using lime stone powder within the replacement ratio of $8{\sim}12%$ and the optimum quantity of sand aggregate ratio in concrete was found to be $48.5%{\sim}50%$ of ratio of sand aggregate.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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• pp.57-61
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• 2006

Waste foundry sand of industrial waste which is happening by vast quantity according to fast development of industry has much the occurrence amount and processing method is depended on reclamation, and is using by fine aggregate for construction by recycling method among others. In this research Waste foundry sand powder into cement replace fare use possibility availability judge wish to Slump and air content decreased the replacement ratio increases by concrete special quality that do not harden according to experiment result, and unit capacity mass and bleeding increased the replacement ratio increases. Hardening concrete intensity special quality displayed strength improvement to replacement ratio 20%, and tendency that watertightness increases most in replacement ratio loft in watertight property appear. Considering the strength and watertight properties, the adequate usage of waste foundry sand powder is the 10% of replacement ratio.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.369-372
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• 2005

This study is about physical properties of concrete with changing displacement ratio of calcium sulfa aluminates(CSA) type admixture. Firstly, test shows that as displacement ratio of CSA increases and setting properties changes, fluidity and air contents decreases. In water to binder ratio 35$\%$ and 45$\%$, concrete using the cement replacing CSA 4$\%$ by volume shows that bleeding decreases 94.7$\%$ and 74.3$\%$ respectively, compared with plain concrete. In addition, setting time was promoted around 3 to 6 hour and 1 to 4 hour respectively. For harden concrete, increase of displacement ratio caused tendency of higher compressive strength as OPC has at early age. Replacing higher CSA admixture led to reduce of drying shrinkage.

• Korean Journal of Radiology
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• v.19 no.6
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• pp.1089-1098
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• 2018

Objective: To investigate the diagnostic yield of contrast-enhanced computed tomography (CT) in Crohn's disease (CD) patients presenting with acute severe lower gastrointestinal bleeding (LGIB), and the role of CT in predicting the risk of rebleeding. Materials and Methods: A consecutive series of 110 CD patients presenting with acute severe LGIB between 2005 and 2016 were analyzed. Among them, 86 patients who had undergone contrast-enhanced CT constituted the study cohort. The diagnostic yield of CT for detecting contrast extravasation was obtained for the entire cohort and compared between different CT techniques. In a subgroup of 62 patients who had undergone CT enterography (CTE) and showed a negative result for extravasation on CTE, the association between various clinical and CTE parameters and the risk of rebleeding during subsequent follow-up was investigated using Cox regression analysis. Results: The diagnostic yield of CT was 10.5% (9 of 86 patients). The yield did not significantly differ between single-phase and multiphase examinations (p > 0.999), or between non-enterographic CT and CTE (p = 0.388). Extensive CD (adjusted hazard ratio [HR], 3.27; 95% confidence interval [CI], 1.09-9.80; p = 0.034) and bowel wall-to-artery enhancement ratio (adjusted HR, 2.81; 95% CI, 1.21-6.54; p = 0.016) were significantly independently associated with increased rebleeding risks, whereas anti-tumor necrosis factor-${\alpha}$ therapy after the bleeding independently decreased the risk of rebleeding (adjusted HR, 0.26; 95% CI, 0.07-0.95; p = 0.041). Conclusion: The diagnostic yield of contrast-enhanced CT was not high in CD patients presenting with acute severe LGIB. Nevertheless, even a negative CTE may be beneficial as it can help predict the risk of later rebleeding.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.55-61
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• 2023

This study aims to develop CLSM fill material for emergency restoration using landfill coal ash. As a result of examining physical properties such as particle size distribution and fines content of landfill coal ash, bottom ash, fly ash, and general soil were mixed, and SP was found to have a density of 2.03 and a residual particle pass rate of 7.8 %. CLSM materials that secure fluidity in unit quantities without using chemical admixtures such as glidants and water reducing agents have a high risk of material separation due to bleeding. As a result of this experiment, it was found that the bleeding ratio did not satisfy the standard in the case of the specimen with a large amount of fly ash and a lot of addition of mixing water. As a result of the compressive strength test, the strength development of 0.5 MPa or more for 4 hours was found to be satisfactory for the specimens using hemihydrate gypsum with a unit binder amount of 200 or more, and the remaining gypsum showed poor strength development. Although it is judged that landfill coal ash can be used as a CLSM material, it is necessary to identify and apply the physical and chemical characteristics of coal ash buried in the ash treatment plant of each power generation company.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.76-82
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• 2018

Grout in duct is very effective protection from tendon corrosion in PSC(Prestressed Concrete) structure. In the work, durability and mechanical tests are performed for two types of grout which are conventionally used one and the improved grout with reduced w/c (water to cement) ratio and silica fume. Tendon system with 1000mm height is prepared and various tests including strength, flow, absorption, and bleeding ratio are conducted. ICM(Impressed Current Method) is adopted for corrosion acceleration in tendon with 12.7mm diameter inside grout. For 2 and 4 days, corrosion acceleration is performed for 2 different type of grout and corrosion amount is investigated. The improved grout shows higher compressive strength by 10 MPa and lower absorption ratio by 50% than the conventional one. It also provides an excellent corrosion reduction to 39.8 %~48.2 % for 2~4 days of acceleration period.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.151-158
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• 2007

The recent government policy for environment is pursuing for a circular waste control system not only to reduce waste as much as possible but also to vigorously use the already produced waste. Copper slag has a higher fineness modulus and a greater specific gravity than natural aggregate. but when the substitutive ratio of fine aggregate is higher than 30%, material segregation occurs by bleeding. Thus, in this study, the strength and the physical properties were tested for the specimens manufactured by varying the types of admixtures, and the substitutive ratio of copper slag to suppress material segregation occurring due to the bleeding of concrete using copper slag as the substitutive material of fine aggregate and to find the adequate substitutive ratio of copper slag.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.489-492
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• 2008

This study analyzed the fundamental properties and strength properties of concrete utilizing Bottom Ash as coarse aggregate for concrete. As a result, compared to non-mixture, the slump decreases about 4.5${\sim}$54.2% as the mixing ratio of Bottom Ash increases. However, influence of the air contents is very little. The bleeding shows similar slump characteristics, and the primary stage of bleeding decreases as the mixing ratio of Bottom Ash increases. As the mixing ratio of Bottom Ash increases, the compressive strength decreases. When Bottom Ash is mixed by 40%, compressive strength decreases about 1.1${\sim}$5.3%. Even when Bottom Ash is mixed over 60%, compressive strength decreases sharply and is revealed about 85.2${\sim}$87.7% of non-mixture concrete strength. To utilize Bottom Ash in large quantities, it is thought that the improvement method of strength has to be discussed such as mixing strengthening element.

• Journal of the Korea Concrete Institute
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• v.21 no.1
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• pp.55-64
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• 2009

This study is aimed to derive the optimum mix proportion of the combined self compacting concrete according to cement types (blast-furnace slag cement and belite cement) and to propose the basic data to field construction work after evaluating the quality properties. Specially, lime stone powder (LSP) as binder and viscosity agent are used in the combined self compacting concrete because slurry wall of an underground LNG storage tank should be kept stability of quality during concrete working. Replacement ratio of LSP is determined by confined water ratio test and main design factors including fine aggregate ratio ($S_r$), coarse aggregate ratio ($G_v$) and water-cement ratio (W/C) are selected. Also, quality properties including setting time, bleeding content, shortening depth and hydration heat on the optimum mix proportion of the combined self compacting concrete according to cement type are compared and analyzed. As test results, the optimum mix proportion of the combined self compacting concrete according to cement type is as followings. 1) Slag cement type-replacement ratio of LSP 13.5%, $S_r$ 47% and W/C 41%. 2) Belite cement type-replacement ratio of LSP 42.7%, Sr 43% and W/C 51%. But optimum coarse aggregate ratio is 53% regardless of cement types. Also, as test results regarding setting time, bleeding content, shortening depth and hydration heat of the combined self compacting concrete by cement type, belite cement type is most stable in the quality properties and is to apply the actual construction work.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.361-364
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• 2002

This paper discusses the influencing factors such as coring position, height to diameter ratio of core specimen(h/d) and coring torque on the strength estimation of concrete by small site coring method in order to verify the validities of small size core method. According to results, as for the influence of drilling position, when core specimens are obtained from the place parallel to placing direction, compressive strength of core specimens are higher than those perpendicular to placing direction. This is due to the loss of the area of core specimen perpendicular to plating direction by bleeding. And in case of $\phi$ 24mm core specimen, when vertical drilling against placing direction is taken. compressive strength of core specimen obtained at the bottom of the structure is higher than that at the top of the structure. As for the influence of height to depth ratio, as h/d ratio increases compressive strength shows to be decreased. As for the influences of rotation speed of drilling machine, as its speed goes up, compressive strength decreases, regardless of core diameter.