• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.219-222
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• 1999

Concrete is to be important quality in placement point and exact test method needed about early judgement method concrete on placement point. But early judgement method of concrete proposed various kind of method because the problems of accuracy and the time required of test exists, it is used within the limits. This study is to propose of early strength judgement by using microwave for accurate estimating early strength of concrete and to develop test machine. Through out this study we find that belows. 1) Strength development of concrete specimen according to the time heated by microwave showed the height strength development in 9 minutes regardless of slump and w/c. 2) As cooling time is long, strength of concrete specimen according to the time heated by microwave showed high strength development and this tendency is like regardless of heating time, w/c and slump. 3) As w/c is high, accelerating strength development according to w/c showed lower strength development and this tendency is like regardless of slump, heating time and cooling time. 4) As slump is big, compressive strength of specimen in standard curing showed lower value and as w/c is big, strength development showed lower

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.419-426
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• 2000

The purpose of this study is to present the application of WFS co-mixtures for retaining wall as flowable backfill. The fly ash, generated at the Tae-An thermoelectric power plant, was used in this research and was classified as Class F. Green Sand, Furane Sand, and Coated Sand, which had been used at a foundry located in Pusan, were used. Couple of laboratory tests and small scale retaining wall tests were performed to obtain the physical properties of the WFS co-mixtures and the possibility of backfill materials of retaining wall. The range of permeability for all the co-mixtures was from 3.0${\times}$10$\^$-3/ cm/s to 6.0${\times}$10$\^$-5/ cm/s. The unconfined strength of the 28-day cured specimens reached around 550kPa. Results of the consolidated-undrained triaxial test showed that the internal friction angle is between 33.5$^{\circ}$ and 41.8$^{\circ}$. The lateral earth pressure against wall decreased up to 80% of initial pressure within a 12 hours and the total lateral earth pressure is less than that of typical granular soil. It was enough to construct the backfill for the standard retaining of 6m with just two steps, like fill the co-mixtures for half of retaining wall, and then fill the others after 1 day. The stability of retaining wall for overturning and sliding increased as the curing time elapsed.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.3
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• pp.123-133
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• 2018

The purpose of this paper is to propose an experimental method to evaluate the resistance of abrasion about 24 MPa, 27 MPa, and 30 MPa compressive strength. These strength are used in the design and construction of concrete hydraulic structures in Korea. The mixing ratios of the ready mixed concrete strengths were investigated countrywide and set the representative mixture proportion ratios of the nine mixed types of OPC, FA and BFS. After making and curing the test specimens, the underwater abrasion test was performed. ASTM C 1138 International Standard was used to fabricate the test equipment, and the surface abrasion resistance of the specimen was tested using the test equipment. In the case of OPC, the 30% abrasion resistance improvement effect was observed at 72 hours as the water-binder ratio decreased. That was reason the coated cement bond strength of the specimen was strong. In the case of BFS and FA, it was improved by 9.9% and 3.8%, respectively, at 72 hours as the water-binder ratio decreased. It was due to the characteristics of the latent hydraulic and pozzolanic reactions. Generally, the relative abrasion resistance of concrete can be evaluated at 24 hours. However, in case of low strength (under 24 MPa), the surface mortar layer wears much faster at the first 12 hours, so it can be considered to evaluate the relative abrasion loss rate at this point.

• Journal of Adhesion and Interface
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• v.4 no.2
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• pp.21-29
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• 2003

Hot AC anodising has been evaluated us pre-treatment for aluminium prior to structural adhesive bonding. Phosphoric and sulphuric acid hot AC anodising showed very promising adhesion promoter capabilities with durability comparable with the best standard DC anodising procedures. AC anodising does not required etching prior to anodising and offers u pre-treatment time down to 20 seconds. The interface/interphase between the aluminium substrate and the adhesive was investigated in order to get a better understanding of the involved adhesion mechanisms and to explain the long-tenn properties. The alkaline medium formed at the oxide layer/adhesive interface has been shown to induce a partial dissolution of the oxide layer leading to the formation of metallic ions which diffuse in the adhesive (EPMA measurements). The effect of diffusion of the Al ions on adhesion and joint durability is still uncertain but studies showed that pre-bond moisture affected the joints durability and to some extent the diffusion length. specially for DC anodised samples. So far no direct correlation could be established between the diffusion length d and the joints durability but new trials with better control over the elapsed time between bonding and adhesive curing are expected to help getting a better understanding of the involved mechanisms.

• Journal of the Korean Society of Tobacco Science
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• v.16 no.2
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• pp.128-133
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• 1994

This study was carried out to get agronomic information about the tobacco culture in paddy soil where incidence of grey tobacco leaves used to appearly uptake of iron, manganese and chlorine due to soil acidity and high water level. Application of lime to paddy soil(pH5.4-5.6) reduced content of iron, manganese known as proceeding materials giving rise to variegated grey tobacco after curing, compared with non-treatment. Grey leaves were found mainly at lower and middle stalk positions, and incidence of grey tobacco was lowered by application of lime in the well drained field but was not affected by level of fertilizer application. Amendment of soil acidity by lime tended to decrease chlorine and manganese content in leaves. Nicotine and mangenese content of leaves were lowered by reduction of one-quarter fertilizer level. In case of lime treatment, increase of yield reached to 4-6% comparing with those of non-treatment but price per kg was not affected. Reduction of N fertilizer level to three-quarters had the equal yield but high quality of leaf comparing with standard fertilization in paddy field.

• The Journal of Advanced Prosthodontics
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• v.5 no.4
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• pp.423-427
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• 2013

PURPOSE. This study evaluated the bond strength between porcelain denture teeth (Bioblend 43D) and four different polymerized denture resins (Lucitone 199, Palapress, Acron MC, Triad) with and without a bonding agent and after four different types of surface treatment (polished, HF etched, sandblasted, air-abraded). MATERIALS AND METHODS. Central incisor porcelain denture teeth were divided into 32 groups of 5 each. Tensile bond strength (MPa) was determined using a testing machine at crosshead speed of 0.5 mm/min. Mean and standard deviation are listed. Data were analyzed by two-way ANOVA. Means were compared by Tukey-Kramer intervals at 0.05 significance level. RESULTS. All surface treatment increased bond strength compared to polished surface and the highest bond strength was found with Palapress resin with etched porcelain surface (8.1 MPa). Bonding agent improved the bond strength of all denture resins to porcelain teeth. Superior bonding was found with Palapress and air-abraded porcelain (39 MPa). CONCLUSION. Resins with different curing methods affect the bond strength of porcelain teeth to denture bases. Superior bonding was found with auto-polymerized resin (Palapress). Application of ceramic primer and bonding agent to porcelain teeth with and without surface treatment will improve the bond strength of all denture resins to porcelain teeth.

• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.47-55
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• 2000

Protections from the frost damage at early ages are one of the serious problems to be considered in cold weather concreting. Frost damage at early ages brings about the harmful influences on the concrete structures such as surface cracks and declination of strength development. Therefore, in this paper, protecting periods of frost damage at early ages according to the standard specifications provided in KCI(Korean Concrete Institute) are suggested by appling logistic curve, which evaluates the strength development of concrete with maturity. W/B, kinds of cement and curing temperatures are selected as test parameters. According to the results, the estimation of strength development by logistic curve has a good agreement between calculated values and measured values. As W/B and compressive strength for protecting from frost damages at early ages increase, it is prolonged. It shows that the protecting periods of FAC(Fly Ash Cement) and BSC(Blast-furnace Slag Cement) concrete are longer than those of OPC(Ordinary Portland Cement) concrete. The protecting peridos from frost damage at early age by JASS are somewhat shorter than those by this paper.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.11a
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• pp.13-16
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• 2008

This paper is to present the performance data for improved direct setting method using tile bond for application of porcelain tile under 1 percent absorptance. For this purpose, improved direct setting method type 1 & 2(tile bond curing time 0, 24H) were compared with the conventional setting methods(including direct setting method and improved pressure setting method) in the sight of the adhesive stability of porcelain tile. It tested for tiles after 14, 28days under standard condition and severe conditions. The severe conditions were water immersion, heat ageing(70℃) and freeze-thaw cycle. On the basis of test results, the adhesive strength of direct setting method was lowest for the conventional setting methods. But improved direct setting method using tile bonds(A, B) came close to the result of improved pressure setting method using tile bonds.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.213-214
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• 2010

An objective of this experimental research is to investigate the diffusion characteristics for chloride ion of concrete subjected to sulfate attack. For this purpose, concretes with three types of cement such as ordinary portland cement(OPC), binary blended cement(BBC), and ternary blended cement(TBC) containing mineral admixtures were made for water-binder ratios of 32% and 43%. The concrete specimens were immersed in sulfate solution for 365 days, and then the resistance against chloride ion penetration of them were estimated by using NT BUILD 492. It was observed from the test results that the resistance to chloride ion penetration of concrete subjected to sulfate attack was greatly decreased than that of standard curing concrete under the same age.

• Journal of Environmental Science International
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• v.19 no.2
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• pp.255-260
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• 2010

A stabilization/solidification (S/S) process for lead (Pb) contaminated soils was evaluated using waste cow bone containing apatite like compounds. Soil samples obtained form firing range were treated with waste cow bone. The effectiveness of stabilization was evaluated based on the Korean Standard Leaching Test (KSLT) and soil pH. The leached concentration reduced with increased in dose of waste cow bone. Overall, the KSLT results showed that Pb concentration in soils are significantly affected by amount of waste cow bone. When soil amended with 20 % of waste cow bone, less than 0.1 mg/kg was leached, and soil pH was increased from 6.5 to 8.4. Same results were obtained when finer waste cow bone was applied. The reachable concentration of Pb in soil showed in inversely proportional to solid/liquid ratio. Aging periods indicate improving mix design was applied. Relatively high lead concentrations was observed at the first 1 days, however leaching profile are reduced significantly over time for all mix designs.