• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.283-293
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• 2015

In order to evaluate corrosion resistance of steel fiber-reinforced concrete, accelerated chloride migration and surface resistivity tests were conducted. In addition air content of fresh concrete, compressive strength and water absorption were measured for investigating fundamental characteristics of concrete. Two different water-cement ratios(0.44, 0.5) and three steel fiber contents(0.25%, 0.5%, 1%) were considered as variables. Note that all specimens cast with same compaction work. As a results, corrosion resistance decreased as steel fiber contents increased regardless of water-cement ratio when the concrete was compacted with same amount of work done. However, for concrete with same steel fiber content, the lower water-cement ratio showed the better corrosion resistance. It is found that enhancement of fluidity and enough compaction should be done for corrosion resistance of SFRC.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.1-10
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• 2013

In this study utilize industry product for OPC(ordinary portland cement) and BFS(blast furnace slag) mixing concrete early age compressive strength elevation and executed study for high strength binder. Association ratio of industry product for high strength binder manufacture is Titanogypsum (4) : Limestone (3) : Waterworks Sludge by ratio of (3) as it is proper move. high strength binder mixing rate appeared that (7~9) % are proper via preliminary test. Could confirm that display high compressive strength incidence rate in early age than plain harmony according as mix high strength binder mixing concrete compressive strength high strength binder. Also, high strength binder generality that give function than high strength binder used in existing displayed more excellent intensity, and compressive strength displayed result that multiply single breadth according as high strength binder substitute that give function increases.

• Journal of Energy Engineering
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• v.14 no.4 s.44
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• pp.241-247
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• 2005

Heat transfer enhancement and pressure loss penalty caused by three-row winglets built in three-row tube-bundles in an in-line arrangement, are compared between 'common flow up' and 'common flow down' winglet configurations. The 'common flow down' winglet-pairs recommended by the previous researchers bring about $10\%$ to $25\%$ increase in heat transfer enhancement and $20\%$ to $35\%$ increase in pressure loss penalty, in comparison with fin-tube bundles without winglets. For the 'common flow up' winglet-pairs, the spanwise distance between the trailing edges (${\Delta}y$) of winglet pairs was changed and investigated. Two types ot winglet are applied for triangular and rectangular shapes. In the triangular winglets with ${\Delta}y$=5 mm in in-line tube bundles, the heat transfer increased up to $10\%$, and simultaneously the pressure loss decreased by $8\%$ to $15\%$ for the Reynolds number (based on two times channel height) ranging from 300 to 2700, when the 'common flow up' winglets were built in. The performance of fin-tube bundles with triangular winglets is much superior to the rectangular one, because of the smaller pressure-loss penalty.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.254-262
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• 2003

In this study, the results of applying cold weather concreting mixed with Accelerator for Freeze Protection(AFP) to full scale structures are presented. Since the determination of W/C and amount of AFP significantly have an effect on strength gain and protection of frost damage in early, a full investigation is needed to determine these values at stage of nux design. The flowability of fresh cold weather concreting with AFP was similar to the same W/C. Lower loss of workability and initial slump flow of concrete using superplasticizer of polycarboxylic ester than that of melamine sulphonate showed that polycarboxylic ester was more effective on elapsed time. Temperature histories of specimens located in insulation boxes at the site was similar to that of structures. Thus, it is cleared that simple adiabatic curing method is effective for evaluating in-place concrete strength than specimens cured by sealing method. The investigation results of development of compressive strength of cold weather concreting included AFP with curing methods by logistic curves indicated that AFP can be effective to gain strength at lower temperature than normal curing temperature. In field testing, vinyl sheets were placed over the concrete sections and AFP enabled concrete to gain $5N/{mm}^2$ to protect frost damage in early ages and specified compressive strength of concrete at 28 days under average temperature of $-2^{\circ}C$ (lowest temperature was $-12^{\circ}C$) during site application.

• Membrane Journal
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• v.4 no.4
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• pp.221-231
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• 1994

The GR51PP(MWCO 50,000) and GR40PP(MWCO 100,000) membranes manufactured by DDS were used in ultrafiltration of dextran(Mw. : 500,000) solution in flat plate ultrafiltration cell filled with various types of turbulence promoters. The flux improvement by using turbulence promoter was higher in laminar flow region than in turbulent flow region. The maximum improvements of permeate flux were foud as 112% and 50% I laminar flow region and turbulent flow region, respectively. Also, the solute rejection of the ultrafiltration membrane was improved by turbulence promoters and its effect was significant in the high transmembrane pressure and laminar flow region. The smaller the spacer mesh size was used, the higher the flux improved, but the pressure drop in ultrafiltration cell also increased. In laminar flow region, pressure drop by the spacer was negligible, but in turbulent flow region it changed significantly depending upon the mesh size of the spacer and therefore, its mesh size must be baken into account in the design of the process. The predicted results of the modified mass transfer correlation had better agreement with experimental results than those of unmodified one, The modified mass transfer correlations for laminar and turbulent flow region are shown as follow. $N_{sh}=0.151(N_{Re})^{0.199}(N_{Sc})^{0.22}(N_{Scm})^{0.197}\;(625 $N_{sh}=0.0165(N_{Re})^{0.428}(N_{Sc})^{0.33}(N_{Scm})^{0.223}\;(5015

• Journal of the korean Society of Automotive Engineers
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• v.2 no.1
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• pp.9-20
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• 1980

디이젤기관의 냉시동성이 가솔린기관에 비하여 떨어지는 것은 이미 우리가 알고 있는 사실이다. 근년에는 소형트럭, 승용차, 소형건설기계 등의 분야에 있어서도 고속디이젤기관을 널리 사용하게 되었고 앞으로 디이젤연료의 중질화 및 세탄가 저하의 영향 등을 고려할 경우 시동성의 확보는 더욱 중요한 문제로 된다. 시동성에 영향을 미치는 인자 혹은 시동성개선의 방책으로서는 분 무의 착화에 직접 관련되는 것 외에 축전지의 저온특성 혹은 기관의 마찰토오크 등 여러가지에 걸쳐 있으나 이들 중에서 특히 분무의 착화에 직접 관련되는 방책에 관해서는 그것이 시동성에 미치는 영향에만 그치는 것이 아니고 시동개시직후에 있어서 배출가스, 혹은 출력성능 등에 미 치는 영향에 대해서도 함께 고려를 하여야 할 경우가 있다. 본고에 있어서는 냉시동시의 분무의 착화에 대하여 직접 관련하거나 그것을 촉진시킨다고 생각되는 몇개의 인자와 구체적인 방책을 취급하므로써 그것들이 시동성 및 시동직후의 청백연 혹은 출력성능 등에 대하여 미치는 영향에 대해서 기술하며 아래에서 취급되는 시동시의 착화를 촉진하기 위한 실제적인 인자 및 방책은 어느 것이나 기본적으로는 하나의 개념에 집약된다. 즉 그것은 연표와 효소로부터 이루어지는 연소계에 있어서 착화조건을 갖추어야함을 말할 것도 없다.

• 월간 기계설비
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• s.267
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• pp.51-60
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• 2012

정부가 중소기업제품의 구매를 촉진하고 판로를 지원함으로써 중소기업의 경쟁력 향상과 경영안정에 이바지할 목적으로 "중소기업제품 구매촉진 및 판로지원에 관한 법률"을 제정하고 중소기업 제품을 적극 사용하도록 권장하고 있다. 또한 조달청에서도 우수조달물품 지정제도를 통해 조달물자의 품질향상과 중소 벤처기업의 판로 지원을 목적으로 성능 및 기술 또는 품질이 뛰어난 물품을 우수조달 물품으로 지정하고 있다. 그러나 건설업계는 중소기업제품의 구매 촉진 및 판로를 지원하기 위한 이들 제도가 공사비 축소로 경쟁력을 약화시키고 있다고 지적하고 있다. 특히, 발주기관에서 자재를 공급함으로써 전문건설업계는 단순 시공만 하게 돼 경쟁력을 약화시키는 요인으로 작용하고 있다는 것. 뿐만 아니라 조달우수제품 구매제도의 경우 제품 납품만이 아닌 시공까지 겸하는 경우가 빈번해 지면서 중소건설업체의 시공업역이 차츰 줄어들고 있다고 지적하고 있다. 이에 따라 본지는 중소기업청의 공사용 자재 직접구매제도와 조달우수제도에 대해 알아본다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.1-9
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• 2019

GGBFS(Ground Granulated Blast Furnace Slag), one of the representative concrete mineral admixtures, improves the long-term durability and engineering performance of concrete by latent hydraulic activity. In this study, considering 3 levels of W/B(0.37, 0.42, 0.47) and GGBFS replacement ratio(0 %, 30 %, 50 %), durability performances for chloride attack are evaluated, and equations which predict behavior of accelerated chloride diffusion are proposed. Also, the relationship between accelerated chloride diffusion coefficient and passed charge is evaluated. In target curing day, accelerated chloride diffusion tests(Tang's method, ASTM C 1202) and compressive strength(KS F 2405) are performed. In the 730 day's results of accelerated chloride diffusion coefficient, GGBFS concrete has up to 28 % of decreasing ratio compared to OPC concrete, and in those of passed charge, GGBFS concrete has up to 29 % of decreasing ratio compared to OPC concrete. Also, it is deemed that the impact of variation of W/B is less in GGBFS concrete than in OPC concrete. The equations which predict accelerated chloride diffusion coefficient and passed charge are drawn, based on the characteristics of mixture and test results. The equation which predicts passed charge shows slightly higher coefficient of determination than that which predicts accelerated chloride diffusion coefficient.

• Journal of the Korea Institute of Building Construction
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• v.13 no.4
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• pp.407-415
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• 2013

The purpose of this research is to verify the performance of hardening accelerator in cement paste through mechanical performance evaluation and micro structure analysis on hardening accelerator for development of super high early strength concrete. The research results showed that hardening accelerator produced $Ca(OH)_2$ when hydrated with cement, enhancing the degree of saturation of Ca ion by using differential thermal analysis. Moreover, porosity was reduced rapidly as capillary pores were filled by hydration products of $C_3S$. According to the experiment using hydration measurement testing, when 1% and 3% of accelerator were mixed, hydration rate increased toward the second peak point compared to high early strength cement, before the first peak point disappeared. It turned out that adding accelerator accelerated the hydration rate of cement, especially $C_3S$. The shape of C-S-H is shown depending on the amounts of accelerator added and the production and age of $Ca(OH)_2$ by using SEM to observes hydration products. Therefore, it's evident that hardening accelerator used in this research increases amounts of $Ca(OH)_2$ and accelerates $C_3S$, it is effective for the strength development on early age.

• Journal of Korea Foresty Energy
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• v.21 no.2
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• pp.34-42
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• 2002

This research was carried out to investigate water repellent effectiveness of natural oil treated wood. Linseed oil, castor oil, olive oil, bean oil, perilla oil and sunflower oil were used in this test. For evaluation of water repellent of natural oil treated wood, moisture absorption test, water-drop contact angle test and color difference test of accelerated decomposition by UV and water were used. The moisture absorption amount of natural oil treated wood was less than untreated wood until 3 hours, but it was increased with time, there was no big difference with oil treated wood and untreated wood after 48hours. Oil treated wood and untreated wood showed big difference on contact angle test. It was no big difference by kind and oil concentration. Natural oil treated wood did not showed stability on the weather aging test. Contact angle test could be used on evaluation of wood surface status treated with natural oil.