• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2015.07a
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• pp.218-219
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• 2015

Precast concrete produced in the industry is advantage that easy to manage, and it save construction period in the field. The specimens according to the type of activator for AAS(Alkali-Activated Slag) mortar cured in an autoclave. The specimens of AAS mortar with sodium was shown the high rate of increase of the compressive strength.

• International Journal of Highway Engineering
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• v.3 no.2 s.8
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• pp.123-130
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• 2001

This study was performed to enhance mechanical properties of high-early-strength concrete using regulated-set cement for early traffic opening with various mixtures. Restraint of moisture and thermal movements of concrete pavement in actual field conditions, by external or internal restraining factors, generates tensile stresses which introduce microcracks and thus reduce the mechanical properties of concrete. Fiber reinforcement of concrete is an effective approch to the control of microcrack and crack development under tensile stresses. Three different types of regulated-set cement which recently have been used in Korea and two different types of fiber were adopted. Fibers were added and their mixtures are compared with plain high-early-strength concrete mixture. From the test results, fiber reinforced concrete was increased mechanical properties of high-early-strength concrete using regulated-set cement than the plain concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.116-127
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• 2014

The studies were carried out to process one cycle for a day to the large section tunnel lining concrete. Climatic characteristics of the tunnel inside are changed, when the temperature of the concrete placement is low, the mold remove time is increased that the heat of hydration speed be delayed because affects the strength development, to compensate for this, after installing the curing sheet on both sides of the steel form and installation of tunnel entrance, when it comes to providing the additional heat source of $28{\pm}2^{\circ}C$ therein, it was to be achieved early strength development control standards (4.5MPa) presented as a crack control scheme or more, thus, It was able to remove after age of 14hr from mold. On the other hand, under the conditions of $10{\pm}1^{\circ}C$ that a natural curing temperature in the tunnel, it was analyzed must ensure the curing time of 36hr or more after concrete placement. Throughout this study, the concrete strength development and the temperature in the early-age concrete, it can find that reverify the curing temperature is greatly affected, even concrete fly ash is mixed 10%, if it is possible to raise the surface temperature for a predetermined time, is not a problem in the early strength development.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.793-796
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• 2008

Recently early strength concrete has been required for economical assurance and the prevention of frost damage in winter through air reduction in construction of concrete structures. This study presented the optimum condition revealing compressive strength 5MPa which has the possibility of removal of form in 24 hours, and researched the changes of unit weight of cement types of high early strength AE water reducing agents, characteristic of compressive strength expression as cure temperature conditions and slump or airspace. Test results showed at $15^{\circ}C$ with compressive strength of 5MPa that premature removal of form was possible in case of using highly early strength PC water reducing agent with unit weight of cement 360 ; 22hours faster than 10, unit weight 360 ; 20hours faster than 7, unit weight 390 ; 18 hours faster than 4 comparing with OP water reducing agent. And at $5^{\circ}C$ in case of using highly early strength PC water reducing agent with unit weight of cement 330 ; 32hours faster than 10, unit weight 360 ; 30hours faster than 7, unit weight390 ; 27hours faster than 4 comparing with OP water reducing agent. Therefore as the temperature rises $10^{\circ}C$, compressive strength of 5MPa reaching hour shortens 10 hours.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.296-302
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• 2016

Studies aimed at reducing the occurrence of cracks by the shrinkage of concrete are in demand because the repair and reinforcement for cracks caused by declining concrete durability costs the user to maintain the concrete structure. In particular, in underground power facilities for power transmission, the cost is a heavy burden to repair and reinforce. For this reason, underground power facilities demanded effective methods for crack reduction at the engineering design step. This study, as a part of the development of shrinkage reducing agent for low shrinkage concrete on underground power facilities, investigated TEA to complement the shrinkage reducing agent to improve the early strength of concrete. In the case of TEA 3% as a shrinkage reducing agent, the early strength was improved significantly, and the shrinkage reducing effect was excellent. In addition, TEA 3.0 % and the shrinkage reducing agent 2.0 % showed excellent shrinkage property and compressive strength. On the other hand, more study of shrinkage reducing materials, including performance reviews on the shrinkage reducing materials with variable factors and type of materials, will be needed to generalize these results.

• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.41-49
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• 2018

The purpose of this study is to develop a floor mortar construction technique which has high strength and inherent mechanical properties and does not cause cracks due to shrinkage after construction. It has been demonstrated that compressive strength, bending strength, flow with floor mortar, and crack reduction performance. As a result, it was confirmed that the developed floor mortar had the same or better performance comparing with the existing foreign products. The results of this experiment can be used as a validation material for high performance and high flowable mortar construction technology with excellent material performance, economical efficiency and construction ability by securing the required performance as floor mortar and selecting the optimal formulation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.1
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• pp.263-270
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• 2011

In this study, the performance of Poly-Naphthalene Sulfonate (PNS) type-admixture used widely in South Korea and Polycarboxilic type-admixture(i.e., WF2000) developed in the J company of the domestic, for precast concrete products produced in the factories, was evaluated. With the 20% reduced usage of WF2000 compared to PNS type-admixture, workability was considerably improved due to high water-reducing ratio, accelerating effect of concrete setting and accelerant dispersant action, which the product has, under the high temperature. In addition, the development of initial and long-term strengths of PHC plies was predominant. For WF2000, it is also possible to correspond with the change of original materials and environmental conditions since the control of water-reducing and supporting forces is feasible. Accordingly, it was noted that WF2000 is superior for deterioration of production & workability and bad casting problems in summer and the solution of initial strength reduction problem due to the delay of setting in winter.

• Korean Journal of Cleft Lip And Palate
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• v.5 no.2
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• pp.117-122
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• 2002

성장기 환자에서의 각 부위별 임플란트 식려 시기를 요약해보면 다음과 같다. 1) 상악전방부 : 외상이나 선천적 결손을 해결하는 방법으로 임플란트를 사용하는 술식이 권장하지만 성장이 완료되지 않았기 때문에 야기되는 문제를 해결하기 위해 성장이 완료될 때까지 연기하는 것이 좋다. 2)상악 후방부: 수직적인 성장량이 최고 1cm까지 일어날 수 있으면 상악동의 흡수로 조기에 임플란트 침강과 치근부의 노출을 야기할 수 있다. 그리고 동시에 보철에 의한 구개열의 횡적인 성장방해를 피해야한다. 3) 하악 전방부 : 무치증 아이에서 임플란트의 조기식립이 적응증이 되는 유일한 곳으로 치아가 없을 때는 치조골의 성장이 최소이며 초기에 횡적, 후방 성장이 대부분 완료된다. 그러나 단일 임플란트 식립은 권장되지 않는다. 4)하악후방부: 늦게까지 성장변화가 지속되기 때문에 전후방, 횡적, 수직적 성장의 많은 양이 일어난다. 하악의 회전성장의 영향을 많이 받아 하악 무치악에서 조기 임플란트 사용한 보고도 적고. 자연치아에 인접하여 임플란트를 식립한 기록은 있으나 골격성장이 완료될 때 까지는 식립하지 않는 것이 좋다.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.435-440
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• 1994

It is considered to pressing problem that the develpment of the rapid and simple method and measuring instrument, can evaluate for quality of concrete at early period. Accordingly in this paper proposed to earlier evaluation method on quality of concrete using resistance method and ultra-sonic pulse velocity test. It was found to the possibility of development on test method and instrument through a series of fundmental investigation.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.61-64
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• 1993

This study is aimed to analyze the influencing factor on the non-destructive testing by measuring rebound number of schmidt hammer and ultrasonic pulse velocity according to the variation of recycled aggregate kinds. And this study is to provide the reference data on application of practical use.