• The Journal of Engineering Geology
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• v.19 no.3
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• pp.417-422
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• 2009

Tunnels that have recently been constructed are characterized by longer length than ever before and furthermore they frequently go through the ground area with poor conditions such as fractured zones. If ground strength is weak, plastic deformation of tunnel occurs, and occasionally a big fall may be brought about. Up to now, the construction work of tunneling has been executed as a sequential method placing the lining concrete after completion of excavation. Such a method requires a long time and much money to complete the tunnel. It is hard to ensure the stability of tunnel if tunnel is left undone for a long time after excavation in fracture zones or plastic grounds. For this reason, we tried to take simultaneous construction of tunnel excavation and lining concrete in order to not only shorten construction schedule but also stabilize the tunnel at the highly fractures zone as soon as possible. As preliminary consideration for simultaneous construction, in-situ tests are performed to calculate the isolation distance over which blasting vibration does not influence the strength of lining concrete. Improvement of ling form, placing method of concrete, ventilation using a dust collector, together with equipment arrangement, was made to assure the simultaneous construction work.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.11a
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• pp.91-94
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• 2006

The way to shorten a construction period is considered to an very important technology development element as reducing the formwork removal periods with promoting strength revelation own concrete. This study executed experiment to review usability of early strength revelation chemical admixture which is judged in ways effective with premature removal of form about concrete. Use of early strength revelation AE water reducin admixture is apperaing so that strength revelation by early hydration promotions is excellent. The results of being applied proposed work process are that compressive strength are appeared more than 5MPa within 16 hours so that removal of vertical form was possible. the concrete compressive strength satisfied with a more than 2/3 of specified concrete strength for removal of horizontal form are appeared in 42 hours of 27 MPa proportioning strength, in 36 hours of 30, 35 MPa proportioning strength so that the 6 days cycle time of concrete structural frame work is cut by 2 days as shortening delayed period in works of removing slab forms. So construction cost reductions and a construction period shortening are judged so that it is possible.

• Journal of Energy Engineering
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• v.28 no.1
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• pp.10-16
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• 2019

The purposes of this study is to secure subsidence stability and economical efficiency of lightweight foamed concrete. The composition of lightweight foamed concrete was designed for OPC by substituting with constant contents of calcium sulfaluminate and fly ash. It is found that the flow of lightweight foamed concrete decreased with early ettringite formation by CSA. The initial strength increased with the decrease of drying time of lightweight foamed concrete when CSA was substitution to 10%. The settlement deep of foamed concrete improved the settlement stability by replacing CSA, which prevented shortening of the coagulation time and bubble puffing.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.301-304
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• 2008

This paper presented an structural efficiency of steel coupling beam jointed single plate shear connections with seat and top angle. Parameters for the test specimens were are seat and top angle, reinforcing of concrete, embedded length, section loss. Steel coupling beam with angle showed excellent strength, stiffness, energy dissipation capacity. The specimen with no reinforcement around the embedded steel plate showed slightly low deformation capacity because of early failure in the precast concrete walls. However, the specimen with reinforcement around the embedded steel plate showed good deformation capacity. Deformation capacity was not decrease despite short embedded length. The specimen with section loss showed excellent deformation capacity. Because shear strength of steel coupling beam was lesser than of connections. These results showed that for workability and cost efficiency, the proposed system is promising for one of steel coupling beam.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.843-854
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• 2013

This paper presents experimental research work for the evaluation of ultimate flexural behaviors of prestressed concrete beams with a corroded tendon. In order to evaluate the effects of loss of prestress or loss of tendon area on the ultimate flexural strength of prestressed concrete beams, static load tests are conducted using five prestressed concrete beams. After exposing prestressing tendons in two test beams using 25mm drill bit, the exposed tendons were corroded using an accelerating corrosion equipment to simulate loss of tendon area. During the tests, steel strains, concrete strains and displacements at the center of test beams were measured, and acoustic emission measurements were conducted to detect wire fractures. Based on the test results, evaluation method for predicting flexural strength of prestressed concrete beams with corroded tendons is investigated. In addition, evaluation methods for predicting the existence of corroded tendons in post-tensioned prestressed concrete beams at service loads are discussed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.2
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• pp.212-218
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• 2020

The purpose of this study is to investigate the fire resistance of ultra-high-performance concrete according to the amount of polypropylene fiber. Different mixtures according to the amount of polypropylene fiber were exposed to a maximum temperature of 900℃; and explosive spalling, residual compressive strength, and ultrasonic velocity of each specimen were evaluated. Test results showed that the fire resistance can be improved by including a small amount of polypropylene fiber in ultra-high performance concrete. It was not observed that explosive spalling occur at a temperature of 900℃ when the polypropylene fibers over 0.4% were included. Residual compressive strength and ultrasonic velocity decreased by 48% and 44%, respectively, compared to those at room temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1077-1082
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• 2001

The most recent building trend is going large, high rise, high strength as overlarge project is developing in domestic construction business. Belite cement has properties like low heat, excellent long term strength, and durability without admixture(fly ash, silica fume). so, Belite cement is suitable for mass structure which is needed high strength, high fluidity and low heat property. This study is to examine the possibility of site adoption microwave-use early strength estimation method. Based on the existed study related the portland cement, the interrelation between Belite cement and microwave-use early strength estimation method is required. In this study, interrelation between mortar and Evaluating strength estimation method is investigated before the concrete experiment.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.289-290
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• 2010

This study investigated the high early strength properties of blended cement using cement with high blaine value in order to reduce a construction period.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.217-222
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• 2000

A large Pc structure building is system that consisted of bearing wall and slab joint. It has general structure stability from unity thar each members tied at joint. The strength of mortar that packing in joint among panels is important to internal force in entire building system. Do, if we could get early strength estimation with microwave. It would bring good construction planning, reduce construction time, and judge building stability and so on. The purpose of this study is to develop early estimation method for making better quality control and constructing good PC panel structure. The results of this study were as follows :1) With sealed molds, reduced moisture volatilization to more than 60% and enlarged 30% accelerated compressive strength than before one. 2) To get more accelerated strength, we should control maximum temperature difference to $30^{\circ}C$ downward 3)Interrelation with 7-day and 28-day strength were 0.831,0.902, and it is above than before one

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.114-121
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• 1996

This study presented a simple test method of early decision on the quality of concrete by the way of refrigeration curing. It is a method of early decision for the quality of hardened concrete, after 28days, through the using refrigeration curing, at -18$\pm$$3^{\cire}C$ for five hours. I could find that there were fixed connections between the solidities after 28days and 48days, by the test of compression on the Re-Mi-Con through the test of standard curing and refergeration curing. (F = 1.02X + 13, $r^2$ = 0.964, S = 10.6kg/$\textrm{cm}^2$) I except that we can reduce the mistakes of construction work by forecasting the quality through the refrigeration curing.