• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.151-156
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• 1998

Concrete structures is appeared the shrinkage after being harden of the hydration effect of cement. To overcome this disadvantage, expansive additives are used. In our country, the most popular expansive additives are hauyne(CSA) or free lime(free-CaO) systems. These expansive additives are used to expansive cement mortar or concrete materials. In this study, we analyzed the expansive property mechanism about the hydration reaction of the free lime systems and in particular we convinced size distributions of the free lime size affect the expansion ratio with expansion ratio with experiments. We carried out the experiment for the expansive properties by using the soundness molds and with various the humidity and dry setting conditions. The hydration reactions of the free lime affect the reaction properties according to the relative humidity by laboratory experiments.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.955-960
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• 2004

In this study, three dimensional FE analysis of concrete slab track has been performed in order to develop the realistic design of precast concrete slab track. The precast slab track system including the precast concrete slab panel and the grout layer is modeled using the three dimensional solid element with crack softening effect. The input load is computed from the one dimensional beam element model constituting the rail and several discrete springs. To investigate the effect of the longitudinal connection of slab panels, two different systems-continuous and discrete systems - are modeled. The analytical results show that the stresses of both the slab panel and the grout layer are in the range of linear elastic, and, at the interface between two adjacent panels, the primary stresses of the grout layer of the discrete system are higher than those of the continuous system. However, The overall stress levels of the grout layer are very low relative to the strength of th grout.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.5
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• pp.374-381
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• 2016

The sealing technique is widely used for repairing the cracks on the surface of concrete and preventing their expansion in the future. However, it is difficult to ensure the safety of the workers when sealing large structures in inconvenient working environments. This paper presents the development of a sealing robot system to seal various shapes of concrete surface in rough conditions for a long time. If the robot can maintain the desired contact force, the cracks can be completely sealed. An impedance force tracking controller with slope estimator is proposed to calculate the surface slope in real time using the robot position. It predicts the next point in order to prevent the robot from disengaging from the contact surface owing to quick slope changes. The proposed method has been verified by experimental results.

• International Journal of High-Rise Buildings
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• v.5 no.3
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• pp.205-211
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• 2016

This paper addresses the key technologies for supertall building construction based on the Lotte World Tower project in Korea. First, the mega-mat foundation construction technologies are shown, including ultra-low heat concrete, heat of hydration control programs, and the logistics plan. Then, high strength concrete technologies of 50~80 MPa are introduced and discussed within the context of the highest pumping record in Korea at 514.25 meters. Structural design concepts of gravity load and lateral force resistance systems are introduced, along with surveying systems using GNSS and temporary installation plans of special heavy equipment like tower cranes, hoists, and high pressure concrete pumps. If it is possible to coordinate these key technologies and others, optimizing for the building's design and construction, supertall building construction can be successfully completed.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.513-518
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• 2003

Recently, advanced systems for water treatment are introduced for water quality improvement. One of those systems is water treatment method using ozone($O_3$). For it has strong oxidizing energy, it is necessary to have materisl stability against $O_3$. In this paper, epoxy resin specimens using as anticorrosive material of concrete structure for drink water are used to serve as a material of deterioration evaluation. It is to be studied weight loss, surface corrosion of specimens, ingredient analysis of floating particle, a solute of chemical ingredient by way of accelerated ozone testing. As the results of experiment, specimen weight is decreased. The surface of specimen is eroded heavily and showed a loss of gloss and floating particle, and in the stability for drinking water, harmful ingredient is not detected in the water.

• Earthquakes and Structures
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• v.15 no.2
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• pp.203-214
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• 2018

Deflection control in tall buildings is a challenging issue. Connecting of the towers is an interesting idea for architects as well as structural engineers. In this paper, two reinforced concrete core-wall towers are connected by a truss bridge with buckling restrained braces. The buildings are 40 and 60-story. The effect of the location of the bridge is investigated. Response spectrum analysis of the linear models is used to obtain the design demands and the systems are designed according to the reliable codes. Then, nonlinear time history analysis at maximum considered earthquake is performed to assess the seismic responses of the systems subjected to far-field and near-field record sets. Fiber elements are used for the reinforced concrete walls. On average, the inter-story drift ratio demand will be minimized when the bridge is approximately located at a height equal to 0.825 times the total height of the building. Besides, because of whipping effects, maximum roof acceleration demand is approximately two times the peak ground acceleration. Plasticity extends near the base and also in major areas of the walls subjected to the seismic loads.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.557-560
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• 2006

Worldwide, Certification systems for standard of material and quality of product exist very variously. Korean industrial Standard (KS) is most representatively certification systems in Korea. But laboratory of korea uses often ASTM, RILEM and JIS and these standards do not get into unionization. so, Granted that experiment is same, result still can different. Therefore, this research measured chloride amount of hardened concrete using identical material and wished to improve accuracy of chloride estimation as that comparison evaluate to each examination.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.525-528
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• 2008

For well-constructed concrete, its service life is a long term and it has an enough durability performance. However, for cracked concrete, it is clear that cracks should be preferential channel for the penetration of aggressive substance such as chloride ions according to author's previous researches. In order to enhance the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of different types of surface treatment system, which are expected to seal the concrete and the cracks to chloride-induced corrosion in particular. In this study, it is examined the effect of surfaced treated systems on chloride penetration through microcracks. Single surface treatments of penetrant or coating and double application were considered as an experimental variation. RCM (Rapid Chloride Migration) testing is accomplished to visualize chloride penetration via cracks.

• Structural Engineering and Mechanics
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• v.51 no.3
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• pp.487-502
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• 2014

In buildings structures, the flexural stiffness reduction of beams and columns due to concrete cracking plays an important role in the nonlinear load-deformation response of reinforced concrete structures under service loads. Most Seismic Design Codes do not precise effective stiffness to be used in seismic analysis for structures of reinforced concrete elements, therefore uncracked section properties are usually considered in computing structural stiffness. But, uncracked stiffness will never be fully recovered during or after seismic response. In the present study, the effect of concrete cracking on the lateral response of structure has been taken into account. Totally 120 cases of 3 Dimensional Dynamic Analysis which considers the real and accidental torsional effects are performed using ETABS to determine the effective structural system across the height, which ensures the performance and the economic dimensions that achieve the saving in concrete and steel amounts thus achieve lower cost. The result findings exhibits that the dual system was the most efficient lateral load resisting system based on deflection criterion, as they yielded the least values of lateral displacements and inter-storey drifts. The shear wall system was the most economical lateral load resisting compared to moment resisting frame and dual system but they yielded the large values of lateral displacements in top storeys. Wall systems executes tremendous stiffness at the lower levels of the building, while moment frames typically restrain considerable deformations and provide significant energy dissipation under inelastic deformations at the upper levels. Cracking found to be more impact over moment resisting frames compared to the Shear wall systems. The behavior of various lateral load resisting systems with respect to time period, mode shapes, storey drift etc. are discussed in detail.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.320-323
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• 2004

In general, polymer concrete has more excellent mechanical properties and durability than Portland cement concrete, but very sensitive to heat and has large deformations. In this study, the long-term creep behaviors was predicted by the short-term creep test, and then the characteristic of creep of recycled-PET polymer concrete was defined by material and experimental variables. The error in the predicted long-term creep values is less than 5 percent for all polymer concrete systems. The filler carry out an important role to restrict the creep strains of recycled PET polymer concrete. The creep strain and specific on using the CaCO3 were less than using fly-ash. the creep increases with an increase in the applied stress, but not proportional the rate of stress increase ratio. The creep behavior of polymer concrete using recycled polyester resin is not a linear viscoelastic behavior.