• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.11a
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• pp.1-4
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• 2006

Because do placing joint after smallest $1{\sim}3$ day about concrete that is placed beforehand in field, it is difficult that remove laitance happening harden concrete. This laitance happens a problem of bond properties, deterioration in strength. In this research got following conclusion as result that do research about bond properties the way of disposal placing joint. Air Jet is loft interior and exterior. Water Jet appeared that laitance Removal Capacity is superior to dimension within 5%. Deterioration in strength is measured 37% by splitting tensile strength test result by laitance. Deterioration in strength by laitance do more than 30% that removal of laitance is predicted must consist necessarily at concrete horizontality placing joint stroke.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.445-448
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• 2004

Recently, bridge deck overlay with latex modified concrete is widely applied in domestic. the capacity of bridge deck overlay depends on bond state on the surface. factors that have an effect on bond state are clean condition on the surface, absence of surface microcracking, absence of laitance, overlay curing. In this study, it is researched that characteristic of bond strength according to moisture condition on the surface and the removal method of concrete. As a result, it shows high bond strength in dry condition when w/c is $31\%$ and in moisture condition when w/c is $38\%$ respectively. characteristic of bond strength according to the removal method of concrete shows high bond strength when using water-jets rather than jackhammers.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.409-412
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• 2006

The goal of waterproofing materials and construction method used for underground structure can be attained only when construction is done perfectly free of laitance, moisture and foreign substances on concrete surface. However, construction engineers agree that it is difficult to perfectly carry out such work in practice and realization of perfect waterproofing for underground structures is impossible in reality. Therefore, this study is to examine and explore waterproofing materials and construction method completely meeting environmental impacts that underground structures receive and thereby suggest waterproofing technology applicable to underground structures, in order to prevent problems caused by leakage for underground structures.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.235-236
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• 2023

Concrete surfaces have weak surface strength due to bleeding and laitance, and problems such as peeling, cracking, and cracking may occur. In particular, underground parking lots can be said to be more vulnerable to peeling, breaking, and cracking if excessive loading of materials and equipment movement are not managed at the initial age after placing of concrete. Cracks, peeling, and cracking problems in slab concrete in underground parking lots of apartments can lead to leakage problems and affect finishing materials constructed on top of topping concrete, reducing the performance required for waterproof materials. Therefore, in this study, the bleeding and surface strength according to the standard of topping concrete and the use of admixture were reviewed to solve the crack, peeling, and cracking problems among the types of defects in underground parking lot slab concrete. As a result, it was derived that the optimal concrete compressive strength is 30MPa or more, and it is a reasonable performance design method to prohibit the substitution of admixtures.

• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.16-22
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• 2001

Pretensioned spun high strength concrete (PHC) pile has to be quality-controlled and provided an adequate concrete cover to assure high load carrying capacity, impact resistance, economy, and durability. During spun pre-casting, the pile section is divided into several segregated layers such as laitance, paste, mortar, and concrete layers. Greater the thickness of segregated layers, more difficult it is to guarantee the capacity and the durability of PHC pile. The experimental study was performed to investigate the effects of centrifugal condition on the segregated layers of materials and the compressive strength of concrete for PHC pile. The considering factors in the test were centrifugal time and magnitude of centrifugal force. These factors have been found to have greater influence on the segregation than the concrete strength. The moderate centrifugal condition has to be considered to maintain quality assurance in the production of PHC pile, especially to provide the adequate concrete cover over its tendons.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.863-866
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• 2008

One of the most important requirements for reinforced concrete constructions is the bond behavior between concrete and reinforcement. In this study, the positions (i.e., vertical, horizontal) and the locations (i.e., 225mm and 75mm) of reinforcement were considered as a main test parameter. The ready mixed recycled aggregate concrete concrete with specified strength of 21MPa was prepared with different replacement ratio(i.e 0%, 100%) of recycled coarse aggregate. From the test results, it was bond that under the same mix proportion (i.e., the mix proportions are the same, except for deformed bars position), the bond strength between the recycled coarse aggregate concrete and the reinforcement has obvious relation with reinforcement position. Also, the specimens of top position showed a lower bond stress than that provided in CEB-FIP Code.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1093-1096
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• 2008

This study investigated the bond behavior between recycled coarse aggregate (RCA) concrete and deformed reinforcing bars. The position (i.e., vertical, horizontal) and the location (i.e., 375mm, 225mm and 75 mm) of deformed bar were considered as a main test parameter in this paper. From the test results, it was found that maximum bond strength of top reinforcement was decreased compared with that of bottom reinforcement. Also bar embedded horizontally 225mm above from base could not satisfy bond strength requirement provided in CEB-FIP code. It was caused by the fact that bonded area at the bottom of horizontal reinforcement was significantly reduced by the poring water and laitance. In this specimen, the bond strength provided by bearing stress and wedging action of concrete was not fully observed.

• Journal of the Korea Institute of Building Construction
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• v.21 no.4
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• pp.377-386
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• 2021

In April 2019, this study was enacted as a test method for the performance of waterproof layers in an environment where complex deterioration and structural behavior are simultaneously applied, but some existing standards were implemented to point out the errors of the method that should be supplemented. Thus, in establishing standards for (tentative) adhesive waterproofing sheets, field workability and quantification of test results were studied on the structural behavior response performance test methods included as test items. In addition, the performance evaluation of adhesive-type composite waterproof sheets was conducted based on the considered contents to review improvements such as applicability as an item of standard standards and field workability related problems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.230-236
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• 2019

Recently, issues related to the quality of concrete have continuously resulted in surface quality problems, such as the exfoliation of concrete surfaces due to the cost reduction of cement and poor quality fine aggregate, scaling of surfaces caused by laitance, and plastic shrinkage cracks. Prompted by social issues, the application of a photo catalyst to road structures is being attempted to solve the environmental problems caused by fine dust and automobile exhaust. In this study, chemical admixtures were developed to improve the surface quality of concrete and to apply and distribute titanium dioxide in nanoscale sizes to provide basic data for the development of a photocatalyst-curing agent. As a result of the experiment, silicon and silane were reviewed as a raw material as a curing agent to develop a high performance curing agent with better film performance than conventional curing agents because they could form a film quickly on a fresh concrete surface. The distributed stability of the ultrasonic disperser showed the best performance through an outdoor test for four weeks to review the dispersion measures for the application of nanomaterials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.2
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• pp.25-32
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• 2023

In this study, a double wall system is introduced, which was invented to simplify the complicated manufacturing process of the existing precast concrete (PC) double wall systems and to remove defects such as laitance that may occur during the production of concrete panels. An experimental study was conducted to investigate the tensile resisting capacity of the steel tube which is embedded in the precast concrete panel to keep the spacing between PC panels and to prevent damage of the PC panels during transportation and casting concrete onsite. The experiment was planned to determine the detail of effective steel tube connection considering the steel plate treatment method according to the formation of the opening, the presence of embedded concrete, and the reinforcement welding for additional dowel action as key variables. As a result, the ultimate tensile strength increased by 20-30% compared to the control specimen (ST) except for the steel tube specimen (ST_CP) which has steel plates bent inward at the end part of the steel tube. Since the specimen (ST_CON) filled with concrete inside the control specimen has no additional process and cost for the steel tube connections compared to the control specimen during the production of the developed double wall system, it is determined to be the appropriate detail of steel tube connection.